Biomechanical comparison of human trunk and thigh muscle activity during walking and horseback riding activity.

INTRODUCTION: Hippotherapy is a physical therapy tool that utilizes horseback riding to improve strength, coordination, gait, and balance. These benefits may be linked to similarities in kinematics and muscle activation between horseback riding and normal human gait, but this is not well represented in the literature, especially for muscle activation. The purpose of this study was to investigate the relationships between muscle activation of horseback riding and healthy human gait. METHODS: The muscle activation of nine healthy female participants (age 18-22) were recorded during walking and horseback riding trials using surface electromyography (EMG). Muscles analyzed include rectus abdominis, lumbar erector spinae, rectus femoris and biceps femoris. Activation waveforms during walking and riding were generated, and from this average and maximum contraction magnitudes were recorded. RESULTS: Average muscle activation was significantly greater in riding for the left (p = 0.008) and right (p = 0.04) biceps femoris. Additionally, average and maximal activation of the left erector spinae were significantly greater in riding (W = 4; critical value for W at n = 9 is 5). Remaining differences in muscle activation between walking and riding were non-significant. DISCUSSION: Peak and average muscle activation magnitude across the gait cycle were similar for most muscle groups. When present, differences were greater in riding. Despite these similarities, EMG waveforms displayed more predictable temporal patterns in walking. CONCLUSION: These findings suggest that hippotherapy could be used to elicit muscle excitation similar to that of normal gait, which may have promising implications for rehabilitation targeting gait correction.

Toward a 3D physical model of diffusive polymer chains.

Recent studies in polymer physics have created macro-scale analogs to solute microscopic polymer chains like DNA by inducing diffusive motion on a chain of beads. These bead chains have persistence lengths of O(10) links and undergo diffusive motion under random fluctuations like vibration. We present a bead chain model within a new stochastic forcing system: an air fluidizing bed of granular media. A chain of spherical 6 mm resin beads crimped onto silk thread are buffeted randomly by the multiphase flow of grains and low density rising air "bubbles". We "thermalize" bead chains of various lengths at different fluidizing airflow rates, while X-ray imaging captures a projection of the chains' dynamics within the media. With modern 3D printing techniques, we can better represent complex polymers by geometrically varying bead connections and their relative strength, e.g., mimicking the variable stiffness between adjacent nucleotide pairs of DNA. We also develop Discrete Element Method (DEM) simulations to study the 3D motion of the bead chain, where the bead chain is represented by simulated spherical particles connected by linear and angular spring-like bonds. In experiment, we find that the velocity distributions of the beads follow exponential distributions rather than the Gaussian distributions expected from polymers in solution. Through use of the DEM simulation, we find that this difference can likely be attributed to the distributions of the forces imparted onto the chain from the fluidized bed environment. We anticipate expanding this study in the future to explore a wide range of chain composition and confinement geometry, which will provide insights into the physics of large biopolymers.