Modulation of isometric quadriceps strength in soccer players with transcranial direct current stimulation: a crossover study
The aim of this study was to evaluate the effect of transcranial direct current stimulation (tDCS) on the maximum isometric muscle contraction (MVIC) of the knee extensors in soccer players at the pre-professional level. Twenty female soccer players aged 15 to 17 years (mean = 16.1; SD = 0.9) with 5.2 ± 2.6 years of training were randomly divided into two groups to receive either active or sham tDCS in a single session (2 mA; 0.057mA/cm2). The MVIC of the knee extensors was evaluated in both lower limbs by manual dynamometry in five sets of contractions divided into four blocks: (0) pre-stimulation, (1) during tDCS, (2) 30 minutes post-tDCS, and (3) 60 minutes post-tDCS. After an interval of seven days, the groups were evaluated again, and the type of initial stimulation was inverted between participants. The MVIC of the knee extensors increased significantly during active tDCS (MD = 0.4; IC = 0.1 to 0.8 N/Kg), 30 minutes post-active tDCS (MD = 0.9; IC 0.4 to 1.4 N/Kg), and 60 minutes post-active tDCS (MD = 1.0; IC 0.3 to 1.6 N/Kg) but not for sham tDCS. Our conclusion was that tDCS temporarily increases isometric quadriceps strength in adolescent female soccer players, which may be useful for both strength training and rehabilitation.