SOD2 and obesity due to melanocortin 4 receptor deficiency: We chose to use the Sod2+/- mouse as this strain does not exhibit any baseline impairment in physical function or lifespan [17] (limiting the influence of developmental defects) and has a similar reduction in muscle Sod2 activity as found in human disorders associated with oxidative stress (aging [18], obesity [19], type 2 diabetes [20]).