Abstract
Transcranial direct current stimulation (tDCS) has been applied in training and competition, but its effects on physical performance remain largely unknown. This study aimed to observe the effect of tDCS on muscular strength and knee activation. Nineteen healthy young men were subjected to 20 min of real stimulation (2 mA) and sham stimulation (0 mA) over the primary motor cortex (M1) bilaterally on different days. The maximal voluntary contraction (MVC) of the knee extensors and flexors, and surface electromyography (sEMG) of the rectus femoris (RF) and biceps femoris (BF) were recorded before, immediately after, and 30 min after stimulation. MVC, rate of force development (RFD), and sEMG activity were analyzed before and after each condition. MVC of the non-dominant leg extensor and flexor was significantly higher immediately after real stimulation and 30 min after stimulation than before, and MVC of the non-dominant leg flexor was significantly higher 30 min after real stimulation than that after sham stimulation (P < 0.05). The RFD of the non-dominant leg extensor and flexor immediately after real stimulation was significantly higher than before stimulation, and the RFD of the non-dominant leg extensor immediately after real stimulation and 30 min after stimulation was significantly higher than that of sham stimulation (P < 0.05). EMG analysis showed the root mean square amplitude and mean power frequency (MPF) of the non-dominant BF and RF were significantly higher immediately after real stimulation and 30 min after stimulation than before stimulation, and the MPF of the non-dominant BF EMG was significantly higher 30 min after real stimulation than that after sham stimulation (P < 0.05). Bilateral tDCS of the M1 can significantly improve the muscle strength and explosive force of the non-dominant knee extensor and flexor, which might result from increased recruitment of motor units. This effect can last until 30 min after stimulation, but there is no significant effect on the dominant knee.
Highlights
An overarching goal pursued by sports professionals and scientists is to seek safe and effective ways to improve exercise performance for athletes
We found that Transcranial direct current stimulation (tDCS) increased the rate of force development (RFD), and its after-effects could last for 30 min, which might be explained by an increased firing rate of previously recruited motor units
The results of this study showed that the activation level of non-dominant biceps femoris (BF) and rectus femoris (RF) was significantly higher immediately after and 30 min after bilateral tDCS over Primary motor cortex (M1) than before
Summary
An overarching goal pursued by sports professionals and scientists is to seek safe and effective ways to improve exercise performance for athletes. Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that alters cortical excitability via a low-intensity direct current (1–2 mA) applied to the scalp, over various regions of the cerebral cortex (Nitsche and Paulus, 2000). Some studies have shown that this technique could effectively improve training and increase performance (Huang et al, 2019; Alix-Fages et al, 2020; Vieira et al, 2020; Grosprêtre et al, 2021). Some studies have shown that tDCS does not affect lower limb strength (Montenegro et al, 2015; Maeda et al, 2017; Romero-Arenas et al, 2019); this may be related to differences in the chosen electrode configuration or stimulation parameters. In a recent meta-analysis, it was shown that unilateral tDCS was more effective than bilateral tDCS in patients with stroke, while bilateral tDCS was more effective than unilateral tDCS to improve motor learning and motor performance in healthy subjects (Halakoo et al, 2020)
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