(21) INFLUENCE OF ACCENTUATED ECCENTRIC LOADING TEMPO DURING A BACK SQUAT ON POST ACTIVATION PERFORMANCE ENHANCEMENT IN A COUNTERMOVEMENT JUMP

Purpose: It is theorized that performing a heavy resistance exercise can enhance the rate of force development (RFD) for countermovement jumps (CMJ). Factors that can influence the magnitude of the enhancement include exercise type, intensity, volume, and rest period. A motor unit can produce its highest force during an eccentric contraction, making accentuated eccentric loading (AEL) a viable option for potentiation. Previous research has shown AEL can enhance jump height. No research has compared the tempo of AEL on subsequent CMJs. Methods: Fifteen subjects participated in this study (age-23.4±4.0 years, height-1.76±0.06m, body mass-85.1±12.2 kg, relative 1RM back squat-1.70±0.21 kg/kg). Each visit was separated by at least one week and each participant completed a 5x3 back squat protocol with 100% 1RM on the eccentric portion and 40% 1RM during the concentric portion of the movement with a 1 second eccentric (FT) or 3 second eccentric tempo (ST). After each set, the participant passively rested for three minutes and then performed two countermovement jumps arms akimbo. Countermovement jumps were performed on a pair of force plates and jumps were then analyzed using a customized Microsoft Excel spreadsheet. Variables extracted for analysis were: jump height (JH), relative peak power (RPP), braking rate of force development (Braking RFD), reactive strength index-modified (RSImod), eccentric and concentric duration, eccentric and concentric impulse, and time to takeoff (TTT). Repeated-measures ANOVA were performed to determine differences between tempo and across sets. Alpha level was set at p ≤ 0.05. Results: Results are displayed in Table 1. There was a statistically significant difference between baseline and all subsequent sets for JH and RPP for both ST and FT conditions (p ≤ 0.05). For eccentric/concentric duration ratio, there was a statistically significant decrease during the FT between baseline and all subsequent sets performed (p ≤ 0.05). Eccentric impulse was greatest following set 1 of the ST condition and was statistically greater compared to sets 2, 4, 5 (p ≤ 0.05). Concentric impulse was lower on every set following FT compared to baseline, while ST caused a lower concentric impulse on all sets with the exception of set 4 (p ≤ 0.05). RSImod and Braking RFD didn’t change under either condition (p ≥ 0.05) Conclusions: These findings indicate that an AEL BS changes the jump strategy of a subsequent CMJ by increasing eccentric impulse and decreasing concentric impulse, regardless of tempo. ST will change the jump strategy earlier but is more fatiguing while FT will take longer but is less fatiguing. Practical Applications: These findings would inform practitioners on how to potentiate athletes who are struggling to produce force eccentrically in ballistic movements. An acute enhancement in eccentric impulse, through potentiation from AEL, would assist athletes in altering their jump strategy to better utilize the eccentric phase. Acknowledgements: None