Peripheral nerve adaptations to 10 days of horizontal bed rest in healthy young adult males

Space analogues, such as bed rest, are used to reproduce microgravity-induced morphological and physiological changes and can be used as clinical models of prolonged inactivity. Nevertheless, non-uniform decreases in muscle mass and function have been frequently reported, and peripheral nerve adaptations have been poorly studied, although some of these mechanisms may be explained. Ten young healthy males (18-33 y) underwent 10 days of horizontal bed rest. Peripheral neurophysiological assessments were performed bilaterally for the dominant (DL) and non-dominant upper and lower limbs (N-DL) on the 1st and 10th day of bed rest, including ultrasound of the median, deep peroneal (DPN) and common fibular (CFN) nerves, as well as a complete nerve conduction study (NCS) of the upper and lower limbs. Consistently reduced F-waves, suggesting peripheral nerve dysfunction, of both the peroneal (DL: p= 0.005, N-DL p= 0.013) and tibial nerves (DL: p= 0.037, N-DL p= 0.005) were found bilaterally, while no changes were observed in nerve ultrasound or other parameters of the NCS of both the upper and lower limbs were observed. In these young healthy males, only the F-waves, known to respond to postural changes, were significantly affected by short-term bed rest. These preliminary results suggest that during simulated microgravity, most changes occur at the muscle or central nervous system level. Since the assessment of F-waves is common in clinical neurophysiological examinations, caution should be used when testing individuals after prolonged immobility.