Article
Skill-related changes in spinal plasticity in regards to long-term skill training – an examination of the lower limb
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Published: | October 23, 2017 |
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Objectives: The fracture triangle comprises Fall, Force and Fragility. If one of these three factors is modified, the chance of breaking a bone is greatly reduced. Fall and Force are directly related to motor behavior. Motor behavior itself is modified due to neuro-musculo-skeletal adaptations and, on cortical and spinal level, refines particular movements by changing the connectivity between neural assemblies. In the present study, we specifically focused on the peripheral contribution to skill related neural adaptation.
Previous studies investigating skill related neuromuscular adaptation have focused mainly on changes in cortical input to voluntary control of muscles. Furthermore numerous studies have shown that sensory muscle feedback is one of the major components of fine muscle control. Motivated by those findings we started to investigate the distribution of synaptic input on a large motor neuron pool.
Methods: The study was approved by the ethics committee of the University Medical Center Göttingen. To assess resulting differences of long-term motor skill training, we examined a control group of sedentary participants and a group of long-term regular training martial artists. We explored with non-invasive high-density surface electromyography (HDsEMG) the distribution of reflex amplitudes of large populations of motor units (MU). The volunteer was seated in a chair while performing sustained plantar flexion at different percentiles of their maximum voluntary contraction (MVC) force. Monosynaptic Hoffmann reflexes (H-reflex) were elicited by stimulating the tibial nerve (TN) with low intensity electrical stimulation that was delivered at the popliteal fossa. Single MU H-reflexes of Soleus and Gastrocnemius muscle were recorded. Each subject performed four trials with different knee angles with adequate resting period between trials.
Results and Conclusion: We found a significant difference (Wilcoxon-Mann-Whitney-test, p = 0.05) between skilled and sedentary group in terms of reflex response amplitudes of single motor units, which may indicate higher reflex excitability of the Triceps surae MU pool in skilled groups.
This distinction is thought to arise from the afferent system's spinal plasticity in regards to long-term motor skill training. To exclude the effect of general long-term sport effects, a longitudinal study should be conducted. Changes in neural assemblies of the lower limb muscles spindle's afferent feedback system due to long-term skill training are thought to cause higher excitability of muscles spindle's IA afferences. In a functional meaning this represents better fine muscle control and therefor better control in space, thereby optimizing the Fall and Force parameters of the fracture triangle.