Abstract
This study examined the effect of three exercise-diet regimens on muscle glycogen
supercompensation and subsequent performance during a 20.9-km run. A diet containing
15% carbohydrate (CHO,L), 50% CHO (M), or 70% (CHO (H) was arranged in three trials
as follows: trial A = 3 days L, 3 days H; trial M = 3 days M, 3 days H; trial C =
6 days M. For each trial a 5-day depletion-taper exercise sequence was conducted on
the treadmill at 73% V̇O2max. The runs were 90, 40, 40, 20, and 20 min, respectively. A day of rest preceded
the 20.9-km performance run. Muscle biopsies were obtained from the gastrocnemius
on days 4 and 7 (both prior to and after the performance run). Trials A, B, and C
elevated muscle glycogen to 207, 203, and 159 mmol glucosyl units/kg wet tissue ImtnGI,
respectively. The performance run in both trials A and B utilized significantly more
glycogen than in trial C: 5.0 and 5.1 mmG/km vs. 3.1 mmG/km. There were, however,
no differences in either performance run times or post-performance run glycogen levels
between the trials. These data demonstrate that (1) muscle glycogen can be elevated
to high levels with a moderate exercise-diet regimen; (2) initial muscle glycogen
levels influence the amount subsequently utilized during exercise; (3) carbohydrate
loading is of no benefit to performance for trained runners during a 20.9-km run.
Key words
dietary carbohydrate - muscle glycogen - human skeletal muscle - physical exertion
