Nix and Hopf demonstrated that low frequency ES of the crushed motor nerve to the soleus in rabbits accelerated improvement in muscle force production by 2 weeks compared to controls. Pocket and Gavin using the rat model showed that the toe-spray reflex in crushed sciatic nerves recovered significantly faster with low frequency and low intensity ES. Al-Majed et al showed that one hour of low frequency 20Hz ES of transected and repaired rat femoral nerves accelerated the slow-staggered regeneration growing across the repair site as well as enhanced preferential motor reinnervation. Even when the ES was delayed by up to 2 weeks post-rat femoral nerve repair, the enhancing effects were still persevered. In a companion study of the same year, those investigators showed that ES upregulated brain-derived neurotrophic factor and its receptor trkB within the first 2 days after surgery. Brushart et al showed that brief low frequency ES improves the specificity of reinnervation. Geremia et al performed a pivotal study showing an increase in axonal regeneration in sensory neurons if the period of post-surgical ES was no more than 1 hr. The effect was blunted if the stimulation period was any longer.