At the onset of dorsiflexion disynaptic reciprocal inhibition (DRI) of soleus motoneurones is increased in order to prevent activation of the antagonistic plantarflexors. This is caused by descending facilitation of transmission in the DRI pathway. Since the risk of eliciting stretch reflexes in the ankle plantarflexors at the onset of dorsiflexion is larger the quicker the movement, we hypothesized that DRI may be up-regulated when subjects are trained to perform dorsiflexion movements as quickly as possible.
  For this purpose, 15 healthy human subjects (7 male, 8 female) with an average age of 26 ± 7 years strength trained the ankle dorsiflexor muscles 3 times a week for 4 weeks. Each training session consisted of 4 sets of 16 isometric dorsiflexions with the aim of increasing force as rapidly as possible, separated by 4min rest periods.
Test sessions were conducted before, immediately after and 2 weeks after the training period. The rate of dorsiflexion force development measured within 30, 50, 100 and 200ms after onset of voluntary explosive isometric dorsiflexion increased by 20-30% (p<0.05).
  DRI was measured as the depression of the soleus H-reflex following conditioning stimulation of the peroneal nerve (1.1 x MT) at an interval of 2-3 ms. Care was taken that the unconditioned soleus H-reflex was maintained constant at ~20% of Mmax in all situations.
The amount of DRI measured at rest did not change with the training. At the onset of dorsiflexion the amount of DRI increased by 6% before the training and by 22% after the training, which was a statistically significant difference (p<0.05). 
  This suggests that DRI at the onset of movement may be up-regulated in healthy subjects following explosive strength training in order to ensure efficient suppression of the antagonist muscles as the dorsiflexion movement becomes faster. This type of training may be of relevance for rehabilitation of individuals with spasticity following damage to central motor tracts.