# Empirical Validation of a Streamlined Three-Repetition Sit-to-Stand Protocol Using MAI Motion
## 4 Discussion  
This study aimed to evaluate whether the kinematic data generated by the MAI Motion system from participants performing the STS test over three repetitions were equivalent to the data obtained from five repetitions. The results indicate a high degree of consistency between the results generated through an analysis of 3x or 5x repeats across multiple parameters, including positive and negative impulse, impulse ratio, and range of motion, evaluated across key joint categories. Statistical and qualitative analysis demonstrated that the results from 3x were comparable to, or even outperformed, those from 5x. This supports the use of a shorter 3x protocol without compromising the reliability or diagnostic benefit of the data. A statistical analysis of the results generated through an investigation of the data from 5x or 3x repeats, including a comparison of DiMs and CVs, showed a lack of significant differences between mean values or the levels of variability of all parameters when considered individually. Significant differences in variability were only observed when comparing grouped data, namely the mean variation across CVs for all 52 parameters in five out of twenty participants (2, 6, 7, 14, and 15) and the'meta-mean' of the CVs for each parameter, with the analysis of 3x repeats generating significantly less variability than that of 5x. These findings are consistent with prior research in functional testing, indicating that beyond a modest number of repetitions, additional cycles yield diminishing returns regarding measurement precision. This likely reflects the effects of participant fatigue due to the increased number of repetitions, potentially resulting in greater variability in neuromuscular control, posture and/or movement, especially across the 4 th and 5 th repeats. Whilst further analysis would be required to address this more formally, previous studies have reported that increased fatigue can lead to adaptations in movement [16], giving rise to changes in biomechanical parameters [17]. Based on these observations and the results presented here, it seems reasonable to propose that 3x repeats are recommended to reduce fatigue-related variability while maintaining measurement accuracy. The high variability observed across impulse ratio measures for knee and hip abduction, ankle angle, and, to a lesser extent, knee angle, is a well-recognised feature in biomechanical analyses [18,19]. This variability likely arises from the inherent complexity  
Figure 5: Positive correlation between age and variability (CV). Participant age and mean CVs (determined from 5x or 3x repeats, respectively) for all 20 participants are depicted in green (5x) or red (3x). Lines of linear regression are included, and Pearson correlation coefficients (r) and \(p\) values are shown. of joint mechanics and neuromuscular control. The knee, despite being primarily a sagittal plane joint, contributes to both shock absorption and propulsion while exhibiting subtle off-axis motion. Hip abduction, which is crucial for frontal plane stability, demands precise neuromuscular regulation--especially in tasks requiring mediolateral balance or single-leg stance. Ankle angle variability further adds to the dynamic interplay of lower limb function. While technical factors may introduce some variation, the consistent patterns observed across trials suggest that this variability primarily reflects true biological diversity rather than measurement limitations. From a diagnostic perspective, the opportunity to effectively capture movement dynamics using digital platforms such as MAI Motion has real-world applicability in musculoskeletal healthcare. For example, for individuals who are frail or exhibit considerable mobility impairments or chronic musculoskeletal conditions, the increased accessibility afforded through remote evaluation, combined with the adoption of a shorter protocol, will make assessments less demanding and more inclusive.