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

• Published in: The European journal of neuroscience 2017-12, Vol.46 (11), p.2648-2661
• Main Authors: Kidgell, Dawson J., Bonanno, Daniel R., Frazer, Ashlyn K., Howatson, Glyn, Pearce, Alan J.
• Format: Article
• Language: English
• Subjects: Adaptation; Central nervous system; Cortex (motor); Excitability; Humans; inhibition; intracortical inhibition; Magnetic fields; Meta-analysis; Motor Cortex - physiology; Muscles; Neural Inhibition - physiology; Pyramidal tracts; Pyramidal Tracts - physiology; resistance exercise; Resistance Training; Reviews; Skeletal muscle; Sports training; Strength training; Systematic review; Transcranial magnetic stimulation
• ISSN: 0953-816X; 1460-9568
• DOI: 10.1111/ejn.13710

Strength training results in changes in skeletal muscle; however, changes in the central nervous system also occur. Over the last 15 years, non‐invasive brain stimulation techniques, such as transcranial magnetic stimulation, have been used to study the neural adaptations to strength training. This review explored the hypothesis that the neural adaptations to strength training may be due to changes in corticospinal excitability and inhibition and, such changes, contribute to the gain in strength following strength training. A systematic review, according to PRISMA guidelines, identified studies by database searching, hand‐searching and citation tracking between January 1990 and the first week of February 2017. Methodological quality of included studies was determined using the Downs and Black quality index. Data were synthesised and interpreted from meta‐analysis. Nineteen studies investigating the corticospinal responses following strength training were included. Meta‐analysis found that strength training increased strength [standardised mean difference (SMD) 0.84, 95% CI 0.55 to 1.13], decreased short‐interval intracortical inhibition (SMD −1.00, 95% CI −1.84 to −0.17) and decreased the cortical silent period (SMD −0.66, 95% CI −1.00 to −0.32). Strength training had no effect on motor threshold (SMD −0.12, 95% CI −0.49 to 0.25), but a borderline effect for increased corticospinal excitability (SMD 0.27, 95% CI 0.00 to 0.54). In untrained healthy participants, the corticospinal response to strength training is characterised by reduced intracortical inhibition and cortical silent period duration, rather than changes in corticospinal excitability. These data demonstrate that strength training targets intracortical inhibitory networks within the primary motor cortex (M1) and corticospinal pathway, characterising an important neural adaptation to strength training. It is now well established the adaptations within the nervous system contribute to strength development during the early phases of strength training; however, the underlying neural mechanisms remain elusive. This study establishes that the corticospinal response to strength training is characterised by reduced intracortical inhibition and cortical silent period duration, rather than increased corticospinal excitability, which suggest strength training targets intracortical inhibitory neurons.