WS2811 expander part 4: Boards and Parts!

After a bit of waiting, the boards showed up from OSHPark. they looked fine as far as I could tell.

I had all the other parts to do a board, but I needed a paste stencil. I went into pcbnew, chose File->Export, and then chose to export the F.Mask (ie solder mask) layer to a SVG. I cleaned it up a bit to remove non-pad elements, went out to the laser cutter and cut a stencil out of 4 mil mylar:


Everything looked pretty good; there was good alignment between the board and the stencil. The spacing between the pads looked a little tight, but it’s a fairly fine pitched board, so it was mostly what I expected.

I carefully aligned the stencil and taped it on, got the solder paste out of the fridge, and applied it. Pulled up the stencil and it looked crappy, scraped it off, did it again, and got something that looked serviceable though there was more paste than I expected. Hmm.

Got out the components:

  • 1 WS2811
  • 1 33 ohm resistor
  • 1 2.7k ohm resistor
  • 6 10k ohm resistors
  • 3 1k ohm resistors
  • 3 NPN transistors
  • 1 100nF capacitor

and it took about 5 minutes to do the placement. Here’s the result:


I didn’t look at the picture at the time, but that’s a *lot* of solder paste.

Into my reflow oven (Controleo 3 driving a B&D toaster oven), let it cycle, seemed fine, here’s the board:


Not my best work. Frankly, it’s a mess; there are obvious places where there is no solder, and obvious pins that are bridged together. I spent about 15 minutes with my VOM testing for continuity and there were 3 solder bridges and 7 unconnected section.

Something clearly went wrong. And I went back to PCBNew and it was *really* obvious.

The layer you should choose for your stencil is F.Paste, not F.Mask. Here are the two next to each other (Mask left, Paste right):


The Mask layer sizes are positively giant compared to the paste ones. So, what happens if you use the Mask layer is that you have:

  • A *lot* more paste on the board, especially the small pads which must have double the amount
  • Solder paste with much reduced clearances.

What that means in reality is that when you put the components on, it squishes the solder paste together and connects pads that shouldn’t be connect. And then when you head it up, you either get bridges or one of the pads wins and sucks all the paste away from the other pad (how it wins isn’t clear, but it is clear that the huge MOSFET pads pulled all of the paste from the transistors next door).

This makes me feel stupid, but it is actually quite good news; it means that the design is fine and I just need to remake a stencil with the correct layer.

Anyway, after a lot more rework than I had expected, I ended up with this:


It’s still an ugly board, but does it work?

Well, I hooked up 5V, GND, and data in to one of my test rigs and a LED to the LED outputs.

And it works; the LED is on when I expect it to be on and off when I expect it to be off. All three outputs are fine.

The next test will be some testing to see how it fares with switching high current. And I’ll probably want to make another one using the correct stencil and hook it up for 12V operation to verify that.

New kit: LED Candy Cane part 1

My first kit – the Dodecahedral Light Engine – has been selling about as well as I expected a very hard to construct project with limited usages to sell, which is not very well. I primarily did it because I was going to do them anyway for my decoration project and wanted a project I could learn on.

I’ve just started working on my second kit, which is going to be a lot easier to build, cheaper, and more widely useful.

One of my favorite displays is a “tree of lights”, which is a tree with custom LED ornaments on it:

The ornaments are made of small sheets of plexiglass with high-power LEDs inserted into the holes, wired up, and waterproofed.

They are really bright; note in the photo that all of the dim lights are normal brightness LEDs, and even at that level the ornaments overpower the camera sensor. They are bright enough that – and I am not making this up – they cast a shadow about 50 feet away when they were at full brightness, so I dialed them back a little in brightness.

These ones are driven directly from 120VAC as that is what the controller provides.

What I want from this project.

  1. A fun, easy-to-assembly ornament
  2. The ability to run off of 5V or 12V (*maybe* 120VAC with a big disclaimer that you shouldn’t really do it)
  3. Tunable brightness
  4. The ability to drive them as WS2811 nodes (see my WS2811 expander posts…)
  5. A frame/armature that is easy to produce automatically (the originals were done with a 5mm end mill in a drill press and took a *long* time).

How do I become a better skier? Stance and Turn Shape

I’ve been seeing a common question recently – how do I become a better skier? – and I’m immodest enough to think that I have something useful to say on that topic. This is a summary of how I approach skier improvement for adults when I’m teaching.

I guess I should start by defining exactly what I mean by better. It’s one or more of the following:

  • Able to ski a wider variety of terrain
  • Able to ski a wider variety of conditions
  • Able to ski more efficiently – with less effort and/or for a longer period.


There are a couple of prerequisites that are required for you to learn efficiently, which I call “happy and casual”…

Your happy place

Skiing is inherently a physical skill, and I can’t physically make your body parts move the way that I want to see them move. The best that I can do is try to provide you with opportunities through which you can discover better ways of moving.

To improve the chances of that happening, you need to be able to pay attention to what is going on, process what is going on rationally, and be able to explore modifications to your current technique.

For that to work well, you need to be calm and focused, which I just label as “happy”.

For us to reach that state, we need to feel safe, and it helps a lot of we are also having fun. If you feel scared or distracted, it is very hard to make progress.

Spending a lot of time skiing slopes that are too hard for you is a great way to be in a mental state where it’s hard to improve, and it’s also a great way to develop bad habits.

However, having said all that, you don’t learn to ski bumps on the bunny hill. Part of learning to ski off piste is getting used to skiing off piste so that you can be in that situation and stay in your happy place, or at least not in your very sad place. A little challenge is good as long as you track your mental state and are functioning well in it.

Your casual place

Compare two scenarios. In the first, you are doing a turn every 5 seconds. In the second, you are doing a turn every second.

Which one is easier to analyze and pay attention to?

The first one is obviously much much easier to analyze.

Part of this is terrain choice – choosing a terrain where, at our current ability, we can make turns that are what I would label as “casual”. They’re easy, I don’t have to work very hard, and most importantly, I’m not scared that I’m going to fall.

The second part is about technique; finding ways to modify your technique so that a given terrain becomes more casual for you.

Note that “casual” is about how you feel in a specific situation. Some people are casual on easy intermediates. Some are casual on black diamond bump runs.


There are two topics that come up all the time, often enough that I consider them to be foundational. And by foundational, I mean that not addressing issues will limit your ability to improve. Those two things are stance, and turn shape.


If you ask 10 ski instructors what the most common technique issue for skiers is, 9 out of 10 will say “leaning too far back/not leaning forward enough” (the tenth is daydreaming about skiing). And from that comes the common advice:

  • Lean more forward
  • Keep your hands up in front of you
  • Don’t look down.

