Horizontal foot orientation affects the distribution of neural drive between gastrocnemii during plantarflexion, without changing neural excitability

<b>Individual data:</b>Individual data of muscle activation level, motor unit properties, and cortico-spinal excitabilities of the gastrocnemius medialis (GM) and lateralis (GL) muscles in different horizontal foot positions.<b>Activation and motor unit properties: </b>HDsEMG signals were recorded using a 64-channel electrode grid. The EMG signals were recorded in monopolar mode, bandpass filtered (10-500 Hz) and digitized at a sampling rate of 2048 Hz using a multichannel acquisition system.<b>Corticospinal excitability: </b>myoelectrical activity was recorded with pairs of self-adhesive surface EMG electrodes. The EMG signals were digitized at a sampling rate of 2000 Hz. A double-cone coil was used and stimulations were delivered by a monophasic magnetic stimulator. To assess corticospinal excitability, single pulses were delivered while TMS intensity was set at a supra-threshold level (120% of motor threshold). The technique of paired pulse TMS was used to assess short latency intracortical inhibitory (SICI) and intracortical facilitation (ICF) in the motor cortex.<b>Efficacy of spinal transmission and pre-synaptic inhibition: </b>myoelectrical activity was recorded similarly as for corticospinal excitability. Percutaneous electrical stimulation was delivered on the tibial nerve by a constant current stimulator to evoke GM and GL electrophysiological responses. The recruitment curves of H reflex and M wave of GM and GL were recorded as well as the pre-synaptic inhibition using the D1 inhibition technique.<b>Supplemental data:</b><b>Motor unit properties </b>results from comparison of the same pool of motoneurons between conditions (tracked motor units).