title: Skeletal muscle work efficiency with age: the role of non-contractile processes.
abstract: Although skeletal muscle work efficiency probably plays a key role in limiting mobility of the elderly, the physiological mechanisms responsible for this diminished function remain incompletely understood. Thus, in the quadriceps of young (n=9) and old (n=10) subjects, we measured the cost of muscle contraction (ATP cost) with 31P-magnetic resonance spectroscopy (31P-MRS) during (i) maximal intermittent contractions to elicit a metabolic demand from both cross-bridge cycling and ion pumping and (ii) a continuous maximal contraction to predominantly tax cross-bridge cycling. The ATP cost of the intermittent contractions was significantly greater in the old (0.30±0.22 mM·min-1·N·m-1) compared with the young (0.13±0.03 mM·min-1·N·m-1, P<0.05). In contrast, at the end of the continuous contraction protocol, the ATP cost in the old (0.10±0.07 mM·min-1·N·m-1) was not different from the young (0.06±0.02 mM·min-1·N·m-1, P=0.2). In addition, the ATP cost of the intermittent contractions correlated significantly with the single leg peak power of the knee-extensors assessed during incremental dynamic exercise (r=-0.55; P<0.05). Overall, this study reveals an age-related increase in the ATP cost of contraction, probably mediated by an excessive energy demand from ion pumping, which probably contributes to both the decline in muscle efficiency and functional capacity associated with aging.
authors.forename: Gwenael
authors.initials: G
authors.lastname: Layec
authors.forename: Corey R
authors.initials: CR
authors.lastname: Hart
authors.forename: Joel D
authors.initials: JD
authors.lastname: Trinity
authors.affiliation: §Aix-Marseille Université, CNRS, CRMBM UMR 7339, 13385, Marseille, France.
authors.forename: Yann
authors.initials: Y
authors.lastname: Le Fur
authors.affiliation: ∥Department of Radiology and Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, U.S.A.
authors.forename: Eun-Kee
authors.initials: EK
authors.lastname: Jeong
authors.forename: Russell S
authors.initials: RS
authors.lastname: Richardson
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry*; D000328:Adult; D000367:Age Factors; D000368:Aged; D005260:Female; D006801:Humans; D007477:Ions; D007717:Knee; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D008928:Mitochondria / Q000502:physiology; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000473:pathology*; D018384:Oxidative Stress; D010101:Oxygen Consumption; D055815:Young Adult
chemical_list: D007477:Ions; D000255:Adenosine Triphosphate