Does that work? Well, it can work, but it often doesn’t work great.

It helps to go back to what instructors call “ski/snow interaction”. What are we trying to achieve with ski/snow interaction? WRT stance, it’s two things:

  • We want to be able to load (put pressure on) the skis so they will bend and we can therefore use the sidecut to do the turning for us.
  • We want to have our weight centered over the skis so that we are going down the slope at the same rate the skis are, so they are not trying to speed up and get away from us.

That boils down to “have enough weight/pressure on the front of the ski so that I can get it to bend and keep up with it”. And the way we exert pressure on the front of the ski is only though the shin pressing on the front of the boot.

Which means there is one bit of anatomy that matters more than the rest: the ankle. If the ankle is flexed and there is pressure on the front of the boot, there is pressure on the front of the ski. If it is not flexed, it doesn’t matter how you are leaning or where your hands are, there isn’t pressure on the front of the boot, there won’t be pressure on the ski.

Here’s an example of  the kind of stance that I commonly see:


Note how the ankle is loose, but also note that the skier is a) leaning forward and b) has hands in front. Those “lean forward, hands up” cue is not working for this skier.

I want that ankle joint to be tighter, something that looks like this:


The ankle joint is tighter – the shin leans forward – but note that the skier is leaning forward less and has hands that are closer to the body.

Looking at the joints in the two images, where are there big changes? The knees have moved forward quite a bit, but the biggest change is in the hips; they have moved forward immensely in the second image. Which leads to my first cue to correct stance; stand up taller and move your hips forward. And also try to keep the angle of your back the same as the angle of your shins.

Not only is this a more functional stance, it’s also a more comfortable stance as it relies more on your skeleton to hold your weight and less on your muscles. Great stuff all around.

That is the stance that I’m searching for.

However, there is something problematic here. Let’s say you are skiing something that is challenging for you to ski and you find yourself in the first position. To get to the preferred, you need to stand up, get your hips forward, and do this while your skis are trying to run away from you. That is generally hard to do because it’s a lot of mass to move, so “stand up and move your hips forward” doesn’t work so great in a dynamic situation.

What is the minimal thing we could do from the first position to get pressure back on the front of the skis? What would be the quickest move? Focus on the ankle…


If we can pull our feet back 5 inches, we can regain the pressure on the front of our skis and get them working properly again, and we can make that move much faster than trying to move our whole body forward. It’s not a perfect stance; it’s still too hunched and is going to burn out your legs faster, but it goes us back to a place where they skis are actually working.

I think that move is foundational in off piste and bumps.

Finding the right stance

Remember the part earlier where I said that my job is to put you in situations where you can discover a better way of moving? The following is what I recommend to so you can discover what the right stance feels like and ingrain it into your neuromuscular connections. It has four steps.

Step 1: Sideslip

In a sideslip, we start with our skis across the hill and roughly equal pressure on both of the skis, and then roll our ankles and knees down the hill until our edges release and we start to slide downhill. Try it facing both directions, and roll your ankles and knees back into the hill to stop.

Here’s a video of what it looks like.

You don’t have to be perfect at sideslip for the purposes of this, but if you have trouble with steps 2 or 3 come back and practice this more.

Step 2: Falling leaf

Start in a sideslip where you are moving straight down the mountain, and slowly shift your weight forward and back on your skis. When you have the weight forward, your sideslip will move sideways down the hill and go forward at the same time. When you have your weight backwards, your skis will go sideways and backwards at the the same time.

Here’s a video of what it looks like. Start by doing it more slowly than the video shows. Pay attention to what your legs and ankles feel like as you are going forward.

Step 3: Diagonal forward sideslip

This is the forward part of the falling leaf held for much longer. Start by going across the hill, and then roll your ankles and knees down the hill slightly to sideslip at the same time. You will need to be in the “forward falling leaf” position for this to work, with ankles flexed and pressure on the front of your boot, and it will feel weird when you first do this. Play around with your stance. Try to stand tall.

It looks like this.

The feeling you get in the forward part of the falling leaf and in the diagonal forward sideslip is the foundation position you want in your stance.

Step 4: Diagonal forward sideslip with turn

Take the diagonal forward sideslip, and add a turn at the end of it. Make sure you are in the sideslip as you start the turn, and then as you exit the turn, get back into the diagonal sideslip. You should find your turns to be much easier.

Turn Shape

We talk about this foundation as “turn shape”, but I think that is probably the wrong way of looking at it. What we really care about is not the shape of the turn, but the direction that your skis are pointing during the turn compared to the direction that your body is moving. Perhaps a few diagrams will help. Let’s say you are skiing the following path:


That looks like a nice smooth turning shape. Let’s overlay the direction the skis are pointing in two different turning techniques:


In what we call “Z” turns, at the beginning of the turn, the skis are pivoted quickly across the path of travel and then held relatively straight until the next turn, where they are pivoted quickly across to the other direction. Z turns are problematic because:

  • They require big movements and therefore a lot of energy
  • Because the turning is quick, they ask more from the condition of the snow; if the snow is scraped off or a icy, they feel much more precarious.
  • The motion is so fast that you can’t actually feel what they skis are doing. Remember my part earlier about turns feeling casual so you can focus on what your skis are doing? Z turns make it hard to do that.

In progressive turns, things happen *slowly*, so you can easily tell what is going on.

So, if progressive turns are so much better, why do so many people do Z turns? It’s very simple; if you try to do progressive turns with a rearward stance, your skis take off downhill when they are pointed at the fall line, and you fall over.

My experience is that you can fix your stance, it’s generally fairly straightforward to move towards more progressive turns, but if you want an exercise, I think shuffle turns work pretty well. They are also good because you can’t do them if your stance is too far back.

WS2811 expander part 3: PCB Revisions again…

More revisions.

I posted the design to /r/PrintedCircuitBoard, and of the comments said:

“Do you need pullups on the outputs of WS2811?”

And of course, I was confident the answer was “no”. For about 5 seconds. And then I measured the WS2811 I have in my breadboard; it gave a nice solid sink when it was on, and when it was off, just a fraction of a volt. Clearly not up to sourcing current to the NPN transistor.

The most likely explanation is that it’s an open collector output:

The collector on the output transistor is just left hanging – it’s only collected to the external pin. The voltage on an open collector can float up above the internal voltage of the IC as long as you don’t exceed the maximum voltage of the transistor

Open collectors are really useful if you want to have a bus architecture with multiple components able to pull the bus low, or if you aren’t sure what voltage of the output is going to be. Since the WS2811 can be used to drive LEDs tied to either 5V or 12V, it makes perfect sense. And it is confirmed by the internets.

Which means that the circuit needs to get a tiny bit more complicated:


Another pullup resistor is added to the mix. Really not a problem from the cost and assembly perspective as the design goes from 9 resistors to 12 resistors.

