Tércio A.R. Barros1, Anthony B. Ciccone2, Jake A. Deckert2, Cory R. Schlabs2, Max J. Tilden2 , Trent J. Herda2 & Joseph P. Weir2, FACSM; 1University of Nebraska, Lincoln, Nebraska; 2University of Kansas, Lawrence, Kansas; tercioarajoedfisica@gmail.com

Repeated maximal effort isokinetic knee extension tests are common in fatigue research. The theory of common drive dictates that surface electromyographic (EMG) amplitude should be highly correlated between synergist muscles. However, researchers collect EMG data from different ROM (range-of-motion) windows. Different data collection windows will inherently result in different datasets from each trial. This may change the interpretation of the same test. PURPOSE: Quantify the relationship magnitudes of EMG RMS between the knee extensor muscles and determine if those relationships are affected by the ROM in which data is collected. 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) completed one bout of 50 repeated maximal effort concentric knee extensions at 180°/s with passive flexion on an isokinetic dynamometer. Position and EMG were sampled at 10k Hz. Custom LabVIEW software was used to analyze data. For the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM), EMG data were captured in 3 different ROM windows: full ROM (F), 120°-150° (M), and load range (L). EMG amplitude was quantified via normalized root mean square (RMS) of the EMG signal in each ROM window. Between-muscle EMG amplitude Pearson correlations of the VL-VM, VL-RF, and RF-VM combinations over each window were calculated. Pearson correlation coefficient (r) values were analyzed via a two-way 3 (window) x 3 (muscle combination) ANOVA. Alpha was set at .05. RESULTS: There was no significant interaction between window and muscle. There was no main effect of muscle. There was a main effect of window where the F and LR windows yielded stronger between-muscle correlations than the M window. RMS amplitude data from F windows yielded stronger between-muscle correlations than LR windows. CONCLUSIONS: When processing repeated isokinetic knee extension data, surface EMG RMS data from the full concentric range of motion results in the strongest between-muscle correlations of synergist muscles. Assuming the task does not deviate from the theory of common drive, EMG RMS data gathered from larger ROM windows are probably better representative of the EMG amplitude during repeated maximal effort isokinetic knee extensions.

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