Automatic stance-swing phase detection from accelerometer data for peroneal nerve stimulation

The development of implantable peroneal nerve stimulators has increased interest in sensors which can detect the different phases of walking (stance and swing). Accelerometers with a potential for implantation are studied as detectors for the swing phase of walking to replace footswitches. Theoretically, one can show that accelerometers can be used to distinguish between stance and swing phase. Using accelerometers attached between the ankle and knee joints, the equivalent acceleration of the ankle joint was calculated. This resulted in a typical and reproducible signal in which the different walking phases were identified. Automatic detection algorithms based on cross-correlation calculations were developed and tested. Measurements from four healthy and four hemiplegic subjects resulted in a total of 317 and 272 steps, respectively. The testing of one of the hemiplegic subjects was considered to be a failure due to large disturbances in the acceleration signal during the swing phase of walking, which may be related to the use of crutches.