But, can I fit it in the current board layout without making it bigger?

I should probably add a parenthetical note here that says it’s often easier to go with a bigger layout, and in fact if you are going to hand solder a board, you *should* go with a bigger layout. Though I’m not sure how practical it is to solder the MOSFETS by hand since the base pad is so big…

Anyway, here’s what the board looked like before:

I need to put a resistor between each of the traces that head from the WS2811 over to the transistors. Hmm.

I initially just tried to fit them in there, and with a big of rerouting, I was able to make it fit. Technically.

Then I decided that it would be a lot easier if I moved the vertical ground trace underneath the transistors and used that to provide the ground connection to the transistors. That meant I could move the VCC vias around more easily, and could do the following:


The fit in reasonably well.

I *think* it’s ready to order the first version of the board, but there’s one more step. I now have on hand the WS2811 ICs and both kinds of transistors. So, I printed out a design with the copper layers shown, and did a test to see if the components really fit on the board.


That shows the WS2811 on the left, the MOSFET on the right, one of the NPN transistors and then a tiny 0805 10K resistor at the top. Everything looks like it will fit fine.

I ordered 3 boards for $7.10 from Oshpark, which is my usual supplier for prototype boards if they are small.

WS2811 expander part 2: PCB Revisions

I’ve done quite a few improvements on the board. Let’s look at before and after:


My usual flow is to do some changes, and then load the board into OSHPark and see how it previews. And then make changes.

I’ve probably redone the majority of the traces on the board. The big changes are:

  1. I replaced the 0603 resistors with 0805. I’m going to do the components by hand, and the larger resistors are easier to place. And I have a set of 0805s sitting in my drawer.
  2. I realized that I hadn’t planned for chaining together more than one board. After 3 or four revisions, I settled on a single 1×6 header to hold both sections. You can either use two 1×3 headers or one 1×6.
  3. The big headers for power and the LED output were bigger but not a standard connector, since I just wanted them to be easier to solder to. That was stupid. They are now spaced to use standard 3.96 mm spacing (Molex KK line if you want branded stuff), so you can either solder or use a connector. This made the board just slightly taller.
  4. The transistors and resistors have been moved, aligned, spindled, and mutilated.
  5. Added holes for mounting, though it’s probably not needed with a board this small. But I had space.
  6. Added some more labels.

Updated schematic


Board shots

I’m thinking this is probably good enough to get my prototype versions built.

WS2811 expander

I’m starting a new decorations project that will involve a fair number of standard LEDs, but not addressable ones. I have a few different use scenarios:

  1. Plug into a standard USB power supply.
  2. Power directly with 120 VAC.
  3. Power either with 5V or 12V and have an easily way to control brightness…

The first two are just wiring, but the third needs something more. My target market is quite used to using WS2812 addressable LEDs, so I’m going to build something that works in that environment.

Quick requirements list:

  1. Runs on 5V or 12V.
  2. Uses WS2812 protocol.
  3. Can drive significant loads (at least 10 amps).
  4. Small and cheap

The second requirement is pretty simple; you can buy the WS2811, which works exactly the same way as the WS2812 lights but is in a separate package. And it very conveniently has a little internal power supply that can use 5V or 12V by changing the value of one resistor. Here’s a typical 5V circuit:


Looks very nice, and almost does what I want, except that it’s designed to only sink 18.5 mA, which is quite a bit less than my 10 amp goal. I don’t strictly have a use for 10 amps right now, but I will likely need at least 1 amp for some uses.

So, I’m going to lean on the IRLR7821PbF MOSFET that I used in my backyard controller, which it looks like I can get for about $0.14 each. It’s pretty easy to use:


I will just drive the gate of the MOSFET with the output of the WS2811, and when the MOSFET turns on, it will pull the LED1 line low, turning on the LED.

Except… the WS2811 outputs are active low, and the MOSFET in this arrangement is active high. So


We add an NPN transistor. If the input is low, the transistor is off and the gate on the MOSFET is pulled high by the 10K resistor. If the input is high, the transistor is on, the gate is pulled low, and the MOSFET is off.

That will be duplicated for all three channels, and we end up with the following:


R9 and R10 are really just empty holes; you bridge R9 with wire if you want to use 5V and R10 if you want to use 12V.

I unfortunately generally forget to take snapshots during PCB design, so here’s the V1 state:


The MOSFETs have lots of 4s on them – I don’t know why – and to the left are the bipolar transistors and the resistors required for that part of the circuit.

The power input holes and the LED holes are designed to use Molex KK 396 headers and connectors so you can either use those or hand wire.

The lower left shows the jumper locations to set voltage.

All resistors are 0603 sized; that makes them compact but still relatively easy to populate.

The only weirdness are the three through-holes next to the LED terminals. I need to tie that backside ground trace to the frontside MOSFET terminal, but I was having trouble fitting enough vias to carry the current. Instead, I just used the through holes, which will be filled with solder and therefore be able to carry plenty of current.

The board is about 40mm x 28mm in size. I might jump up to 0805 resistors to make it a little easier to fabricate.

Before I send it off to be fabricated, I need to have the transistors in hand so I can verify the layout works.

The endurance athlete’s guide to fueling and weight loss part 6: Recommendations

This post will make considerably more sense if you have read the previous posts

After five long and sometimes tedious posts, I’m finally going to tell you exactly what your base diet should be and and how to fuel during exercise to achieve your goals.


I sincerely wish I could do that, but the reality is that everybody is different (genetics, age, sex, metabolic condition) and we all have different goals (win that race/lose weight/have fun), so I’m not able to do that.

What I do think I can do is talk to you a bit about my philosophy of endurance eating and fueling and how you might apply it to your situation. And then I’m going to turn you loose to experiment/adapt/modify the recommendations to adapt them to your specific situation.


Based on the way our biochemistry works, here’s are the principles I advocate:

  • Train in ways to improve fat burning, and therefore improve the ability to use fat as a fuel so that more fat is burned and less glycogen is used, so there is less hunger.

  • Fuel in ways to support glycogen stores and therefore support endurance and performance without getting in the way of fat burning.

  • Eat in ways to support the first two goals and to leave us generally healthy.

The application of these principles is going to depend on your current weight, fitness state, goals, number of cats you own, etc. In the following sections I’m going to talk about some broad guidelines, but you will need to do experimentation and tuning yourself.

Train in ways to improve our fat burning

Doing training to specifically increase fat burning has been a thing for a long time; there was, for example, a big push towards LSD (either Long Steady Distance or Long Slow Distance) training in cycling in the early 2000s. And it worked okay, at least for some people.

