Effects of flywheel resistance training on countermovement jump performance and vastus lateralis muscle stiffness: A controlled study

This study aimed to investigate the effects of an 8-week resistance training using flywheel (FW) device on countermovement jump (CMJ) performance and resting stiffness of the vastus lateralis (VL) muscle. Physically active adults were randomly assigned to a training intervention group (T; <i>n</i> = 18) and a control group (C; <i>n</i> = 13), which received no intervention. Jump performance variables and ultrasound-assessed resting VL shear modulus were measured before and after the intervention. Analysis of covariance revealed statistically significant group differences in jump height (<i>T</i> = +9%; C = -3%), rate of force development (<i>T</i> = +32%; C = +4%), peak power (<i>T</i> = +9%; C = -1%), and peak force (<i>T</i> = +7%; C = -1%). Jump performance improved only in the training group (all CMJ variables <i>p</i> < 0.05). Conversely, no significant changes within groups were observed in the resting shear wave modulus results (<i>p</i> > 0.05). VL stiffness decreased in the training group (-4%) and increased in the control group (+6%). Our results suggest that resistance training using FW device with individually allocated high-load FW inertia induces significant improvements in jump performance, which are not underpinned by changes in VL muscle stiffness.