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

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

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Updated Apr 4, 2026

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.

Simplified

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

Abstract

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