But what it was missing was the dietary and fueling aspect; if you have a lot of glucose in your system during the training, you get improved endurance but you get little improved fat metabolism.

While thinking about this section, I remembered a mountain training ride I did with a couple of friends back in 2006 or so; it was scheduled for about 115 miles and around 8K of up. I was getting ready, stuffing my jersey pockets with little ziplocs of drink mix and other foods – probably 1500 calories worth – and I noticed one of my friends just standing there. I asked him what he was taking for food, and he pulled out a little bag of trail mix. He said, “I usually don’t eat much on rides, but I’ll have some of this if I get hungry”. Another paradox that the “you have to eat lots of carbs” model doesn’t explain.

The way that we improve our fat burning is exercise in situations where glucose is scarce. What does “scarce” mean in practice?

I don’t know.

Perhaps “scarcer” would be a better word to use, and in fact fits in better as I advocate an incremental approach. Take the amount of carbs that you eat before/during/after, and reduce it by some amount.

If you generally don’t eat on your workouts, pick one of your workouts – perhaps a longer weekend one – and do it fasted.

If you are a carbs before/during/after kind of athlete, look at the amount you are eating and cut them down. From a biochemical perspective, targeting the pre-workout carbs – so that you start with lower glycogen stores and steady blood glucose – is probably going to be more impactful, so maybe you cut down or eliminate that snack first. Or maybe you cut down all your carbs by 30%. And then go out and do your workout.

Generally speaking, longer steady workouts are much better for this than fast short ones. Use whatever definition of “long” that works for you.

Do that for a few weeks or even a month or two, evaluate how it’s working compared to your goals, and see if you want to make further changes.

Fuel in ways to support our glycogen stores

Didn’t I just tell you to reduce your carbs during training, and now I’m telling you to increase them?

Not quite.

While there are some athletes who eat full keto (very low carb) diets and use either no or very few carbs during workouts and races, there’s no prize for doing that nor is it a morally superior approach.

What we are trying to achieve biochemically is to have enough available glucose for our muscles to support us for the exercise so that we can achieve our goals, both from a weight perspective and from a performance perspective.

If we are doing the “better fat burning” training described in the last section, then the best approach can be described as “the minimal amount of carbs required to keep you from bonking”, as that will give you the most improvement in fat burning. We will deliberately eat in ways that put us close to running out of glycogen. Which is why it is absolutely essential during this training to carry carbs with you, especially if you are starting from a high-carb fueling strategy, because it is very hard to know exactly how close you are to bonking. If you start to get hungry and/or feel your energy dropping quickly, eat some carbs.

If you are in this purely for the fat burning side, then stick with this strategy. You will increase your fat burn during the ride and reduce the amount you eat during the ride. Both are good.

If your session is more performance/endurance sensitive – perhaps a goal event or a intense training session – then look at how long/hard it is going to be, make a guess at how many carbs you will burn, and plan a replacement strategy so that you have comfortable reserves at the end. If you are a better fat burner than before you won’t need as much as you did before, but you will likely need some. The pro cyclists who work to be very good fat burners still eat a *lot* of carbs during a hard day of racing.

Small amounts of carbs on an ongoing basis can be a pain to implement. If you want a simpler approach, consider UCAN’S SuperStarch, which acts like a time-release glucose. and is therefore quite convenient to use. Pricey, however. (note 1) I use it on my longer & harder events – say 4+ hours – but generally don’t on shorter events, where I just have water, even if fasted.

Recovery nutrition

Conventional wisdom says that you need to refill your glycogen stores as quickly as possible to take advantage of the brief window where glycogen replacement is increased when exercise is finished. The window does exist, but in most cases, we don’t really need our glycogen stores to be refilled especially soon, and those are extra calories that aren’t required. There’s an interesting study that shows that having the post exercise carbs reduces insulin sensitivity and glucose tolerance the next morning.

On the other hand, if you want to have something sweet, right after exercise that has depleted your glycogen stores is biochemically the best time to do so, and in particular, it’s a time when fructose likely doesn’t have the same downsides (note 2), so some fruit can be nice. I like peaches.

My general advice is to tend to not eat targeted recovery food, but if you find that you are ravenously hungry after long workouts, a bit of carbs after exercise can blunt that reaction.

Eat in ways to support the first two goals and to leave us generally healthy

Diet is a huge topic that I could write endless posts on. I will try to keep it simple and at least mostly related to the goals that we have been talking about.

Limit refined carbs and processed food

Refined sugar (sucrose) is an obvious target, and it’s bad for a lot of reasons – there is lots of glucose that you have to deal with, and lots of fructose that can lead to insulin resistance. Note that sucrose is added to a significant number of processed foods; this is a byproduct of the 1980/1990ss fat phobia, when manufacturers found that reducing fat made food taste awful but you can make it taste less awful if you add a lot of sugar. So, you’ll need to read labels.

And now for a bit of heresy… I think you should be careful with the amount of fruit you eat. There are many fruit advocates that assert that the sugars in fruit behave differently than refined sugars and therefore fruit is not an issue. It *is* true that:

  1. The sugar is bound up in the flesh of the fruit so that it takes longer to be absorbed than sugar outside of the flesh.
  2. A piece of fruit is much more filling than the equivalent amount of refined sugar.

But that just means that fruit is a gentler source of sugar, not that you can eat as much as you want. The impact of fruit hasn’t been well-studied in clinical trials, but I did find a study that looked at the relationship of fruit consumption to gestational diabetes, and the effect was significant (note 3).

If you have a lot of extra weight and/or type II diabetes, I would try to get rid of as much fructose as possible, from all sources.

And some more heresy… I think that other refined carbs are also important, though not as important as sugars. They lack fructose, but they still have a big load of glucose in them. This is mostly anything made with wheat flour (even whole wheat flour), so bread, pizza, pasta.

Yeah, I know, I like them all as well. I used to eat a lot of them when I was younger but they don’t agree with me now that I’m on the far side of 50. YMMV.

Alcohol is also something to limit, for the same reason as fructose.

And yes, I’ve totally killed the “ride and then celebrate” scene. Sorry to be such a buzzkill.

Choose an appropriate fat/carb ratio for your situation

From a general health perspective, the data I’ve seen suggests that if you are healthy in general and insulin sensitive, you will probably do fine on a moderate carb/low fat diet or a low carb/ moderate fat diet, as long as its a whole food diet (note 4). So just choose one that works for you.

If you are insulin resistant and/or have not being able to reduce your weight easily in the past, I’d recommend trying one of the low-carb approaches as they make more sense for that metabolic state. I usually recommend either Mark Sisson’s Primal, or the Duke University “No sugar No starch” diet.

