## 4 Discussion  
This study aimed to assess the test-retest and inter-rater reliability of a rotary axis encoder-flywheel system for assessing hip rotation exercises. These results demonstrate good to excellent relative reliability for hip external and internal rotation in mean and peak velocity, power, and force. Previously examined linear encoders have reported acceptable reliability for power, force, and velocity during free-weight exercises such as jumps [31], squats [32; 33; 34], and bench press [33]. Additionally, some studies have focused on the reliability of the encoder-flywheel system. [PERSON] et al. [10] and [PERSON] et al. [12] achieved an ICC exceeding 0.88 when assessing velocity with a flywheel-squat exercise using a linear encoder. On the other hand, some studies investigated the reliability of a rotary axis encoder-flywheel system in both multi-joint exercises (squat, half squat, lunge) [7; 35] or single-joint exercises (leg curl) [2]. In both cases, the measurement system demonstrated good to excellent relative reliability. These findings support that both linear and rotary encoders are generally reliable systems for measuring strength, power, and velocity across a range of exercises in asymptomatic individuals. Nevertheless, our study is the first to demonstrate an excellent relative reliability of a protocol for measuring a hip rotation exercise using a rotary axis encoder-flywheel system. Focusing on the rotary axis encoder-flywheel system, previous studies have established the primary emphasis on the test-retest reliability of power and peak power as the main outcomes of interest [2; 7; 35]. The analysis of inter-rater reliability and the inclusion of the mean and peak values of velocity and force were novel aspects of this study. It could be noted that both force and velocity are widely used outcomes for monitoring performance, even in flywheel exercises [36; 37]. In addition, the exercise performance may be conditioned by the patient's positioning relative to the flywheel and the instructions provided by the examiners. Proper adjustment of the belts may be particularly relevant to isolate the activation of the hip rotator muscles and prevent the activation of other muscle groups that could potentially influence the output during the assessment. Various data collection methods have been employed with the encoder-flywheel system, ranging from separate phase analysis [2; 7; 10] to the calculation of the eccentric:concentric ratio [2; 38]. In the present study, pooled output from both concentric and eccentric phases was recorded. This approach has the potential to streamline data output per repetition, ultimately facilitating the development of a protocol with greater practical applicability. It has been suggested that a minimum of three familiarization sessions is required to achieve measurement value stabilization when both phases are computerized, particularly for multi-joint exercises that involve greater movement variability and muscular engagement [38]. However, our results demonstrated good to excellent relative reliability with just a single familiarization session, likely attributed to the analysis of a single-joint exercise. Conversely, [PERSON] et al. [2] focused on a leg-curl flywheel exercise and reported lower relative reliability in power when recording the pooled phase (eccentric:concentric ratio) than when compared to the independent phase analysis. These differences may depend on the specific exercise analyzed, the collecting data method, and the measurement protocol. Remarkably, the present study reveals absolute reliability values >10% for peak power and force of absolute reliability. These values are not directly comparable to the study by [PERSON] et al. [2] because they did not provide coefficients of variation. In contrast, [PERSON] et al. [7] achieved acceptable coefficients of variation (CV = 5.9-6.8%) in squat power. An independent phase data collection and a larger sample of repetitions assessed were the main differences from this study. [PERSON] et al.