title: Effects of long-term bed rest on H-reflex and motor evoked potential in lower leg muscles during standing.
abstract: Maximal H-reflex amplitude (Hmax) compared with maximal M-response (Mmax) has been generally used to assess the efficacy of the monosynaptic transmission from Ia afferents to alpha motoneurons in spinal cord. In previous studies, it has been demonstrated that H-reflex in soleus muscle (SOL) is inhibited during free standing due to an increase in presynaptic inhibition of the Ia afferent terminals to SOL motoneurones (Katz et al. 1988, Koceja et al. 1993). Transcranial magnetic stimulation (TMS) of human motor cortex excites the corticospinal system monosynapticaly connecting to spinal alpha motoneurones. However, it is not clear whether or not the motor evoked potentials (MEPs) in SOL and tibialis anterior (TA) muscles induced by TMS are modulated during standing (Ackermann et al. 1991, Lavoie et al. 1995). Considering that postural control functions change with exposure to weightlessness, we supposed that the excitability of SOL and TA spinal motoneurons from Ia afferents and/or corticospinal tracts during free standing would change after long-term bed rest (BR). The aim of this study was to investigate the effect of BR on H-reflex and MEP in SOL and TA during free standing.
authors.affiliation: Motor Dysfunction Division, National Rehabilitation Center for the Disabled, Saitama, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Yamanaka
authors.forename: S
authors.initials: S
authors.lastname: Yamamoto
authors.forename: K
authors.initials: K
authors.lastname: Nakazawa
authors.forename: H
authors.initials: H
authors.lastname: Yano
authors.forename: Y
authors.initials: Y
authors.lastname: Suzuki
authors.forename: T
authors.initials: T
authors.lastname: Fukunaga
mesh_terms: D000328:Adult; D001510:Bed Rest; D004576:Electromyography; D019054:Evoked Potentials, Motor; D006181:H-Reflex / Q000502:physiology*; D018475:Head-Down Tilt; D006801:Humans; D008280:Magnetics; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology; D011187:Posture; D017729:Presynaptic Terminals / Q000502:physiology