Document Type : Original Article
Authors
1 Exercise Physiology Department Faculty of Physical Education and Sport Sciences Kharazmi University of Tehran
2 Physiology group, Physical education Faculty, Kharazmi university, Tehran, Iran
3 Institute of Cognitive and Brain Sciences Shahid Beheshti University
4 Faculty of Medical and Health Sciences, Monash University, Australia
Abstract
Objective: A change in corticospinal excitability will cause a change in the neural output and finally a change in the maximum force. Various training and non-training factors play a role in this neuromuscular response, and the intensity of the intervention seems to be one of the effective factors in this regard. The aim of current research was to investigate the responses of the central nervous system using the TMS after several preparatory contractions with different intensities. Methodology: 8 subjects (average age 24.8±2.70 years and weight 72.4±8.52 kg) performed the research protocol in three separate sessions with 20, 50 and 80% intensities of RMS MVC preparatory contractions in hand grip movement. the amount of corticospinal excitability, the electrical activity of the anterior superior ulnar muscle and the maximum force in the hand grip movement were measured several times after that and they compared with the repeated ANOVA statistical method. Results: The amplitude of motor evoked potential (MEP) increased after preparatory contraction with intensity of 20%, but decreased with increasing intensity of preparatory contraction to 50% and 80%, in such a way that there was a difference between intensity of 20% and 80% (P<0.001) and between 20% and 50% (P<0.041), while there was no significant difference between 50% and 80%. on the other hand, the amount of voluntary force measured by the maximum voluntary contraction and its electrical activity did not show any significant change (p>0.05) immediately and after 5 minutes’ contraction of the preparation. Conclusion: It can be concluded that corticospinal excitability increases after low-intensity preparatory activity, but decreases with increasing activity intensity to medium and high levels. Thus, there is a complex interplay between changes in supraspinal excitability following preparatory contractions and their effect on the individual's ability to improve or maintain force output, and so that needs further investigation.
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