Aging muscles don't always listen

NEWARK, Del., March 9 (UPI) -- A University of Delaware researcher is learning why people's muscles don't respond as well or as quickly as they age.

"As a result of age-related changes in muscle and neurons, elderly people are often frustrated by poor control during precision tasks, and slowed physical responses contribute to more falls as people grow older," Christopher Knight, a professor at Delaware's College of Health Sciences, said.

Knight studied the "motor-unit firing rates" of subjects between the ages of 18 and 88 by implanting electrodes near a series of neurons between their thumbs and index fingers and then asking them to trace designs on a computer screen with their index fingers.

The results showed lower firing rates among older subjects versus younger subjects -- a diminished ability of the muscle fibers to "hear" and respond to the neurons' commands.

"The repeated contraction of muscles is essential to movements such as walking," Knight said. "However, our muscles have a reduced capacity to contract or twitch as we grow older. We lose fast-twitch muscle fibers as we age."

Knight said the goal of the research is to improve movement quality in older adults as well as people with movement disorders such as multiple sclerosis or cerebral palsy or who are recovering from strokes.