Capacity to increase walking speed is limited by impaired hip and ankle power generation in lower functioning persons post-stroke
Introduction
Gait in persons post-stroke is typically slower compared to non-disabled individuals. Several studies have related impaired walking speed in post-stroke hemiparesis to muscle weakness, spasticity, and impaired balance and sensation [1], [2], [3], [4], [5], [6], [7], [8], [9]. Comparison of gait performance in fast and self-selected speeds using biomechanical analysis has the potential to further delineate factors limiting gait performance in hemiparetic persons. Testing the ability to increase gait speed may reveal impairments of locomotor function other than the impairments reflected by reduced walking speed alone.
In non-disabled persons, strategies employed to change from slow to free and fast walking conditions have been documented in terms of changes in joint angles, moments and power, as well as muscle coordination [10], [11], [12], [13], [14]. The combination of increased ankle power generation and increased hip power generation has been proposed as an important mechanism in increasing walking speed [10], [12], [13], [14]. Requiao et al. [15] analyzed muscle utilization ratio and concluded that an increased contribution of both ankle plantarflexors and hip flexors is associated with increased walking speed in control subjects. Nadeau et al. [8] used the muscle utilization ratio with hemiparetic subjects and determined that additional recruitment of the hip flexor muscles was required to achieve faster walking speeds in the presence of plantarflexor weakness. Milot et al. [16] reported a shift towards similar muscular utilization levels of ankle plantarflexors and hip flexors at higher speeds. These studies focused on hemiparetic persons able to walk at relatively normal walking speeds. Little is known about the mechanisms used to increase walking speed in hemiparetic persons with significantly decreased locomotor function.
Our study compared the mechanisms used to increase walking speed in two groups of hemiparetic persons demonstrating higher and lower levels of locomotor function as classified according to walking speed in self-selected and fast conditions. We evaluated the changes in joint kinematics and joint powers that occurred between self-selected and fast walking in these subjects and compared these observations to data collected from control subjects walking at comparable speeds.
Based on previous findings [8], [16], we hypothesized that higher functioning hemiparetic subjects would use the same mechanisms to increase speed as control subjects, but lower functioning hemiparetic subjects would fail to effectively recruit both the hip flexors and ankle plantarflexor muscles of the paretic side. This failure in lower functioning hemiparetic subjects would not only limit the potential to increase walking speed but would also introduce compensations on the non-paretic side.
Section snippets
Subjects and methods
The study sample included 12 persons with post-stroke hemiparesis who were able to walk at least 10 m without an ankle foot orthosis or walking aid. Subject characteristics and demographics are presented in Table 1. Control data were collected from a group of 10 subjects (six males and four females) with average age of 43 years (S.D.: 11.6) and no major orthopedic or neurologic pathology affecting their gait performance. All procedures were approved by the Stanford University panels on human
Results
Age and mean time since stroke were similar between the hemiparetic subjects (Table 1). LFH-subjects had significantly lower scores on the lower extremity portion of the Fugl-Meyer Motor Assessment (p < 0.05).
Discussion
This study analyzed biomechanical mechanisms contributing to gait speed modulation between self-selected and faster walking speeds in hemiparetic persons and compared these strategies to non-disabled control subjects walking over comparable speed ranges. We found that higher functioning hemiparetic subjects and control subjects increased both ankle plantarflexion power and hip flexor power to increase walking speed, whereas lower functioning hemiparetic subjects failed to demonstrate this
Conflict of interest
I, Ilse Jonkers, hereby certify that there are no conflicts of interest.
Acknowledgements
Ilse Jonkers is a Postdoctoral Fellow of the Research Foundation, Flanders and receives additional funding from the Belgian Educational Foundation and the Koning Boudewijn Fonds. This work was supported by VA RR&D Merit Review Grant no. B2792R to CP. We thank Abigail Andrade, C. Maria Kim, M.Sc., PT, Kirsten Unfried, M.S., and Lise C. Worthen, M.S. for their assistance in collecting and reducing the kinematic data and Marilynn Wyatt, PT, MA for suggestions to a previous version of this
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