Title page for ETD etd-082799-123657

Type of Document Master's Thesis
Author Smith, Michelle R.
Author's Email Address mismith2@vt.edu
URN etd-082799-123657
Title Effects of Pre-exercise Muscle Glycogen Status on Muscle Phosphagens, Sarcoplasmic Reticulum Function, and Performance During Intermittent High Intensity Exercise
Degree Master of Science
Department Human Nutrition, Foods, and Exercise
Advisory Committee
Advisor Name Title
Rankin, Janet L. Walberg Committee Chair
Houston, Michael E. Committee Member
Williams, Jay H. Committee Member
  • muscle biopsy
  • creatine phosphate
  • carbohydrate
  • cycle exercise
  • calcium
Date of Defense 1999-08-09
Availability unrestricted
Eight competitive cyclists performed two cycling trials, one following a high

carbohydrate diet (H-CHO) and the other following a low carbohydrate diet (L-CHO).

Trials consisted of repeated 60s maximal effort sprints to fatigue at a workload designed

to elicit 125-135% VO2peak at 90rpm. Three min of recovery separated sprints. Muscle

biopsies taken at rest (biopsy 1), 85% max interval rpm (biopsy 2), and 70% max interval

rpm (biopsy 3) revealed a main effect of diet on muscle glycogen levels: 609 ± 38 HCHO

vs. 390 ± 42 mmol/kgdw L-CHO at biopsy 1, 383 ± 29 vs. 252 ± 28 mmol/kgdw at

biopsy 2, and 346 ± 29 vs. 196 ± 18 mmol/kgdw at biopsy 3 (p<0.01). Similar decreases

in muscle glycogen (45%), creatine phosphate (CP) (35%), and sarcoplasmic reticulum

(SR) Ca2+-uptake (56%) were shown in both trials from biopsy 1 to 3. SR Ca2+-release

decreased by 53% in H-CHO subjects and 36% in L-CHO subjects. Total exercise time

tended to be longer in H-CHO than L-CHO subjects (57.5 ± 10 vs. 42.0 ± .89min)

(p=0.09). H-CHO subjects exercised significantly longer than L-CHO subjects from

biopsy 2 to 3 (33.6 ± 10 vs. 18 ± 3.6min) (p< 0.05). Results suggest that fatigue from 40-

60min of intermittent 60s high intensity cycling intervals is associated with reductions in

muscle glycogen, CP, and SR function, and that the latter part of performance is impaired

by low muscle glycogen. These data do not support a relationship between muscle

glycogen status and SR function in intermittent high intensity exercise.

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