A team of researchers the University of Nottingham Schools of Graduate Entry Medicine and Biomedical Sciences say that the suppression of muscle breakdown, which also happens during feeding, is blunted with age.
Muscle mass is important because a loss of muscle which decreases strength and increases the likelihood of falls and fractures - and a 'double whammy' affects people aged over 65. But weight training may 'rejuvenate' muscle blood flow and help retain muscle for older people.
Why is there ongoing loss of muscle in older people? When they eat they don't build enough muscle with the protein in food and their insulin hormones (released during a meal) fail to shut down the muscle breakdown that rises between meals and overnight. In young people, insulin acts to slow muscle breakdown. Common to these problems may be a failure to deliver nutrients and hormones to muscle because of a poorer blood supply.
The research just published in the American Journal of Clinical Nutrition compared one group of people in their late 60s to a group of 25-year-olds, with equal numbers of men and women. Michael Rennie, Professor of Clinical Physiology, said, "We studied our subjects first — before breakfast — and then after giving them a small amount of insulin to raise the hormone to what they would be if they had eaten breakfast, of a bowl of cornflakes or a croissant."
"We tagged one of the amino acids (from which proteins are made) so that we could discover how much protein in leg muscle was being broken down. We then compared how much amino acid was delivered to the leg and how much was leaving it, by analysing blood in the two situations.
"The results were clear. The younger people's muscles were able to use insulin we gave to stop the muscle breakdown, which had increased during the night. The muscles in the older people could not."
"In the course of our tests, we also noticed that the blood flow in the leg was greater in the younger people than the older ones," added Rennie. "This set us thinking: maybe the rate of supply of nutrients and hormones is lower in the older people? This could explain the wasting we see."
Following this up led Beth Phillips, a PhD student working with Professor Rennie, to win the Blue Riband Award for work she presented at the summer meeting of The Physiological Society in Dublin. In her research Beth confirmed the blunting effect of age on leg blood flow after feeding, with and without exercise. The team predicted that weight training would reduce this blunting. "Indeed, she found that three sessions a week over 20 weeks 'rejuvenated' the leg blood flow responses of the older people. They became identical to those in the young," said Rennie.
"I am extremely pleased with progress," he said. "Our team is making good headway in finding more and more out about what causes the loss of muscle with age. It looks like we have good clues about how to lessen it with weight training and possibly other ways to increase blood flow."
The research was funded by the UK's Biotechnology and Biological Sciences Research Council (BBSRC) as part of ongoing work on age-related muscle wasting and how to lessen that effect.