Control of the body's centre of mass motion during over-ground and treadmill walking in the pelvic reference frame: Implications for wearable sensing

Treadmill-based training protocols have played an important role in gait and balance training in rehabilitation settings, and the position of the body’s center of mass (COM) relative to the base of support provides an important measurement of postural stability. With the advance in wearable technology, the movement of the COM has been estimated using inertial measurement units (IMU) or by placing a single marker on the pelvis. However, there has not been a consensus over the differences in the movement control of COM relative to pelvis between treadmill walking (TW) and over-ground walking (OW). The current study aimed to quantify and compare the motions of the COM with respect to the pelvic reference frame during TW and OW. Fifteen young male adults walked barefoot on an 8-meter walkway, as well as on an instrumented treadmill at their self-selected speed while their pelvis position, COM positions, and center of pressure (COP) positions were measured. Paired t-tests were performed between OW and TW for all the variables. The results showed that compared to OW, treadmill walking produced significantly greater variations of COM displacements in every direction, namely anterior/posterior, proximal/distal, and medial/lateral, and significantly greater excursions of the COM in the medial/lateral direction with respect to the pelvis coordinate system. The results suggest that the estimation of the COM position with an IMU attached to the pelvis is more accurate during OW than TW.