Ummatul Siddique1, Simin Rahman1, Ashlyn K Frazer2, Alan J Pearce3, Glyn Howatson4,5, Dawson J Kidgell6. 1. Department of Neurology, Institute of Neurosciences, Kolkata, India. 2. Department of Physiotherapy, School of Primary and Allied Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University, PO Box 527, Frankston, Melbourne, VIC, 3199, Australia. 3. Faculty of Science, Health and Engineering, School of Allied Health, La Trobe University, Melbourne, Australia. 4. Faculty of Health and Life Sciences, Northumbria University, Newcastle-upon-Tyne, UK. 5. Water Research Group, School of Environmental Sciences and Development, Northwest University, Potchefstroom, South Africa. 6. Department of Physiotherapy, School of Primary and Allied Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University, PO Box 527, Frankston, Melbourne, VIC, 3199, Australia. dawson.kidgell@monash.edu.
Abstract
BACKGROUND: Resistance-training causes changes in the central nervous system (CNS); however, the sites of these adaptations remain unclear. OBJECTIVE: To determine sites of neural adaptation to resistance-training by conducting a systematic review and meta-analysis on the cortical and subcortical responses to resistance-training. METHODS: Evidence from randomized controlled trials (RCTs) that focused on neural adaptations to resistance-training was pooled to assess effect estimates for changes in strength, cortical, and subcortical adaptations. RESULTS: The magnitude of strength gain in 30 RCTs (n = 623) reported a standardised mean difference (SMD) of 0.67 (95% CI 0.41, 0.94; P < 0.001) that measured at least one cortical/subcortical neural adaptation which included: motor-evoked potentials (MEP; 19 studies); silent period (SP; 7 studies); short-interval intracortical inhibition (SICI; 7 studies); cervicomedullary evoked potentials (CMEP; 1 study); transcranial magnetic stimulation voluntary activation (VATMS; 2 studies); H-reflex (10 studies); and V-wave amplitudes (5 studies). The MEP amplitude during voluntary contraction was greater following resistance-training (SMD 0.55; 95% CI 0.27, 0.84; P < 0.001, n = 271), but remained unchanged during rest (SMD 0.49; 95% CI -0.68, 1.66; P = 0.41, n = 114). Both SP (SMD 0.65; 95% CI 0.29, 1.01; P < 0.001, n = 184) and active SICI (SMD 0.68; 95% CI 0.14, 1.23; P = 0.01, n = 102) decreased, but resting SICI remained unchanged (SMD 0.26; 95% CI - 0.29, 0.81; P = 0.35, n = 52). Resistance-training improved neural drive as measured by V-wave amplitude (SMD 0.62; 95% CI 0.14, 1.10; P = 0.01, n = 101), but H-reflex at rest (SMD 0.16; 95% CI - 0.36, 0.68; P = 0.56; n = 57), during contraction (SMD 0.15; 95% CI - 0.18, 0.48; P = 0.38, n = 142) and VATMS (MD 1.41; 95% CI - 4.37, 7.20; P = 0.63, n = 44) remained unchanged. CONCLUSION: There are subtle neural adaptations following resistance-training involving both cortical and subcortical adaptations that act to increase motoneurone activation and likely contribute to the training-related increase in muscle strength.
BACKGROUND: Resistance-training causes changes in the central nervous system (CNS); however, the sites of these adaptations remain unclear. OBJECTIVE: To determine sites of neural adaptation to resistance-training by conducting a systematic review and meta-analysis on the cortical and subcortical responses to resistance-training. METHODS: Evidence from randomized controlled trials (RCTs) that focused on neural adaptations to resistance-training was pooled to assess effect estimates for changes in strength, cortical, and subcortical adaptations. RESULTS: The magnitude of strength gain in 30 RCTs (n = 623) reported a standardised mean difference (SMD) of 0.67 (95% CI 0.41, 0.94; P < 0.001) that measured at least one cortical/subcortical neural adaptation which included: motor-evoked potentials (MEP; 19 studies); silent period (SP; 7 studies); short-interval intracortical inhibition (SICI; 7 studies); cervicomedullary evoked potentials (CMEP; 1 study); transcranial magnetic stimulation voluntary activation (VATMS; 2 studies); H-reflex (10 studies); and V-wave amplitudes (5 studies). The MEP amplitude during voluntary contraction was greater following resistance-training (SMD 0.55; 95% CI 0.27, 0.84; P < 0.001, n = 271), but remained unchanged during rest (SMD 0.49; 95% CI -0.68, 1.66; P = 0.41, n = 114). Both SP (SMD 0.65; 95% CI 0.29, 1.01; P < 0.001, n = 184) and active SICI (SMD 0.68; 95% CI 0.14, 1.23; P = 0.01, n = 102) decreased, but resting SICI remained unchanged (SMD 0.26; 95% CI - 0.29, 0.81; P = 0.35, n = 52). Resistance-training improved neural drive as measured by V-wave amplitude (SMD 0.62; 95% CI 0.14, 1.10; P = 0.01, n = 101), but H-reflex at rest (SMD 0.16; 95% CI - 0.36, 0.68; P = 0.56; n = 57), during contraction (SMD 0.15; 95% CI - 0.18, 0.48; P = 0.38, n = 142) and VATMS (MD 1.41; 95% CI - 4.37, 7.20; P = 0.63, n = 44) remained unchanged. CONCLUSION: There are subtle neural adaptations following resistance-training involving both cortical and subcortical adaptations that act to increase motoneurone activation and likely contribute to the training-related increase in muscle strength.
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