INFLUENCE OF SEX AND MUSCLE ACTION ON MECHANOMYOGRAPHIC MEAN POWER FREQUENCY OF THE VASTUS LATERALIS

Sergio Perez Jr.1, Stephanie Sontag1, Trent Herda2, Adam Sterczala3, Jonathan Miller2, Mandy Parra4, Hannah Dimmick5, Michael A. Trevino1 1Oklahoma State University, Stillwater, Oklahoma; 2University of Kansas, Lawrence, Kansas; 3University of Pittsburgh, Pittsburgh, Pennsylvania; 4Baker University, Baldwin City, Kansas; 5University of Calgary, Calgary, Alberta PURPOSE: To examine mechanomyographic mean power frequency (MMGMPF)-torque relationships for the vastus lateralis (VL) in sedentary males and females. METHODS: Eleven females (mean ± SD; age = 22.7 ± 5.5 yrs) and eight sedentary males (age=19.4 ± 0.7 yrs) volunteered for this study. An MMG sensor was placed over the VL and subcutaneous fat (sFAT) was measured via ultrasonography at the sensor site. Participants completed 3 isometric maximal voluntary contractions (MVCs) of the knee extensors on an isokinetic dynamometer followed by an isometric trapezoid muscle action at 40% MVC. For linearly increasing and decreasing muscle actions, linear regressions models were fit to the log-transformed MMGMPF-force relationship and the slope (b term) was calculated. MMGMPF was averaged during the steady force segment. A 2way mixed factorial ANOVA (sex [male vs. female] x segment [ramp up vs. ramp down]) examined differences in the b terms during the linearly increasing and decreasing muscle actions. Independent samples t-tests examined sex-related differences in skinfold measurements and MMGMPF during steady torque. Pearson’s product moment correlations were used to determine relationships among sFAT and the b terms and MMGMPF. Alpha was set at 0.05. RESULTS: For the b terms, there was no significant two way interaction (p = 0.714) or main effect for sex (p = 0.259). There was a significant main effect for segment (p = 0.001). The b terms were greater during the linearly increasing (0.154 ± 0.131) than decreasing (0.006 ± 0.113) segment when collapsed across sex. During steady torque, MMGMPF was significantly greater (p = 0.002) for males (26.36 ± 2.57 Hz) than females (20.91 ± 3.64 Hz), while sFAT was significantly greater (p = 0.001) for females (1.59 ± 0.69 cm) than males (0.57 ± 0.32 cm). sFAT was significantly correlated with MPF during the plateau (p \u3c 0.001, r = -0.736), but not the b terms for either segment (p \u3e 0.05). CONCLUSION: MMGMPF distinguished between muscle activation and deactivation strategies, but not between sexes. MMGMPF during steady torque was greater for males; however, this may be due to the influence sFAT low-pass filtering the MMG signal to a greater extent for females. Higher targeted torques may be necessary to distinguish muscle activation and deactivation strategies between sexes