Effects of 14-week strength training period on passive movement evoked fields, stretch reflex functioning, muscle strength and balance

Abstract

Strength training is known to affect the nervous system in various ways most often leading to improvements in performance. Changes occurring due to training or aging can provide us more information about the nervous system controlling our movements. Reflexes are an essential part of our body’s “toolbox” in movement control and force production. One of particular interest is the functioning of the stretch reflex that is highlighted in some of the motor control theories aswell. Stretch reflex is widely known muscle response to stretch but the question whether a transcortical loop exists and affects the muscle response is still under debate.

The purpose of this study was to find out whether the stretch reflex response measured with magnetoencephalography from the brain and with electromyography from the muscles are affected by strength training. Timing of the cortical and muscle responses were investigated to find out whether transcortical loop could exist. Functional changes due to training were measured with isometric MVCs and dynamic balance test.

A total of 21 subjects were measured from which a total of 12 subjects were included for further analysis and divided into groups based on age: young (n=7) and elderly (n=5).

Results support the timewise possibility of transcortical loop to exist but cannot unambiguously prove it. Responses measured from the muscle during movement initiation suggest changes in the motor control in the working muscles due to strength training. Different age groups showed similar trends in the adaptations highlighting the possibilities of strength training even with greater age.