title: Effects of experimental weight perturbation on skeletal muscle work efficiency in human subjects.
abstract: Maintenance of reduced or elevated body weight results in respective decreases or increases in energy expended in physical activity, defined as 24-h energy expenditure excluding resting energy expenditure and the thermic effect of feeding, beyond those attributable to weight change. We examined skeletal muscle work efficiency by graded cycle ergometry and, in some subjects, rates of gastrocnemius muscle ATP flux during exercise by magnetic resonance spectroscopy (MRS), in 30 subjects (15 males, 15 females) at initial weight and 10% below initial weight and in 8 subjects (7 males, 1 female) at initial weight and 10% above initial weight to determine whether changes in skeletal muscle work efficiency at altered body weight were correlated with changes in the energy expended in physical activity. At reduced weight, muscle work efficiency was increased in both cycle ergometry [mean (SD) change = +26.5 (26.7)%, P < 0.001] and MRS [ATP flux change = -15.2 (23.2)%, P = 0.044] studies. Weight gain resulted in decreased muscle work efficiency by ergometry [mean (SD) change = -17.8 (20.5)%, P = 0.043]. Changes in muscle efficiency at altered body weight accounted for 35% of the change in daily energy expended in physical activity.
authors.affiliation: Div. of Molecular Genetics, Russ Berrie Medical Science Pavilion, 6th Fl., 1150 St. Nicholas Ave., New York, NY 10032, USA. mr475@columbia.edu
authors.forename: Michael
authors.initials: M
authors.lastname: Rosenbaum
authors.forename: Krista
authors.initials: K
authors.lastname: Vandenborne
authors.forename: Rochelle
authors.initials: R
authors.lastname: Goldsmith
authors.forename: Jean-Aime
authors.initials: JA
authors.lastname: Simoneau
authors.forename: Steven
authors.initials: S
authors.lastname: Heymsfield
authors.forename: Denis R
authors.initials: DR
authors.lastname: Joanisse
authors.forename: Jules
authors.initials: J
authors.lastname: Hirsch
authors.forename: Ellen
authors.initials: E
authors.lastname: Murphy
authors.forename: Dwight
authors.initials: D
authors.lastname: Matthews
authors.forename: Karen R
authors.initials: KR
authors.lastname: Segal
authors.forename: Rudolph L
authors.initials: RL
authors.lastname: Leibel
mesh_terms: D001823:Body Composition; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000592:standards; D005260:Female; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D009765:Obesity / Q000378:metabolism / Q000503:physiopathology*; D015203:Reproducibility of Results; D015430:Weight Gain / Q000502:physiology; D015431:Weight Loss / Q000502:physiology