Abstract
Stretching is a major treatment for restoring the ankle range of motion while decreasing the ankle stiffness. An automatic stretching machine can provide long-term continual stretching at home. However, no commercial stretching machines are currently available, and therefore, no safety guidelines exist for them. In this study, we prototyped a stretching machine using a chassis from a commercial foot exerciser for preventing disuse syndrome, and then proposed three safety concepts as general requirements for stretching machines. The concepts were determined based on risk assessments, which included (1) preventing excessive force from being applied to the foot, (2) responding to the ankle stiffness and the range of motion of each different individual, and (3) preventing unintended operations by the user. The above concepts allowed us to develop a stretching machine taking into account safety measures. Further, the stretching effect of the prototype was tested on sixteen healthy young subjects (22.3 pm 3.6hbox { years}). We found that the passive resistance of the subjects at specific dorsiflexion angles decreased significantly after stretching the ankle using the prototyped machine.
Highlights
Ankle contracture is a common after effect of diseases and injuries such as ankle fracture, stroke, or cerebral palsy
We propose safety concepts tailored to ankle stretching machines based on the risk assessment of a commercial foot exercise machine
We propose the following three safety concepts based on the risks identified during the risk assessment process
Summary
Ankle contracture is a common after effect of diseases and injuries such as ankle fracture, stroke, or cerebral palsy. It is caused by the stiffened soft tissues comprising muscles and tendons around the joint, which reduces the ankle range of motion (ROM). Yamada et al developed a machine for three-dimensionally controlling the foot using wire-driven mechanisms to stretch the muscles related to equinovarus [8, 9]. This machine moves the foot by pulling two wires with
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