Investigating the Post-Activation Performance Enhancement Effects on Skeletal Muscles Under Varied Loading Conditions

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With the advancement of sports science, Post-Activation Potentiation (PAP) has become a focal point of research, garnering significant attention for its underlying physiological mechanisms. Current studies suggest three primary mechanisms: 1) phosphorylation of myosin regulatory light chains (RLCs); 2) increased recruitment of high-threshold motor units; and 3) a reduction in sarcomere length heterogeneity within muscle fibers due to pre-stimulation (Liu \& Li, 2017). These mechanisms collectively contribute to an effect known as Post-Activation Performance Enhancement (PAPE), which significantly enhances muscle strength and explosiveness shortly after activation (Blazevich \& Babault, 2019). During the activation process of motor units with increasing loads, low-threshold motor units are recruited first, followed by high-threshold motor units. As the load increases, the root mean square (RMS) value increases linearly, further promoting the overlap of motor unit potentials and the rise in RMS values. This overlap in activation timing among adjacent motor units results in greater overall muscle force output (Liu, 2008; Tian, 2009). The significance of this lies in the fact that as the degree of muscle activation increases, especially under incremental loads, the muscle's ability to adapt to subsequent strength or explosive tasks may be enhanced. In competitive sports, optimizing the relationship between warm-up and performance is crucial. Research indicates that the duration of PAPE varies with individual differences, training type, intensity, and recovery intervals. The characteristics of the PAPE effect also differ. Additionally, following constant loads, the enhancement and decay rates of performance in PAPE show varying rates at different times, and these rates do not exhibit a symmetrical linear change in absolute value (Liang, M 2020; Guo, W et al. 2018; Liu, R and Li, Q. 2017). The competition pace in sports demands precise modulation of performance enhancement rates after activation, and athletes can leverage these characteristics by selecting appropriate loading forms to trigger PAPE at critical moments in competition. To explore the enhancement or decay rates of performance over different time domains, our research team designed a protocol consisting of incremental loads.

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