自由歩行における歩調・歩幅の生体力学的決定基準

抄録

There are numerous combinations of cadence and stride length that result in a walk with a certain speed. However, natural walking has high predictability, and is done within a limited range of cadence and stride for each individual. The purpose of this study is to clarify the determination criteria of this daily motion from a biomechanical viewpoint. One of the factors that determines the criteria is the efficiency of energy consumption during walking. Conventionally, the energy consumed by body exercise was estimated from the oxygen consumption volume at the respiration. In this study, consumed energy in muscles was calculated using a musculoskeletal model and measured articular motion in walking. With this simulation, the cause and the mechanism in energy change can be analyzed. Articular moments in walking were calculated with a rigid link model of seven two-dimensional segments which were constructed independently in sagittal and frontal planes. The link system was attached to eleven muscles, and the muscle activities were assumed to be controlled in order to minimize muscle fatigue. Using these assumptions, muscle tension was calculated under the restriction of equilibria between the articular moment and the muscular moment by an optimization technique. Furthermore, supposing a metabolic model of muscle that has two elastic elements and two viscosity elements, the force of the construction element in each muscle was estimated from the calculated muscle tension and the measured articular motion. The metabolic energy calculated from the mechanical work of the contraction element and the heat loss from each element of the muscle model agreed well with the experimental results by gas analysis. Articular motion in walking was measured by a semiconductor camera using infrared markers. External force on foot was measured by a force platform. Electromyograms of six surface muscles were measured for the evaluation of the calculated muscle tensions. Totals of 600 various kinds of cadences and stride lengths were obtained from ten male subjects. From the results of the calculated metabolic energy in these walking experiments, it was found that there was a combination of cadence and stride length which minimized the metabolic energy per unit distance and unit body weight. The walking speed at the minimum energy point agreed with the average speed of free walking. The cause of the minimization was as follows. The energy expended by muscle activities in the sagittal plane for promotion increased in high-speed walking. In contrast, the energy expended by muscles to support body weight and fundamental metabolic energy increase in low-speed walking. Accordingly, it was concluded that cadence and stride length in natural walking were determined so as to minimize total metabolic energy per unit of locomotion distance.