Abstract
Purpose
We investigated the coupling between muscle glycogen content and localization and high-intensity exercise performance using a randomized, placebo-controlled, parallel-group design with emphasis on single-fiber subcellular glycogen concentrations and sarcoplasmic reticulum Ca2+ kinetics.
Methods
Eighteen well-trained participants performed high-intensity intermittent glycogen-depleting exercise followed by randomization to a high- (CHO, ~1 g CHO·kg-1·h-1, n = 9) or low-carbohydrate placebo diet (PLA,
Results
The exercise and carbohydrate manipulations led to distinct muscle glycogen concentrations in CHO and PLA at the whole-muscle (291 ± 78 vs 175 ± 100 mmol·kg-1 dw, P = 0.020) and subcellular level in each of three local regions (P = 0.001-0.046). This was coupled with near-depleted glycogen concentrations in single-fibers of both main fiber types in PLA, especially in the intramyofibrillar region (within the myofibrils). Furthermore, increased ratings of perceived exertion and impaired repeated sprint ability (~8% loss, P < 0.001) were present in PLA, the latter correlating moderately to very strongly (r = 0.47-0.71, P = 0.001-0.049) with whole-muscle glycogen and subcellular glycogen fractions. Finally, sarcoplasmic reticulum Ca2+ uptake, but not release, was superior in CHO, whereas neuromuscular function, including prolonged low-frequency force depression, was unaffected by dietary manipulation.
Conclusions
Together, these results support an important role of muscle glycogen availability for high-intensity exercise performance, which may be mediated by reductions in single-fiber levels, particularly in distinct subcellular regions, despite only moderately lowered whole-muscle glycogen concentrations.
We investigated the coupling between muscle glycogen content and localization and high-intensity exercise performance using a randomized, placebo-controlled, parallel-group design with emphasis on single-fiber subcellular glycogen concentrations and sarcoplasmic reticulum Ca2+ kinetics.
Methods
Eighteen well-trained participants performed high-intensity intermittent glycogen-depleting exercise followed by randomization to a high- (CHO, ~1 g CHO·kg-1·h-1, n = 9) or low-carbohydrate placebo diet (PLA,
Results
The exercise and carbohydrate manipulations led to distinct muscle glycogen concentrations in CHO and PLA at the whole-muscle (291 ± 78 vs 175 ± 100 mmol·kg-1 dw, P = 0.020) and subcellular level in each of three local regions (P = 0.001-0.046). This was coupled with near-depleted glycogen concentrations in single-fibers of both main fiber types in PLA, especially in the intramyofibrillar region (within the myofibrils). Furthermore, increased ratings of perceived exertion and impaired repeated sprint ability (~8% loss, P < 0.001) were present in PLA, the latter correlating moderately to very strongly (r = 0.47-0.71, P = 0.001-0.049) with whole-muscle glycogen and subcellular glycogen fractions. Finally, sarcoplasmic reticulum Ca2+ uptake, but not release, was superior in CHO, whereas neuromuscular function, including prolonged low-frequency force depression, was unaffected by dietary manipulation.
Conclusions
Together, these results support an important role of muscle glycogen availability for high-intensity exercise performance, which may be mediated by reductions in single-fiber levels, particularly in distinct subcellular regions, despite only moderately lowered whole-muscle glycogen concentrations.
| Original language | English |
|---|---|
| Pages (from-to) | 2073-2086 |
| Number of pages | 14 |
| Journal | Medicine & Science in Sports & Exercise |
| Volume | 54 |
| Issue number | 12 |
| DOIs | |
| Publication status | Published - 16 Jul 2022 |
Keywords
- fatigue
- intermittent exercise
- metabolism
- excitation-contract
- carbohydrate