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

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 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 myosin heavy chains, and a shift towards fast myosin heavy chains 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.