Rob J. MacLennan1,2, Alina P. Swafford2, Dennis P. Kwon2, Jason M. DeFreitas1, Matt S. Stock2 1Oklahoma State University, Stillwater, Oklahoma;2University of Central Florida, Orlando, Florida

Muscular fatigue has been reported to have varying effects depending on sex. Both males and females incur deficits in strength resulting from strenuous activity but males suffer greater relative deficits. Similarly, in a fatigued state, males may be relatively less able to activate muscles. PURPOSE: We sought to determine whether the decrease in strength that males and females suffer is related to changes in their voluntary activation(%VA). METHODS: Twenty-two untrained, college-aged, males (11) and females (11) participated. Subject’s dominant lower leg was strapped to an attachment set at an angle of 110° (180° = full extension) for isometric knee extensions. At pretesting, subjects performed maximal voluntary contractions (MVC) and the interpolated twitch technique was applied to assess %VA. Following initial testing, a fatiguing protocol was performed which consisted of 20 six-second MVCs with 3 seconds in between. In the fatigued state, subjects again performed an MVC and %VA was assessed. Linear regression was performed to determine if the variance in fatigability, as measured by change in MVC, can be accounted for by changes in %VA for each sex. RESULTS: Regression showed that 15.3% and 1.1% of the variance in force loss could be explained by changes in %VA in males and females, respectively. However, neither of these models were significant (p = 0.233 and p = 0.760). The results are shown in the figure below for both males (circles) and females (triangles).A 2-way mixed-factorial ANOVA showed neither a group × time interaction (p = 0.296), nor a main effect for time (p = 0.288) for %VA. CONCLUSION: The findings suggest that voluntary activation was not responsible for the force loss with fatigue in either males or females. For the females, this could be partially due to the fact that many of them had minimal changes in MVC from the fatigue protocol, whereas all of the males showed at least a 10% deficit. However, there were no differences in %VA between males and females.

MacLennan Figure 1.docx (154 kB)
Figure 1

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