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

Abstract

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.

Effect of 10 days of unilateral lower limb suspension on knee extensors neuromuscular function and spinal excitability

“…More precisely, since the H-M LATENCY , an index of conduction velocity through the spinal reflex loop, was not changed in their studies (13,30), authors primarily attributed the slowed conduction of H-reflex and M-wave responses to the conduction velocity in the supply nerves, the branching axon terminals, and/or transmission across the neuromuscular junction (67). No change in nerve conduction through the reflex arc occurred after 10 days of ULLS for the lower limb muscles, and confirm similar evidences from Manganotti et al (68) who used the bed rest model during an identical period of disuse. Further studies using ULLS protocols exceeding 10 days are needed to better understand the modulation kinetics of nerve conduction in knee extensors.…”

“…No change in nerve conduction through the reflex arc occurred after 10 days of ULLS for the lower limb muscles, and confirm similar evidences from Manganotti et al . (68) who used the bed rest model during an identical period of disuse. Further studies using ULLS protocols exceeding 10 days are needed to better understand the modulation kinetics of nerve conduction in knee extensors.…”

Respiratory sequelae of COVID-19: pulmonary and extrapulmonary origins, and approaches to clinical care and rehabilitation

“…The mechanisms that contribute to this reduction in exercise tolerance are not known, but bed rest in otherwise healthy individuals results in rapid-onset muscle wasting, 132 reduced muscle endurance, and denervation. 133 , 134 Even more profound muscle loss is seen in the inpatient hospital setting, particularly in ICUs, where the additional mechanisms of inflammation, hypoxia, and nutritional imbalance might be involved. 135 , 136 Thus, it is likely that deconditioning contributes to the reduction in exercise tolerance seen after COVID-19.…”

Early Biomarkers of Altered Renal Function and Orthostatic Intolerance During 10-day Bedrest

“…Bedrest represents a valuable experimental model to mimic the effects of microgravity on Earth ( Mukai and Ohshima, 2012 ; Goswami and Valenti, 2020 ). However, few studies investigated the human functional decline during 10-day bedrest and most of these focused on skeletal muscle, peripheral nerve adaptations, aerobic capacity, and bone alterations ( Center et al, 2007 ; Mukai and Ohshima, 2012 ; Manganotti et al, 2021 ).…”