Differential effects of ballistic versus sensorimotor training on rate of force development and neural activation in humans

Balancing exercises on instable bases (sensorimotor training SMT]) are often used in the rehabilitation process of an injured athlete to restore joint function. Recently it was shown that SMT was able to enhance rate of force development (RFD) in a maximal voluntary muscle contraction. The purpose of this study was to compare adaptations on strength capacity following ballistic strength training (BST) with those following an SMT during a training period of 1 microcycle (4 weeks). Maximum voluntary isometric strength (MVC), maximum RFD (RFDmax) and the corresponding neural activation of M. soleus (SOL), M. gastrocnemius (GAS), and M. tibialis anterior (TIB) were measured during plantar flexion in 33 healthy subjects. The subjects were randomly assigned to a SMT, BST, or control group. RFDmax increased significantly stronger following BST (48 +/- 16%; p < 0.01) compared to SMT (14 +/- 5%; p < 0.05), whereas MVC remained unchanged in both groups. Median frequencies of the electromyographic power spectrum during the first 200 ms of contraction for GAS increased following both BST (45 +/- 21%; p < 0.05) and SMT (45 +/- 22%; p < 0.05), but median frequencies for SOL increased only after SMT (13 +/- 4%; p < 0.05). Additionally, mean amplitude voltage increased following BST for SOL (38 +/- 12%; p < 0.01) and for GAS (73 +/- 23%; p < 0.01) during the first 100 ms, whereas it remained unchanged after SMT. It is concluded that BST and SMT may induce different neural adaptations that specifically affect recruitment and discharge rates of motor units at the beginning of voluntary contraction. Specific neural adaptations indicate that SMT might be used complementarily to BST, especially in sports that require contractile explosive properties in situations with high postural demands, e.g., during jumps in ball sports.