Date of Award

2011

Degree Type

Thesis

Degree Name

Master of Science (Sports Science)

School

School of Exercise, Biomedical and health Sciences

Faculty

Computer Health and Science

First Advisor

Professor Kazunori Nosaka

Second Advisor

Ms Jane Dundas

Abstract

The present study investigated the effects of transcranial direct current stimulation (tDCS) on maximal voluntary contraction strength (MVC) and the time to failure (TTF) of an isometric muscle endurance test of the elbow flexors. Prior to the main study, the test-retest reliability of MVC and TTF measures was investigated using 10 men (33.2 ± 9.4 y) for the measurements separated by 60 min (within-day) and one week (between-day). Coefficient of variation (CV), Intraclass correlation (ICC, R), a paired t-test and the Bland-Altman plots revealed that TTF at 30% MVC task was reliable, and was able to detect a possible effect of tDCS on TTF, if the magnitude of effect was greater than 11%. Based on the reliability study results, it was hypothesised that tDCS would increase TTF from the first test to the second test separated by 60 min, when a tDCS treatment was administered immediately before the second test. Fifteen men (27.7 ± 8.4 y) were tested for MVC and TTF at 30%-MVC before and immediately after tDCS or sham intervention (10 min) in three separate sessions. In two sessions direct current (2 mA) was delivered through saline-soaked sponge electrodes, with the anode placed on the scalp overlying the right motor cortical representation of the left arm and the cathode secured over the right shoulder. One session was a sham intervention (current delivery for the first 30s). The order of the intervention sessions was randomised and counterbalanced amongst the subjects and subjects who were blinded to intervention type. Changes in MVC strength and TTF from pre to post intervention were compared between the interventions by a two-way repeated measures ANOVA. No significant differences were evident for the two tDCS sessions. MVC strength (baseline: 66.0 ± 11.4 Nm) decreased by 5.9 ± 4.2 % (P<0.05) in the post-intervention measures, but no significant difference in the changes was evident between sham and tDCS interventions. TTF did not change significantly from pre (309.2 ± 91.6 s) to post intervention (327.2 ± iv 128.5 s), and no significant difference was found between interventions. In conclusion, tDCS did not affect TTF and MVC of the elbow flexors. It appears that the tDCS intervention did not affect cortical excitability due to ceiling effects that made it unable to modulate voluntary activation of motor units. Since the present study did not assess motor evoked potentials (MEP) that could show changes in cortical excitability following tDCS or sham treatment, further studies are required to examine the effects of tDCS on cortical excitability.

Share

 
COinS