They all signed an informed consent form approved by Universit�� Laval ethics committee. Procedures Group 1. The participants were instructed to jump (i.e., countermovement jump) as high as they could. They were allowed to use their arms and there was no constraint on the amplitude of the countermovement but the landing of the jump needed to be on the platform. They performed www.selleckchem.com/products/FTY720.html 3 jumps. Each jump was separated by approximately 30 s. Group 2. The participants performed 4 jumps with a countermovement as well. In contrast to Group 1, their arms were crossed on their chest and the amplitude of the countermovement was controlled. A flexible plastic plate was positioned at the rear of the force platform and was adjusted so that it hit the subject��s buttock at a knee angle corresponding to 90�� in the eccentric phase indicating that they had to initiate the concentric phase of the jump.

Before data acquisition, subjects were familiarized with this specific technique. A kinematic analysis of the knee angle that followed the data acquisition showed that all subjects generally complied with the technique as the mean knee angle at the end of the downward movement was 89.6�� (SD = 6.9). Apparatus Group 1. GRF parameters were recorded for all jumps with a force platform (AMTI OR6-1) fixed on the floor and surrounded by a wide wooden base. All three forces (Fx, Fy, Fz) and torques (Mx, My, Mz) were first amplified (AMTI MSA-6) and sampled at 1 kHz (12-bit A/D conversion). A reflective marker (Ligth Emitting Diode, LED) was fixed on each subject��s left greater trochanter.

Two-dimensional video recordings of the jumps were taken using standard guidelines (Payton, 2008). A digital camera (Point Grey Flea) was located 3.5m from the subject, 0.9m from the floor and filmed the sagittal plane. Data collection for the digital camera and the force platform were triggered and synchronized using a frequency generator (WPI model A310-C) that also provided equidistant pulses to capture images at 50 Hz. All jumps were further analyzed by tracking displacement of the LED using MaxTraq software (Innovision Systems). GRF and kinematic data for all jumps were then imported into the Matlab environment and merged in a single file for further processing.

Displacement-time signals were digitally filtered with a fourth-order Butterworth filter (10 Hz lowpass cutoff frequency with dual pass to remove Anacetrapib the phase shift), and the maximum height of each jump was determined from the calibrated displacement-time signals of the LED placed on the greater trochanter. All force platform signals were first processed with a calibration routine and then filtered with similar parameters. Group 2. The participants jumped on a large custom-made force platform (80 cm2) built using 4 strain gages (Tedea Huntleigh, model 1241 �C 250 kg). All signals were first amplified (HP 8811A) before being sampled at 200 Hz (12-bit A/D conversion).