Fig 1.
Net vertical Ground Reaction Force (GRF), power and velocity time curves during a representative trial of a Vertical Countermovement Jump (VCJ).
The countermovement (CM) phase of the VCJ (A—E) starts with a short period of unweighting (A—B). Lower limb muscles activate to brake as the body accelerates downwards (B—C) and GRF returns to zero at peak downwards velocity (C). The arms raise backwards, as the body decelerates (C—E) to a momentary halt at transition point (E) where velocity and power have returned to zero. The push-off phase of the jump is immediately initiated as the body segments extend and accelerate upwards to take-off (E—G), which occurs shortly after peak power and velocity have been reached respectively and the GRF curve returns to zero.
Table 1.
Vertical Countermovement Jump (VCJ) phases, outcome variables and baseline raw values for each.
Fig 2.
The bifurcated anode (red) is placed centrally and paravertebrally over T11, T12 thoracic vertebrae and the bifurcated cathode (black) is placed centrally and lateral to the umbilicus. 2.5 mA of anodal direct current was applied for 15 minutes, providing 0.0833 mA/cm2 current density and 0.075 C/cm2 of total current applied.
Fig 3.
Mean change relative to baseline in VCJ performance after sham and active anodal tsDCS.
Data are the mean ratios to pre-tsDCS values and 95% CIs for 12 subjects pooled over all four repeated VCJ sets (0–180 min), post-sham (0) and active (1) tsDCS stimulation. Significant differences between sham and active tsDCS are indicated on the X axis. Mean changes were different from baseline where the 95% CI did not cross the red dotted line (baseline value, 1.00). Significance was indicated as: *P ≤ 0.05, **P ≤ 0.005 and ***P ≤.0.001. CM; countermovement, disp; downward vertical displacement, GRF; vertical ground reaction force, PO; push-off, P to P; peak to peak, trans; transition, unweight; unweighting.
Table 2.
Outcome from general linear mixed model ANOVA.
Table 3.
Substantive effects of tsDCS on changes in VCJ performance outcomes between sham and active tsDCS.
Fig 4.
VCJ effort with the highest peak to peak power during each set of 5 maximal VCJ efforts.
Over all 12 subjects and all test sessions, the best VCJ effort, determined as the VCJ with the highest peak to peak power was most frequently achieved during the second and fourth attempts in the sham tsDCS session and the fifth attempt during the active tsDCS session.
Fig 5.
Changes relative to baseline in 12 VCJ performance outcomes performed at four successive time points following sham and active tsDCS.
Data were calculated as ratios to pre-tsDCS values, indicated by the red dotted horizontal line at 1, for four successive VCJ sets repeated from 0–180 min following sham (0) and active (1) tsDCS stimulation. Changes in all 12 VCJ performance outcomes were stable over time post-tsDCS (P > 0.05).