Journal
JOURNAL OF APPLIED PHYSIOLOGY
Volume 98, Issue 1, Pages 307-314Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/japplphysiol.00612.2004
Keywords
magnetic resonance spectroscopy; muscle strength; skinned fibers
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Funding
- NCRR NIH HHS [2P41 RR 02305] Funding Source: Medline
- NICHD NIH HHS [R01 HD 37645, R01 HD 40850] Funding Source: Medline
- EUNICE KENNEDY SHRIVER NATIONAL INSTITUTE OF CHILD HEALTH &HUMAN DEVELOPMENT [R01HD037645] Funding Source: NIH RePORTER
- NATIONAL CENTER FOR RESEARCH RESOURCES [P41RR002305] Funding Source: NIH RePORTER
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Cast immobilization is associated with decreases in muscle contractile area, specific force, and functional ability. The pathophysiological processes underlying the loss of specific force production as well as the role of metabolic alterations are not well understood. The aim of this study was to quantify changes in the resting energy-rich phosphate content and specific force production after immobilization. P-31-magnetic resonance spectroscopy, three-dimensional magnetic resonance imaging, and isometric strength testing were performed in healthy subjects and patients with an ankle fracture after 7 wk of immobilization and during rehabilitation. Muscle biopsies were obtained in a subset of patients. After immobilization, there was a significant decrease in the specific plantar flexor torque and a significant increase in the inorganic phosphate ( Pi) concentration ( P < 0.001) and the P-i-to-phosphocreatine (PCr) ratio ( P < 0.001). No significant change in the PCr content or basal pH was noted. During rehabilitation, both the P-i content and the P-i-to-PCr ratio decreased and specific torque increased, approaching control values after 10 wk of rehabilitation. Regression analysis showed an inverse relationship between the in vivo Pi concentration and specific torque ( r = 0.65, P < 0.01). In vitro force mechanics performed on skinned human muscle fibers demonstrated that varying the Pi levels within the ranges observed across individuals in vivo ( 4 - 10 mM) changed force production by &SIM; 16%. In summary, our findings clearly depict a change in the resting energy-rich phosphate content of skeletal muscle with immobilization, which may negatively impact its force generation.
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