## 1 Introduction  
Anatomical and physiological differences between the medial (MG) and lateral (LG) heads of the gastrocnemius muscle are well-documented, with the MG typically exhibiting a 20-30% greater cross-sectional area and volume compared to the LG [1, 2]. These morphological differences are accompanied by divergent neural activation patterns, as the MG and LG can be independently recruited depending on the contraction type and joint configuration [3,4]. Such task-specific activation has been observed during a variety of functional activities, including postural swaying [5,6], reactive perturbations [7], walking [8], running [9], and sprinting [10]. Manipulating resistance training variables is essential to optimizing muscular activation, with volume, load, and frequency being the most commonly examined factors [11]. Within the context of resistance training, range of motion (ROM) is a critical but often underexplored variable, despite its established relevance for modulating muscle activation and promoting hypertrophic adaptations [12]. While training through a full ROM has been shown to enhance lower-limb muscle development [12], the specific interaction between ROM and exercise execution type--namely, bilateral versus unilateral movement--in MG and LG activity during heel raise exercises (HREs) remains insufficiently understood. Dynamic plantar flexion exercises such as heel raises are widely used to enhance running and jumping performance, assess muscle function through calf raise tests [13], and prevent or rehabilitate stroke-related impairments and lower leg injuries, including Achilles tendon damage [14]. In this context, the precise assessment of muscle activation patterns, including coactivation around key joints like the knee, has become crucial for understanding joint stability and developing effective injury prevention strategies [15,16]. Performing HREs under different foot, knee angle, and ankle ROM conditions has been proposed to target region-specific gastrocnemius activity. Evidence remains inconclusive regarding the effect of foot position on MG and LG activation during dynamic, weight-bearing tasks [17, 18, 19, 20, 21, 22]. Knee flexion appears to differentially influence MG and LG activity under controlled conditions (e.g., seated or prone), with the LG being less affected [23, 24, 25]. In functional movements (e.g., unilateral weight-bearing HREs at 0\({}^{\circ}\) and 45\({}^{\circ}\)), electromyography (EMG) amplitudes are similar, indicating limited differentiation between muscles [26]. With the knee extended, the MG and LG exhibit distinct neuromuscular responses during HREs performed on the ground [2,27] and at full ankle ROM [28]. While LG and soleus activation correlates across various exercise conditions, the MG does not show such consistency [28]. A longitudinal study revealed that the MG and LG respond differently to full- vs. half-ROM training in terms of muscle thickness gains [29], suggesting task-dependent activation patterns. Given the limited evidence on MG and LG responses across the ankle ROM during bilateral and unilateral HREs, further investigation is warranted. EMG studies during plantar flexion suggest that limb dominance influences muscle activation [27,30,31]. However, no prior studies have compared MG and LG activity between dominant and non-dominant legs during HREs, justifying bilateral analysis. Such insights may inform performance and rehabilitation strategies targeting muscular asymmetries. Concerning EMG normalization, previous studies have compared maximal voluntary isometric contractions with a dynamic normalization method [32,33]. Sprint running has been recommended over isometric tasks due to its simplicity and higher normalization values. Dynamic tasks (e.g., sprint running, squat jump) elicit similar neural drive and muscle coordination to the target exercise, with consistent relative activation levels [33]. Sprint running is also a reliable and reproducible EMG reference for the triceps surae.