Like the changes in fueling, I recommend that you make any dietary changes on an incremental basis.  If you end up going low carb, there is quite a bit of anecdotal data that suggests that endurance athletes are generally happier with diets that have a few more carbs in them (ie not keto), and an interesting study here where none of the participants stuck at a very-low-carb/keto diet but they all did eat a significantly lower-carb diet than they had in the past.

Case studies

Because my advice is non-specific, I thought I’d include a few case studies that have specific examples of what people have done.

One of the posts that started me on this journey was noted cycling coach Joe Friel’s blog post entitled “Aging: My Race Weight”.

My case study is in my blog post Down 20?

Chris Froome and other Team Sky cyclists use a low carb diet a their base diet – Froome famously tweeted this picture of a rest day breakfast that was very low carb. They do supplement with carbs based on the event. There’s a bit of insight into their approach here.

In Closing

I hope this has been helpful. If you have questions, please send me a comment; I’m planning on a follow-up post to clear up things that weren’t clear.


  1. SuperStarch is an interesting story. There is a disease called glycogen storage disease where a person is unable to store glucose as glycogen, and therefore is unable to regulate their blood glucose. The traditional treatment was corn starch every 2 hours, which was hugely impactful. SuperStarch is corn starch that has been modified so that the starch molecules become very long, which means that is slowly digested and therefore results in a slow release of glucose – exactly what is needed for people with this disorder. It also turns out to be quite useful as a carb replacement fuel for athletes. Here’s a paper with links to the clinical studies does with SuperStarch.
  2. Fructose in combination with high blood glucose preferentially metabolizes to fatty acids, which can accumulate in the liver. But if you have depleted glycogen stores, the glucose in the fruit goes straight into those stores and the fructose gets metabolized to more glucose.
  3. The odds ratio between the group that ate the most fruit and the group that ate the least was 4 – those who ate the most fruit were 4 times as likely to get gestational diabetes than those who ate the least. That is really a ridiculously high ratio for a nutritional study; it is uncommon to see anything above 1.5. It was still an observational study, however.
  4. Gardner’s DIETFITS study is a pretty good one. I recommend watching his video here.

The endurance athlete’s guide to fueling and weight loss part 5: Hunger etc..

Please read the previous posts if you haven’t seen them before…

We are moving closer to the post where I hope to give useful advice on the different tactics you might use to improve fueling or lose some weight. Or perhaps both.

This was going to be a short post as I was having trouble coming up with a good way to talk about hunger, but I came across some new (to me) information that I hope will be informative.


Hunger lies at the intersection of energy balance, brain function, psychology, and group dynamics. Oh, and evolutionary biology. That makes it complex and hard to understand, and therefore not very amenable to easy explanations or simplification. It’s much more complex than – for example – how blood glucose is controlled. I’m therefore going to have to simplify quite a lot, and there will be a number of areas where it’s just not clear (to me) what is going on. That said, let’s get started.

The evolutionary purpose of hunger is to drive us to eat in ways that maintain our energy stores – and in particular, our fat stores – at a certain level. Or perhaps within a certain range. What factors could set the low and high limits of that range? (note 1).

Let’s start at the lower end – what drives the lower end of the fat storage range?

  • If we have too little stored energy, we won’t be able to survive when food becomes scarce.
  • If we are female, we need extra stored energy to be able to build and feed a child.
  • And at the upper range?

  • If we have too much stored energy, we may not be able to move around effectively, which could compromise our survival.
  • There may also be impact based upon climate, but I’m going to ignore that for this discussion.

    Another way to describe the range is “enough fat, but not too much fat”. Where “enough” and “too much” have definitions that are a bit squishy. But you get the idea…

    The regulation of hunger – and therefore the regulation of energy intake – is driven by two hormones, leptin and ghrelin. To oversimplify things:

    Leptin is produced by fat cells, and serves to reduce hunger. Generally speaking, the larger the fat storage, the higher the leptin levels will be. You can think of leptin levels like the gas gauge on a car; if your fat tank is empty, leptin reads low, if you fat tank is full, leptin reads high.

    Ghrelin is produced by the stomach, and serves to enhance hunger. It’s a shorter term signal.

    Based on a simple understanding of how the hormones work, we would expect that Ghrelin levels would be proportional to how long it was since we ate; the longer we went without food, the more hungry we would be.

    Here’s a graph of Ghrelin values over a typical day:

    (note 2)

    The solid line is the average while the dotted lines show the upper and lower range.

    That’s not what I expected. Ghrelin levels are lowest right when we get up, which is when we have gone the longest without eating and would therefore expect them to be highest. It turns out that ghrelin levels have a few somewhat interesting features:

  • They are adaptive based upon when we usually eat and our circadian rhythms.
  • They increase when we start to eat. This is familiar to most of us; not being really hungry but finding out that as we smell dinner or start eating, we are suddenly hungry.
  • There’s another strange feature of ghrelin related to fasting. Here’s a study (note 3) that looked at ghrelin levels over an 84 hour fast:


    That’s just weird. The mean ghrelin levels decrease from day do day, which means you are actually quite a bit less hungry on day three of fast than you are in day one. While weird, this is pretty well established by research.

    Also note that there seems to be a greater reduction for women, for reasons that are not well understood.

    Why our bodies behave this way is not really known. The best theory I know is one from an evolutionary standpoint; while it is good to be hungry if food is available, it can quickly become counter-productive if food is scarce.

    Moving onto leptin, what do leptin levels look like? (note 4):


    That is what we generally expect – at least there seems to be a decent linear relationship between BMI and leptin levels. It’s a bit messy, probably because BMI does not correlate perfectly to fat mass, and likely because of individual variations as well. The differences between male and female leptin levels are asserted to be caused by a) women having more fat mass at a given BMI and b) women having more of the kind of fat cells that produce more leptin than men, though I don’t think the question is truly settled.


    Leptin is supposed to inhibit significant weight gain; if you gain excess fat, your leptin levels rise, your hunger drops, and you lose fat mass until your leptin levels drop. And that seems to work for some people, especially those who are young, choose their parents well, and male. But it’s pretty obvious it does not work well in a lot of cases.

    Is there anything known about the disfunction? Well, a bit…

    Leptin and ghrelin levels based on types of food

    I found a very nice experiment (note 5) that looks into leptin and ghrelin response based on different kinds of food. Take a group of people, have them fast overnight, and then give them one of three drinks:

  • 500 calories with 80%/10%/10% from carbs, fat, and protein
  • 500 calories with 10%/80%/10% from carbs, fat, and protein
  • 500 calories with 10%/10%/80% from carbs, fat, and protein
  • In other words, a carb-heavy (glucose-heavy), fat-heavy, and protein-heavy drink (note 6). This is done in what is called a “crossover” study, which means that each subject had all three drinks on different days.

