Study supports nervous system role in age-related weakness
New evidence to support the belief that the nervous system plays an important role in age-related weakness, according to findings by researchers from the Ohio Musculoskeletal and Neurological Institute (OMNI) at the Ohio University Heritage College of Osteopathic Medicine, which were published in JAMA Network Open.
In the study, researchers led by Brian Clark, PhD, director of OMNI, compared how much muscle strength older people could muster voluntarily with how much force their muscles put out when stimulated electrically. The results of this research suggest that physical weakness in aging may be due, at least in part, to impairments in brain and nerve function, rather than changes in the muscles themselves, Clark said.
The study looked at a group of 66 older adults, with an average age in their 70s, who were first categorized as severely weak, modestly weak or strong based on their measured performance on a standardized physical test.
In the study, the subjects were asked to push against resistance with their leg extensor muscles, using as much strength as they could generate. When they reached their self-perceived limit, the muscle they were using was then stimulated electrically. If this caused the muscle to put out more force, researchers said, was a sign that the strength limitation the person experienced came from somewhere other than the muscle itself.
When the added force that came from electrical stimulation was expressed as a percentage increment, it showed that the weaker the test subjects, the larger a boost their muscles got. The subjects in the "severely weak" group, who were on average older, got an increase of 14.2 percent, twice the 7.1 percent increase shown by those in the "strong" group.
The researchers didn't investigate the nature of whatever nervous system mechanism might account for the ceiling on willed strength. However, the researchers suggested it could be a matter of neuron function, or could have a psychological or motivational element, or both. Regardless, Clark said the study has implications for addressing age-related loss of muscle strength, which can seriously reduce seniors' mobility.