Obesity-induced decreases in muscle performance are not reversed by weight loss

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BACKGROUND/OBJECTIVES:Obesity can affect muscle phenotypes, and may thereby constrain movement and energy expenditure. Weight loss is a common and intuitive intervention for obesity, but it is not known whether the effects of obesity on muscle function are reversible by weight loss. Here we tested whether obesity-induced changes in muscle metabolic and contractile phenotypes are reversible by weight loss.SUBJECTS/METHODS:We used zebrafish (Danio rerio) in a factorial design to compare energy metabolism, locomotor capacity, muscle isometric force and work-loop power output, and myosin heavy chain (MHC) composition between lean fish, diet-induced obese fish, and fish that were obese and then returned to lean body mass following diet restriction.RESULTS:Obesity increased resting metabolic rates (P < 0.001) and decreased maximal metabolic rates (P = 0.030), but these changes were reversible by weight loss, and were not associated with changes in muscle citrate synthase activity. In contrast, obesity-induced decreases in locomotor performance (P = 0.0034), and isolated muscle isometric stress (P = 0.01), work-loop power output (P < 0.001) and relaxation rates (P = 0.012) were not reversed by weight loss. Similarly, obesity-induced decreases in concentrations of fast and slow MHCs, and a shift toward fast MHCs were not reversed by weight loss.CONCLUSION:Obesity-induced changes in locomotor performance and muscle contractile function were not reversible by weight loss. These results show that weight loss alone may not be a sufficient intervention.

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