Just Read Your CnP Interview-
And I had one question — how many grams of carbohydrates are actually necessary to replenish the glycogen stores in muscles (e.g. g/# of muscle)? (allowing for genetic and situation variances for individuals of course). I had always understood/been told that glycogen stores are generally depleted by an exhaustive workout (“to failure”). What would actually cause full (or close to it) depletion (e.g. a marathon)?
Thanks for the informative interview. Keep up the good work, I’m about to read your nutrition articles on your site (please pardon me if the answers to these questions are already up there!)
Glad you enjoyed the interview- though it WAS a bit off the cuff!
Glycogen stores, as you mentioned, are very individual- even dependent on muscle type in a given individual.
Generally speaking, a healthy 160 pound human male can store about 120-130 grams of glycogen in the liver (which is re-synthesized rapidly, and available to all cells in the body), and about 10 grams per kilogram of muscle tissue (which CANNOT be released to other tissues- it’s selfish in that regard). A 6’0″, 200 pound male (who could be assumed to have, say 50 kilos of skeletal muscle… as a WAG) could therefore technically store 620 grams of glycogen, or around 2400 calories worth- far more than you could even tap into from an intense weight training session.
Bear in mind, though, that individual muscles cannot release glycogen to OTHER muscle cells, so it’d be possible for this individual to “bonk” after his liver and leg muscle glycogen stores were depleted, which could be as low as 1200-1300 calories. This means that if he were to run a marathon with ZERO intake, assuming a 50% calorie contribution from aerobic pathways, running moderately quickly, he’d hit the wall before finishing (It takes about 4,000 calories of energy for this individual to finish a marathon, and he’d bonk after 2600 were gone). If he slowed down, and could provide, say, 75% of calories through aerobic pathways, at perhaps a fast walk, he COULD complete it with no additional intake (~5200 calories available before glycogen gone). This is why faster and larger runners NEED to take in simple sugars while exercising- these sugars are immediately available both for fuel to muscles AND to the liver for glycogen re-synthesis. Anyway, so yes, a marathon COULD deplete glycogen completely- really I use the 3000-3500 calorie mark (assuming not fasted) to determine when a real “bonk” will happen, assuming fairly vigorous activity and no additional food intake during activity. Actually a half marathon could deplete stores if you ran it fast enough- it’s all about intensity over duration and relative anaerobic contribution.
Back to weight training- if you think about the total time under tension of even a SERIOUS lifting workout, you’d be lucky if you spent ten total minutes actively contracting over a 1.5 hour workout. Given the maximum rate of energy production by most trained humans over a 10 second period is around 2700 watts (data from olympic athletes- track cyclists, who can often squat over 500 pounds), or 2300 calories per hour, even the strongest, most powerful individuals would be hard pressed to burn more than about 350 calories in a hard weight training session. Which puts most of us mere mortals at maybe half that. Muscular failure is more a function of temporary ATP/CP depletion, which means the contractile proteins can no longer maintain the ion gradient needed to force contraction and maintain muscle control. This can happen long before glycogen stores are even remotely tapped into.
Yes, a lot of assumptions were made here (and I’m sure you could argue plus or minus 10-25% for ANY of these numbers), but this hopefully puts it a bit in perspective- ~200 calories of glycogen is about 50 grams of carbohydrates, and given the body can synthesize around 15-20 grams of glycogen per hour, and is doing so during the workout from any food remaining in the gut, unless you haven’t eaten in 12 hours you really only need ~30 additional grams of carbohydrates post workout, of which the body will use about 15-20 per hour to top off your stores.
So you can skip the MASSIVE post workout feedings- a post workout shake with 20-30 grams of glucose and 5-10 grams of protein is more than adequate to replenish stores and halt catabolism, and a real meal within 2-3 hours should be plenty to begin the repair and adaptation process.