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Bion 11 Spaceflight Project: Effect of Weightlessness on Single Muscle Fiber Function in Rhesus MonkeysAlthough it is well known that microgravity induces considerable limb muscle atrophy, little is known about how weightlessness alters cell function. In this study, we investigated how weightlessness altered the functional properties of single fast and slow striated muscle fibers. Physiological studies were carried out to test the hypothesis that microgravity causes fiber atrophy, a decreased peak force (Newtons), tension (Newtons/cross-sectional area) and power, an elevated peak rate of tension development (dp/dt), and an increased maximal shortening velocity (V(sub o)) in the slow type I fiber, while changes in the fast-twitch fiber are restricted to atrophy and a reduced peak force. For each fiber, we determined the peak force (P(sub o)), V(sub o), dp/dt, the force-velocity relationship, peak power, the power-force relationship, the force-pCa relationship, and fiber stiffness. Biochemical studies were carried out to assess the effects of weightlessness on the enzyme and substrate profile of the fast- and slow-twitch fibers. We predicted that microgravity would increase resting muscle glycogen and glycolytic metabolism in the slow fiber type, while the fast-twitch fiber enzyme profile would be unaltered. The increased muscle glycogen would in part result from an elevated hexokinase and glycogen synthase. The enzymes selected for study represent markers for mitochondrial function (citrate synthase and 0-hydroxyacyl-CoA dehydrogenase), glycolysis (Phosphofructokinase and lactate dehydrogenase), and fatty acid transport (Carnitine acetyl transferase). The substrates analyzed will include glycogen, lactate, adenosine triphosphate, and phosphocreatine.
Document ID
Document Type
Fitts, Robert H.
(Marquette Univ. Milwaukee, WI United States)
Romatowski, Janell G.
(Marquette Univ. Milwaukee, WI United States)
Widrick, Jeffrey J.
(Marquette Univ. Milwaukee, WI United States)
DeLaCruz, Lourdes
(Marquette Univ. Milwaukee, WI United States)
Date Acquired
August 19, 2013
Publication Date
January 1, 1999
Subject Category
Life Sciences (General)
Funding Number(s)
Distribution Limits
Work of the US Gov. Public Use Permitted.

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