Using fast Fourier transform and polynomial fitting on dorsal foot kinematics data to identify simulated ankle sprain motion from common sporting motions

Ankle sprain is very common in sports, and a commonly suggested aetiology is the delayed peroneal muscle reaction time. Recent studies showed successful attempts to deliver electrical stimulation to the peroneal muscles externally to initiate contraction before it could react, however, the success relies on a workable method to detect ankle sprain injury in time. This study presented a fast Fourier transform and polynomial fitting method with dorsal foot kinematics data for quick ankle sprain detection. Five males performed 100 simulated ankle sprain and 250 common sporting motion trials. Eight gyrometers recorded the 3D angular velocities at 500Hz. Data were trimmed with a 0.11s window size, the suggested duration of pre-injury phase in ankle sprain, and were transformed from time to frequency domain by fast Fourier transform and fitted with a 5th order polynomial. First order coefficients from polynomial fitting on frequency space were obtained. The method achieved a 97.0% sensitivity and 91.4% specificity in identifying simulated sprains, vertical jump-landing, cutting, stepping-down, running and walking motions, with vertical jump-landing excluded due to its relatively low specificity (67.3%). The method can be used to detect ankle sprain in sports with mainly floor movements and minimal vertical jump-landing motion.