Increased physical activity does not improve obesity-induced decreases in muscle quality in zebrafish (Danio rerio)

Obesity has a negative effect on muscle contractile function, and the effects of obesity are not reversed by weight loss. It is therefore important to determine how muscle function can be restored, and exercise is the most promising approach. We tested the hypothesis (in zebrafish, Danio rerio) that moderate aerobic exercise (forced swimming for 30 min per day, raising metabolic rates to at least twice resting levels) will alleviate the negative effects of obesity of muscle function. We allocated zebrafish randomly to experimental treatments in a fully factorial design with diet treatment (three levels: lean control, diet-induced obese, obese followed by weigh loss [obese-lean]), and exercise (exercise and sedentary control) as independent factors. Treatments were conducted for 10 weeks, and we measured locomotor performance, isolated muscle mechanics, and myosin heavy chain composition. Obesity led to decreased muscle force production per unit area (p = 0.01), and slowed muscle contra...