Stretchable piezoresistive vs. capacitive silicon sensors integrated into ski base layer pants for measuring the knee flexion angle

Abstract The knee is the most often injured body part in alpine skiing. The loads on different structures of the knee, and thus the risk of injury, is influenced by the flexion angle of the knee joint. A mechatronic ski binding continuously supplied with information about the knee joint’s flexion angle could adjust its release settings to react to the situation appropriately. In this study, a silicon-based piezoresistive sensor fibre and capacitive silicon sensor were compared with respect to their ability to measure the knee flexion angle. Each sensor type was incorporated in base layer compression pants. These sensor-underwear-systems were validated using a flexion test rig and in a human subject test ( n = 20). The pants with capacitive sensors performed better, as they were more accurate (e.g. mean error 3.4° ± 5.1° of the capacitive sensor vs. 10.6° ± 7.5° of the resistive sensor in the human subject test) and had fewer hysteresis effects. Flexible sensors integrated into compression underwear can provide valuable data of the knee angles for performance measurements in sports or safety systems, and thus may help to reduce knee injuries.