Corticospinal responses following strength training: a systematic review and meta-analysis

Background: Strength training results in adaptive changes in skeletal muscle, however, adaptive changes in the central nervous system also occur. Over the last 15 years, noninvasive brain stimulation techniques, such as transcranial magnetic stimulation, have been used to study the neural adaptations to strength training. The present review explored the working hypothesis that the early neural adaptations to strength training may in fact be due to changes in corticospinal excitability and inhibition and, such changes, contribute to the early gain in strength following short-term training. Methods: A systematic review, according to PRISMA guidelines identified studies by database searching, hand-searching and citation tracking in August 2016. Methodological quality of included studies was determined using the Downs and Black quality index. Data were synthesised and interpreted from meta-analysis. Results: Twenty studies investigating the corticospinal responses following strength training were included. Meta-analysis found that short-term strength training increased strength (standardized mean difference [SMD] 0.76, 95% CI 0.46 to 1.06) and decreased corticospinal inhibition (SMD -0.53, 95% CI -0.93 to -0.13). Short-term strength training had no effect on motor threshold (SMD -0.12, 95% CI -0.49 to 0.25), corticospinal excitability (SMD 0.23, 95% CI -0.10 to 0.56) or short-interval intracortical inhibition (SMD -0.90, 95% CI -1.86 to 0.07). Conclusion: The corticospinal response to short-term strength training is characterised by a reduction in corticospinal inhibition, rather than an increase in corticospinal excitability. These data demonstrate that strength training targets intracortical inhibitory networks within the corticospinal tract and which characterizes an important neural adaptation to strength training