Margin of Stability May Be Larger and Less Variable during Treadmill Walking Versus Overground

Abstract

Margin of stability (MOS) is considered a measure of mechanical gait stability. Due to broad application of treadmills in gait assessment experiments, we aimed to determine if walking on a treadmill vs. overground would affect MOS during three speed-matched conditions. Eight healthy young participants walked on a treadmill and overground at Slow, Preferred, and Fast speed-matched conditions. The mean and variability (standard deviation) of the MOS in anterior-posterior and mediolateral directions at heel contact were calculated. Anterior-posterior and mediolateral mean MOS values decreased with increased speed for both overground and treadmill; although mediolateral mean MOS was always wider on the treadmill compared to overground. Due to lack of optic flow and different proprioceptive inputs during treadmill walking, subjects may employ strategies to increase their lateral stability on treadmill compared to overground. Anterior-posterior MOS variability increased with speed overground, while it did not change on treadmill, which might be due to the fixed speed of treadmill. Whereas, lateral variability on both treadmill and overground was U-shaped. Walking at preferred speed was less variable (may be interpreted as more stable) laterally, compared to fast and slow speeds. Caution should be given when interpreting MOS between modes and speeds of walking. As sagittal plane walking is functionally unstable, this raises the consideration as to the meaningfulness of using MOS as a global measure of gait stability in this direction.

Different Types of Mastoid Process Vibrations Affect Dynamic Margin of Stability Differently

“…However, during this process of sensory reweighting from unreliable to reliable sensory system, the increase/decrease of MOS could be observed to maintain dynamic gait stability (McAndrew et al, 2011 ). Based on the formula of MOS (Süptitz et al, 2012 ; Fallahtafti et al, 2021 ), two factors could lead to a larger MOS: (1) the BOS was toward COM or (2) XCoM was far away from COM. In the current study, the spatial gait parameter supported that a larger MOSap was attributed to the BOS being toward the COM (shorter step length) when both types of mastoid vibrations were applied compared to the condition of no vibration.…”

“…A more negative MOSap was observed as the walking speed increased. In other words, a more negative MOSap indicated that the margin was exceeded, and the extrapolated COMap was outside of the BOS (Fallahtafti et al, 2021 ). In the current study, we defined that a more negative MOSap indicated a larger MOSap.…”

“…In the current study, we defined that a more negative MOSap indicated a larger MOSap. Additionally, the MOSml decreased with increasing walking speed, implying a negative correlation in the above-mentioned speed range (Fallahtafti et al, 2021 ). In the current study, when adding the walking speed as a covariate, the results showed no interactions between walking speed and mastoid vibration in the MOSap, MOSml, MOSap variability, MOSml variability, step length, step length variability, the step width, or the step width variability.…”

“…Dynamic modified MOS was defined based on Hof's study (Hof et al, 2005 ) and Süptitz et al's ( 2012 ) and Fallahtafti et al's ( 2021 ) studies. First, the CoM was calculated as the average position of markers from the right and left anterior and posterior superior iliac spine (McAndrew et al, 2011 ).…”

“…ẋ treadmill was the treadmill speed. And, , where g = 9.81 m/s 2 and l was the distance from CoM to the heel marker at the initial heel contact (Süptitz et al, 2012 ; Fallahtafti et al, 2021 ). The treadmill speed was calculated by an equation: (the distance from heel marker contacted the ground to heel marker off the ground)/(the time from heel contacted the ground to heel off the ground) per step cycle for each leg.…”