The effects of plyometric jump training on lower limb stiffness in healthy individuals: a meta-analytical comparison

Objectives: To examine the effects of plyometric jump training (PJT) on lower limb stiffness. Methods: Systematic searches were conducted in PubMed, Web of Science, and SCOPUS. Studies included healthy males and females who undertook a plyometric jump training programme, isolated from any other training type. Results: There was a small effect size (ES) of PJT on lower limb stiffness (0.33 [0.07, 0.60], Z = 2.47, p = 0.01). Untrained individuals exhibited a larger ES (0.46 [0.08, 0.84], p = 0.02) than trained (0.15 [-0.23, 0.53], p = 0.45). Those interventions with a greater number of weeks (>7 weeks) had a larger ES (0.47 [0.06, 0.88], p = 0.03) than those with fewer weeks (0.22 [-0.12, 0.55], p = 0.2). Two sessions or fewer per week exhibited a larger ES (0.39 [0.01, 0.77], p = 0.04) than programmes which incorporated more than two sessions (0.20 [-0.10, 0.50], p = 0.18). Fewer than 250 jumps per week (0.50 [0.02, 0.97], p = 0.04) showed a larger ES than 250 to 500 jumps (0.36 [0.00, 0.72], p = 0.05) which, in turn, was larger than the negative ES for more than 500 jumps per week (-0.22 [-1.10, 0.67], p = 0.63). More than 7.5 jumps per set showed a larger effect size (0.55 [0.02, 1.08], p = 0.04) than fewer than 7.5 jumps (0.32 [0.01, 0.62], p = 0.04). Conclusions: PJT enhances lower body stiffness which can be optimised with lower volumes (<250 jumps per week) over a relatively long period of time (>7 weeks).