Publications

This study compared acute performance, neuromuscular, and thermal responses to a maximal isometric conditioning activity (ICA) versus a standardized volleyball pre-training activation (VPA) in highly trained male volleyball players, and to explore putative mechanisms underpinning post-activation performance enhancement (PAPE) considering training load.

In a randomized crossover, 14 men (27 ± 3 y) completed two sessions: VPA (mobility/plyometric drills; 9 min), and ICA comprising 3×5×3-s maximal isometric back-squat contractions (knee angle 120°; 3-min inter-set rest). Countermovement jump (CMJ) height (primary), relative peak power (PP), RSImod, and contraction time (CT) were recorded pre and 3, 6, 9, and 12 min post. Rectus femoris muscle viscoelastic properties and skin surface temperature (SST) were assessed at matched time points. Analyses used repeated-measures ANOVA, responder analysis, correlations, and regression.

Period×Sequence interactions favored ICA for CMJ and PP when delivered in Period 2 (lower training volume): ∆CMJ was higher under ICA versus VPA (p = 0.005, d = 1.20); PP likewise greater (p = 0.026, ηp2 = 0.35). ICA yielded more beneficial responders than VPA (9/14 vs 1/14; McNemar exact p = 0.021). In Period 2, reductions in rectus femoris muscle stiffness independently predicted CMJ gains (β_std = -0.495, p = 0.005), whereas SST changes did not (p = 0.974). RSImod and CT showed no differences.

A brief, high-effort isometric squat protocol was associated with superior acute improvements in jump performance compared with a standard volleyball warm-up, but this advantage emerged specifically when the preceding training volume was reduced (Period 2), suggesting that residual fatigue from training may reduce the effects of PAPE. Gains align with neuro-mechanical rather than thermal mechanisms, supporting ICA as a practical, equipment-minimal priming strategy for elite volleyball.

Keywords: isometric contraction, plyometric exercise, musculoskeletal physiological phenomena, volleyball, athletic performance

This study indicated that a high-intensity ICA, consisting of three sets of five three-second maximal isometric squats, was associated with enhanced CMJ performance in highly trained volleyball players — an advantage that was most evident, and statistically confined to, the period of reduced preceding training volume. The observed potentiation was associated with reductions in rectus femoris passive stiffness rather than changes in skin surface temperature. Specifically, decreases in rectus femoris passive stiffness were associated with improvements in CMJ performance, whereas changes in SST were not. These findings should be interpreted as associative rather than mechanistic, as they do not establish a causal relationship between changes in VP and the PAPE response. Importantly, the beneficial effects of the isometric protocol were most pronounced when applied after a period of reduced training volume, suggesting that the athletes’ acute readiness and preceding workload critically modulate the expression of PAPE. These findings reinforce the dual-process framework in which potentiation and fatigue coexist and underscore the necessity of balancing activation and recovery to achieve optimal performance benefits.

From a practical standpoint, maximal isometric squats represent a simple, time-efficient, and equipment-minimal strategy that can be easily implemented in warm-up or pre-competition settings to acutely improve jump performance. Coaches and practitioners are encouraged to individualize the application of conditioning activities according to the athlete’s neuromuscular state and training load, ensuring that potentiation is achieved without excessive fatigue.