Impact of Muscle Glycogen Availability on the Capacity for Repeated Exercise in Man

Jul 22, 2015Medicine and science in sports and exercise

How Muscle Sugar Levels Affect the Ability to Do Repeated Exercise in People

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Abstract

Participants who consumed a high-carbohydrate beverage during recovery prolonged their exercise duration by an average of 32 minutes compared to those on a low-carbohydrate beverage.

Muscle glycogen concentrations were significantly higher after recovery in participants consuming high-carbohydrate drinks (269 ± 84 mmol · kg dry mass(-1)) compared to those on low-carbohydrate drinks (157 ± 37 mmol · kg dry mass(-1)).
The rate of muscle glycogen breakdown during the second exercise run was greater in participants consuming high-carbohydrate beverages (3.1 ± 1.5 mmol · kg dry mass(-1) · min(-1)) than in those on low-carbohydrate beverages (1.6 ± 1.3 mmol · kg dry mass(-1) · min(-1)).
At the point of fatigue after recovery, muscle glycogen levels were higher in the high-carbohydrate group (123 ± 28 mmol · kg dry mass(-1)) compared to the low-carbohydrate group.
Fatigue during repeated exercise is linked to low muscle glycogen levels, highlighting its role in endurance performance.

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PURPOSE: This study aims to examine whether muscle glycogen availability is associated with fatigue in a repeated exercise bout following short-term recovery.

METHODS: Ten endurance-trained individuals underwent two trials in a repeated-measures experimental design, each involving an initial run to exhaustion at 70% of VO2max (Run 1) followed by a 4-h recovery and a subsequent run to exhaustion at 70% of VO2max (Run 2). A low-carbohydrate (L-CHO; 0.3 g · kg body mass(-1) · h(-1)) or high-carbohydrate (H-CHO; 1.2 g · kg body mass(-1) · h(-1)) beverage was ingested at 30-min intervals during recovery. Muscle biopsies were taken upon cessation of Run 1, after recovery, and at exhaustion during Run 2 in L-CHO (F2). In H-CHO, muscle biopsies were obtained after recovery, at the time point coincident with fatigue in L-CHO (F2), and at the point of fatigue during the subsequent exercise bout (F3).

RESULTS: Run 2 was more prolonged for participants on H-CHO (80 ± 16 min) than for participants on L-CHO (48 ± 11 min; P < 0.001). Muscle glycogen concentrations were higher at the end of recovery for participants on H-CHO (269 ± 84 mmol · kg dry mass(-1)) than for participants on L-CHO (157 ± 37 mmol · kg dry mass(-1); P = 0.001). The rate of muscle glycogen degradation during Run 2 was higher with H-CHO (3.1 ± 1.5 mmol · kg dry mass(-1) · min(-1)) than with L-CHO (1.6 ± 1.3 mmol · kg dry mass(-1) · min(-1); P = 0.05). The concentration of muscle glycogen was higher with H-CHO than with L-CHO at F2 (123 ± 28 mmol · kg dry mass(-1); P < 0.01), but no differences were observed between treatments at the respective points of exhaustion (78 ± 22 mmol · kg dry mass(-1) · min(-1 )for H-CHO vs 72 ± 21 mmol · kg dry mass(-1) · min(-1) for L-CHO).

CONCLUSION: Increasing carbohydrate intake during short-term recovery accelerates glycogen repletion in previously exercised muscles and thus improves the capacity for repeated exercise. The availability of skeletal muscle glycogen is therefore an important factor in the restoration of endurance capacity because fatigue during repeated exercise is associated with a critically low absolute muscle glycogen concentration.

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Impact of Muscle Glycogen Availability on the Capacity for Repeated Exercise in Man

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