Michael Lee1, Simon C Gandevia, Timothy J Carroll. 1. Health and Exercise Science, School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney, Australia.
Abstract
OBJECTIVE: We investigated whether an increase in neural drive from the motor cortex contributes to the cross-limb transfer of strength that can occur after unilateral strength training. METHODS: Twitch interpolation was performed with transcranial magnetic stimulation to assess changes in strength and cortical voluntary activation in the untrained left wrist, before and after 4 weeks of unilateral strength-training involving maximal voluntary isometric wrist extension contractions (MVCs) for the right wrist (n=10, control group=10). RESULTS: Wrist extension MVC force increased in both the trained (31.5+/-18%, mean+/-SD, p<0.001) and untrained wrist (8.2+/-9.7%, p=0.02), whereas wrist abduction MVC did not change significantly. The amplitude of the superimposed twitches evoked during extension MVCs decreased by 35% (+/-20%, p<0.01), which contributed to a significant increase in voluntary activation (2.9+/-3.5%, p<0.01). Electromyographic responses to cortical and peripheral stimulation were unchanged by training. There were no significant changes for the control group which did not train. CONCLUSION: Unilateral strength training increased the capacity of the motor cortex to drive the homologous untrained muscles. SIGNIFICANCE: The data show for the first time that an increase in cortical drive contributes to the contralateral strength training effect.
OBJECTIVE: We investigated whether an increase in neural drive from the motor cortex contributes to the cross-limb transfer of strength that can occur after unilateral strength training. METHODS: Twitch interpolation was performed with transcranial magnetic stimulation to assess changes in strength and cortical voluntary activation in the untrained left wrist, before and after 4 weeks of unilateral strength-training involving maximal voluntary isometric wrist extension contractions (MVCs) for the right wrist (n=10, control group=10). RESULTS: Wrist extension MVC force increased in both the trained (31.5+/-18%, mean+/-SD, p<0.001) and untrained wrist (8.2+/-9.7%, p=0.02), whereas wrist abduction MVC did not change significantly. The amplitude of the superimposed twitches evoked during extension MVCs decreased by 35% (+/-20%, p<0.01), which contributed to a significant increase in voluntary activation (2.9+/-3.5%, p<0.01). Electromyographic responses to cortical and peripheral stimulation were unchanged by training. There were no significant changes for the control group which did not train. CONCLUSION: Unilateral strength training increased the capacity of the motor cortex to drive the homologous untrained muscles. SIGNIFICANCE: The data show for the first time that an increase in cortical drive contributes to the contralateral strength training effect.
Authors: Kristian Thorborg; Thomas Bandholm; Mette Zebis; Lars Louis Andersen; Jesper Jensen; Per Hölmich Journal: Knee Surg Sports Traumatol Arthrosc Date: 2015-03-22 Impact factor: 4.342
Authors: Garrett M Hester; Mitchel A Magrini; Ryan J Colquhoun; Alejandra Barrera-Curiel; Carlos A Estrada; Alex A Olmos; Alyssa R Bailly; Phuong L Ha; Jason M DeFreitas Journal: Eur J Appl Physiol Date: 2019-03-14 Impact factor: 3.078