| The purpose of this study was to determine the effect of the acoustic startle on neuromuscular activation and functional stability by gender. Fifteen (11 females and 4 males) National Collegiate Athletic Association Division I athletes participated in the study. A post-test with repeated measures design was used. The categorical independent variable was group (female luteal, female follicular, and male). The within-group independent variables were condition (startle; and control, non-startle), startle time (pre and post), and functional task time (preparatory and reactive). The dependent variables were muscle activation (hamstring/quadriceps electromyography [EMG] coactivation) and functional stability (rate of loading, ground contact time, and peak force). Statistical analyses consisted of multiple analyses of variance with repeated measures. When appropriate, a family-wise post-hoc self-corrected test within the statistical program or within group post-hoc t-tests with a Bonferroni correction were completed. Alpha was set at p ≤ .05.;The acoustic startle resulted in a significant increase in obicularis oculi (195%) EMG activity, regardless of group, and hamstring (male, 940%; female follicular, 2,350%; and female luteal, 260%) EMG activity poststartle. Although this result was anticipated, the acoustic startle had no significant effect on hamstring or quadriceps EMG activity or functional stability during the functional task. The pre-acoustic startle hamstring/quadriceps coactivation was significantly greater for the female luteal group (661%) than for the female follicular group, which was due to significantly greater hamstring muscle activation in the former. In addition, the hamstring and quadriceps EMG activities were greater poststartle for both female groups than for the male group, but were statistically significant for the female follicular hamstring (331%) and female luteal quadriceps (493%) only.;An acoustic startle affected neuromuscular activation immediately following the perturbation, with gender and menstrual cycle phase contributing to the effect. The effect of the acoustic startle on dynamic functional stability and acute non-contact injury risk is yet to be determined. Improved research design and methodology for testing the acoustic startle response, as well as inclusion of modulating factors such as mood, anxiety, and stress, are needed to advance the understanding of its role as an injury risk factor. |
