Metabolic response in type I and type II muscle fibers during a 30-s cycle sprint in men and women

1. Metabolic response in type I and type II muscle fibers during a 30-s cycle sprint in men and women Mona Esbjornsson-Liljedahl, Carl Johan Sundberg, Barbara Norman, and Eva Jansson Journal of Applied Physiology 1999

2. Background • Reduction in glycogen and ATP is greater in type II than in type I fibers during sprint exercise. • Women have lower systemic concentrations of blood lactate and plasma catecholamines than do men after sprint exercise. • Glycolytic enzyme activities are lower in muscle from women than from men.

3. Hypothesis • The reduction in muscle glycogen content during sprint exercise would be smaller in women than in men. • A potential gender difference in glycogen reduction would be greater in type II than in type I fibers.

4. Subjects • 20 men and 19 women • College students • Active but not at a competitive level • 14 of the women were taking oral contraceptives

5. Methods • Subjects performed a Wingate test on a cycle ergometer • Began pedaling as fast as possible • Load was dropped (0.075 kp/kg body weight) • Cycle at maximal effort for 30 seconds

6. Measurements • Blood was sampled through a catheter 20 min. pre-exercise and at 3,6, and 9 min. post-exercise • Muscle biopsies from vastus lateralis were taken pre-exercise and within 10 seconds post exercise

7. Results • Peak power • Absolute: 27% lower in women • Relative to body mass: 15% lower • Relative to fat free mass: NSD • Mean power • Absolute: 30% lower in women • Relative to body mass: 18% lower • Relative to fat free mass: 8% lower

8. Results • Fiber type • No gender differences in relative numbers of different fiber types • Relative area of type II fibers smaller in women • CSA of type I: NSD • CSA of type IIA: 33% smaller • CSA of type IIB: 31% smaller • Weighted mean fiber area: 20% less

9. Results • Blood lactate • Increase in blood lactate 22% smaller in women

10. Results • Exercise induced changes in ATP, ADP, IMP, and PCr did not differ between genders in any fiber type. • Changes in glycogen and lactate did not differ between genders in type II fibers.

11. Results • Glycogen reduction was 42% smaller in women than men in type I fibers. • Lactate content was 20% lower in women in type I fibers after exercise. • Increase in lactate in type I fibers was slightly smaller in women, but it was not significant (p=.09)

12. Discussion • The smaller reduction in glycogen in type I fibers in women may contribute to smaller accumulation of blood lactate in women. • This may be due to lower activity of anaerobic enzymes or smaller increase in plasma catecholamines.

13. Discussion • The lack of difference in ATP, PCr, and glycogen in type II fibers may argue against a lower activation of these fibers in women.

14. Discussion • Hypothesis was not confirmed; greater gender difference in type I fibers. • It was suggested that women do not activate as many type II fibers as men, but this study shows that change in lactate and glycogen in type II fibers is the same between the genders.

15. Questions?