## 4 Discussion  
The current study investigated the temporal similarities in shape between electromyography (EMG) signals from seven lower limb muscles and center-of-pressure (COP) signals, known as the EMG-COP correlation, in physically active young adults performing bipedal balancing tasks on both stable and multiaxially unstable surfaces. This study focused on leg dominance, surface stability, sway direction, and foot position. The findings revealed significant effects of leg dominance, surface stability, and sway direction on the EMG-COP correlations for specific muscles. Based on the current empirical findings, three points can be discussed. First, this study reveals a significant asymmetry in muscle activity related to leg dominance, particularly in the tibialis anterior (TA) muscle. A higher correlation coefficient for the TA is observed during non-dominant leg stance compared to dominant leg stance. This suggests that even during bipedal balance tasks, the non-dominant leg plays a more prominent role in postural control [43], compensating for the dominant leg's reduced involvement, aligning with the idea that the non-dominant leg plays a more prominent role in maintaining balance during challenging tasks [44]. This asymmetry is especially important in bimanual motor tasks, such as standing, which require coordinated muscle activity between both legs to maintain an upright posture [41]. Relying on one leg for stability in these tasks could increase the risk of injury [19; 20], as muscle fatigue and overuse may result from unequal load distribution. Therefore, balancing muscle engagement across both legs in bimanual tasks should be a key focus in training and injury prevention strategies [45]. This finding underscores the need to give greater attention to leg dominance when assessing balance and developing injury prevention protocols [24; 45]. Second, this study emphasizes the crucial roles of thigh muscles (RF, ST, BF) and plantarlexors (GM, SO) in maintaining bipedal balance on stable surfaces, as these muscles counteract postural sway by stabilizing the knee and ankle joints [28]. Unlike the tibialis anterior (TA) and peroneus longus (PL), which are key for postural control during unipedal balance [28], the thigh and plantarflexor muscles are more essential for bipedal stability. Their role diminishes on unstable surfaces, supporting prior assumptions that unstable surfaces challenge postural stability [12; 25; 26; 27], disrupting upright stances by reducing sensory input and compromising ankle torque, thereby requiring a shift in muscle recruitment and postural strategies to maintain balance [32]. The decreased influence of these muscles on unstable surfaces may indicate a shift in reliance on other muscles or strategies to maintain balance. Third, this study highlights distinct roles for specific muscles in controlling bipedal postural stability across the sagittal and frontal planes. The semitendinosus (ST) and tibialis anterior (TA) muscles show stronger correlations with anteroposterior (AP) postural sway than mediolateral (ML) sway, reflecting their key roles in forward-backward stability similarly to unipedal stance [28]. Interestingly, while ST and TA correlate with ML sway during unipedal balancing [28], this pattern is not observed in bipedal standing, as evidenced in this study. This suggests that muscle recruitment differs between unipedal and bipedal tasks, emphasizing the need for targeted training based on specific activity demands [28; 46]. In terms of practical applications, the current results highlight the critical role of specific muscles in maintaining balance [28] and the importance of recognizing asymmetry in lower limb muscle activation [47]. This is particularly relevant for developing injury prevention and rehabilitation interventions, as sports-related lower limb injuries often differ in prevalence between the dominant and non-dominant legs [21, 22, 23, 24].