    You sample their blood before they have the drink, and then every 30 minutes afterwards, and measure a bunch of different things. Based on how ghrelin works, I would expect that eating would suppress the ghrelin levels and then over time, they would rebound to their previous levels.

    What happens?


    All three produce a significant suppression of ghrelin production, but carbohydrate produces the biggest reduction. Interestingly, however, after about two hours the carbohydrate ghrelin level goes shooting up and after 3 hours it is higher than the fat or protein curves and soon after becomes higher than the initial ghrelin level.

    Or, to put this another way, five hours after eating 500 calories of mostly glucose we would be *more hungry* than we were at the start.

    The authors write, “Our finding of a rebound of total and especially acyl-ghrelin above baseline after high-carbohydrate meals could provide some physiological basis for claims made by low-carbohydrate diet advocates that ingesting carbohydrates prompts an early hunger rebound”.


    They did measure subjective appetite which showed no effect, though unfortunately they had technical difficulties with the appetite reporting system and that data was therefore not published.

    I’d also like to note that there are many experiments that measure satiety (the inverse of hunger) and show that carbohydrates lead to more satiety than fats or protein. And they do, if you only measure them for 2-3 hours.

    The experiment also measured blood glucose over time:


    If I eyeball the two charts, it looks like ghrelin production starts to go up steeply about the time blood glucose drops quickly at 140 minutes, and is highest when the blood glucose is the lowest. The pattern here matches what is known as either “reactive hypoglycemia” or “postprandial hypoglycemia” – basically the blood glucose drops below initial levels a few hours after eating.

    It’s important to note that the drinks were dominated by a specific macro and drinks with mixed macros may show unexpected results. Though 500 calories is not really that much and these were consumed in a fasted state, and as we know that is the time when the body is best able to handle a lot of glucose.

    You can find the leptin chart in the paper if you’d like to see it; there were small drops over time but nothing very striking.

    Fructose vs Glucose

    Is there a difference between fructose and glucose? Let’s look at another experiment (note 7).

    In this experiment, we take 12 normal-weight women and feed them three meals containing 55%, 30%, and 15% of carbohydrate/fat/protein and take blood samples every 30-60 minutes.

    Of the 55% of the calories that come from carbs, 30% either comes from a fructose-sweetened or glucose-sweetened beverage.  Take a normal meal pattern and make the carbs either fructose heavy or glucose heavy. And sample their blood periodically:


    Wow. Lunch and dinner show large spikes in ghrelin for both drinks, but the late-night spike of the fructose drink is much higher. Also notice the difference in levels at 8am the next day; the level of ghrelin in those who had glucose is quite low, but it’s pretty high for those who had fructose.

    Fructose gives us bigger positive ghrelin peak than glucose.

    They also measured blood glucose levels:


    Based on what we know about glucose and fructose metabolism, that is what we would expect; because the fructose is processed in the liver, there is much less glucose. We would expect that the liver processes the fructose to triglycerides. Is there data to support that?


    Yep. Vastly higher triglyceride levels show the fructose being converted to fat and released into the bloodstream, and those levels persist through the night.

    They also measured leptin levels:


    Leptin levels rose much less for the high-fructose meal, which means there was less inhibition of appetite.

    Overall, fructose led to a greater increase in ghrelin (higher appetite) and a lesser increase in leptin (less appetite suppression).

    So, carbohydrates in general aren’t great, and fructose is worse.

    The best theory I’ve seen around why fructose behaves so differently is that significant fructose supplies were rare in historical times, and therefore it was advantageous for humans to eat as much as possible when they found them. That sounds reasonable, though like many studies in evolutionary biology they are hard to support.

    Leptin resistance

    The mystery of why leptin isn’t behaving as we would expect – why people still eat a lot even with high leptin levels – has been labeled “leptin resistance”, by analogy with insulin resistance; the idea is that for some reason the brain is not sensitive to the levels of leptin.

    Whether there is actual resistance or whether there are other factors that are overpowering the leptin signal is not clear.

    There are a number of theories round what is actually happening. Among them are:

  • There is a defect in transporting leptin from the bloodstream into brain cells across the blood/brain barrier.
  • The cells within the brain become less sensitive to leptin.
  • Dietary fructose leading to elevated triglycerides reducing leptin transport across the blood/brain barrier.
  • Here’s two papers if you want more information (note 8) (note 9).


    I’m including this section for completeness. There is some research on how dopamine is affected by sugar ingestion, and while I think there something going on there that partially explains why sugar is addictive – at least for some people – I’m not confident enough in my understanding and the quality of the research to have much to offer.

    I do offer a few papers:

    Hunger Summary

    The main points from the preceding section on hunger:

    • Carbs – and especially fructose – seem to interfere with the hunger control system.

    • Hunger is not directly related to how long it’s been since you ate; it has a daily rhythm and decreases when fasting.

    Energy balance and weight loss

    If you have read official guidelines and advice about weight loss, you can generally boil them down to one bit of advice:

    Eat less and move more

    This is often summed up as the “Calories in / Calories out” (CICO) model; eat less means fewer calories in, move more means more calories out, and the result will be weight loss.

    It is also typical to see appeals toward the Laws of Thermodynamics. The more rabid adherents to the model treat it as if they have discovered one of the deep secrets of the universe.

    If you have read the earlier posts and have learned anything about biochemistry, I’m sincerely hoping that you suspect that the reality might just be a *tiny* bit more complicated than the simple world of “eat less and move more”. Especially since that advice fails for a large number of people, at least for the long term.

    There is truth to the CICO model in one sense, if you are losing weight you are burning more calories than you are taking in. And vice versa. But that’s the result, not the driver; the driver is the biochemistry at work.

    The key to understand how things really work – and why CICO isn’t very useful in many cases – is related to how the body responds to a reduction in food intake. The body essentially has three options to balance things out:

    1. It can burn stored fat.
    2. It can tear down muscles (ie “lean mass”) and burn that.
    3. It can reduce its energy use.

      We are hoping that it would do #1 – after all, the whole point of the fat storage system is to provide an energy reserve when food is scarce. But remembering the earlier posts, there are a couple of things that can get in the way of that. First off, we need to be good at burning fat in general. And second, we need to be in a hormonal state where fat burning is possible.

      If either of those aren’t true – or are true only to a limited extent – then we are stuck with tearing down muscle and reducing energy use. And, in fact, that is what we see in a lot of diet studies; people will lose lean mass – sometimes a significant amount – and people report being cold, tired, and hungry all the time.

      And they don’t really lose all that much weight.

      If we can get rid of the conditions that are blocking fat metabolism – and, since we are athletes, up the amount of fat we burn when exercising – then the body should naturally start burning more stored fat, and we should lose weight. Or, to put it another way, we are going to focus on the fat burning side of the house.

