Regional changes in gastrocnemius architecture with knee position.

<p>Mean values and standard deviation (whiskers) are shown for the fat thickness (panel <i>a</i>), the MG fibre length (panel <i>b</i>), and their pennation angle (panel <i>c</i>). These values were obtained from panoramic ultrasound images (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126888#pone.0126888.g005" target="_blank">Fig 5</a>), separately for the proximal (dark, shaded bars) and distal (light, shaded bars) muscle regions. Asterisks denote statistical differences at <i>P</i> < 0.05.</p

Displacement of innervation zone with knee flexion.

<p>Short epochs (250 ms) of the 15 single-differential EMGs collected from a single participant are shown. Signals in the left and right panels were obtained during knee extended and knee flexed positions, respectively. Propagating potentials are observed in the most distal channels, which were covering the most distal MG fibres. The channel in the array positioned most closely to the innervation zone of the muscle distal fibres is indicated with grey, shaded rectangles. Note the innervation zone moved distally from knee extended to knee flexed position.</p

Changes in the spatial distribution of RMS values with knee position.

<p>Median values and inter-quartile intervals are shown for the RMS amplitude (<i>a</i>), the <i>active channels</i> (<i>b</i>) and the barycentre coordinate (<i>c</i>). These variables were respectively normalised with respect to the maximal RMS value obtained at 100% MVC attempts performed during knee extended position, the total number of channels located over the MG superficial aponeurosis and the distance between the femoral condyle and the distal extremity of the superficial aponeurosis (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126888#pone.0126888.g001" target="_blank">Fig 1</a>). Asterisks denote statistical significance at <i>P</i><0.05.</p

Electrodes positioning and gastrocnemius architecture.

<p>A schematic illustration of the relative position of surface electrodes on the medial gastrocnemius (MG) muscle is shown. The parameters considered to characterise architectural differences between the MG proximal and distal regions are further illustrated in the figure; pennation angle, fibre length and fat thickness. Proximal and distal MG regions were respectively defined as the proximal and distal half of the distance between the distal extremity of the superficial aponeurosis and the most proximal electrode. Only the surface EMGs detected by electrodes positioned in correspondence of the superficial aponeurosis were retained for analysis.</p

Changes in the surface EMGs with changes in knee position.

<p>A short epoch of raw, surface EMGs is shown during plantar flexion contractions exerted with the knee fully extended (<i>a</i>) and the knee flexed at 90 deg (<i>b</i>). Only nine of the 15 channels in the array were positioned on skin regions covering the MG superficial aponeurosis. The RMS amplitude computed from EMGs detected by each of these nine channels is shown on the right side of each panel, with black circles denoting the channels providing RMS amplitudes greater than 70% of the maximum. Dashed lines indicate the barycentre coordinate computed for these channels.</p