Biomechanical measurement by inertial sensors: An application to swimming

Inertial Measurement Units, IMUs, are non-invasive sensors suitable for measuring the kinematics of human motion. IMU Orientation data feed a biomechanical model enabling movement reconstruction. IMUs are particularly advantageous, with respect to other technological solutions, when measuring movements in water. Swimming kinematic study aims to a performance optimization by identifying, and consequently correcting, gesture defects while learning the proper technique. In this paper we combine IMU orientation measurements with two different biomechanical models, both characterized by a low computational load. Our aim is rapidly obtaining the movement reconstruction demonstrating it to the swimmer at the poolside during the training session. Using an optoelectronic system, considered the gold standard reference, we firstly characterized the measurement system, consisting of sensors and models, in dry environment. Then a number of regular, well trained, and occasional swimmers tested the proposed system. We used obtained data to compare stroke cycles for crawl, breaststroke, and backstroke styles. We discuss advantages and limits of the different available techniques to determine the stroke cycle. Within the measurement approach, hand position determines the stroke cycle identification. The here proposed measurement system is promising, offering good performance with the simplest biomechanical model.