Loading strategies for countermovement jump: an exploratory comparison of modality and load

BACKGROUND: Vertical jump ability is an important indicator for assessing lower-limb explosive power. Loaded jump training, using either peripheral (barbell) or centralized (weighted vest) loading, enhances jump performance through neuromuscular adaptation. However, it's unclear how these modalities (barbell vs. weighted vest), particularly across different external load magnitudes (30%, 40%, 50% of body mass (BM)), affect jump mechanics, postural stability, and motor control. This pilot study aimed to examine how load type and magnitude influence performance, posture control, and kinetics during countermovement jumps (CMJ). METHODS: Seventeen trained males (age 20.2 ± 3.2 yrs; body mass 72.3 ± 7.3 kg) performed CMJ under two loading strategies (weighted vest, barbell; randomized crossover), each at 30%, 40%, and 50% BM, with three trials per load. Dual force plates captured ground reaction force (GRF) and center of pressure (COP). Measured outcomes included jump height, reactive strength index-modified (RSI-mod), momentum, push-off displacement, bilateral strength asymmetry (BSA), postural sway, and kinetic variables. Data were analyzed using linear mixed model (LLM), generalized mixed model (GLMM), and two-way ANOVAs, and effect size was assessed via partial η2. RESULTS: Compared with a weighted vest, a barbell showed higher jump height, jump momentum, and push‑off distance (p-values ranged from 0.005 to 0.041; partial η2 ranged from 0.043 to 0.078), whereas increasing load from 30% to 50% body mass progressively reduced jump height and RSI_mod in both groups. For postural stability, at 30% body mass the weighted vest showed smaller landing ML COP displacement than the barbell (p < 0.019, partial η2 = 0.138). With increasing load from 30% to 50% BM, ML COP decreased with the barbell (p < 0.001, partial η2 = 0.088) and moved opposite in weighted vest group. Kinetically, increasing load increased braking and landing demands (e.g., greater maximum yielding force, higher maximum landing force/acceleration, longer braking and shorter yielding durations (all p < 0.002, partial η2 = 0.121 ~ 0.423)), while group differences were limited to higher braking acceleration under the barbell condition (p = 0.029, partial η2 = 0.011). Overall, centralized loading conferred a low‑load stability advantage, while peripheral loading favored task‑level jump performance. Load increased braking/landing demands irrespective of centralized or peripheral loading. CONCLUSION: Within the tested load range (30-50% BM), load distribution strategy and magnitude significantly affect jump performance and postural stability during CMJ, with trade-offs for stability and power. Below approximately 30-40% BM, the weighted vest confers greater stability (lower ML displacement) compared to barbell, while at larger load (50%BM), barbell would be appropriate for force lead performance.