Dynamic and Static Force Generation Tests

All tests were performed using an FT 700 Power Cage, integrated with a 400 series Force Plate 795 mm x 795 mm (Fitness Technology Inc, Adelaide, Australia). The sampling frequency of the force plate was 600 Hz. Before using this tool, calibration was applied following the manufacturing guidelines; briefly, two known masses were placed over the force plate to determine the calibration coefficient. The force plate was zeroed prior to each trial.

There were four different tests which included three dynamic tests and one static test. These tests are explained in detail in the following sections.

2.1.4.1 Single-Leg Squat Hop Test

The participants were asked to stand on one leg and then were instructed to semi-squat to about 45˚ (visually estimated) for three seconds prior to hopping vertically as high as possible from a semi-squat position, without a countermovement. The test period was set for 5 seconds. To make sure that the participants did not perform any countermovement in the lower extremities before they hopped, raw force-time data was checked after every trial to

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make sure that there were no changes in the force-time data (remain stable without a dip in the force). If there was a countermovement, as evident from a visual inspection of the force-time data, the trial was repeated and not collected.

The participant’s hands were kept on their hips during the test (see Figure 2.7), and the reason behind this was to avoid any excessive force that might be produced from swinging the arms (Harman et al. 1990), thereby making sure that the resultant force-time data was created by the lower limbs’ performance only. Moreover, keeping the hands on the hips reduces the effect of arm motion to better reflect lower limb performance (Impellizzeri et al., 2007). Participants were required to land in the same place as take-off, and after initial contact, flexion was permitted to permit the absorption of landing forces. Once the test was finished, participants applied the same procedure with the other leg.

Figure 2.7. Squat hop force generation test

2.1.4.2 Single-Leg Countermovement Hop Test

Participants were asked to stand on one leg, and after an initial stationary phase of at least two seconds in the upright position as motionless as possible, the participants performed a countermovement hop as high as possible, dipping to a self-selected depth with hands kept on hips and then accelerated upward with maximal effort. The reason behind keeping both hands on hips during the test was, as explained above, to avoid any excessive force that might be produced from swinging the arms (Harman et al. 1990). Furthermore, keeping the hands on the hips reduces the effect of arm motion to better reflect lower limb performance (Impellizzeri et al., 2007). Participants were required to land in the same place as take-off, and

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after initial contact, flexion was permitted to permit the absorption of landing forces. The test period was set for 5 seconds. Once the test was finished, participants applied the same procedure with the other leg.

2.1.4.3 Single-Leg Ten Consecutive Hops Test

Participants were asked to stand on one leg and then were instructed to hop continuously ten times vertically as high as possible, and participants were asked to make a countermovement with the lower extremities before hopping. The test period was set for 10 seconds. The instructions were given to the participants as follows: ‘execute ten consecutive maximal vertical hops with minimal ground contact time’ and asked not to perform a ‘tucking’ movement with the leg while in flight. Participant’s hands were kept on the hips during the test. The reason behind keeping both hands on the hips during the test was, as explained above, to avoid any excessive force that might be produced from swinging the arms (Harman et al., 1990). Additionally, keeping the hands on the hips reduces the effect of arm motion to better reflect lower limb performance (Impellizzeri et al., 2007). Participants were required to perform all hops in a consecutive effort as high as possible without a pause between hops (Cormack et al., 2008). Once the test was finished, the participants applied the same procedure with the other leg.

2.1.4.4 Single-Leg Isometric Mid-Thigh Pull Test

This was the only static force test. The participants were asked to stand on one leg using their preferred position to place the bar at the midpoint of the thigh. They were asked to select the hip- and knee-joint angles that they would normallyutilise to perform a mid-thigh pull, and then the bar was fixed in this position/height using lifting straps. Their preferred positions/angles were used because it was found by Comfort et al. (2015) that there is no effect on kinetic variables when the bar position on the thigh is constant, using different knee- and hip-joint angles and the preferred position during the IMTP. It was therefore suggested that when evaluating athletic development, researchers should use the posture that the individual athlete prefers; this might also help to minimise the learning effect. The participant’s hands were strapped to the bar with standard lifting straps and athletic tape. The bar was pointed to mid-thigh distance when bending both legs (participants achieved ankle dorsiflexion, knee and hip flexion, while maintaining an upright torso, with a neutral spine posture), and then they were instructed to pull the bar as fast and as hard as possible, and also to push from the lower extremities at the same time for a duration of five seconds (using a stop watch) until instructed to relax (see Figure 2.8). The test period was set for 10 seconds,

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whereas five seconds were given for pulling and the remaining five seconds for the instructions before and after performing the pull. Once the test was finished, the participants applied the same procedure with the other leg.

Figure 2.8. IMTP force generation test