title: Histochemical responses of human soleus muscle fibers to long-term bedrest with or without countermeasures.
abstract: Effects of 2- or 4-month bedrest in -6 degrees head-down tilt position with or without countermeasures on the histochemical properties of fiber phenotype and cross-sectional area (CSA) were studied in human soleus. The CSAs in slow fibers decreased approximately 32% during 4-month bedrest. This reduction was normalized after 1-month recovery. Although the reduction of percent slow fibers was not significant statistically, the percent intermediate fibers was significantly elevated 4 months after bedrest. Such shift in fiber type was not normalized following 1-month recovery. Effects of wearing an anti-g Penguin suit which has a modest, but continuous resistance at the knee and ankle (Penguin-1) or with knee resistance without loading on the ankle (Penguin-2) for 10 consecutive hours daily were also investigated during approximately 2 months of bedrest. The subjects performed knee extension and flexion for the last 15 min of each hour while in a supine position in bed. Bedrest-induced fiber atrophy was prevented in the Penguin-1 group but not the Penguin-2 group. Transformation of fiber type was not prevented in either Penguin suit group. It is suggested that long-term bedrest causes an atrophy and a shift of fiber phenotype toward fast-twitch type in human soleus. Data also indicated that loading on the muscle is an effective countermeasure for prevention of fiber atrophy but not fiber-type transformation.
authors.affiliation: Department of Physiology and Biomechanics, National Institute of Fitness and Sports, Kanoya, Japan. ohira@nifs-k.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Ohira
authors.forename: T
authors.initials: T
authors.lastname: Yoshinaga
authors.forename: I
authors.initials: I
authors.lastname: Nonaka
authors.forename: M
authors.initials: M
authors.lastname: Ohara
authors.forename: T
authors.initials: T
authors.lastname: Yoshioka
authors.forename: K
authors.initials: K
authors.lastname: Yamashita-Goto
authors.forename: R
authors.initials: R
authors.lastname: Izumi
authors.forename: K
authors.initials: K
authors.lastname: Yasukawa
authors.forename: C
authors.initials: C
authors.lastname: Sekiguchi
authors.forename: B S
authors.initials: BS
authors.lastname: Shenkman
authors.forename: I B
authors.initials: IB
authors.lastname: Kozzlovskaya
mesh_terms: D000328:Adult; D001284:Atrophy; D001510:Bed Rest; D001706:Biopsy; D048429:Cell Size / Q000502:physiology; D006801:Humans; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000737:chemistry* / Q000473:pathology*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000473:pathology*; D018995:Myosin Heavy Chains / Q000032:analysis*; D013026:Space Flight; D019442:Space Suits
chemical_list: D018995:Myosin Heavy Chains