## 4 Discussion  
This study aimed to evaluate the muscular excitation and synergies of the IS and its PSEs in highly skilled male athletes. The results confirmed the hypothesis and showed that different muscle excitation patterns could be detected in the IS compared to its PSEs. The main finding of the study is that the TRI and DEL were found to have very important roles in the execution of the IS. The large excitation of these two muscles (TRI: 2286.6 \(\pm\) 460.3 \(\upmu\)V; DEL: 1351.3 \(\pm\) 612.6 \(\upmu\)V) and their synergistic activity in the W1 and W2 synergies during the execution of the IS may be associated with the extension of the humerus [21; 22]. Therefore, the main muscles involved in the maintenance of the IS differ from those used in other whole-body horizontal hold elements in the still rings specialty of artistic gymnastics. Additionally, the triceps represent bi- articular muscles that extend the elbow joint and the shoulder, together with the posterior deltoid [23]. During the W1 synergy, these two muscles (TRI and DEL) are co-active with the TRA (333.1 \(\pm\) 114.2 \(\upmu\)V), SER (337.8 \(\pm\) 83.8 \(\upmu\)V) and INF (548.9 \(\pm\) 115.5 \(\upmu\)V). During the execution of the IS, the TRA muscle promotes scapular adduction (essential for correct scapular alignment during the isometric hold), the SER controls scapular stabilization on the thorax and the INF maintains the external rotation of the humerus. Unlike other hold gymnastics elements, the role of the INF muscle in this element is likely limited to the maintenance of humeral external rotation [4; 24]. In addition, despite the relatively high excitation of the DOR muscle registered (838.2 \(\pm\) 338.7 \(\upmu\)V), its action is probably less relevant than the roles of the TRI and DEL, as the DOR did not show any synergistic activation with other muscles. Finally, the low excitation of the BIC (97.3 \(\pm\) 24.6 \(\upmu\)V) and PEC (77.2 \(\pm\) 50.49 \(\upmu\)V), active in the W3 synergy only, suggests that the principal action of these muscles is to stabilize the humerus and control the movement of the rings [25].The present study showed that muscle excitations and synergies were different in the IS compared to its PSEs. Specifically, the reduced muscular excitation recorded in many muscles during \(\text{IS}_{\text{CP}}\) compared to theIS may be attributed to the decreased load and increased stability provided by the cable pulley system. This finding is consistent with previous investigations conducted on the support scale [7], and confirms that muscle excitation may be lower when the load is reduced by the cable pulley system and when a stable condition is compared to an unstable one [26]. Furthermore, the muscular synergies observed in the IS\({}_{\text{CP}}\) suggest a low degree of similarity between this element and the IS performed on regular rings. None of the extracted muscle synergies included the activation of the DEL muscle, and the W2 synergy only appeared to include some muscles active during the W2 synergy of the IS. Conversely, holding 75% of an athlete's body weight in IS\({}_{\text{CW}}\) did not result in significant differences in muscle excitation compared to the IS. This is consistent with the findings of [PERSON] and colleagues [4], who reported similar muscle excitations of the PEC, BIC, SER, DOR and TRI when the swallow element was reproduced using a counterweight system. Additionally, although the W1 synergy led to the activation of the PEC and TRA only, the IS\({}_{\text{CW}}\) was the only exercise showing similar muscle synergies compared to those of the IS element. Specifically, the W2 and W3 synergies showed comparable muscle activation, while the W4 synergy was distinguished by the additional activation of the DOR, which was not observed in W4 in the IS element. These findings suggest that a 25% reduction in body weight resulting from the use of a counterweight pulley system can maintain the muscle actions typical of the IS element.