# Investigating the Effect of Motion Capture Suits on the Test-Retest Reliability of Gait Parameters
## 4 Discussion
### Reliability  
Comparing reliability of joint angles in both non-suited and suited conditions, we can begin to evaluate whether MOCAP suits are reliable enough to use for data collection. At the ankle and knee, reliability of the PiG non-suited trials was better (Ankle ICC = 0.531, Knee ICC = 0.832) than the suited (Ankle ICC = 0.435. Knee ICC = 0.707). Large confidence intervals (Figure 2) in the ankle and knee angle are masking potential differences between suited and non-suited conditions, as we see large differences in mean ICC values but observe no statistical difference (Ankle \(p\) = 0.32, Knee \(p\) = 0.13). These large confidence intervals, particularly at the ankle, were a result of the wide reliability range across the four metrics measured in the gait cycle. Therefore, just looking at ICC values, we cannot conclude that the MOCAP suit in conjunction with the PiG model is a viable option for research repeatedly estimating ankle and knee angles from MOCAP data. In contrast, hip angle metrics in the suited condition (ICC = 0.945) had greater reliability than in the non-suited condition (ICC = 0.899). The reliability of hip joint angles across all gait events were not significantly different between the suited and non-suited conditions, suggesting that using the MOCAP suit in conjunction with the PiG model may be a viable option for hip angle data collection. The ICC results presented here contrast with findings from [PERSON] et al. (2023) [4], who looked at the between-day reliability of the PiG model during running. They reported higher reliability in ankle angle metrics: ankle initial contact (ICC = 0.87), peak flexion (ICC = 0.68) and extension (ICC = 0.90) [4], compared to the current study. We may see differences as participants run barefoot, increasing the accuracy of marker placement on the feet, whereas in the present study markers were attached to the participant's shoes. It has previously been noted [26] that walking barefoot does change the gait characteristics and therefore measuring parameters barefoot, although this might increase marker placement accuracy, may decrease the ecological applicability of the results. While PiG knee angle metric reliability was comparable to those reported in [PERSON] et al. (2023) [4], the PiG hip angle metrics were more reliable in both conditions of the present study when compared to the results of [PERSON] et al. (2023) [4] (ICC at initial contact = 0.8). However, [PERSON] et al. (2023) [4] assessed between-day reliability. Therefore, we cannot make direct comparison to the ICCs reported in the current study, which were taken from trials taken within one testing session. The CGM2 model seems to be a much more reliable alternative to the PiG model when using MOCAP suits, with good to excellent reliability across all joints in both suited and non-suited conditions (ICC: 0.769-0.965). The least reliable joint was the knee with an average ICC of 0.855. The non-suited condition did not perform significantly more reliably at any of the three joints and, as a result, the use of MOCAP suits in conjunction with the CGM2 model can be recommended as an alternative to placing markers directly onto the skin to repeatedly assess ankle, knee and hip angles in the sagittal plane. These results are comparable to the reliability of the CGM2 model reported by [PERSON] et al. (2023) [4], who reported sagittal ICC values of the ankle, knee and hip between 0.73 and 0.93. The large difference in reliability when comparing the two models may be a result of the way the shank segment is defined in each model. The CGM2 model uses both lateral and medial joint markers to define the knee and ankle joint centres, with the shank orientation determined by the lateral ankle marker, a bony landmark. The PiG, however, only uses lateral markers to determine joint centres and determines the shank orientation on a tibial marker, which is placed halfway down the shank. This marker is not over a bony landmark and will therefore be hard to place consistently.