The effect of walking with reduced trunk motion on dynamic stability in healthy adults

Abstract

BackgroundMost people with Parkinsons Disease (PD) walk with a smaller mediolateral base of support (BoS) compared to healthy people, but the underlying mechanisms remain unknown. According to the extrapolated center of mass (XCoM) concept, a decrease in mediolateral XCoM excursion would require a smaller mediolateral BoS to maintain a constant margin of stability (MoS) and remain stable. As people with PD typically walk with reduced trunk motion, we hypothesized that the mediolateral MoS might stay the same despite a smaller BoS. Research questionAs proof of principle, we assess whether walking with reduced trunk motion results in a smaller step width in healthy adults, without altering the mediolateral MoS. MethodsFifteen healthy adults walked on a treadmill at preferred comfortable walking speed in two conditions. First, the regular walking condition without any instructions, and second, the reduced trunk motion condition with the instruction: Keep your trunk as still as possible. Treadmill speed was kept the same in the two conditions. Trunk kinematics, step width, mediolateral XCoM excursion and mediolateral MoS were calculated and compared between the two conditions. ResultsWalking with the instruction to keep the trunk still significantly reduced trunk kinematics. Walking with reduced trunk motion resulted in significant decreases in step width and mediolateral XCoM excursion, but not in the mediolateral MoS. Furthermore, step width and mediolateral XCoM excursion were strongly correlated during both conditions (r=0.887 and r=0.934). SignificanceThis study shows that walking with reduced trunk motion leads to a gait pattern with a smaller BoS in healthy adults, without altering the mediolateral MoS. Our findings indicate a strong coupling between CoM motion state and the mediolateral BoS. We expect that people with PD who walk narrow-based, have a similar mediolateral MoS as healthy people, which will be further investigated.