Against Glycogen Repletion...

[NU_nutrition_TS]

I'm putting this here, save taking my 'Protein builds muscle, carbs don't' thread any further

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J Appl Physiol 42: 129-132, 1977; 8750-7587/77
Muscle glycogen repletion after high-intensity intermittent exercise
J. D. MacDougall, G. R. Ward and J. R. Sutton

Six subjects exercised to exhaustion on a cycle ergometer at intensities corresponding to approximately 140% of their maximal aerobic power. Subjects attempted to pedal for 1-min intervals with 3-min rest periods between, and continued until 30 s of exercise could no longer be maintained. Venous blood was sampled for lactate and glucose analysis. Muscle biopsies were extracted from the quadriceps before and immediately after exercise and at 2-, 5-, 12-, and 24-h intervals thereafter for total glycogen analysis. Three subjects consumed a mixed controlled diet (approx. 3,100 kcal) during the 24 h after exercise, and three consumed the same diet plus an additional 2,500/kcal carbohydrate. Following exercise, glycogen concentration had dropped to a mean value of approximately 28% of its preexercise value. After 2 h, it had recovered to 39%, at 5 h to 53%, at 12 h to 67%, and at 24 h to 102% of its preexercise value, with no difference in resynthesis rate between the two groups. It was concluded that, following glycogen depletion through intense intermittent exercise, complete recovery to preexercise values may be accomplished within 24 h; and that within this time period, the rate of resynthesis cannot be accelerated by a higher than normal carbohydrate intake.

Like I said, just eat a normal diet over 24 hours and glycogen repletion takes care of itself.

Let's look at the other side of the coin - does having high GI carbs before exercise spare glycogen?

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J Appl Physiol 58: 731-737, 1985; 8750-7587/85
Journal of Applied Physiology, Vol 58, Issue 3 731-737, Copyright © 1985 by American Physiological Society

Glycogen depletion during prolonged exercise: influence of glucose, fructose, or placebo

V. A. Koivisto, M. Harkonen, S. L. Karonen, P. H. Groop, R. Elovainio, E. Ferrannini, L. Sacca and R. A. Defronzo

We examined the influence of various carbohydrates of fuel homeostasis and glycogen utilization during prolonged exercise. Seventy-five grams of glucose, fructose, or placebo were given orally to eight healthy males 45 min before ergometer exercise performed for 2 h at 55% of maximal aerobic power (VO2max). After glucose ingestion, the rises in plasma glucose (P less than 0.01) and insulin (P less than 0.001) were 2.4- and 5.8-fold greater than when fructose was consumed. After 30 min of exercise following glucose ingestion, the plasma glucose concentration had declined to a nadir of 3.9 +/- 0.3 mmol/l, and plasma insulin had returned to basal levels. The fall in plasma glucose was closely related to the preexercise glucose (r = 0.98, P less than 0.001) and insulin (r = 0.66, P less than 0.05) levels. The rate of endogenous glucose production and utilization rose similarly by 2.8-fold during exercise in fructose group and were 10-15% higher than in placebo group (P less than 0.05). Serum free fatty acid levels were 1.5- to 2-fold higher (P less than 0.01) after placebo than carbohydrate ingestion. Muscle glycogen concentration in the quadriceps femoris fell in all three groups by 60-65% (P less than 0.001) during exercise. These data indicate that fructose ingestion, though causing smaller perturbations in plasma glucose, insulin, and gastrointestinal polypeptide (GIP) levels than glucose ingestion, was no more effective than glucose or placebo in sparing glycogen during a long-term exercise.

Mmm! So even a placebo was as effective as glucose in sparing glycogen. Or could those results be interpreted to indicate that glucose doesn't actually do anything at all?!

