“We found a dramatic reduction in muscle protein synthesis brought on by inactivity that caused the muscle loss,” said William J. Evans, Ph.D., director of the Nutrition, Metabolism and Exercise Laboratory in the Donald W. Reynolds Institute on Aging at the University of Arkansas for Medical Sciences (UAMS).
The 12 study participants with an average age of 67, described as moderately active prior to the study, remained in bed continuously for 10 days. During that time, they consumed a diet with the recommended daily allowance of protein (0.8 g/kg per day).
Measurements taken before and after bed rest included the muscle protein synthesis rate over the course of 24 hours, lean body mass, urinalysis and a leg-strength test. Evans said the protein synthesis rate drives the increase or reduction in muscle mass, as protein in muscle cells is always being created or broken down. When the rate decreases, more protein is being broken down than created, causing muscle loss.
According to the study, there was a 30 percent decrease in the rate of protein synthesis in muscle cells between the measurements taken before and after the 10 days of bed rest. Muscle mass was measured as a change in lean body mass. The study reported an average 1.5 kg reduction in whole body lean mass and 0.95 kg loss in leg lean mass after bed rest. “This is a striking loss of muscle in healthy individuals. When you consider the chronically ill facing longer hospitalizations or bed rest, the magnitude of muscle loss is extraordinary and should be treated”, Evans said.
He noted that the older adult participants in the UAMS study experienced more muscle loss in 10 days than did younger participants after 28 days as reported in a 2004 article in the Journal of Clinical Endocrinology Metabolism.
MEDICA.de; Source: University of Arkansas for Medical Sciences