(8) SEX DIFFERENCES IN THE SHORT-TERM AFTEREFFECTS OF A WEIGHTED VEST ON COUNTERMOVEMENT JUMP PERFORMANCE

Purpose: The purpose of this study was to examine the post activation performance effect (PAPE) (i.e. short-term aftereffects) of a weighted vest on countermovement jump (CMJ) performance among males and females. Methods: 15 males (age: 23.9 ± 2.2 years, mass: 88.8 ± 10.9 kg, height: 1.83 ± 0.06 m) and 14 females (age: 22.6 ± 1.2 years, mass: 64.1 ± 8.6 kg, height: 1.64 ± 0.08 m) volunteered to participate in this cross-sectional study. All participants had a history of sports participation, reported regularly engaging in exercise, and reported no history of significant injury or surgery. Following a standardized warm-up, participants completed CMJs on a force platform that recorded ground reaction force data. The CMJs were performed in three different conditions: 1) baseline, 2) weighted, 3) post. CMJs were first performed without additional load (baseline condition). Next, subjects donned a weighted vest with a load of 10% body mass (range: 9.2-10.9%) and performed additional CMJs (weighted condition). Then, subjects removed the weighted vest and performed a final set of CMJs (post condition). Seven CMJ trials were performed per condition. Rest periods were included between trials and conditions to minimize fatigue (30 s between trials, 60 s between conditions). The following variables were generated from the ground reaction force data collected during the CMJs: peak force, peak velocity, peak power, jump height, and the modified reactive strength index (mRSI). For each variable a mixed-model ANOVA, with a between-subjects factor of “sex” (male, female) and a within-subjects factor of “condition” (baseline, weighted, post), was conducted (alpha level = 0.05), with post-hoc tests for pairwise comparisons. The results reported here are for the comparisons between the baseline and post conditions. Pairwise comparisons were conducted separately for males and females when there was a significant sex-by-condition interaction effect. The average percent change (%∆) was calculated for each variable to quantify the magnitude of the change from baseline. Results: There were sex-by-condition interaction effects for peak power (p=0.01), jump height (p=0.04), and the mRSI (p=0.02), and main effects of condition for peak force (p< 0.001) and peak velocity (p< 0.001). Males exhibited increased peak power (p=0.01; %Δ = 4.3%), jump height (p=0.02, %Δ = 8.1%), and mRSI values (p=0.001, %Δ = 17.6%) in the post condition (vs. baseline). In contrast, females did not exhibit significant changes for any of these variables (p≥0.12). Overall, subjects exhibited greater peak velocities (p=0.01, %∆ = 3.0%) in the post condition (vs. baseline). Peak force did not differ significantly between conditions (p=0.06, %∆ = 1.9%). Conclusions: For males, performing CMJs with a weighted vest (10% body mass load) acutely enhanced lower body power, jump height, and reactive strength. However, this response was not observed in our female sample and may be due to lower absolute and relative strength in the female participants, which is a factor previously shown to moderate PAPE. Practical Applications: For males, performing CMJs with a weighted vest appears to be an effective priming strategy to enhance neuromuscular performance. These effects can be elicited with relatively light loads of 10% body mass, and short rest periods (~1-minute). This supports the efficacy of including a weighted vest to elicit a PAPE response in males when performing jump related training. Acknowledgements: None