The Nitty-Gritty of Nutrition, Part 3 – Fuel Costs

[This is Part 3 of the “Nitty-Gritty of Nutrition” Series. Click here to read “Part 1 – The Macro on Nutrients“, or “Part 2 – Calories In, Calories Out“]

How you’ve managed to stick around for this much reading is beyond me, but kudos! In the last part of this series, we went over the common mistakes with caloric burn rates and caloric replenishment, as well as the upper-limits of replenishment. In this final segment of this series we’ll deal with the caloric deficits inherent to cycling, and some post-ride scarfing that – when done right – can help make up for it.

Unblancing Act

Try as you may, the output is stacked against you.
Try as you may, the output is stacked against you.

So… notice a problem here with the numbers we’ve seen over the last few posts? Let me give an example:

  • Average glycogen reserves: ~2,100 Calories
  • Yesterday I did a ride in which I burned 734 Cal/hr
  • I ingested about 150 Cal/hr (really, I should do MUCH better than this)
  • Calories available after processing: 135 Cal/hr
  • Hourly caloric deficit: 599 Cal/hr
  • Total ride time: 2 hours
  • Total caloric deficit: 1,198

Now, for a 2 hour ride, that’s okay. I have more than enough glycogen stores that I shouldn’t bonk (assuming I start replenishing right after the ride), and in fact I didn’t bonk, even with my low ingestion rate. But if I were to extend this to a four hour event, that caloric deficit is would’ve been huge – 2,396 Calories. Even with having eaten 600 Calories over those four hours, my tank is definitely on empty, and I probably started feeling that approaching wall around the 3:30 mark if not sooner. Had I eaten twice as many Calories, I would’ve been at a deficit of 1,856, which my glycogen stores should be able to just about cover, meaning I’d have been getting worn down but most likely wouldn’t have bonked.

This shows the importance of refueling on the bike. There’s no way to completely replace the number of calories you’ll burn – riding just burns too many per hour, even at moderate levels. And if you try, you’ll regret it (read: barfing on side of road). So you take the energy you start with, and you replenish what you can to stretch it as far as you can. About the best on-the-bike replenishment rate you can get is about 35%.

This allows us to do some rough math:

  • I have about 2,100 Cal of energy stored in glycogen
  • On a medium-hard ride I burn about 700 Cal/hr
  • 2,100 Cal / 700 Cal/hr = 3 hours before my glycogen stores are depleted.
  • I can replace about 35% (max) of my lost Calories = 735
  • Now I can go for about four hours at this 700 Cal/hr rate instead of three.

NOTE: There are other ways of saving energy – drafting, reducing power output, more efficient pedal stroke, more aerodynamic body positioning, lighter gear. The more you can reduce your energy output, the longer your energy reserves last. For example, if drafting saves you 30% of the effort, and you can be in the draft just half the time, you’ve saved 15% of your energy, or reduced that 700 Cal/hr output to 595 Cal/hr, making your stores last nearly 3.5 hours instead of 3. With on-the-bike feeding + drafting, you’ve gone from 3 hours of energy to 4.75 hours of energy.

Post-Ride Refueling

Refueling is just as important as energy conservation.
Refueling is just as important as energy conservation.

With a deficit of almost 1,200 Calories, you might be thinking, “Man, even with regular eating, how do I build up my reserves again?” Well, I’m glad I pretended you asked. Immediately following vigorous exercise, your glycogen absorption rate into muscles remains high over the next four hours (with the first two hours being the most important, as that rate can fall by 50% after the first two hours).

In the first four hours following a hard event or training, try to ingest 3-4 grams carbohydrates / 1kg body weight, with a maximum of 10 grams / 1kg body weight in the 24 hour post-ride period. This should be enough to thoroughly replenish your glycogen stores.

Some people think that adding protein after a hard workout will help with energy replacement. Protein cannot replace carbohydrate calories – so adding protein won’t mean you can remove needed carbs. However, some studies have shown that adding protein to a calorically dense carbohydrate drink may promote early glycogen replacement, especially if a second event will occur within 24 hours. And we have to remember that protein is used in muscle repair, so even if it doesn’t boost our glycogen stores much, it will be needed to repair our muscle tissue damage from these events, so it doesn’t hurt to incorporate it so long as you’re replenishing your calories at the same time.

[NOTE: Sources include McKinley Health Center (University of Illinois), Cycling Performance Tips, many Wikipedia articles and subsequent related sources, Nature.com, and several reports from the National Center for Biotechnology Information (NCBI)]