Effects of Plyometric Training on Lower Body Muscle Architecture, Tendon Structure, Stiffness and Physical Performance: A Systematic Review and Meta-analysis

BACKGROUND: Plyometric training (PT) has been widely studied in sport science. However, there is no review that determines the impact of PT on the structural variables and mechanical properties of the lower limbs and physical performance. OBJECTIVE: The aim of this systematic review and meta-analysis was to determine the effects of PT on lower body muscle architecture, tendon structure, stiffness and physical performance. METHODS: Five electronic databases were analysed. The inclusion criteria were: (1) Availability in English; (2) Experimental studies that included a PT of at least eight sessions; and (3) Healthy adults subjects. Four meta-analyses were performed using Review Manager software: (1) muscle architecture; (2) tendon structure; (3) muscle and tendon stiffness; (4) physical performance. RESULTS: From 1008 search records, 32 studies were eligible for meta-analysis. Muscle architecture meta-analysis found a moderate effect of PT on muscle thickness (Standard Mean Difference (SMD): 0.59; [95% Confidence Interval (CI) 0.47, 0.71]) and fascicle length (SMD: 0.51; [95% CI 0.26, 0.76]), and a small effect of PT on pennation angle (SMD: 0.29; [95% CI 0.02, 0.57]). The meta-analysis found a moderate effect of PT on tendon stiffness (SMD: 0.55; [95% CI 0.28, 0.82]). The lower body physical performance meta-analysis found a moderate effect of PT on jumping (SMD: 0.61; [95% CI 0.47, 0.74]) and strength (SMD: 0.57; [95% CI 0.42, 0.73]). CONCLUSION: PT increased the thickness, pennation angle and fascicle length of the evaluated muscles. In addition, plyometrics is an effective tool for increasing tendon stiffness and improving jump and strength performance of the lower body.