Abstract
The present study tested if the quadratic relationship which exists between stepping frequency and gait dynamics in walking can be generalized to stairmill climbing. To accomplish this, we investigated the joint angle dynamics and variability during continuous stairmill climbing at stepping frequencies both above and below the preferred stepping frequency (PSF). Nine subjects performed stairmill climbing at 80, 90, 100, 110 and 120% PSF and treadmill walking at preferred walking speed during which sagittal hip, knee and ankle angles were extracted. Joint angle dynamics were quantified by the largest Lyapunov exponent (LyE) and correlation dimension (CoD). Joint angle variability was estimated by the mean ensemble standard deviation (meanSD). MeanSD and CoD for all joints were significantly higher during stairmill climbing but there were no task differences in LyE. Changes in stepping frequency had only limited effect on joint angle variability and did not affect joint angle dynamics. Thus, we concluded that the quadratic relationship between stepping frequency and gait dynamics observed in walking is not present in stairmill climbing based on the investigated parameters.
Highlights
The complex movement of human walking has been modelled as an inverted pendulum where the centre of mass (CoM) travels in a series of arcs during each single support phase while the stance leg is kept relatively straight [1,2]
There was a significant overall effect of both task (F1,8 1⁄4 45.6, p, 0.001) and joint (F2,8 1⁄4 68.2, p, 0.001) on the mean ensemble standard deviation (meanSD) when comparing treadmill walking at preferred walking speed (PWS) and stairmill climbing at 100% preferred stepping frequency (PSF)
We did not observe any differences in the rate of trajectory divergence for the hip, knee and ankle joint angle between stairmill climbing at PSF and treadmill walking at PWS, we did observe significantly higher joint variability for all three joint angles during stairmill climbing at PSF compared to treadmill walking at PWS
Summary
The complex movement of human walking has been modelled as an inverted pendulum where the centre of mass (CoM) travels in a series of arcs during each single support phase while the stance leg is kept relatively straight [1,2] Based on this model, the preferred stepping frequency (PSF) of healthy individuals has been estimated by computing the resonant frequency of a force-driven harmonic oscillator [3]. Walking at PSF coincides with a minimum rate of trajectory divergence of the knee joint angle (measured by the largest Lyapunov exponent) and minimum amount of variability of the movement trajectories in comparison to stepping frequencies above and below PSF [10] This relationship has been observed for a range of walking speeds above and below the self-selected preferred walking speed (PWS) [11]. It seems to be both mechanically and energetically disadvantageous to force the stepping frequency during walking and the walking speed above or below what is freely chosen
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