Another negative of taking glucose before/during exercise in the belief that it will prolong performance or spare glycogen:

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J Appl Physiol 43: 695-699, 1977; 8750-7587/77
Journal of Applied Physiology, Vol 43, Issue 4 695-699, Copyright © 1977 by American Physiological Society

Effects of elevated plasma FFA and insulin on muscle glycogen usage during exercise
D. L. Costill, E. Coyle, G. Dalsky, W. Evans, W. Fink and D. Hoopes

Seven men were studied during 30 min of treadmill exercise (approximately 70% VO2 max) to determine the effects of increased availability of plasma free fatty acids (FFA) and elevated plasma insulin on the utilization of muscle glycogen. This elevation of plasma FFA (1.01 mmol/1) with heparin (2,000 units) decreased the rate of muscle glycogen depletion by 40% as compared to the control experiment (FFA = 0.21 mmol/1). The ingestion of 75 g of glucose 45 min before exercise produced a 3.3-fold increase in plasma insulin and a 38% rise in plasma glucose at 0 min of exercise. Subsequent exercise increased muscle glycogen utilization and total carbohydrate (CHO) oxidation 17 and 13%, respectively, when compared to the control trial. This elevation of plasma insulin produced hypoglycemia (less than 3.5 mmol/1) in most subjects throughout the exercise. These data illustrate the regulatory influence of both plasma insulin and FFA on the rate of CHO usage during prolonged severe muscular activity.

So having more circulating fatty acids DOES spare glycogen during exercise but taking carbs beforehand just increases glycogen usage and CHO oxidation - and makes you hypoglycaemic during the exercise - not very desirable!

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Muscle metabolism during intense, heavy-resistance exercise

Per A. Tesch, Erland B. Colliander and Peter Kaiser
Department of Environmental Medicine, Karolinska Institute, Box 60400, S-10401 Stockholm, Sweden

European Journal of Applied Physiology

Summary The objective of this study was to examine the muscle metabolic changes occurring during intense and prolonged, heavy-resistance exercise. Muscle biopsies were obtained from the vastus lateralis of 9 strength trained athletes before and 30 s after an exercise regimen comprising 5 sets each of front squats, back squats, leg presses and knee extensions using barbell or variable resistance machines. Each set was executed until muscle failure, which occurred within 6–12 muscle contractions. The exercise: rest ratio was approximately 1ratio2 and the total performance time was 30 min. Concentrations of adenosine triphosphate (ATP), creatine phosphate (CP), creatine, glycogen, glucose, glucose-6-phosphate (G-6-P), agr-glycerophosphate (agr-G-P) and lactate were determined on freeze-dried tissue samples using fluorometric assays. Blood samples were analyzed for lactate and glucose. The exercise produced significant reductions in ATP (p<0.01) and CP (p<0.001), while agr-G-P more than doubled (p<0.05), glucose increased tenfold (p<0.001) and G-6-P fourfold (p<0.001). Muscle lactate concentration at cessation of exercise averaged 17.3 mmol · kg–1 w.w. Glycogen concentration decreased (p<0.001) from 160 to 118 mmol · kg–1 w. w.* It is concluded that high intensity, heavy resistance exercise is associated with a high rate of energy utilization through phosphagen breakdown and activation of glycogenolysis.

* Just a 26.25% reduction in glycogen - definitely not depletion!

[NU_nutrition_TS]

Another study abstract that shows low muscle glycogen does not impair high intensity exercise performance:

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SYMONS, J. D. and I. JACOBS. High-intensity exercise performance is not impaired by low intramuscular glycogen. Med. Sci. Sports Exerc., Vol. 21, No. 5, pp. 550-557, 1989. The purpose of this study was to evaluate the effects of glycogen availability on short-term, high-intensity exercise performance. Eight males completed performance evaluation tasks (PET) consisting of maximum isokinetic strength and endurance, isometric strength, and electrically evoked force of the leg extensors, twice during each of two conditions. On day 1 (D1) of the control condition (C) subjects performed the PET, followed by strenuous exercise designed to deplete glycogen stores of the leg extensors. After consuming a mixed diet for 48h (days 2 and 3) they performed the PET again on day 4 (D4). The experimental condition (E) was identical to C, except that a strictly controlled low carbohydrate diet was consumed during Days 2 and 3. Biopsies from the vastus lateralis before the PET on D4 confirmed differences between conditions in intramuscular glycogen (426 +/- 43 vs 153 +/- 60 mmol glucose units[middle dot]kg-1 d.w. for C and E respectively, P < 0.001). Results obtained from the PET were not different between conditions on D4, nor within conditions when D1 and D4 were compared. Resting blood glucose, hematological variables indicative of hydration and acid-base status, and post PET blood lactate were similar for all trials. It is concluded that short-term, high-intensity exercise performance of glycogen depleted leg extensors is not impaired.

(C)1989The American College of Sports Medicine

[ATZ]

Isometrics. Not really applicable to many sports or lifting.

