Michael A. Trevino1, Eric M. Mosier & Trent J. Herda1

1University of Kansas, Lawrence, Kansas

PURPOSE: This study examined the mechanomyographic mean power frequency (MMGMPF)-force relationships for 5 aerobically-trained (AT), 5 resistance-trained (RT), and 5 sedentary (SED) individuals. METHODS: Five AT (age=19.20±0.45 yrs), 5 RT (age=25.00±4.53 yrs), and 5 SED (21.20±2.17 yrs) volunteered for this investigation. The AT ran 61±15 miles∙wk-1, all but one RT subject were capable of a one repetition maximum back squat ≥ twice their body mass, and the SED did not participate in any structured physical activity for 3 years prior. Each participant was seated on a Biodex isokinetic dynamometer and isometric leg extensor strength assessments were performed on the right leg at a 90° flexion with isometric strength measured using the force signal from a load cell fitted to the Biodex. Participants performed three maximal voluntary contractions (MVC) followed by an isometric trapezoid muscle action at 60% MVC calculated from the highest MVC. An MMG sensor was placed over the vastus lateralis (VL) and thigh skinfolds were collected at the electrode site. The MMG and force signals were simultaneously sampled at 2 kHz and were bandpass filtered (fourth-order Butterworth) at 5-100 Hz. For the linearly increasing and decreasing muscle actions, linear regression models were fit to the log-transformed MMGMPF-force relationships and the slope (b term) and anti-log of the y-intercept (a term) were calculated. An average of MMGMPF was calculated for the entire steady force segment. Separate 2-way mixed factorial ANOVAs (training status [AT vs. RT vs. SED] x segment [linear increase vs. linear decrease]) were used to examine the b and a terms during the linearly increasing and decreasing muscle actions. Separate 1-way ANOVAs were used to examine MMGMPF during the steady force segment and skinfold thickness among the AT, RT, and SED. When appropriate, follow-up analyses were performed using paired and independent samples t-test with Bonferroni corrections. An alpha level was set at 0.05 to determine statistical significance. RESULTS: The b and a terms were not different among training statuses (P>0.05) or linearly increasing and decreasing segments (P>0.05). The 95% confidence intervals for the b terms suggested deceleration in MMGMPF throughout the force spectrum for linearly increasing and decreasing muscle actions. MMGMPF during the steady force segment (P=0.287) and skinfold thicknesses (P=0.142) were not different among training status. CONCLUSION: MMGMPF did not distinguish between training statuses or muscle actions. Higher targeted forces with faster contraction rates may be necessary for MMGMPF to distinguish between training statuses and muscle actions.

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