title: Changes in inorganic phosphate and force production in human skeletal muscle after cast immobilization.
abstract: 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. (31)P-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 (P(i)) 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 P(i) concentration and specific torque (r = 0.65, P < 0.01). In vitro force mechanics performed on skinned human muscle fibers demonstrated that varying the P(i) levels within the ranges observed across individuals in vivo (4-10 mM) changed force production by approximately 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.
authors.affiliation: Dept. of Physical Therapy, PO Box 100154, University of Florida, Gainesville, FL 32610, USA. npathare@phhp.ufl.edu
authors.forename: Neeti
authors.initials: N
authors.lastname: Pathare
authors.forename: Glenn A
authors.initials: GA
authors.lastname: Walter
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Stevens
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Yang
authors.forename: Enyi
authors.initials: E
authors.lastname: Okerke
authors.forename: John D
authors.initials: JD
authors.lastname: Gibbs
authors.forename: John L
authors.initials: JL
authors.lastname: Esterhai
authors.forename: Mark T
authors.initials: MT
authors.lastname: Scarborough
authors.forename: C Parker
authors.initials: CP
authors.lastname: Gibbs
authors.forename: H Lee
authors.initials: HL
authors.lastname: Sweeney
authors.forename: Krista
authors.initials: K
authors.lastname: Vandenborne
mesh_terms: D016512:Ankle Injuries / Q000503:physiopathology* / Q000601:surgery; D000843:Ankle Joint; D002370:Casts, Surgical; D005260:Female; D006801:Humans; D007103:Immobilization / Q000009:adverse effects*; D007287:Inorganic Chemicals / Q000378:metabolism; D007537:Isometric Contraction; D008279:Magnetic Resonance Imaging; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009133:Muscular Atrophy / Q000209:etiology* / Q000503:physiopathology*; D010710:Phosphates / Q000378:metabolism*; D013314:Stress, Mechanical
chemical_list: D007287:Inorganic Chemicals; D010710:Phosphates