Effects Of Transcranial Direct Current Stimulation On Biomechanical Characteristics During Countermovement Jump

Background: Transcranial Direct Current Stimulation(tDCS)is one of the Non-invasive Brain Stimulation techniques,which enables to modulate cerebral cortical excitability by delivering weak and direct electric current on brain areas of interest.Researches show tDCS can improve sports performance such as strength,endurance and motor learning,but little is known about the effects on multi-joint movements,especially the biomechanical characteristics of Countermovement Jump(CMJ).The current study aims to explore the effects of tDCS on CMJ performance according to changes of instantaneous characteristics and temporal characteristics during CMJ before and after tDCS.Methods: Subjects: Fifteen male university students(mean ± SD;age: 19.47±1.60 years;height: 182.67±5.63cm;body mass: 69.20±8.22kg).Study design: Random and crossover experimental conditions: Anodal tDCS(A-tDCS)and Sham tDCS(S-tDCS),48-72 hours apart.tDCS procedure: For A-tDCS,anodal electrodes were placed on primary motor area(M1)bilaterally,while the cathodal electrodes were placed on bilateral shoulders.The current intensity is 2 mA,which lasts 20 minutes.As for sham condition,placement of electrodes was identical to that of anodal condition,notwithstanding the stimulator was switched off after 30 seconds.Data record and analysis: Kinematic and kinetic data were record by 3D motion capture system(Vicon,UK)and force plates(Kistler,Switzerland)synchronously before and after(immediately and 30 minutes)stimulation.All the data were analyzed using Visual 3D and Origin software.Statistical analysis: Two-way repeated measure ANOVA(condition×time)and LSD post-hoc analysis were performed for all the variables.Results:(1)Instantaneous Characteristics: The CMJ height of post-stimulation(immediately and 30 minutes)is significantly higher than that of pre-stimulation(0.5825±0.0872 vs.0.5641±0.0843,0.5770±0.0851 vs.0.5641±0.0843,p < 0.05)for A-tDCS,but significantly lower than that of prestimulation(0.5576±0.0703 vs.0.5674±0.0694,0.5516±0.0679 vs.0.5674±0.0694,p < 0.05)for S-tDCS.Moreover,the peak velocity(concentric phase)of center of mass(COM)in A-tDCS is faster significantly than that of S-tDCS immediately and at 30 minutes(3.15±0.31 vs.3.00±0.20,3.18±0.36 vs.2.97±0.21,p < 0.05).Compared to StDCS,the peak propulsion power(concentric phase)in A-tDCS is larger immediately and at 30 minutes(65.10±7.02 vs.60.07±5.07,64.86±7.87 vs.59.28±5.69,p < 0.05).And it is larger than that of pre-stimulation immediately(65.10±7.02 vs.63.66±6.52,p < 0.05).The leg stiffness(34.95±9.44 vs.32.83±10.91,p < 0.05)of post-stimulation(immediately)increase significantly compared to pre-stimulation(2)Temporal Characteristics: For Force-time curve(F-t),the vertical impulse of post-stimulation(immediately and 30 minutes)is larger than that of pre-stimulation(6.60±0.20 vs.6.40±0.12,6.57±0.19 vs.6.40 ± 0.12,p < 0.05),and the rate of force development(RFD)increases significantly than pre-stimulation in A-tDCS(54.13±13.84 vs.49.63±12.78,p < 0.05).For Force-displacement curve,the returned energy(68.29±9.83 vs.65.30±8.76,p < 0.05)and active work done by muscle(66.40±14.34 vs.61.00±8.18,p < 0.05)of poststimulation(immediately)increase significantly compared to pre-stimulation.Conclusion: Anodal tDCS enables to enhance sports performance during CMJ,and generates positive effects on both instantaneous characteristics and temporal characteristics.As a result,it can improve explosive capacity and neuromuscular performance.In addition,this study provides promising evidence on practical application among many sports involved vertical jump.