2.3.1. Actigraph GT3x

The Actigraph GT3x (Actigraph LLC, Pensacola, FL, USA) is the most widely used accelerometer for physical activity evaluations in clinical research [32]. The Actigraph GT3x is a small (4.6 cm × 3.3 cm × 1.5 cm) and lightweight (42.5 g) triaxial accelerometer designed to measure accelerations in the range of 0.05–2 *g* with a band-limited frequency of 0.25–2.50 Hz. This corresponds to the range in which most human activities are performed [33]. We chose a standard configuration with a standard sampling frequency of 30 Hz and no specific filtering. The device was initialized using 1-s epochs. The Actigraph data can be downloaded to a personal computer via a reader interface unit. In our work, we used the step count estimate provided by the ActigraphGT3x. It can be worn on the wrist, hip, or ankle [34]. We chose to place the devices on the wrists and ankles on the affected and unaffected sides, and on the hip on the unaffected side. The sensor was only placed on the unaffected hip because Rand et al. [35] reported that there was no difference in the estimation of the number of steps whether the sensor was on the affected or unaffected hip. This was, therefore, done to simplify the protocol. The sensor was attached to the different placements by an elastic band provided by the manufacturer. This choice was made to judge the impact of the impairments and the positioning of the estimations of the sensor.
