William Reed, Lacey Harper, Melanie Antonio, Valentina Taddia, Breanna McDonald, Micah Poisal, Kaden Buford, Esther Steingold, Garrett Hester. Kennesaw State University, Kennesaw, GA.

BACKGROUND: Research examining balance after fatigue tends to employ exercise that is strenuous or specific to an isolated joint. Albeit informative, we felt it important to examine responses to activity more closely resembling acts of daily living. The plantar flexors are particularly susceptible to fatigue derived from walking due to their relatively large contribution compared to more commonly studied muscles of the thigh. In addition, rate of torque development (RTD) is thought to be more sensitive to fatigue than peak torque (PT). The purpose of our ongoing study is to determine the differences, if any, for responses in maximal and rapid torque production after brisk walking in young and middle-aged females. Here, we report on preliminary findings based on participants completed to date. METHODS: Four untrained females (31.5±17.7 yrs) completed a testing visit 3-7 days following a familiarization session. Subjects performed rapid, maximal voluntary isometric contractions of the plantar flexors before and 2.5, 6.5, and 10.5 min after a 6-min brisk walking task. The instructions for the walking task were to “cover as much distance as possible.” PT and rate of torque development at peak (RTDPK), early (0-50 ms and 0-100 ms (RTD0-100)), and late (0-200 ms) time phases were calculated from the torque-time curve. Friedman’s test and relative changes were computed to examine responses across time. RESULTS: Notable, but non-significant, relative decreases were found for RTD0-100 (-41%; p=0.068) and RTDPK (-29%; p=0.058), whereas PT (+5%; p=0.682) and other RTD measures (p>0.05) were unaffected. CONCLUSIONS: These preliminary findings suggest early RTD is more sensitive than later RTD and PT to walking-induced fatigue, but interpretation is limited due to our small sample size which resulted in underpowered analyses. An impaired rate of muscle activation by the central nervous system is one possible explanation for the fatigue-related decrease in early RTD. Nonetheless, as our sample size increases and age-related comparisons are feasible, a primary aim is to determine if these preliminary findings remain consistent in females 45-60 yrs of age. Information gained from the future analysis will elucidate the importance of maintaining rapid torque production in middle-age.

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