## 1 Introduction
Notably, muscle-specific recruitment could be modified by foot placement and hip adjustments--such as high foot position increasing gluteus maximus activation, or adduction squeezing recruiting adductor longus. However, most reviewed studies emphasized the concentric phase, and few included comprehensive muscle group comparisons. The review concluded that a major limitation in the literature is the lack of standardized, multi-muscle EMG analysis during eccentric-only tasks, particularly in protocols that simulate real-world multi-joint loading. A small amount of research has examined EMG activity across various muscles during multi-joint tasks with greater emphasis on isolating the eccentric phase. [PERSON] et al. [12] investigated EMG-force relationships during squat ramping and found differing activation patterns under eccentric conditions; however, their study focused on a small number of thigh muscles and lacked eccentric-only phase isolation (e.g., where the eccentric was not preceded by a concentric action). [PERSON] et al. [13] used a motorized isotonic system to investigate EMG responses during accentuated-eccentric barbell squats. They observed reduced EMG activity in the knee extensors and gluteus maximus during the eccentric phase of the accentuated-eccentric condition compared to the concentric phase of the traditional squat, despite increased external loading. However, the isotonic nature of the system and the lack of precisely controlled joint angular velocities limit the internal validity required for highly confident interpretation. Taken together, these findings highlight several persistent gaps in the literature: (1) muscle selection bias, as most studies prioritize prime movers over synergists and stabilizers and thigh muscles over lower limb muscles; (2) combined eccentric-concentric cycles, where eccentric actions are embedded within concentric-eccentric cycles; and (3) a lack of investigation into eccentric-only loading under tightly controlled (e.g., velocity) multi-joint conditions. Despite the increasing availability of isokinetic and isotonic dynamometers capable of delivering pure eccentric loads, there is still little known about how various lower limb muscles compare in their activation magnitude under these specific conditions. [PERSON] et al. [14] and [PERSON] et al. [15] partially address this gap by providing the most relevant insights to date, having examined lower limb muscle activation using a lower body multi-joint eccentric isokinetic dynamometer (Eccentron BTE Technologies, Hanover, MD, USA). [PERSON] et al. [14] studied stroke patients undergoing virtual reality-based eccentric training on an Eccentron dynamometer and found that slow-velocity eccentric actions produced significantly higher EMG activation in the VL, vastus medialis, and GM compared to faster movements. [PERSON] et al. [15] examined EMG activity across four traditional eccentric exercises and the Eccentron isokinetic device in healthy adults. The Eccentron elicited the highest muscle activation across all major lower limb groups (average EMG = 60.4% of max), highlighting its efficiency as an eccentric loading modality. Yet, neither study focused largely on the eccentric-based lower limb multi-muscle comparison aspect as they were more primarily interested in comparing across eccentric-based exercises [15] and training programs [14]. Taken together, this body of work underscores the need for a lower limb multi-muscle activation comparison profile under eccentric-only, multi-joint, standardized (isokinetic) submaximal loading conditions. Such a profile would help clinicians identify over- or under-recruited muscles during eccentric protocols, providing evidence to optimize eccentric exercise schemes and reduce injury risk in diverse populations. Therefore, the purpose of this study was to compare neuromuscular activation (surface EMG) of four lower limb muscles during a submaximal, eccentric-only, multi-joint isokinetic resistance exercise.