Aging muscles become hard of hearing

March 21, 2007

But regular exercise can help speed up response time

By Sara Goudarzi

As people age, neurons have to yell louder at the body's muscles to

whip them into action, according to a new study, but exercise could

reverse the aging effect.

Researchers examined the relationship between neuron activity and

corresponding muscle force for 23 subjects between the ages of 18

and 88. They found a diminished ability of the muscles to respond to

the commands of neurons amongst the older participants.

Specifically, the researchers looked at the dorsal interosseous

muscle, situated between the index finger and thumb. This muscle is

activated by 120 individual neurons. Each subject had a small needle-

like electrode inserted into their index finger. The electrode was

hooked up to a computer which recorded the electrical impulses as

they traveled from the neurons to the muscle fibers.

The participants were asked to use that finger to follow the outline

of a wavy line with peaks and valleys on a computer screen.

" More force — which this indicated by a corresponding higher firing

rate of neurons — is exerted just before you begin the upturn toward

one peak and then it eases off again in the downturn toward a

valley, " said Knight, a researcher from the University

of Delaware.

The tests showed neuron firing rates and muscle responsiveness were

lower in older participants than the younger subjects.

" 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. "

This type of reduced neuron activity, Knight said, could be improved

however with exercising.

" After power training with weights, we see an increase in firing

rates, " Knight said. " For safety, we're commonly advised to do

things slowly when exercising, but it's important to also do some

fast exercises. You need a fast movement to prevent a fall. Even in

the frail elderly, it is possible to use exercise bands for manual

resistance to improve the speed of movement. "

The study was detailed in the January issue of the Journal of

Applied Physiology.

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