Effects of experimental weight perturbation on skeletal muscle work efficiency in human subjects
Laval University, Quebec City, Quebec, CanadaAJP Regulatory Integrative and Comparative Physiology (Impact Factor: 3.11). 07/2003; 285(1):R183-92. DOI: 10.1152/ajpregu.00474.2002
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.
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- "The adaptive responses to energy restriction in individuals that are overweight or obese are numerous and have been reviewed elsewhere (Sainsbury A, Seimon RV, Hills AP, Wood RE, King NA, Gibson AA, Byrne NM, submitted manuscript; Sainsbury and Zhang, 2012; King et al., 2012; Melanson et al., 2013; Leibel et al., 2015; MacLean et al., 2015; Rosenbaum et al., 2010; Maclean et al., 2011; Sumithran and Proietto, 2013; Sainsbury and Zhang, 2010). They include increased appetite (Mason et al., 2015; Purcell et al., 2014; Sumithran et al., 2011, 2013), reduced physical activity (Hunter et al., 2015; Camps et al., 2013) or the energy cost of physical activity (Hunter et al., 2015; Martin et al., 2011; Rosenbaum et al., 2003; Novak and Levine, 2007; Bonomi et al., 2013), reduced energy expenditure greater than that expected from the reduction in body mass (Knuth et al., 2014; McNeil et al., 2015), and hormonal effects that can adversely affect body composition by promoting the accumulation of adipose tissue (particularly central adiposity) and stimulating the loss of lean tissues (Sainsbury and Zhang, 2012; Stolzenberg-Solomon et al., 2012; Carpenter et al., 2012; Seimon et al., 2013; Wright et al., 2013). Indeed, studies in lean animals and humans clearly show that negative energy balance markedly inhibits activity of the hypothalamo-pituitary-thyroid (de Vries et al., 2015), -gonadotropic and -somatotropic axes (or reduces circulating insulin-like growth factor-1 [IGF-1] levels) (Steyn et al., 2011), while concomitantly activating the hypothalamo-pituitary-adrenal axis (Sainsbury and Zhang, 2012; Seimon et al., 2013). "
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- "(−10.5% to −20.4% vs. −1.4% to −2.1%, respectively for energy cost and body fat) as well as the literature (Lazzer et al., 2004; Ohrström, Hedenbro, & Ekelund, 2001). Consequently, other parameters were suggested to play an important role in the reduced energy cost of walking (Hunter et al., 2008; Peyrot et al., 2012; Rosenbaum et al., 2003). "
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- "Interestingly, when external weight is added to match the subject’s baseline weight, energy expenditure to complete a given workload remains below baseline . It has been speculated that this increase in skeletal muscle efficiency may be related to the persistent hypothyroidism and hypoleptinemia that accompany weight loss, resulting in a lower respiratory quotient and greater reliance on lipid metabolism . "
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