The effect of obesity on the contractile performance of isolated mouse soleus, EDL, and diaphragm muscles

Obesity affects the major metabolic and cellular processes involved in skeletal muscle contractility. Surprisingly, the effect of obesity on isolated skeletal muscle performance remains unresolved. The present study is the first to examine the muscle specific changes in contractility following dietary induced obesity using an isolated muscle work-loop (WL) model that more closely represents in vivo muscle performance. Following 16-week high calorific feeding, soleus (SOL), extensor digitorum longus (EDL), and diaphragm (DIA) were isolated from female (CD-1) mice and contractile performance compared against a lean control group. Obese SOL produced greater isometric force, however isometric stress (force per unit muscle area), absolute WL power and normalised WL power (watts per kg muscle mass) were unaffected. Maximal isometric force and absolute WL power of the EDL was similar between groups. For both EDL and DIA, isometric stress and normalised WL power were reduced in the obese groups. Obesity caused a significant reduction in fatigue resistance in all cases. Our findings demonstrate a muscle specific reduction in contractile performance and muscle quality that is likely related to in vivo mechanical role, fibre type and metabolic profile, which may in part be related to changes in MyHC expression and AMPK activity. These results infer that beyond the additional requirement of moving a larger body mass, functional performance and quality of life may be further limited by poor muscle function in obese individuals. As such, a reduction in muscle performance may be a substantial contributor to the negative cycle of obesity.