AGE-RELATED DIFFERENCES IN MUSCULAR ENDURANCE AND FATIGUE RESISTANCE OF THE KNEE EXTENSORS AND FLEXORS

Kelly E. Joniak1, Jennifer N. Norman1, Ryan M. Miller1, Aaron D. Heishman1,2, Eduardo D.S. Freitas1, Samuel R. Buchanan1, Michael G. Bemben1, FACSM.1University of Oklahoma, Department of Health and Exercise Science, Norman, Oklahoma. 2University of Oklahoma, Department of Athletics, Basketball Strength and Performance, Norman, Oklahoma. Previous research suggests that increasing age and the ability to sustain maximal force may be task dependent. Given the changes observed in skeletal muscle with increasing age, younger individuals may display greater fatigue resistance at higher contraction velocities, whereas older individuals may have an advantage at slower contraction velocities. PURPOSE: The purpose was to compare measures of muscular endurance and fatigue resistance of the knee extensors (KE) and knee flexors (KF) in young and older women when performing maximal concentric contractions at a fast (240deg/s) and slow (60deg/s) contraction velocity. Additionally, two measures used to assess fatigue resistance were compared. METHODS: Twenty-four women divided into younger(YW: 21.6±0.8years, 166.1±7.9cm, 64.1±9.4kg) and older women(OW: 62.7±1.8years,160.7±3.8cm, 60.5±6.8kg) performed two 30-repetition isokinetic (set 1: 240, set 2: 60deg/s) contraction tests with the KE and KF. Fatigue resistance and muscular endurance were assessed for the KE and KF and quantified by the total amount of work performed (TW, J) and two measures of work fatigue, expressed as percent loss by comparing the TW performed across the last 10 repetitions relative to the TW of the first 10 (WF10) and the TW of the last three repetitions relative to the first three repetitions (WF3) for each contraction velocity and muscle group. RESULTS: The YW completed significantly more TW for both muscle groups at both velocities (KE: p≤0.001; KF: p≤0.001). The OW were more fatigable during the 240deg/s for both muscle groups (KE: WF10: p=0.002,WF3:p=0.001; KF: WF10: p=0.015,WF3: p=0.001), whereas YW displayed greater fatigability during the 60deg/s contractions (KE: WF10: p=0.002,WF3: p<0.001; KF: WF10: p=0.024,WF3:p=0.006). Interestingly, except for KE at 60deg/s, WF10revealed significantly lower fatigue resistance values than WF3(p≤0.043), with all four comparisons displaying significant relationships (r=0.43-0.71; p≤0.034). CONCLUSIONS: These data suggest that OW display greater fatigue resistance at slower velocities (60deg/s), whereas YW have an advantage at faster contraction velocities (240deg/s). Further, differences in WF10and WF3warrant future research to identify which captures a more accurate assessment of muscular fatigue.