Resistance Priming in Improving Strength: The Effects of Unilateral Isometric Strength Activation on cross-activation of Bilateral Quadriceps and Hamstring Strength at 24 and 48 Hours

Purpose This study aims to investigate whether unilateral low-volume, high-intensity isometric strength activation (ISA) can enhance jump performance and bilateral isokinetic flexion and extension strength within 24 and 48 hours post-intervention. Methods A total of 68 participants (40 males and 28 females) were included. Participants were randomly assigned to either the experimental group or the control group using a balanced randomization scheme. Athletic performance was assessed using unloaded countermovement jump (CMJ), unloaded squat jump (SJ), and isokinetic knee flexion and extension strength tests. The experimental group received an isometric activation protocol, while the control group maintained their regular exercise routines. Results The isometric activation protocol led to varying degrees of improvement across genders in the experimental group. Among male participants, there were significant increases in CMJ performance 24 hours post-activation. SJ performance also improved significantly. Furthermore, SJ performance remained significantly elevated 48 hours post-intervention compared to baseline (p < 0.05, JH: ES = 0.829). For female participants, SJ performance showed significant improvement 24 hours after activation, although no other significant changes were observed.Regarding knee flexion and extension strength, at an angular velocity of 60°/s, the male group exhibited significantly greater strength at 48 hours post-intervention compared to 24 hours . In the female group, bilateral knee strength significantly improved at both 24 and 48 hours post-intervention. Conclusions ISA interventions can enhance knee joint strength in both male and female participants within 24 and 48 hours post-intervention, and also induce a cross-activation effect.