Proceedings of The Physiological Society

Physiology 2014 (London, UK) (2014) Proc Physiol Soc 31, PCB147

Poster Communications

Does walking over a destabilising cobblestones surface change the corticospinal excitatory output to human lower limb muscles?

E. Ottersen1, D. C. James1, K. N. Mileva1

1. Sport and Exercise Science Research Centre, London South Bank University, London, United Kingdom.

  • Figure 1. Population average (mean

The motor control system undergoes challenges on a daily life basis, especially when movement is performed on irregular surfaces (1) due to variations in the sensory information received and processed by the central nervous system. This investigation aimed to establish whether a brief session of walking over cobblestones can enhance the excitability of peripheral and central elements of the neuromuscular system. EMG responses to peripheral nerve (PNS) and transcranial magnetic (TMS) stimulation were recorded in tibialis anterior (TA) and soleus (SOL) muscles prior to (pre), immediately- (post) and 30-min after (residual) walking for 5 min over cobblestones or even surface. After familiarization, 7 healthy participants (24±58y; 3M, 4F) completed the 2 main trials in random order over separate visits. The stimulations were performed on an isokinetic dynamometer. PNS was applied to the innervating nerves (SOL: tibial nerve; TA: common peroneal nerve) of the right leg. TMS was delivered to the motor cortex area related to the right-side lower limb muscles. PNS intensity started at 5mA and was increased by 5mA up until response saturation. TMS started at 30% of maximum Magstim output and increased to 70% at intervals of 5%. Three single pulses were delivered at each PNS and TMS level and averaged to assess the muscle compound (M-wave) and motor evoked (MEP) potentials. Peak-to-peak amplitude and total area of TA and SOL responses, as well as the TA silent period (SP) were extracted for analysis. PNS and TMS motor thresholds (MT) were determined from the recruitment curves. The MEPs in response to TMS of 120%MT were normalized to M-waves evoked by PNS of 130%MT. All data were expressed as ratio to baseline (pre) for statistical comparison. No significant interaction effects (P>0.05) were observed for any outcome measure (Fig. 1). However, significant between-subjects differences were found (P<0.001). The present findings demonstrate that walking over cobblestones for 5 min does not affect significantly the excitability of the corticospinal (TA) and spinal (TA and SOL) pathways to lower limb muscles. This is surprising in light of the notable kinematic changes induced by walking over a destabilizing surface (1) and the reliance of neuromuscular function on feed-forward motor control components required with a similar task (2). Several limitations may have precluded interaction effects in our data. It is likely that: 1) the experimental intervention was not long enough; 2) the between-subjects variability was too large, to induce significant adaptations. Future work will benefit from the present results and considerations and requires a more rigorous investigation.

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