Purpose: The aim of the study was to establish the optimum variable resistance (VR) intensity for loaded countermovement jump (LCMJ) to induce post-activation potentiation (PAP). Methods: Eleven male athletes (age 23 ± 2.3 years, height 1.77 ± 0.05 m, body mass 73.7 ± 9.0 kg) attended one familiarization and four testing sessions. Subjects performed their own pre-competition warm up before performing two countermovement jumps (CMJ) for baseline measure. Subsequently, they performed 2 × 3 unloaded (UCMJ) or loaded CMJ (LCMJ) with one of the three VR intensities, Orange (6.7 ± 0.6 kg), Red (14.0 ± 0.9 kg) and Blue (24.0 ± 1.4 kg), in random order, before performing two more CMJ for post-test measure. Each testing session was separated by at least 48 h. Results: There was significant increase in jump height in all conditions (P < 0.05), but no significant difference in change in jump height between conditions (P > 0.05). There were small to moderate effect when comparing Orange and the other conditions. Peak force and velocity increased in Red (P < 0.05) and Orange (P < 0.05), respectively. Change in jump height was significantly correlated to change in peak velocity (r = 0.46, P = 0.002) and peak power (r = 0.46, P = 0.002). Conclusion: The findings of the study showed that UCMJ and LCMJ were effective in improving jump height acutely, and an intensity level of about 10% body weight contributed by VR seems to be the optimum resistance level.
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