Introduction: Strength training (ST) studies have demonstrated strengthening one limb produces increased strength of the contralateral homologous muscle. This increase in strength is thought to be due to changes in motor cortex (M1) excitability, suggesting unilateral ST may affect synaptic connectivity within the M1, leading to an increased ability to produce force, however, this hypothesis has never been tested. The aim of this project was to use transcranial magnetic stimulation (TMS) to investigate the effect of unilateral ST on M1 excitability. Method: 16 subjects (29.5±7.0 years) participated in the study and were randomly allocated into either ST or control group (C). ST subjects (n = 7) completed 12 supervised ST sessions over 4 weeks that involved 4 sets of 6 repetitions of a dumbbell biceps curl for the right arm only. Strength testing (1 repetition maximum, 1RM) of the right and left biceps and TMS at 10% above motor threshold (MT) during 10% background muscle activity was obtained prior to and following training. Corticospinal parameters of MT, motor evoked potential amplitude (MEP), and Electromyographic silent period duration (EMG SP) were obtained prior to and following training. Results: There was 26.4% increase in strength of the trained right limb and this resulted in a 16.3% transfer of strength to the left untrained arm (p = .001). No differences in strength between the right and left arms of the control group were noted. There was a 10.6% increase in MEP amplitude of the right M1 following training, although not significant (p = 0.06), there was a large effect size (ES = 1.25). There was no change within the control group. No significant differences in EMG SP durations for the right hemisphere were noted in the trained or control group (p > 0.05). Discussion: The findings suggest that unilateral ST does increase strength of the untrained homologous muscle. Although not statistically significant, the large ES and percentage change in MEP amplitude suggests, that for a given level of background contraction, there was an increase in the size of the descending corticospinal volley, intimating that the change in strength of the untrained arm may be due to improved motor unit activation. Conclusion: Strength training one limb; increased strength of the opposite limb by 16.3%; this improvement maybe due to changes in M1 excitability. Since descending corticospinal volleys terminate onto alpha motoneurons, the change in strength may have been due to improved motor unit activation.
|Number of pages||1|
|Journal||Journal of Science and Medicine in Sport|
|Publication status||Published - Jan 2010|
|Event||Australian Conference of Science and Medicine in Sport 2009 - Brisbane, Brisbane, Australia|
Duration: 14 Oct 2009 → 17 Oct 2009