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Spinal direct current stimulation enhances vertical jump power in healthy adults

Berry, Helen and Conway, Bernard (2015) Spinal direct current stimulation enhances vertical jump power in healthy adults. In: Neuroscience 2015, 2015-10-17 - 2015-10-21, McCormick Place.

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Abstract

Transcutaneous spinal direct current stimulation (tsDCS) is a safe, non-invasive neuromodulation tool that can affect sensory, motor and pain spinal cord circuits and pathways. The polarity dependent neuroplastic effects are reported to persist after stimulation in a dose dependent manner. It is not known whether tsDCS neuromodulation can translate to any measurable change in functional motor power production post stimulation. In this study we investigate the effect of 15 min of anodal lumbosacral cord level tsDCS on vertical countermovement jump (VCJ) power production up to 3 hours after stimulation in healthy volunteers: the VCJ is a test of maximal lower limb power and involves a powerful eccentric countermovement. In tandem with this, we mapped concomitant changes in lower limb posterior root-muscle (PRM) reflexes over the same time course.We employed a double-blind, randomized, crossover sham-controlled design approved by our local ethics committee. 13 healthy individuals completed 5 maximal effort VCJs on a force platform before and 0, 20, 60 and 180 min after sham and active tsDCS (25 VCJs per session, at least 7 days apart). 6 of the subjects completed 2 further sham/active tsDCS session where lower limb PRM reflexes were induced before and up to 180 min after tsDCS using single pulse biphasic stimulation of the spine via the same electrode montage as in place for tsDCS.tsDCS induced a mean (95% CI) 15.4 (7.4—23.5)% difference in max (sham – 6.4%, active + 9%, p <0.001) and a 11.4 (5—17.8)% difference in ave (sham - 5%, active + 6.4%, p < 0.001) countermovement power, leading to an overall difference of 4.2 (2.1—6.4)% in max (sham -3.6%, active +0.6%, p < 0.001) and 3.7 (1.9—5.6)% difference in ave peak to peak VCJ power (sham -2.7%, active +1%, p < 0.001). These changes did not significantly differ between time point post tsDCS. We found that over both tsDCS conditions, changes in hamstring PRM reflexes were moderately correlated with changes in ave VCJ force (r = 0.60, p <0.001). Anodal tsDCS preserved and enhanced countermovement power production over three hours, whereas there was a significant fatigue effect after sham tsDCS. These changes appear to be due to changes in force potentiation mechanisms, demonstrated by excitability changes in reflex circuitry. We have shown for the first time that anodal tsDCS quickly, easily and painlessly counters the fatigue normally associated with repeated maximal power performance. tsDCS-induced fatigue resistance and an enhancement of motor power in the absence of physical training have important implications for rehabilitation after central nervous system injury.