Influence of Intended Slow and Fast Eccentric Back Squat Velocity on Subsequent Countermovement Jump Performance

Background: The back squat is a key strength and conditioning exercise used to develop lower-limb strength and power, yet little is known about how movement velocity influences its acute performance-enhancing effects, such as improvements in countermovement jump height and power. The present study examined the acute effects of slow (v_slow) versus fast (v_fast) eccentric-phase velocity during back squats performed withmaximal concentric velocity on subsequent countermovement jump (CMJ) performance, using a randomized, crossover design. Methods: Fourteen male subjects (age = 22.9 ± 1.9 years; height = 1.8 ± 0.1 m; mass = 76.4 ± 8.3 kg) visited the laboratory on two separate days and completed a comprehensive task-specific warm-up followed by three v_slow or v_fast back squats at 70% of one-repetition maximum. Three CMJs were performed before and 30 s, 4 min, 8 min, and 12 min after the interventions. Jump height, peak power, kinetic energy, maximum knee angle, and knee angular velocities in both eccentric (downward) and concentric (upward) phases were recorded. Results: No significant (p > 0.05) between-condition differences were detected in any measure. Compared to pre-intervention, significant increases (collapsed data) were detected in jump height (6.0%; d = 0.68-0.83), power (3.6-6%; r = 0.32-0.38), and kinetic energy (5.0-8.0%; d = 0.62-0.86) at 30 s and 4 min. Conclusions: Given the lack of between-condition differences, the eccentric movement velocity of moderate conditioning back squats with maximal concentric velocity exercises does not appear to influence subsequent jump performance enhancements. Thus, either conditioning activity can be used to improve subsequent jump performance. However, as performance was enhanced only at 30 s and 4 min post-intervention, the window of opportunity is narrow, and timing should be carefully considered when including such activities in pre-competition routines.