Unilateral Stiffness Interventions Augment Vertical Stiffness and Change of Direction Speed.

Maloney, SJ, Richards, J, Jelly, L, and Fletcher, IM. Unilateral stiffness interventions augment vertical stiffness and change of direction speed. J Strength Cond Res 33(2): 372-379, 2019-It has previously been shown that preconditioning interventions can augment change of direction speed (CODS). However, the mechanistic nature of these augmentations has not been well considered. The current study sought to determine the effects of preconditioning interventions designed to augment vertical stiffness on CODS. Following familiarization, 10 healthy males (age: 22 ± 2 years; height: 1.78 ± 0.05 m; body mass: 75.1 ± 8.7 kg) performed 3 different stiffness interventions in a randomized and counterbalanced order. The interventions were: (a) bilateral-focused, (b) unilateral-focused, and (c) a control of CODS test practice. Vertical stiffness and joint stiffness were determined preintervention and postintervention using a single-leg drop jump task. Change of direction speed test performance was assessed postintervention using a double 90° cutting task. Performances following the unilateral intervention were significantly faster than control (1.7%; p = 0.011; d = -1.08), but not significantly faster than the bilateral intervention (1.0% faster; p = 0.14; d = -0.59). Versus control, vertical stiffness was 14% greater (p = 0.049; d = 0.39) following the unilateral intervention and 11% greater (p = 0.019; d = 0.31) following the bilateral intervention; there was no difference between unilateral and bilateral interventions (p = 0.94; d = -0.08). The findings of the current study suggest that unilateral preconditioning interventions designed to augment vertical stiffness improve CODS within this experimental cohort.