U. S. researchers have said that muscles age because of the way a network of blood vessels that threads through muscles responds to the hormone insulin.

Blood vessels open wide and allow nutrients to reach muscle cells when young people naturally release insulin after eating a meal, researchers at the University of Texas Medical Branch at Galveston have said.

Published in the Journal of Clinical Endocrinology & Metabolism, the study suggests insulin in elderly people does not result in the muscle repairing, "vasodilating," effect.

Study senior author Dr. Elena Volpi said in a statement, "We found that by blocking vasodilation, we reproduced in young people the entire response that we see in older persons, a blunting of muscle protein response and a lack of net muscle growth. In other words, from a muscle standpoint, we made young people look 50 years older."

It has been also reported that Volpi and colleagues infused insulin equivalent to the amount generated in response to a single meal into the thigh muscles of two sets of young volunteers. One set was given a drug that blocked vasodilation, while the other set responded normally.

Volpi also said that muscle protein synthesis levels were measured using chemical tracers and muscle tissue biopsies were done. (With Inputs from Agencies)