Carbohydrate feedings and exercise performance: effect of initial muscle glycogen concentration

Jun 1, 1993Journal of applied physiology (Bethesda, Md. : 1985)

How Starting Muscle Energy Levels Affect the Impact of Carbohydrate Intake on Exercise Performance

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Abstract

Cyclists with low preexercise muscle glycogen levels showed significantly decreased power output and pace during a time trial.

High glycogen levels with a carbohydrate (CHO) beverage resulted in the fastest performance times (117.93 minutes).
Ingesting a CHO drink prevented the decline in serum glucose observed during trials with a non-CHO beverage.
No significant differences were found in oxygen consumption, power output, or self-selected pace during the initial stages of exercise.
Power output and pace were significantly lower in the low glycogen with non-CHO beverage trial compared to other conditions.
The carbohydrate drink provided an average of 116 grams of CHO per trial.

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To determine whether the ergogenic benefits of carbohydrate (CHO) feedings are affected by preexercise muscle glycogen levels, eight cyclists performed four self-paced time trials on an isokinetic ergometer over a simulated distance of 70 km. Trials were performed under the following preexercise muscle glycogen and beverage conditions: 1) high glycogen (180.2 +/- 9.7 mmol/kg wet wt) with a CHO beverage (HG-CHO), 2) high glycogen (170.2 +/- 10.4 mmol/kg wet wt) with a non-CHO beverage (HG-NCHO), 3) low glycogen (99.8 +/- 6.0 mmol/kg wet wt) with a CHO beverage (LG-CHO), and 4) low glycogen (109.7 +/- 5.3 mmol/kg wet wt) with a non-CHO beverage (LG-NCHO). The CHO drink (ingested at the onset of exercise and every 10 km thereafter) provided 116 +/- 6 g CHO/trial and prevented the decline in serum glucose observed during both NCHO trials. Performance times ranged from 117.93 +/- 1.44 (HG-CHO) to 122.91 +/- 2.46 min (LG-NCHO). No intertrial differences (P > 0.05) were observed for O2 consumption (75% of maximal O2 consumption), power output (237 W), or self-selected pace (8.44 min/5 km) during the initial 71-79% of exercise. Over the final 14% of the time trial, power output and pace (231 W and 8.62 min/5 km) were similar for the HG-CHO, HG-NCHO, and LG-CHO conditions, but both variables were significantly lower during the LG-NCHO trial (198 W and 9.67 min/5 km, P < 0.05 vs. all other trials).(ABSTRACT TRUNCATED AT 250 WORDS)

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Carbohydrate feedings and exercise performance: effect of initial muscle glycogen concentration

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