Measuring a heartbeat or a pendulum is easy. Measuring a dancer's full-body period, in real time, on stage, is not — which is exactly the technical problem this course is named after.
Modern tools attack it from several angles: wearable accelerometers (measuring acceleration directly), motion-capture markers, and camera-based pose estimation (tracking joints frame by frame from ordinary video).
Each gives a stream of numbers over time — a position, a velocity — from which period, frequency and amplitude can all be recovered.