Somato-autonomic reflexes are important as the basis of acupuncture's visceral action. Recent studies revealed that autonomic nerves are innervating most of neuromuscular junctions in the skeletal muscles. In this talk, I will present research on somato-autonomic reflexes, which may contribute to skeletal muscle homeostasis. In humans and animals, muscle sympathetic nerves are known to excite during exercise. However, its physiological significance has not fully understood. We measured the tetanic force (TF) of the hindlimb muscles evoked by motor nerve stimulation in anesthetized rats. After acute transection of lumbar sympathetic trunk (LST), the specific sympathetic pathway to the hindlimb, TF decreased by approximately 10%. The similar decrease was observed after transecting the lumbar dorsal roots or the cervical spinal cord. The results indicate there is a feedback mechanism whereby the spinal cord- and brain-mediated somatosympathetic reflex elicited by hindlimb muscle contraction enhances the contractile force of that muscle. We next examined the possibility that this feedback mechanism between muscle contraction and sympathetic activity is altered by aging using young (4-9 months old) and old (32-36 months old) rats. The extent of TF change due to LST transection was significantly attenuated in the old rats; more attenuation with greater muscle atrophy. Although there was no significant overall difference in TF potentiation by stimulating the peripheral end of cut LST at 5-20 Hz between old and young rats, the frequency threshold of LST stimulation to produce TF potentiation was elevated in old rats. Conversely, the LST stimulation-induced increase in resting muscle tonus was greater in old rats than in young rats. Such changes in sympathetic muscle force regulation may contribute to age-related muscle weakness and chronic muscle pain. We previously showed that a gentle mechanical stimulation of the skin has a morphine-like inhibitory effect on the somato-cardiac sympathetic reflex in anesthetized rats. We examined changes in subjective and objective symptoms in 12 subjects with chronic neck-shoulder discomfort by applying microcones (SOMARESON) on the neck and shoulders for 2 weeks. Subjective symptom intensity (VAS, max. 10) decreased from approximately 7 to 2, and the objectively examined ranges of motion of the neck and shoulder joints were increased. If sympathetic nerves are involved in skeletal muscle contraction and tonus in humans, somato-autonomic reflexes may be involved as the mechanism to improve symptoms in chronic muscle pain.