Abstract
While muscular power is influenced by both neuromuscular and neurochemical mechanisms, the literature has largely emphasised neurochemical pathways, often leading to an unclear distinction between post-activation potentiation (PAP) and PAPE and inconsistent conclusions regarding the contribution of muscle architecture. The primary aim of this research was therefore to examine the acute effects of a back-squat conditioning activity on pennation angle – specifically the magnitude, persistence, and decay of architectural change across the post-conditioning recovery window – alongside concurrent voluntary performance responses (countermovement jump) at each measurement time point. Eleven trained athletes (n=11; mean age: 23.09 ± 3.27 years; mean body weight: 74.35 ± 11.03 kg; mean height: 174.28 ± 13.06 cm) participated in this investigation. The methodology involved assessing countermovement jump (CMJ) performance, quantifying muscle pennation angles via ultrasonography, and evaluating electromyographic (EMG) activity in selected lower-limb muscles. Baseline measurements for CMJ, ultrasound (US), and EMG were obtained to establish pre-conditioning reference values. Participants then completed a conditioning activity consisting of three repetitions of back squats at 75% of their one-repetition maximum (1RM), followed by a 7–10-minute rest (recovery) interval prior to the second CMJ assessment. A further 7–10-minute rest period was implemented before the final CMJ. Ultrasound imaging was performed to measure pennation angles of the vastus lateralis (VL), rectus femoris (RF), biceps femoris (BF), and lateral gastrocnemius (LG) at seven discrete time points: Baseline (at rest), Post warm-up, Post-conditioning contractions, Post-recovery 1, Post-Jump 1, Post-recovery 2, and Post-Jump 2. EMG was recorded concurrently to assess muscle activation during jump performance. A computerised statistical programme (SPSS version 27, IBM) was used to analyse the data (repeated-measures ANOVA with Bonferroni post hoc tests), with statistical significance set at p < 0.05.
Key findings revealed a significant increase in jump height from baseline (31.1cm) to Jump 1 (35.3cm) and Jump 2 (36.7cm) (p = 0.03, ES = 0.521), indicating a strong PAPE effect. Concurrently, a consistent pattern of significant decline was observed for relative peak power, decreasing from 55.9 W/kg at baseline to 51.4 W/kg Jump 2 (p = 0.006, ES = 0.459). Vertical velocity at take-off also significantly decreased from 2.68 m/s at baseline to 2.47 m/s at Jump 2 (p
= 0.003, ES = 0.521), and absolute peak power dropped significantly from 4491 W to 3956 W at Jump 2 (p = 0.020, ES = 0.355). Regarding muscle architecture, the VL showed a statistically ...