Determining the Neuromuscular Adaptations to Strength Training in Older Adults: A Systematic Review and Meta-analysis

Introduction: There are observable decreases in muscle strength as a result of ageing that occur from the age 50. The age-related loss of maximal force production is thought to occur as a result of changes within the neuromuscular system. Changes in both maximal force production and rate of force development (RFD) are due to age-related changes within supraspinal (i.e., reduced motor cortex excitability, increased cortical inhibition), spinal (reduced spinal motoneurone excitability which influences motor unit recruitment and discharge rates) and muscular changes (mainly reduced muscle mass). Strength training in older adults is a suitable intervention that may counteract the age-related loss in force production. However, the neuromuscular adaptations to strength-training in older adults is largely equivocal and therefore, a systematic review with meta-analysis will serve to clarify the present circumstances regarding the benefits of strength-training in older adults Methods: The review was conducted in accordance with the latest Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Post standardized search strategy using different electronic databases and full text screening of selected articles, 54 studies that were heterogenous in relation to sample size, settings, outcomes and intervention characteristics were selected. Meta-analyses were performed using a random-effects model. A best evidence synthesis (BES) was performed for variables that had insufficient data for meta-analysis. Results: 19 randomized controlled trials (RCTs) studies (n=306) reported a moderate increase in strength (26.13%; SMD 0.67; 95% CI 0.37, 0.97; P < 0.0001) post strength training. Additionally, rate of force development (RFD) (SMD 0.65; 95% CI 0.09, 1.22; P = 0.02; n = 48) and surface electromyography (sEMG) (SMD 0.28; 95% CI -0.41, 0.97; P = 0.42; n = 20) also improved following training in older adults. Results from BES reported strong evidence to suggest that strength-training increases maximal force production and RFD in older adults and moderate evidence for increased agonist activity. There was limited evidence from the included studies for strength-training to improve voluntary activation, spinal excitability and muscle mass. Discussion: Overall, the findings suggest that strength-training performed between two and twelve weeks increases strength, RFD and muscle activity, which likely improves motoneurone excitability by increased motor unit recruitment and improved discharge rates. The review identified important gaps in the literature as there is a need to explore the sites of adaptation within the nervous system, using synergistic electrophysiological techniques, such as transcranial magnetic stimulation to probe the elements of the neuromuscular system from the cortex to the muscle. Impact and application to the field: Strength-training in older adults is a suitable intervention that may counteract the age-related loss in force production. Conflict of Interest Statement: “My co-authors and I acknowledge that we have no conflict of interest of relevance to the submission of this abstract”