[NU_nutrition_TS]

Actually isometric and isokinetic strength. All that means is 'same length' (the muscle does not lengthen or shorten during the contraction) and 'same movement or motion' (the muscle lengthens and shortens over the contraction but the speed of the movement remains constant). Either way you are still contracting the muscle fibres against resistance and that still requires them to use energy - this merely indicates that low glycogen is not an impairment to that.

Standard training is usually isotonic which means 'same tension' (the muscle shortens/lengthens and the speed of the movement over the contraction will vary - slower at the 'sticking point' and faster at the start and finish - keeping the tension constant).

[ATZ]

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Effect of carbohydrate availability on time to exhaustion in exercise performed at two different intensities.
Lima-Silva AE, De-Oliveira FR, Nakamura FY, Gevaerd MS.

Laboratório de Aptidão Física, Desempenho e Saúde, Universidade Federal de Alagoas, Maceió, AL, Brasil.

This study examined the effects of pre-exercise carbohydrate availability on the time to exhaustion for moderate and heavy exercise. Seven men participated in a randomized order in two diet and exercise regimens each lasting 3 days with a 1-week interval for washout. The tests were performed at 50% of the difference between the first (LT1) and second (LT2) lactate breakpoint for moderate exercise (below LT2) and at 25% of the difference between the maximal load and LT2 for heavy exercise (above LT2) until exhaustion. Forty-eight hours before each experimental session, subjects performed a 90-min cycling exercise followed by 5-min rest periods and a subsequent 1-min cycling bout at 125% VO2max/1-min rest periods until exhaustion to deplete muscle glycogen. A diet providing 10% (CHO(low)) or 65% (CHO(mod)) energy as carbohydrates was consumed for 2 days until the day of the experimental test. In the exercise below LT2, time to exhaustion did not differ between the CHO(mod) and the CHO(low) diets (57.22 +/- 24.24 vs 57.16 +/- 25.24 min). In the exercise above LT2, time to exhaustion decreased significantly from 23.16 +/- 8.76 min on the CHO(mod) diet to 18.30 +/- 5.86 min on the CHO(low) diet (P < 0.05). The rate of carbohydrate oxidation, respiratory exchange ratio and blood lactate concentration were reduced for CHO(low) only during exercise above LT2. These results suggest that muscle glycogen depletion followed by a period of a low carbohydrate diet impairs high-intensity exercise performance.

Hmmm

[ATZ]

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Curr Sports Med Rep. 2007 Jul;6(4):225-9. Related Articles, Links

Low-carbohydrate diets and performance.

Cook CM, Haub MD.

Department of Human Nutrition, Kansas State University, Manhattan, KS 66506, USA.

Athletes are continually searching for means to optimize their performance. Within the past 20 years, athletes and scientists have reported or observed that consuming a carbohydrate-restricted diet may improve performance. The original theories explaining the purported benefits centered on the fact that fat oxidation increases, thereby "sparing" muscle glycogen. More recent concepts that explain the plausibility of the ergogenicity of low-carbohydrate, or high-fat, diets on exercise performance pertain to an effect similar to altitude training. We and others have observed that although fat oxidation may be increased, the ability to maintain high-intensity exercise (above the lactate threshold) seems to be compromised or at least indifferent when compared with consumption of more carbohydrate. That said, clinical studies clearly demonstrate that ad libitum low-carbohydrate diets elicit greater decreases in body weight and fat than energy-equivalent low-fat diets, especially over a short duration. Thus, although low-carbohydrate and high-fat diets appear detrimental or indifferent relative to performance, they may be a faster means to achieve a more competitive body composition.

Conclusions:

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It is evident that higher-carbohydrate intake tends to elicit fewer perturbations in athletic performance compared with low carbohydrate intake. Many report that restricting carbohydrate intake elicits improvements in oxidative mechanisms, especially fat oxidation. However, any performance benefits of this approach have not been demonstrated consistently [9]. Weight loss is one area in which LCDs might be of benefit compared with higher-carbohydrate diets. Research consistently demonstrates that LCDs elicit faster weight loss than low-fat diets; however, it remains to be fully understood if the more rapid weight loss improves athletic performance.

[Ripped Barbarian]

you've got to consider liver glycogen, i believe that is far more important factor than muscle glycogen!

