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C-15U FREE COMMUNICATION/POSTER SKELETAL MUSCLE FATIGUE

GENDER DIFFERENCES IN CENTRAL AND PERIPHERAL FACTORS OF SKELETAL MUSCLE FATIGUE

Gore, S A.1; Keller, B A.1

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Medicine & Science in Sports & Exercise: May 2003 - Volume 35 - Issue 5 - p S144
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Women generally exhibit greater fatigue resistance than men, due in part to differences in muscle mass. Less muscle mass in women results in decreased oxygen demand and increased oxygen delivery at the same relative workload compared to men, yielding greater endurance.

PURPOSE

The purpose of this study was to examine gender differences in muscle fatigue between men and women matched for lean muscle mass.

METHODS

Male and female athletes (mean age=19.7±1.35 y) were matched for thigh lean muscle volume (N=8 pairs). Strength was measured as maximum voluntary contraction (MVC). To determine MVC, subjects performed a 5-sec max isometric contraction with a superimposed electrical stimulus (SES) at 3x threshold (26-pulse, 100-Hz, 250-ms train). Central activation ratio (CAR=MVC/MVC+electrical stimulation) was calculated to insure maximum motor unit recruitment. Subjects then completed a fatigue protocol of intermittent, 5-sec sustained isometric leg extension at 50% of initial MVC with alternating 5-sec rest periods until exhaustion. At termination, a final 5-sec MVC was done with SES and CAR was calculated to quantify the contribution of central factors to fatigue. Gender differences in time to fatigue, rate of fatigue, percent of initial strength at fatigue, and CAR were assessed with paired t-tests.

RESULTS

There were no significant differences (p < .05) within matched pairs for time to fatigue (M=14.15±5.75, F=20.04±9.44 min), rate of fatigue (M=−5.19±2.39, F=−4.46±3.07 ft lbs/min), or percent of initial strength (M=62.15±7.36, F=57.75±9.24%). There was no significant in CAR (M=0.91±.04, F=0.94±.02). (Mean±SD)

CONCLUSION

Greater fatigue resistance typically observed in women is probably due to differences in muscle mass. When matched for lean muscle mass, gender differences in strength and time to fatigue disappear. It is likely that vascular occlusion at absolute workloads is similar in matched women and men, yielding the same demands for, and delivery of oxygen to the working muscle. Thus, there appear to be no intrinsic gender differences in muscle quality.

©2003The American College of Sports Medicine