Ward, R E, Boudreau, R M, Caserotti, P, Harris, T B, Zivkovic, S, Goodpaster, B H, Satterfield, S, Kritchevsky, S, Schwartz, A V, Vinik, A I, Cauley, J A, Newman, A B & Strotmeyer, E S 2015, ' Sensory and Motor Peripheral Nerve Function and Longitudinal Changes in Quadriceps Strength ', Journals of Gerontology. Series A: Biological Sciences & Medical Sciences, vol. 70, no. 4, pp. 464-470 . https://doi.org/10.1093/gerona/glu183Test
Poor strength in late-life contributes to poor physical function (1), mobility disability (2), hospitalization (3), and mortality (4). Given its major role in late-life outcomes, investigating risk factors for strength decline in older adults is essential. Although age-related muscle atrophy plays a major role in declining strength, maintaining or gaining muscle mass does not guarantee prevention of strength loss with age (5), suggesting that other factors must contribute. One proposed contributing factor to strength decline is poor peripheral nerve function (6). Estimated motor unit loss using surface electromyography (sEMG) is cross-sectionally associated with lower strength in older adults (age ≥60 years) (7). Moreover, strength gains occurring during early phases of training prior to increases in muscle size are associated with increased amplitude measured using sEMG (8). This technique assesses the sum of motor unit potentials, providing a global measure of neuromuscular activity. Nerve Conduction Studies (NCS) allow direct stimulation of the nerve and measurement of the signal magnitude and the speed of response across the nerve. This method is considered the clinical gold standard to measure the degree of nerve damage and to distinguish between demyelination and axonal degeneration (9). Small clinical studies have found cross-sectional associations between motor axon loss or axonal degeneration, estimated using NCS, and muscle weakness in patients with Charcot-Marie-Tooth disease (10) and chronic inflammatory demyelinating polyradiculoneuropathy (11). In a large cohort of older adults, the Health, Aging, and Body Composition Study found that both motor peripheral nerve function measured using NCS and sensory peripheral nerve function were related to lower quadriceps and ankle dorsiflexion strength cross-sectionally, independent of lean mass (6). Clinically, early identification of changes in nerve function that may be able to predict strength decline may lead to timely intervention and help prevent resulting disability. Therefore, we utilized standard clinical assessments to evaluate the relationship between nerve function and strength loss. Our primary aim was to investigate the longitudinal relationship between clinical measures of sensorimotor nerve function and subsequent change in quadriceps strength over 6 years. We hypothesized that poor sensory and motor nerve function would be associated with both lower quadriceps strength and faster declining strength. As an exploratory aim, we also examined the relationship between concurrent change in sensorimotor nerve function and quadriceps strength.
