## 1 Introduction  
Eccentric muscle actions, where a muscle lengthens while under load, are essential to human movement and commonly implemented across rehabilitation, injury prevention, resistance training, and general fitness applications. Because they produce higher force with lower energy cost, eccentric exercises are well-suited for rebuilding strength, preventing atrophy, and promoting muscle growth and enhancing function [1]. Consequently, eccentric-based resistance training has seen rapid growth in both research and real-world practice [2]. Eccentric exercise is often performed using isokinetic dynamometers, which have become increasingly common in both research and clinical settings for assessing and training eccentric muscle function under controlled conditions [3; 4]. By maintaining a constant velocity during movement, these devices enable isolation of eccentric loading and provide consistent, reproducible neuromuscular loading profiles during the exercise task. When combined with surface electromyography (EMG), isokinetic protocols offer valuable insights into which lower limb muscles are most active during specific movements, information essential for designing targeted rehabilitation programs, optimizing performance training, and minimizing the risk of overload-related injuries. Additionally, while the present study focuses mainly on larger lower limb muscle groups, it is noted that intrinsic foot musculature also plays an important role in postural control, stability, and efficient force transfer during complex multi-joint movements [5]  
Early EMG research on eccentric muscle actions primarily focused on single-joint movements. For example, [PERSON] et al. [6] demonstrated that quadriceps activation was lower during eccentric versus concentric knee extensions. Similarly, [PERSON] and [PERSON] [7; 8] have described distinct neural control strategies (including motor unit firing patterns) during eccentric versus concentric loading of the ankle dorsiflexors. While informative, these studies do not reflect the complexity of real-world or functional movements, which typically involve the coordinated activation of multiple joints and muscle groups. The unique biomechanical properties of eccentric actions--including higher force output, distinct force-velocity relationships, and altered neural control--directly influence how multiple joints and muscle groups are recruited and coordinated in complex tasks. To address the complexity of functional movements, recent efforts have explored multi-joint tasks, but with notable limitations. EMG investigations of lower limb resistance exercises have often focused narrowly on specific muscles or exercise variations. In a comparative study of leg press configurations, [PERSON] et al. [9] showed that muscle activation varies substantially with changes in foot and hip position. The gluteus maximus was most active in the horizontal high-foot leg press, while the rectus femoris, vastus lateralis (VL), and gastrocnemius (GM) exhibited higher activation in low foot versus high foot placement variations. [PERSON] et al. [10] extended this work by comparing multi-joint (leg press) and single-joint (knee extension, kickback) exercises. They found the VL was more active in the leg press, while the rectus femoris and biceps femoris (BF) were preferentially recruited in the isolated (single-joint) tasks. Together, these studies emphasize the role of joint configuration in influencing muscle activation across different muscles within and between muscle groups, but these are limited in that they do not isolate the eccentric loading phase or include broader (e.g., synergism, antagonist, stabilizer) muscles across multiple joints during multi-joint eccentric movement tasks. [PERSON] et al. [11] systematically reviewed EMG activity in different leg press variants and found the vastus medialis and VL consistently exhibited the highest activation, particularly at 90\({}^{\circ}\) of knee flexion.