Changes In Select Emg Parameters During An Agility Test Performed To Fatigue.

Abstract

PURPOSE: To determine the effect of fatigue (FAT) on the mean median frequency (MF) and peak amplitude (PA) of select muscles. METHODS: Surface EMG of the vastus medialis (VM), vastus lateralis (VL), semitendinosus (ST) and biceps (BF) and rectus femoris (RF) were recorded at 4800Hz in 16 female, DI soccer players (19.7 ± 1.1 yrs), during an agility test. Subjects completed 4 trials of the test, alternating sides. Rest between trials ensured non-FAT. Subjects then ran trials starting every 30s, alternating sides, until a 5% decrement in their non-FAT times occurred on 2 successive runs. Two trials from each side were then run and recorded as the FAT trials. For each muscle, the EMG data were band pass filtered. The MF of a 107 ms moving window was calculated using a time-frequency analysis based on power spectra estimation (short-time Fourier transform) for each muscle, for each trial. The mean MF for the trial was determined using the obtained MFs. The mean PA for each muscle was determined by dividing the trial into 107 ms windows obtaining the PA of the window and then obtaining the mean of the individual PAs. The average MFs and PAs for each trial were grouped into 3 trial periods: the first 4 non-FAT, 4 middle and the last 4 FAT trials. Linear mixed models, with trial period as a repeated factor, were used to test for differences in average MF and PA between trial periods. RESULTS: For all 5 muscles for both legs, there was a significant difference in average MF and PA across trial periods (p <0.001). Pairwise comparisons showed a significant decrease for both the MF and PA from the non-FAT trials to the middle trials on all muscles for both legs (p <0.001). Significant decreases from middle trials to FAT trials were noted for all muscles for both legs for PA (p <0.05) except the left BF, while for MF, significant differences were noted for the right RF and VL, and the left VM, RF, and VL (p-<0.01). Across all muscles MF decreased 7.6% from the non-FAT to middle trials and decreased another 3.1% from middle to FAT trials. Similarly, across all muscles PA decreased 17.5% from the non-FAT to middle trials and further decreased 16.9% from middle to FAT trials. CONCLUSIONS: In the current testing paradigm, during a dynamic task in which performance decreases overtime, a decrease in the average MF and PA are potential indicators of muscle fatigue.