50 Chapter 3 Participants were allowed fingertip support at shoulder height on the wall in front of them. The objective of the test was to raise the heel as high as possible on each repetition, returning it to the incline board, and performing as many repetitions as possible while minimizing anterior movement. A digital metronome set at 60 beats per minute guided the test, with participants ascending on one beat and descending on the next (i.e., 30 repetitions per minute). To acclimate to the metronome pace, each participant performed 10 bilateral standing heel rises as a warm-up prior to testing. Participants were informed of the test termination criteria: 1) the heel can no longer be lifted from the incline board, 2) the pace of the digital metronome can no longer be followed, 3) the knee angle or trunk position can no longer be maintained, or 4) more than fingertip support on the wall is needed for balance. If a termination criterion was observed, a verbal prompt was given. Testing was terminated when there was no response to two consecutive prompts. Throughout the testing procedure, participants received verbal instructions to maintain the specific parameters, including heel excursion, cadence, balance support, and knee angle. The HRET was conducted once on each leg, and the order of testing was quasi-randomized, based on the moment of inclusion. A 2-minute rest period was provided to participants following the completion of the first single-leg HRET, after which the test was repeated using the opposite limb. Outcome measures By tracking the vertical displacement of the round sticker on the foot of participants and based on the mass (kg) of individuals, the Calf Raise Application calculates various metrics. The primary outcome measures in this study were the number of repetitions, total positive work (J), total vertical displacement (cm) and peak height (cm). These Calf Raise Application metrics are validated and show excellent reliability.14,19 Secondary outcome measures, as reported in the application, were vertical height loss (%) and peak power (W). The exact working mechanism and validation of the Calf Raise Application have been described in detail elsewhere.14,19 Statistical analysis Given the objective of establishing normative values and the skewed distribution of the data, we used quantile regression for the analysis as it estimates medians without imposing distributional assumptions. Potential differences in HRET metrics between the dominant and non-dominant leg were analysed using a Mann-Whitney U-test. When no statistically significant differences were observed, mean HRET metrics were used to develop the quantile regression model. Initially, bivariate models were constructed to examine the relationship between each covariate (age, gender, height, mass, BMI, leg dominance, and PAL) and the HRET metrics. Subsequently, a multiple quantile regression model was developed, incorporating the covariates that demonstrated a significant influence on HRET
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