Application of the ActiGraph GT9X IMU for the assessment of turning during walking and running

Abstract

Objective. The primary purpose of this study was to examine the use of the ActiGraph GT9X gyroscope and magnetometer for turn detection and quantifying turn degree during walking and running. The secondary purpose was to examine the effect of varying turn degrees during walking and running on oxygen consumption. Approach. Participants (N = 17) completed pivot trials, straight-line treadmill walking and running (3-6 mph) and four turn conditions (45°, 90°, 135°, and 180°) during over-ground walking and running. Pivot trials were completed for 1 min and walking/running trials were completed for 6 min, both with a turn frequency of 10 turns/min. Data were collected using a GT9X device (right hip) and a Cosmed K4b2 (measured oxygen consumption). Raw GT9X gyroscope and magnetometer data were processed through various low-pass filter frequencies (0.25-2.0 Hz). Treadmill and pivot trials were used to develop thresholds for turn detection using gyroscope and magnetometer data and cross-validated using the over-ground trials. Linear mixed models were used to compare actual and estimated number of turns, measured and estimated turn degree, and differences in VO2 across walking and running speed and turn degree. Main results. Greater than 98% of turns were detected when using gyroscope data filtered at 0.25 Hz and turn degree was estimated within 2.2° of measured turn degree across all speeds. In general, the VO2 of walking and running increased as the turn degree increased beyond 135°. Significance. The GT9X gyroscope, when filtered at 0.25 Hz can be used to detect the number of turns and estimate turn degree. The magnetometer, when filtered at 0.75 Hz, was useful for detecting the number of turns, however turn detection was more accurate using the gyroscope.