Max J. Tilden1, Anthony B. Ciccone2, Jake A. Deckert2, Cory R. Schlabs2, Tércio A.R. Barros2, Trent J. Herda2 & Joseph P. Weir2, FACSM 1University of Kansas, Lawrence, Kansas; 2University of Nebraska, Lincoln, Nebraska; e-mail: m341t775@ku.edu

Repeated maximal effort isokinetic knee extension tests are commonly used to examine fatigue. Electromyographic (EMG) median power frequency (MPF) is thought to be related to peripheral fatigue. Multiple synergist muscles contribute to knee extension torque, and multiple range-of-motion (ROM) windows have been used to collect surface EMG data. MPF data taken from different ROM windows could alter the interpretation of magnitude of muscle-specific fatigue. PURPOSE: Quantify the EMG MPF slopes of three knee extensor muscles over three ROM windows commonly used in isokinetic tests. METHODS: Nine healthy males and nine healthy females (age=21.1±1.4 y; height=173.8±12.4 cm; mass=72.1±14.7 kg) performed 50 maximal effort concentric knee extensions at 180°/s, with passive flexion, on an isokinetic dynamometer. Custom LabVIEW software collected position and EMG data for each repetition at 10 Hz. For the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM), normalized EMG MPF data were captured in 3 different ROM windows: full ROM (F), 120°-150° (M), and load range (L). Pearson correlations of normalized EMG MPF and repetition number were calculated for each muscle over each ROM window. Pearson correlation coefficient (r) values were analyzed via a two-way (3) muscle x (3) window ANOVA. Alpha was set at .05. RESULTS: There was no significant (p=.516) interaction between muscle and window. There was no significant (p=.577) main effect of window on EMG MPF slope across repetitions. There was a significant (p=.022) main effect of muscle, where normalized EMG MPF slopes for RF were more negative than VL (95% CI for difference: -.244 to -.103) and VM (95% CI for difference: -.212 to -.016). There was no significant (p=???) difference between VL and VM EMG MPF slopes (95% CI for difference: -.074 to .102). CONCLUSION: EMG MPF slope data suggests that, during a 50-repetition repeated maximal effort knee extension test, the RF muscle experiences more fatigue than the VL and VM muscles. Furthermore, when analyzing EMG MPF, ROM window does not affect the interpretation of MPF slope.

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