## 4 Discussion
[7] employed an average of twelve repetitions divided into two sets, while we used an average of three repetitions within a single set. Thus, the data collection method could have significantly influenced the absolute reliability of power outcomes. While the use of an independent phase data collection and a larger sample of repetitions can generate more stable values, it requires more time and may appear less practical in a clinical or sports training context. Regarding the provided cutoffs points for relative SEM [39], there was moderate to high variability in peak power (%SEM = 7.78-13.55%), low to moderate variability in peak force (%SEM = 5.59-8.12%), and low variability in mean and peak velocity, mean power, and mean force (%SEM \(<\) 7%). Even though the relative SEM suggests minimal variability in mean power, it is important to note that the absolute test-retest reliability reveals CV values exceeding 10%. Nevertheless, the absolute reliability of mean power (CV = 10.6-12%) seems to be higher than that of peak power (CV = 18.2-18.6%). Thus, peak power and force outcomes displayed the greatest variability and unsatisfactory absolute reliability. This is likely attributed to the smaller sample size of data considered at a specific moment within a repetition, compared to the mean data derived from the entire repetition. One possible contributing factor could have been the compensatory activation of other muscle groups and the difficulty in maintaining pelvic stability during the exercises. Consequently, the use of mean power and force values seems more suitable, as they have shown an acceptable intra-rater reliability and low variability (%SEM = 2.58-6.14%). Therefore, the primary implication of this study is the development of a reliable measurement protocol using the rotary axis encoder-flywheel system to assess velocity, power, and force in hip internal and external rotation exercises. This measurement system seems to be appropriate for its use in research and training monitoring. It enables the assessment of individual performance status through inertial training and holds potential applicability for velocity and power-based training regimens. Nonetheless, the results suggest advising against the use of peak force and power outcomes. This study is not without limitations. Firstly, the sample consisted of asymptomatic participants engaged in recreational physical activity. Consequently, the results may not be extrapolated to elite athletes, sedentary or unconditioned individuals, older adults, or populations with medical conditions. Secondly, the study only incorporated a single familiarization session, whereas some research suggests a minimum of two such sessions to ensure participants' adequate familiarity with the procedures [38]. Thirdly, the frequency-amplitude of hip rotation movements was not standardized, allowing participants to perform them according to their ability. This aspect could have contributed to performance variability between participants, influencing the results. Fourthly, all measurements for test-retest and inter-examiner reliability were carried out in the same session. While the recommended physical recovery periods between each set were ensured, psychological fatigue might have influenced these results. Finally, only hip rotation exercises were analyzed. Future studies should assess the reliability in different flywheel exercises and aim to establish the optimal data collection procedure with the rotary axis encoder-flywheel system. Subsequent research should also evaluate both the reliability and tolerance of this system among individuals with specific pathologies for its integration and application within the healthcare domain. Additionally, future studies should focus on developing theoretical models to explore relationships among the studied outcome measures.