Investigating the Post-Activation Performance Enhancement Effects on Strength-trained Athletes Under Varied Loading Conditions: A Time-domain Features Perspective

First, participants underwent a squat 1-RM test using the NSCA testing protocol. The induction exercise was barbell-loaded squats. In the constant load group, the stimulation intensity was set at 90% of the 1-RM, with one set of four repetitions of barbell half-squat jumps . In the incremental load group, the stimulation intensities were set at 5RM, 4RM, 3RM, and 2RM, with one set of one repetition of barbell half-squat jumps for each load intensity. Both the 1-RM test and squat induction exercises were conducted using a Smith machine, and protective personnel were present on both sides. The testing movement involved static half-squat jumps that aimed to enhance the stability of the test and reduce interference from arm swinging. The static half-squat jump required participants to stand with their feet shoulder-width apart on the force plate, hands on hips, and knees flexed to a semi-movement range, and they had to maintain the position for one to two seconds. Following this, participants exerted maximal effort to jump upward (with no visually noticeable downward squatting during takeoff) before naturally descending and maintaining the position for another one to two seconds. Throughout the entire process, both feet were to remain within the force plate area.

Experimental procedure The participants began with a 10-minute slow jog and dynamic lower-limb stretches. As a baseline, the participants' dynamic data for unloaded static half-squat jumps were collected after a 5-minute rest. Following another 5-minute rest, the constant load group underwent one set of four half-squat jump inductions at an intensity of 90% 1-RM. The incremental load group underwent inductions at each load intensity, with one set of barbell half-squat jump exercises for each intensity. The participants received verbal cues and encouragement for each repetition. Dynamic data for static half-squat jumps were collected at 15 seconds, 3 minutes, 6 minutes, 9 minutes, and 12 minutes after the end of each exercise session. At each time point, two valid repetitions were collected, with verbal cues and encouragement provided to the participants for each repetition. Each set of two half-squat jumps did not exceed 10 seconds. The interval between static half-squat jump testing and 1-RM testing was greater than 48 hours .