Leatha A Clark1,2, Todd M Manini3, Nathan P Wages1,2, Janet E Simon1,4, David W Russ5, Brian C Clark1,2. 1. Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens. 2. Department of Biomedical Sciences, Ohio University, Athens. 3. Department of Aging and Geriatric Research, University of Florida, Gainesville. 4. School of Applied Health Sciences and Wellness, Ohio University, Athens. 5. School of Physical Therapy & Rehabilitation Sciences, University of South Florida, Tampa.
Abstract
BACKGROUND: Weakness is a risk factor for physical limitations and death in older adults (OAs). We sought to determine whether OAs with clinically meaningful leg extensor weakness exhibit differences in voluntary inactivation (VIA) and measures of corticospinal excitability when compared to young adults (YAs) and OAs without clinically meaningful weakness. We also sought to estimate the relative contribution of indices of neural excitability and thigh lean mass in explaining the between-subject variability in OAs leg extensor strength. METHODS: In 66 OAs (75.1 ± 7.0 years) and 20 YAs (22.0 ± 1.9 years), we quantified leg extensor strength, thigh lean mass, VIA, and motor evoked potential (MEP) amplitude and silent period (SP) duration. OAs were classified into weakness groups based on previously established strength/body weight (BW) cut points (Weak, Modestly Weak, or Not Weak). RESULTS: The OAs had 63% less strength/BW when compared to YAs. Weak OAs exhibited higher levels of leg extensor VIA than Not Weak OAs (14.2 ± 7.5% vs 6.1 ± 7.5%). Weak OAs exhibited 24% longer SPs compared to Not Weak OAs, although this difference was insignificant (p = .06). The Weak OAs MEPs were half the amplitude of the Not Weak OAs. Regression analysis indicated that MEP amplitude, SP duration, and thigh lean mass explained ~62% of the variance in strength, with the neural excitability variables explaining ~33% of the variance and thigh lean mass explaining ~29%. CONCLUSION: These findings suggest that neurotherapeutic interventions targeting excitability could be a viable approach to increase muscle strength in order to reduce the risk of physical impairments in late life.
BACKGROUND: Weakness is a risk factor for physical limitations and death in older adults (OAs). We sought to determine whether OAs with clinically meaningful leg extensor weakness exhibit differences in voluntary inactivation (VIA) and measures of corticospinal excitability when compared to young adults (YAs) and OAs without clinically meaningful weakness. We also sought to estimate the relative contribution of indices of neural excitability and thigh lean mass in explaining the between-subject variability in OAs leg extensor strength. METHODS: In 66 OAs (75.1 ± 7.0 years) and 20 YAs (22.0 ± 1.9 years), we quantified leg extensor strength, thigh lean mass, VIA, and motor evoked potential (MEP) amplitude and silent period (SP) duration. OAs were classified into weakness groups based on previously established strength/body weight (BW) cut points (Weak, Modestly Weak, or Not Weak). RESULTS: The OAs had 63% less strength/BW when compared to YAs. Weak OAs exhibited higher levels of leg extensor VIA than Not Weak OAs (14.2 ± 7.5% vs 6.1 ± 7.5%). Weak OAs exhibited 24% longer SPs compared to Not Weak OAs, although this difference was insignificant (p = .06). The Weak OAs MEPs were half the amplitude of the Not Weak OAs. Regression analysis indicated that MEP amplitude, SP duration, and thigh lean mass explained ~62% of the variance in strength, with the neural excitability variables explaining ~33% of the variance and thigh lean mass explaining ~29%. CONCLUSION: These findings suggest that neurotherapeutic interventions targeting excitability could be a viable approach to increase muscle strength in order to reduce the risk of physical impairments in late life.
Authors: Anne B Newman; Varant Kupelian; Marjolein Visser; Eleanor M Simonsick; Bret H Goodpaster; Stephen B Kritchevsky; Frances A Tylavsky; Susan M Rubin; Tamara B Harris Journal: J Gerontol A Biol Sci Med Sci Date: 2006-01 Impact factor: 6.053
Authors: Leatha A Clark; David W Russ; Dallin Tavoian; W David Arnold; Timothy D Law; Christopher R France; Brian C Clark Journal: Exp Gerontol Date: 2021-06-04 Impact factor: 4.253
Authors: Brooke A Vaughan; Janet E Simon; Dustin R Grooms; Leatha A Clark; Nathan P Wages; Brian C Clark Journal: Front Aging Neurosci Date: 2022-01-31 Impact factor: 5.750