This study aimed to compare muscle activation and neuromuscular symmetry during isometric squat exercises performed on stable and unstable surfaces. Nineteen recreationally active males (aged 18–27) participated in the experiment. A hard floor represented the stable surface, while the unstable conditions included a BOSU ball with the dome side up, a BOSU ball with the flat side up, and a gymnastics mat. Participants performed two 10 s sets of isometric squats on each surface using body weight. Electromyographic (EMG) activity was recorded from the vastus medialis (VM), vastus lateralis (VL), medial gastrocnemius (MG), and lateral gastrocnemius (LG). The central focus of this study was neuromuscular symmetry, which is defined in biomechanics as the balanced muscle activity between homologous and synergistic muscle groups. Since surface instability may influence muscle coordination and postural control, this study investigated whether muscle activation symmetry differs across varying surface conditions. The results showed no statistically significant differences in muscle activation across all surfaces for VM, VL, MG, and LG (p > 0.05). These findings indicate that surface stability does not significantly impact the activation or symmetry of these lower limb muscles during isometric squats. Therefore, different surfaces may be used interchangeably in training or rehabilitation programmes without altering muscle engagement. This flexibility could be advantageous for athletes, clinicians, or individuals aiming to diversify exercise modalities or adapt routines based on surface availability.
