Histochemical responses of human soleus muscle fibers to long-term bedrest with or without countermeasures.
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.
Ohira
Y
Y
Department of Physiology and Biomechanics, National Institute of Fitness and Sports, Kanoya, Japan. ohira@nifs-k.ac.jp
Yoshinaga
T
T
Nonaka
I
I
Ohara
M
M
Yoshioka
T
T
Yamashita-Goto
K
K
Izumi
R
R
Yasukawa
K
K
Sekiguchi
C
C
Shenkman
B S
BS
Kozzlovskaya
I B
IB
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
D018995:Myosin Heavy Chains