- no.17, pp.235-244, 2004-08-25
Body care motions apply a large amount of stress on caregivers' muscles and spines, so most of them suffer from low back pain. One of the major factors of low back pain is the low back muscular load to keep the deep flexion posture. This study concerned development of a suit-type back muscle supporter named "the care suit," which reduces low back load. Elastic fiber belts (support lines) are arranged on the back and leg parts of the suit. The support lines are relaxed so as not to interfere with daily trunk motion, arm motion, walking, and sitting motion, but to exert tensile force and extension moment in the deep flexion posture. The care suit is a two-piece design to improve comfort and convenience. To optimize the layout of the support lines we developed a small reel-type device to measure body surface deformation. As the result of measurement by this device and a system for posture measurement during several motions, the back support lines are arranged in an x-shape from the side neck point to the point internally dividing the Jacoby-line at a ratio of 1 to 2. The leg support lines branch at the rear face of the thigh and are attached to the apex of the patella. The maximum tension of support lines is limited by the user's shoulder pain to 140 N for males and 85 N for females. The effect of the care suit was evaluated by electromyograms of back muscles. The action potential in the deep flexion posture was 25% decreased. In comparison with the conventional corset, the effect of the care suit for back muscle was equal, but the care suit is superior in that it does not interfere with flexion motion. The lumbar joint muscular moment during a diaper change operation was calculated from body posture through a rigid body link model. The results of this calculation showed that the stored load during the operation was decreased by 30% by the care suit. Furthermore the summation of intervertebral disk compressive force was reduced by 15% during the operation. Therefore the care suit is effective for reduction of not only continuous muscular load but also spinal load. Practical use by caregivers also resulted in good evaluations as it reduced continuous muscle load for a diaper change operation, bed making operation, etc. Conclusively, the low back load during body care motions can be reduced by the care suit developed in this research. This care suit is under patent application.