P2.194 Thursday, Jan. 5 Effect of Variable Neural Recruitment on Biomechanics of Walking STEVENS, CS*; JERRY, C; MARTIN, P; CINCO, T; AHN, AN; Harvey Mudd College firstname.lastname@example.org
Almost all humans walk, but there are two distinct patterns of neural control in the calf muscles amongst individuals. Half of the subjects measured recruit their medial gastrocnemius (MG) more than their lateral gastrocnemius (LG) muscle at most walking speeds (“MG-biased”). The remaining subjects recruited both the MG and LG relatively equally (“unbiased”). Additionally, subjects with greater LG activity have higher peak pressures under the medial side of the foot (Morag & Cavanaugh, 1999). Therefore, we hypothesized an MG-biased recruitment pattern would correlate with greater pressure under the medial side of the foot during walking. First, we measured muscle thickness using ultrasonography. As subjects walked, we simultaneously measured plantar pressure distribution with 4 force transducers under the 1st, 4th, 5th metatarsal heads and the heel, 3D gait kinematics with Qualysis, and muscle activity patterns of the MG and LG muscles with electromyography. Six of 12 subjects walked with an MG-biased recruitment pattern and 6 with an unbiased pattern. In agreement with our previous study, MG-biased subjects had larger MG muscles and shorter heels than unbiased subjects. Subjects also continued to show no difference in joint kinematics correlating with muscle bias. In rejection of our hypothesis, MG-biased recruitment patterns were independent of pressure measured on the medial side of the foot. However, MG-bias recruitment increased with variation of both the pressure-time integrals and the peak pressures under the medial side of the foot. Although MG-biased subjects do not tend to have higher medial pressures, when subjects recruit the MG more than the LG, pressures under the medial side of their foot become more variable. The biomechanics of walking may be affected by differing neural control patterns in the calf.