30 Sep Could Muscle Strength in Older Adults Be Improved by Stimulating Nerves?
MedicalResearch.com Interview with:
Dr. Clark
Brian Clark, Ph.D.
Executive Director, Ohio Musculoskeletal and Neurological Institute
Osteopathic Heritage Foundation Harold E. Clybourne, D.O.
Endowed Research Chair
Professor of Physiology
OHIO University
MedicalResearch.com: What is the background for this study?
Response: Muscle weakness strongly contributes to mobility limitations and physical disability. Over 40% of the 46 million older adults in the U.S. have one or more physical limitations when performing daily tasks essential for maintaining independence. Preserving physical function is a major public health priority as it will drastically reduce health care costs and improve quality of life. Over the past several decades, the scientific and medical communities have recognized that muscle weakness is a major factor in determining the incidence of physical limitations and general poor health in older adults.
It has long been presumed by many that age-related weakness is principally caused by loss of muscle mass (i.e., sarcopenia). However, over the past 10-20 years the presumption has been questioned. For instance, a 2009 study reported that the decline in leg extensor muscle strength in older adults —observed longitudinally over 5 years—occurs more rapidly than the concomitant loss of quadriceps mass, and that in a subset of older adults that actually gained muscle mass there was still a substantial loss of strength. Findings of this nature clearly illustrate that that the loss of strength is only modestly associated with loss of mass in older adults. The mechanisms of muscle strength, however, are multifactorial and determined by a combination of both neurological and muscular factors (of which muscle mass is one of the factors).
Degradation in nervous system function is one potential contributor to weakness. This work sought to determine whether, and to what extent, older adults with clinically meaningful leg extensor muscle weakness exhibit differences in voluntary (neural) activation capacity when compared to stronger older adults. To do so, we used a combination of voluntary and electrically stimulated contractions of the quadriceps femoris to quantify the nervous system’s ability to fully activate the muscles.
Here, we electrically stimulated the quadriceps femoris muscle group supramaximally and measured the “added force” during a maximal voluntary contraction to quantify the degree of voluntary (neural) inactivation (i.e., some motor nerves are not recruited or are not firing fast enough to produce fused contractions).
MedicalResearch.com: What should readers take away from your report?
Response: Weakness in older adults in conceptualized by many as a disorder of skeletal muscle. However, this work presents evidence indicating that weak older adults have significant deficits in their nervous systems ability to fully activate their leg extensor muscles. While these data do not point to the underlying mechanism per se, they do suggest that medical treatments targeting the nervous system could be used to enhance muscle strength to prevent future heal risks in weak older adults.
MedicalResearch.com: What recommendations do you have for future research as a result of this work?
Response: There are several critical next steps. The first critical step is arguably to ascertain specific neural mechanisms responsible for the neural deficit, and the follow-up is to examine the whether neurotherapeutic interventions, such as select pharmacological agents and/or neurorehabilitation strategies, can enhance strength and mobility in older adults.
MedicalResearch.com: Is there anything else you would like to add?
Response: One thing that should be recognized is that physical activity and exercise targets both the nervous and muscular systems. Accordingly, exercise strategies are undoubtedly ideally suited to counteract age related weakness. Unfortunately, in the United States, only ~13% of older adults meet the physical activity recommendations for both aerobic and muscle strengthening exercises.
Disclosures, are listed in the manuscript. I have received grants from many agencies and industry sponsors (the NIH funded the current work), as well as consulting fees. I am also a co-founder of a start-up. With this said, these conflicts do not directly relate to this manuscript.
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Last Updated on September 30, 2019 by Marie Benz MD FAAD