Movement technique

The subjects were required to perform all squat exercises to a parallel depth, which was defined as the femoral line being parallel to the ground. Prior to initial testing, the subjects performed a parallel-depth squat with a plastic bar, during which bar displacement was measured using a ceiling-mounted linear position transducer (PT5A-150, Celesco Transducer Products, Chatsworth, CA) attached 10 cm from the bar's center and right knee flexion angle was measured using an electrogoniometer (MLTS700, AD Instruments USA) sampling at 1000 Hz. Maximal knee flexion angle and minimum bar displacement achieved during this squat were then used as the standard depth for all subsequent squats and jump squats. Data were displayed in real time during testing and repetitions in which peak knee flexion deviated ± 2.5° or bar displacement deviated ± 1.25 cm from the standard were not accepted. Verbal and visual feedback was given to the subjects after each repetition to improve consistency.