The 90° angle of the knee joint was controlled by video-recording the SQJ AZD9291 supplier attempt with a JVC GR-D720E video camera (Victor Company of Japan Ltd., Yokohama, Japan) which was connected to a PC through an IEEE 1394 interface (Texas Instruments Inc., Dallas, TX, USA).

The camera was fixed on a stationary tripod placed at a height of 1.2 m and at a distance of 7 m from the participants. The optical axis of the camera was perpendicular to the sagittal plane of the participants. The recorded video was displayed simultaneously on the capture screen of the Kinovea 0.8.15 software (Joan Charmant & Contributors, Bordeaux, France). This enabled to project a right angle mark on the displayed video, which helped the researchers to guide the participants in order to acquire the initial squatting position. When the desired 90° knee angle was obtained, the participants were instructed to “jump as high and as fast as possible without a countermovement or the use of an arm-swing”. This instruction was provided because the arm swing and the countermovement have independent effects on lower extremity work and their combined effect produce greater jump height by enabling mechanisms see more other than the concentric strength of the

leg extensor muscles which is assessed by the SQJ test.10, 32 and 33 A couple of trials were allowed for familiarization. For an SQJ to be considered valid, the participants had to land on the force-plate and had to avoid any downward movement of the body. The latter was evaluated immediately using the time history curve of the recorded vertical ground reaction force (vGRF). If the vGRF curve progressed lower than the line representing the body mass at the initial stages

of the propulsion phase, the attempt was not considered valid and it was repeated. The progression of the vGRF curve below the line representing the body mass indicates a downward movement of the body which is caused by a countermovement. As mentioned above, the validity of the SQJ test requires the absence of a countermovement, because the it allows muscles to be activated in a higher level and thus a greater amount of force is produced compared to the concentric contraction of the leg extensor muscles.33 In all cases, a minimum of 1-min interval was permitted between the executions of the SQJ in order to avoid fatigue. Only the best attempt, as indicated by the height of the jump achieved, was selected for further analysis. The values of the anthropometric characteristics of the participants were collected using a Laffayette skinfold caliper (Laffayette Instrument Co, Laffayette, IN, USA) and an SECA 220 scale with telescopic measuring rod (Seca Deutschland, Hamburg, Germany). Warm-up was conducted on a Monark 817E cycle ergometer (Exercise AB, Vansbro, Sweden). An AMTI OR6-5-1 force-plate (AMTI, Newton, MA, USA) was used to record the vGRF, which was sampled at a nominal frequency of 500 Hz.