## 4 Discussion
Greater MTU elongation, however, does not necessarily pair with lower ME. In an optimal case, tendon elongation within the MTU would be greater, elevating the amount of stored strain energy. EMG data revealed higher quadriceps activation during knee flexion as opposed to during extension, implying sufficient muscle tension to stretch the patella tendon, specifically under a low stretch load. However, under slow knee flexion velocity lasting for 1.5 s, it is possible that the passive elastic elements store strain energy in a less effective manner. During a 2 s stretch, it is possible that cross-bridge bonds fail to maintain position across the entire lengthening phase. When these bonds disconnect and reattach, stored strain energy within the sarcomere's elastic elements may decrease, possibly explaining lower ME under high stretch loads [38; 39; 40]. Nevertheless, low stretch velocities have produced SSC effects in studies with isolated muscles [40]. The tendon stress was nearly twice as high during higher stretch load SSC contraction than in low stretch load SSCs because the tendon force was substantially higher as well (Table 1). Although thicker tendons may store more elastic strain energy [41], our results did not show a positive correlation between the patella tendon CSA and ME under high stretch loads with maximal pretension. In fact, a negative correlation was found between the patella tendon CSA and ME under moderate pretension with high stretch loads. Under maximal pretension, muscle tension is near maximal from the start of knee flexion, so most MTU elongation occurs in the tendon, with high initial tendon stiffness. Increased EMG activity during eccentric phases at higher loads indicates greater muscle recruitment, resulting in a higher peak tendon force and tendon stress. As tendon stiffness influences the muscle's force-length and force-velocity profiles, it is reasonable to assume that under high stretch loads and maximal pretension, the fascicles do not operate at their optimal force-length-velocity potential because of the relatively high MTU elongation [42; 43; 44]. In this case, a thinner, more compliant patella tendon could increase stored and reused strain energy [2], and thus enhance ME. Our results could not support this idea since the patella tendon length and the CSA showed no association with ME in these SSC conditions. Based on earlier reports, the AmAt ratio is most likely to be a relevant factor in order to perform efficient muscle work and to maintain the safety factor of the tendon [6; 45; 46]. These conclusions were based on cadaver and animal studies that assumed an AmAt that could reduce the risk of injury by optimizing tendon structure to resist the tensile force during daily activities to be optimal. More specifically, they suggested that having a thinner tendon combined with longer muscle fascicles and a larger muscle mass with a 34:1 AmAt ratio could be an optimum area ratio [6]. In contrast to this idea, our results showed no correlation between AmAt and ME at any SSC condition. The lack of association between the AmAt ratio and ME could indicate that the cross-sectional dimensions of muscle and tendon relative to each other do not influence muscle-tendon dynamics. It must be noted that the SSC conditions in this study do not represent SSC contractions during daily activities; therefore, ME of SSC conditions that can mimic these activities may result in different outcomes. This study has some limitations. The low sample size limits the generalizability of our findings, so conclusions are specific only to this sample. Additionally, our approach for calculating the physiological cross-sectional area (PCSA) was based on the vastus lateralis fascicle length [27]. Although this method has shown high reliability [47; 48], individual quadriceps muscles may have different fascicle lengths, potentially affecting PCSA estimates. We also did not measure actual muscle and tendon length changes, which could provide further insights into ME mechanisms.