      This post is already quite long so I’ve tried to limit the detail in this section; if you want more I highly recommend Peter Attia’s post on fat flux.


      There is a lot more that I could write about WRT hunger and energy balance, but I think this is enough for now.

      Our strategy is going to make dietary modifications to reduce hunger and improve our ability to use fat to generate energy while exercising, with a goal to lose weight/improve our ability to perform in long events.

      Which takes us to the tactics portion of the series. What do I think you should actually *do* to implement these strategies, so that you can – with any luck – see the benefits that I’m talking about.

      That will be post #6. When I get that done, I’m planning on doing at least one post to cover any questions.

      Post #6: Recommendations


      1. I’ve tried to base this section on what I’ve learned about evolutionary pressure, fat stores, and hunger.
      2. From Jason Fung’s excellent discussion on hunger and fasting here.
      3. Fasting unmasks a strong inverse association between ghrelin and cortisol in serum: studies in obese and normal-weight subjects
      4. Mechanisms behind gender differences in circulating leptin levels. This result is widely replicated in other studies.
      5. Acyl and Total Ghrelin Are Suppressed Strongly by Ingested Proteins, Weakly by Lipids, and Biphasically by Carbohydrates
      6. The beverages were mostly composed of a glucose beverage, whey protein/nonfat milk, and heavy whipping cream for the carb/protein/fat drinks.
      7. Dietary Fructose Reduces Circulating Insulin and Leptin, Attenuates Postprandial Suppression of Ghrelin, and Increases Triglycerides in Women
      8. Leptin resistance: a prediposing factor for diet-induced obesity
      9. Mechanisms of Leptin Action and Leptin Resistance
      10. MarksDailyApple, by Mark Sisson’s. Mark is an advocate for a way of eating named “Primal”.

      The endurance athlete’s guide to fueling and weight loss part 4: Better fat burning in actual athletes

      Please read the introduction and earlier posts if you haven’t…

      In the last post, I finished by asking what factor or factor might cause the difference between these two athletes:



      The differences might be genetic, differences in diet, or differences in training. Or maybe something else. What do you think is at play?

      We don’t know all the factors, but it turns out that this athlete does not have a sweet tooth, so he eats closer to the recommended cyclist diet; lots of carbs, but not a ton of sugar. At least in his base diet; I don’t know what he eats before/during/after training. And he’s better at burning fat.

      Hmm. It’s almost as if there might be a dietary effect here, that the availability of carbohydrate in the diet and on the bike might have an effect on fat burning ability. How could we test that?

      Well, let’s put two cyclists – how about these two cyclists? – in a situation where there is much less carbohydrate available, let them train for 10 weeks, remeasure their VO2Max, and see what changes. Since we want to maximize the effect, we’ll put them on a very low carb “keto” diet, which is something like 30 grams of carbs per day.

      What happens?

      Well, athlete #1 is not happy on the keto diet, and that’s really no surprise; he’s not good at producing energy from fat *at all*. If you take away his carbs he will feel horrible on the bike. He ends up making the following adjustments from has previous diet:

    1. He minimizes all sources of sugar
    2. He limits bread, rice, pasta, and potatoes to once or twice a week.
    3. He reduces the food he eats on the bike to an occasional banana plus water
    4. Not really a low-carb diet, but certainly a *lower than before carb* diet.

      Ten weeks of training go by, he retakes the test, and we generate a new graph (previous results are dotted):


      This athlete is now a significantly better fat burner; rather than hitting only 25% of calories from fat, he’s averaging 40% or so across most of his range. His beta oxidation system is better.

      Athlete 2 started with the same very-low-carb diet, and he didn’t stick to it strictly either, but he did mostly get rid of grains and fruit from his diet, and he ended up lower-carb than athlete 1.

      10 weeks go by, and we get this:


      Yowsa! He nearly doubled the amount of energy he got from fat in parts of his range, and averages over 70% for most of the range. There is also a significant shift to the right, and he produces a higher maximum relative power. That’s great, the low carb diet made him much more powerful!

      Not so fast. Remember that this is *relative power*, and we know that he lost some weight as part of his 10 weeks training, so most of the improvement is likely from the reduction in weight. Though the training may also have helped.

      What did we see across these two athletes?

      First – and most importantly – we saw that a dietary switch made significant changes in the fat metabolism ability for both athletes. This really isn’t very surprising knowing what we know about the underlying biochemistry, but it does show very clearly that beta oxidation capability can be trained.

      Second, we saw a correlation between the amount of carbohydrate in the diet and the overall ability to metabolize fat.

      I do want to add a few caveats. The first is that two cyclists is a very low sample size, and the second is that we can’t tell the difference between changes due to base diet and changes due to food before/during/after. And there may be a genetic component at play here.

      Returning to my RAMROD example from the last post, let’s add in two more lines, corresponding to getting 50% of calories from carbs and supplementing 200 cal/hour (yellow) and getting 25% from carbs and supplementing 25 cal/hour (blue). These lines are closer to the “after” graphs of the two cyclists.


      If I can get up to 50% fat utilization and supplement at 200 calories per hour, I should be able to go 12 hours without running out of glycogen. And if I can get up to 75% from fat, I can supplement at only 25 calories per hour and still easily make it to 12 hours.  I can almost get to 12 hours without eating anything at all…

      It may be better than that. Remembering back to the first post where we talked about triglycerides, and how those are composed of a glycerol backbone with three fatty acids attached to it. If we are burning lots of fatty acids in beta oxidation, that means the fat cells are breaking apart triglycerides, and that means we have a lot of extra glycerol around.

      Since the body doesn’t want to waste energy, it will try to use the glycerol for something useful, and it can turn it into glucose through gluconeogenesis. That means if we are burning a lot of fat, we will get some glucose out of it to support the glycolysis side. And no, I don’t know how much “some” turns out to be, this is hard to study.

      Some more data

      Is there more data out there that would be interesting?

      Jeff Volek and Stephen Phinney have done a number of studies looking at low-carb/keto diets and athletes (note 1), and here’s one that I think is relevant to this topic:

      Metabolic characteristics of keto-adapted ultra-endurance runners

      One of the problems with dietary studies is that the studies are expensive and time is limited, so it’s very hard to do studies where you change an athlete’s diet and check to see how it affects her for the next 12 months. That is why many of the studies around keto diets and athletes are extremely short; less than 3 weeks. Knowing what we know about how long it takes to achieve training gains in general, it’s pretty clear that 3 weeks is on the short side to see adaptations, so I don’t think most of those studies are very good.

