A loss of responsiveness to insulin is thought to plays a major role in the loss of physical strength that occurs with aging.  Elena Volpi, from University of Texas Medical Branch at Galveston (USA), and colleagues studied 14 elderly men and women, examining the response of thigh muscle to the two different blood insulin levels.  After injecting insulin into the muscle tissue resulting in a blood insulin level double that produced by a typical meal, “their muscles were stimulated like those of young people," with protein synthesis and muscle growth promoted.    The team attributes the decline of muscle tissue with age to changes in the vascular system; and in particular, changes in the endothelium – the layer of cells lining blood vessels.  In that insulin prompted endothelium dilation, the hormone exposes more muscle to the nutrients present in blood.