Acute Effects of Whole-Body Vibration and Unilateral BOSU-Based Preconditioning on Countermovement and Squat Jump Height and Early-Race Breaststroke Performance in Competitive Swimmers: A Randomized Crossover Study

Whether acute dry-land preconditioning improves jump height and swimming outcomes in breaststroke remains unclear. This original experimental study used a randomized crossover design to compare two whole-body vibration (WBV) protocols and a unilateral BOSU-based protocol with an active stable-ground half-squat Control condition in 14 competitive breaststroke swimmers. Sessions were separated by at least 72 h. Countermovement jump (CMJ) height, squat jump (SJ) height, 25 m breaststroke split time, and 50 m breaststroke final time were assessed before and after each condition. Linear mixed-effects models showed significant Condition × Time interactions for CMJ height and 25 m split time, but not for SJ height or 50 m final time. Planned interaction contrasts showed greater pre-to-post changes than Control for both WBV conditions in CMJ height and 25 m split time. WBV 4 mm produced the largest point estimates for both primary outcomes, although superiority was not established. BOSU estimates were favourable but non-significant. WBV therefore showed the most consistent evidence of favourable acute responses relative to an active half-squat Control, whereas unilateral BOSU remained promising but inconclusive. Swimming findings apply only to the fixed assessment sequence, and the 25 m split should be interpreted as a composite early-race indicator.