[NU_nutrition_TS]

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Hmmm

They deliberately depleted muscle glycogen to begin with on that study. No one really depletes their muscle glycogen outside of these extreme laboratory measures (unless starving and exercising over days). If, in the normal state of affairs - as illustrated in the study I quoted several posts back - only around a quarter of existing muscle glycogen is depleted during a resistance workout taken to failure, then even low carbohydrate diets would replenish that over two days!

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Conclusions:

The operative phrase in this study is: "or at least indifferent" - i.e., no significant difference!

As RB states liver glycogen is also important (and always gets replenished as a priority) as serum glucose tends to flow into/out of muscle glycogen, which acts as a buffer.

In most studies, the more carbs you feed prior to exercise the more is oxidised during exercise. On lower carb intakes fatty acids (and/or ketones) tend to supplement a lower rate of glucose oxidation and, in both cases, muscle glycogen usage remains about the same as does performance and time to exhaustion.

I suspect there are many more elements involved in exhaustion than just glycogen depletion and some of it may be psychological - if you believe low glycogen is going to have a major impact it probably will!

But all this is merely repeating what has already gone before in this thread. Ultimately it all boils down to the evolutionary perspective on modern human biology - again. If lack of dietary carbohydrates (whether due to overall food scarcity or a reliance on non-carbohydrate foods) resulted in such debilitating glycogen depletion and impaired physical performance, humankind would have become extinct long ago. There have been many periods during human evolution when food availability has been scarce and humans lived for periods in a semi-starved state until food once more became abundant. When it did they would have had to hunt and gather it - a very labour intensive activity. Survival of the species, under such circumstances, would dictate that adaptations would be made to be able to function optimally enough to hunt and gather in a semi-starved, glycogen depleted (or impaired) state.

[NU_nutrition_TS]

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As RB states liver glycogen is also important (and always gets replenished as a priority) as serum glucose tends to flow into/out of muscle glycogen, which acts as a buffer.

In most studies, the more carbs you feed prior to exercise the more is oxidised during exercise. On lower carb intakes fatty acids (and/or ketones) tend to supplement a lower rate of glucose oxidation and, in both cases, muscle glycogen usage remains about the same as does performance and time to exhaustion.

Just as an update to the above - with special reference to liver glycogen depletion/repletion - here is some corroborative evidence from a study published last year for the glycogen sparing nature of low carb diets:

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Low-carbohydrate diet burns more excess liver fat than low-calorie diet, study finds

DALLAS — Jan. 20, 2009 — People on low-carbohydrate diets are more dependent on the oxidation of fat in the liver for energy than those on a low-calorie diet, researchers at UT Southwestern Medical Center have found in a small clinical study.

The findings, published in the journal Hepatology, could have implications for treating obesity and related diseases such as diabetes, insulin resistance and nonalcoholic fatty liver disease, said Dr. Jeffrey Browning, assistant professor in the UT Southwestern Advanced Imaging Research Center and of internal medicine at the medical center.

The different diets produced other differences in glucose metabolism. For example, people on a low-calorie diet got about 40 percent of their glucose from glycogen, which is comes from ingested carbohydrates and is stored in the liver until the body needs it.

The low-carbohydrate dieters, however, got only 20 percent of their glucose from glycogen. Instead of dipping into their reserve of glycogen, these subjects burned liver fat for energy.

The findings are significant because the accumulation of excess fat in the liver — primarily a form of fat called triglycerides — can result in nonalcoholic fatty liver disease, or NAFLD. The condition is the most common form of liver disease in Western countries, and its incidence is growing. Dr. Browning has previously shown that NAFLD may affect as many as one-third of U.S. adults. The disease is associated with metabolic disorders such as insulin resistance, diabetes and obesity, and it can lead to liver inflammation, cirrhosis and liver cancer.

“Energy production is expensive for the liver,” Dr. Browning said. “It appears that for the people on a low-carbohydrate diet, in order to meet that expense, their livers have to burn excess fat.”

Results indicate that patients on the low-carbohydrate diet increased fat burning throughout the entire body.

Full article: Low-carbohydrate diet burns more excess liver fat than low-calorie diet, study finds

[anab0lic]

Wow great read, although large chunks of it went over my head.

I am curious for those that run very low carb diets (under say 20-30g a day) has this worked well in terms of putting on LBM?