## 2 Material and Methods
### Data Analysis  
The z-position profile acquired from the QMS incurs errors associated with system calibration, which were of the magnitude < 0.5 mm (consistent with human error in the measurements of the ABJ). As such, the signal is already very smooth, as shown in Figure 2. Therefore, low-pass filters identified the maximum height from the data without further processing. Jump height was determined using different methods. From the ABJ, the jump height was directly measured by reading the values from the sliding tape. For the QMS, the evaluation of jump maximum height is straightforward by tracking the reflective markers placed on the hip joint, calculating a mean marker position from both hip markers, then calculating the difference between the initial standing height and the vertical peak height of the jump. The jump height was also indirectly estimated based on flight-time, defined between the take-off and landing events, by considering as reference the mass centre starting position when standing. From the FP, jump height was indirectly estimated by either (a) calculating the vertical trajectory of the whole-body mass centre or (b) by using the jump flight-time (contactless period). For the first approach, the vertical ground reaction force was normalised by subtracting the subject's weight, and then the acceleration of the whole-body mass centre was calculated by dividing these forces by the body mass [7]. The vertical trajectory of the jump was obtained by double integration in time of this acceleration data, from the initial movement until the landing (contact) of the jump, using [PERSON]'s rule [7; 10]. The height was evaluated by selecting the displacement at the highest point of the trajectory. The jump height was also determined based on the elapsed time between the maximum and minimum vertical jump velocity (assumed flight time) calculated from the single integration of the acceleration data and by applying the kinematic equations for constant acceleration [15]. Figure 2: Vertical displacement of single hip marker measured using QMS. The EJ directly calculates jump height, which is estimated based on the contactless period of the jump (assumed flight-time) and is triggered by contact pressure. The MP device was placed upon the pelvis to closely represent the vertical acceleration of the whole-body mass centre and QMS markers. The system automatically computes the jump height based on the flight time corresponding to the elapsed time between the maximum and minimum vertical jump velocity. Similar to the FP, the jump height can also be estimated from the vertical trajectory of the mass centre by double numerical integration of vertical acceleration data. The vertical trajectory of the jump based on the double integration of the acceleration is highly influenced by the selection of the jump-starting time. However, the presence of experimental noise within the acceleration profiles extracted from FP and MP makes identifying this event challenging. To overcome this problem, a 3-point moving average filter was applied 4 times to the acceleration profiles to remove high-frequency noise and to enable clearer identification of jump initiation. Applying a low-pass filter will lead to the attenuation of high-frequency noise and the removal of large-signal components of the jump associated with signal perturbations. However, these are essential for the correct identification of the jump-starting point. The balance between the attenuation of the noise and the removal of the signal components can be managed by the repetition of the moving average process. Thus, through the analysis of the filtered acceleration profiles, the multiple of 4 was found to be sufficient to attenuate high-frequency noise without removing the jump signal variation, which is necessary for the identification of initiation of the jump.