      In this study, Volek and Phinney instead looked at two groups of elite ultra-endurance runners, 10 who followed a high-carb diet, and 10 who followed a low-carb diet. Since each group was on their habitual diet, it’s a pretty good bet they were adapted to it pretty well. I will note at the outset that this is an observational study and therefore there is the possibility that the runners who chose low-carb are genetically better at burning fat than the high-carb ones.

      From the hypothesis about trainability, what difference would we expect to see in fat burning rates between the two groups? Here’s the first graph:


      The graph shows the peak fat oxidation during a 3-hour run for all of the athletes. Every low carb athlete is significantly better at burning fat than even the best fat-burning high carb athletes. If we look at the averages (circles to right), the average in the low carb group was 2.3 times higher than the high-carb group.

      I’d also like to note that the average for the low carb group was 1.54 grams/minute. That would be 92.4 grams/hour, or a whopping 92.4 * 9 = 832 calories / hour from fat burning alone.

      Where did that peak fat oxidation occur? Here’s another graph:


      Here we are looking at the relative intensity of that fat peak for each runner; the HC group peak was at 54.9% of VO2max, and the LC group peak was at 70.3%. Not only are the low carb athletes burning more fat, they are hitting their peak at a higher intensity.

      It is pretty clear that the low carb athletes are burning vastly more fat during a long run than the high carb athletes. And this study was with elite athletes doing ultra-distance events, which means even the high-carb athletes are likely to be decent fat burners.

      There are some other interesting graphs in the paper that I recommend looking at (note 2), and we may come back to it later.


      We found out that there seems to be a strong training effect and we can expect to improve the rate at which we burn fat through training. We also learned that if we can do that, it can make fueling more straightforward on long rides; we may need to still supplement, but likely not as much.

      In the next post, we’re going to take a little excursion into talking about weight loss and hunger.

      Part 5: Hunger etc.


      1. Phinney and Volek have written a couple of books that cover this same subject area: “The Art and Science of Low Carbohydrate Living” and “The Art and Science of Low Carbohydrate Performance”.
      2. Section 3.2 talks about submaximal substrate utilization, and features two charts that show the average oxidation rates (in grams/minute) for both fats and carbohydrates. The low carb group was very steady across the whole 180 minutes of the run; both fat and carbohydrate utilization is nearly a flat line. The high carb group saw a drop in carbohydrate and increase in fat over time; they also saw a slight reduction from 13.2 cal/minute at the start of the run to 12.0 cal/minute at the end.

      The endurance athlete’s guide to fueling and weight loss part 2: Energy Systems

      Please read the introduction and earlier posts before reading this one.

      In our last episode, we learned about how fat and carbohydrate get into our systems and the fundamental asymmetry between those two systems.

      In this episode, we will look at how fat and glucose are used for energy. My focus is going to be on muscles since these posts are for athletes; there are similar concepts that apply to other tissues but they are beyond the scope of this discussion (see note 1)

      I’m going to have to dive into some biochemistry to create a framework for further discussion; I have tried to simplify it as much as possible, and the post is relatively short.

      This is a summary of the overall processes at work for aerobic energy production; there are others that are at work for non-aerobic production.

      Each of the boxes is a complex series of chemical steps (note 2)


      We’ll start at the bottom and work our way up.

      Citric acid cycle

      Our goal is to take fat and carbohydrates and create ATP, which is what powers our muscles. At the center of the diagram is a compound named acetyl coenzyme A, abbreviated as “Acetyl CoA”. You can think of Acetyl CoA as the common energy compound produced from either glucose or fatty acids. That’s not absolutely correct, but it’s correct enough.

      The Acetyl CoA feeds into the citric acid cycle (sometimes known as “Kreb’s Cycle” after one of the discoverers). If you want to see the details, here’s a link:

      Image result for don't press this button image

      You pressed it, didn’t you?

      Biochemistry is just ridiculously complex.

      All of this takes place inside of each of most of our cells. You probably studied cells when you were in biology class, and the diagrams looked something like this:

      Image result for simple cell nucleus mitochondria

      Specifically, the citric acid cycle happens within the mitochondria, which you can see are those oval-shaped structures within the cell. I generally think of cells as being these little spheres or flat discs, and some are, but muscle cells are a bit different:

      Image result for muscle cell nucleus mitochondria

      Not at all like a globule or a flat disc; I especially like the nucleus stuck on the side as an afterthought.

      Muscle cells need a lot of energy so they have tons of Mitochondria. Thousands of them.

      And how are we going to get all the Acetyl CoA that we need to drive those muscles?

      Glycolysis and Beta Oxidation

      Glycolysis is the the process that converts Glucose to Acetyl CoA. Beta oxidation is the process that convert fatty acids to Acetyl CoA. Both of these processes happen in the mitochondria.

      There is a very important point to be made about glycolysis and beta oxidation. Even though they both occur in the mitochondria and even though they both feed into the citric acid cycle, they use different chemical pathways and therefore use different machinery.

      The citric acid cycle, glycolysis, and beta oxidation can all be trained. Not only can the body build more mitochondria, it can improve the rate at which each bit of machinery in the mitochondria works. That is one of the adaptations that makes us better at aerobic exercise.

      But the body only makes improvement to the parts of the machinery that are being stressed, so if it’s glycolysis that is being stressed, improvements will be made in the glucose metabolism, and similarly if beta oxidation is stressed, improvements will show up in fat metabolism.

      This point is going to be fundamental to our next discussion, so I’ll state it again in a different way – you can be an athlete with a very powerful glycolysis pathway and a crappy beta oxidation pathway. And vice versa.

      Another interesting outcome is that to achieve higher performance, you need to improve either glycolysis or beta oxidation *and* the citric acid cycle. You can do a bunch of work to improve your beta oxidation and you’ll burn more fat and fewer carbs, but you won’t see higher performance if the citric acid cycle is unchanged (note 3).


      This was a short post and I’m not sure I really need a summary, but the short one is that both fat burning and glucose burning have separate chemical reactions (glycolysis and beta oxidation) that feed into a shared set of chemical reactions (the citric acid cycle) that ultimately give the energy to drive the muscles.

      That’s all for this post. The next post will take this post and apply it in real-world situations.

      Part 3: Carbohydrate and fat use in actual athletes


      1. That would take us into ketone bodies and their usage in different tissues.
      2. Like, ridiculously complex. In glycolysis, to get from glucose to pyruvate – which is fed into the citric acid cycle – takes a series of 10 different chemical transformations. Beta oxidation goes through 5 steps but repeats them for every two carbon atoms on the fatty acid, and it’s more complex for unsaturated fatty acids. The citric acid cycle has 9 steps.
      3. This depends a bit on what you mean by “performance” and it ties into fueling, which will come up very soon in a future post.