Individualized isometric neuromuscular electrical stimulation training promotes myonuclear accretion in mouse skeletal muscle

Skeletal muscle is a plastic tissue that adapts to exercise through fusion of muscle stem cells (MuSCs) with myofibers, a physiological process referred to as myonuclear accretion. However, it is still unclear whether myonuclear accretion is driven by increased mechanical loading per se , or occurs, at least in part, in response to exercise-induced muscle injury. Here, we developed a carefully monitored and individualized neuromuscular electrical stimulation (NMES) training protocol of the mouse plantar flexor muscles. Each NMES training session consisted of 80 isometric contractions at a submaximal mechanical intensity corresponding to ≈15% of maximal tetanic force to avoid muscle damage. NMES trained mice were stimulated for 2 × 3 consecutive days separated by one day of rest, for a total of 6 sessions. Experiments were conducted on C57BL/6J and BALB/c males at 10-12 weeks of age. NMES led to a robust myonuclear accretion and higher MuSC content in gastrocnemius muscle of both mouse lines, without overt signs of muscle damage/regeneration or muscle hypertrophy or force improvement. This new mouse model of myonuclear accretion relying on the main function of skeletal muscles, i.e. , force production in response to electrical stimuli, will be of utmost interest to further understand the role of MuSCs in skeletal muscle adaptations. ### Competing Interest Statement The authors have declared no competing interest.