The Effect of Lightweight Wearable Resistance on the Squat and Countermovement Jumps: Does Load Dampen the Performance-Enhancing Effect of the Stretch-Shortening Cycle?

This study investigated the effects of lightweight wearable resistance on the kinetics and kinematics of squat jumps (SJ) and countermovement jumps (CMJ) with 2%, 4%, and 6% body mass (BM). Twenty male athletes (age: 18.05 ± 0.6 years; weight: 76.4 ± 7.6 kg; height: 182.4 ± 5 cm) were assessed on a force plate. Key variables included jump height (JH), concentric (ConT) and eccentric (EccT) phase durations, concentric impulse (CI), mean force (CMF), mean velocity (CMV), mean power (CMP), and relative metrics. Elastic utilization ratios (EUR) were calculated to quantify stretch-shortening cycle enhancement. Load led to decrements in both jumps but with varying sensitivity. With 2% BM the CMJ significantly reduced JH (−8.6%), EccT (−7%), CMV (−4.1%), rCI (−4.1%), rPP (−4.4%), and velocity at PP (−4.8%), whereas variables in the SJ were non-significant until 4–6% BM. EURs observed the greatest differences with 2% BM with JH, CMV, rCMP, and VPP all significantly decreasing (p < 0.05). The varying sensitivity to load across variables observed in the two jumps supports the hypothesis that SJ and CMJ offer distinct diagnostic insights due to varying MTU contraction dynamics and neural factors. This has implications for WR use in training. Further, absolute metrics showed limited load sensitivity. However, when accounting for body mass, relative metrics revealed substantial declines. This indicates absolute values can misrepresent the effects of WR loading.