The reasons why stroke patients expend so much energy to walk slowly

doi:10.1016/j.gaitpost.2012.03.019

Gait & Posture

Volume 36, Issue 3, July 2012, Pages 409-413

https://doi.org/10.1016/j.gaitpost.2012.03.019 Get rights and content

Abstract

Background

The energy consumed per covered distance (C) is increased in hemiparetic stroke adults during walking.

Objective

To ascertain if increased C in stroke patients is a result of increased mechanical work, of decreased efficiency of work production by muscles or of slow walking speed.

Methods

C and mechanical work were computed in 20 patients walking on a force measuring treadmill at speeds ranging from 1 km h⁻¹ to their own maximum speed (WS_MAX). Works done by healthy and pathological limbs were computed separately.

Results

For hemiparetic patients, C was around 1.7 times greater than normal. When these patients had a slower WS_MAX, they had greater C and mechanical work (r = −0.44 and −0.57, respectively). The increased C was related to the external work performed to lift the center of body mass when the healthy limb was supporting the body weight (r = 0.77).

Conclusions

The increase of C in stroke patients is more pronounced when WS_MAX is slow. Moreover, this increase is related to increased mechanical work done by muscles and is not related to slow walking speed or decreased efficiency. As in healthy subjects, C and external work presented optimum speeds, indicating a preserved pendular mechanism of walking.

Introduction

Spastic hemiparetic stroke patients expend up to two times more energy to walk than healthy subjects, and that limits their activities and participation. Though it is obvious that those patients walk at slow speeds (for review, Waters [1]), the relation between energy consumption and walking speed remains partly unknown. In healthy subjects, since the energy consumed per unit of time increases as a quadratic function of walking speed (power, W kg⁻¹), the energy per covered distance (energy cost, C, J kg⁻¹ m⁻¹) fits a well-known U-shaped curve [2]. This curve presents minimum values around spontaneous speeds (±4.5 km h⁻¹). When speed varies from this optimum, C progressively increases [3].

In stroke patients walking at various speeds on a treadmill, Reisman et al. [4] have shown that energy cost of stroke patients decreased with increasing walking speed. Average maximum walking speed of all patients was 68.2 ± 28.9% higher than spontaneous one. It corroborates the hypothesis of authors [5] who believe that increased energy cost in stroke patients is explained by their very slow walking speed [1]. A normal energy consumption would then be reached if patients were able to walk as fast as healthy subjects.

However, in addition to slow walking speed, the increased energy cost could be related either to the increased mechanical work done by muscles, or the decreased efficiency of production of this work. Detrembleur et al. [6] found, in nine stroke patients compared to controls walking at same speeds, that increased energy cost was proportional to increased mechanical work.

Therefore, the aim of the present study is two-fold: first, to study more deeply the relationships between energetics and mechanics to understand the origin of increased C in stroke patients; second, to evaluate the effects of walking speed on mechanics and energetics.

Section snippets

Study population

Twenty post-stroke chronic (more than 6 months) hemiparetic patients (age: 50 ± 12 years; weight 78 ± 18 kg; height: 173 ± 11 cm) were enrolled in the present study. Inclusion criteria included the ability to walk independently on a treadmill without any assistive device, at a minimum of two different speeds (≥1 km h⁻¹), for a time allowing metabolic measurement (around 3 min at each speed). After giving their informed consent, all patients participated freely in the study, which was approved by the

Results

The maximal walking speed on the treadmill (WS_MAX) and the spontaneous walking speed adopted overground (WS_spont) varied from patient to patient, ranging from 1.7 to 5.5 km h⁻¹ and from 2.1 to 5.1 km h⁻¹, respectively. However, both speeds were well correlated (r = 0.81, p < 0.0001), and mean WS_MAX (3.5 ± 1.1 km h⁻¹) and WS_spont (3.4 ± 0.8 km h⁻¹) were similar. They were lower than usual spontaneous walking speeds in healthy subjects (4.5 km h⁻¹). Neurological impairments correlated significantly with WS_MAX (r =

Discussion

The present study confirms that stroke patients expend more energy to walk than healthy subjects. The increased C was not explained by their slow walking speed. Indeed, C was greater in patients than in healthy subjects walking at a comparable slow speed. This change of C was related to an increase of the mechanical work, mainly done by the healthy leg to lift the center of body mass, but poorly related to the efficiency of work production, confirming previous results [6], [14].

In stroke

Conclusion

The energy cost increase is mainly due to mechanical work done by the healthy limb, mainly to lift the COM_b. Future studies should examine kinematics and kinetics to explain the mechanical work increase. This could allow targeted treatment to improve energy cost of stroke patients, and then their walking ability.

Conflict of interest statement

Authors disclose any financial and personal relationship with other people that could inappropriately influence their work.

Acknowledgments

This study was sponsored by the Association Nationale d’Aide aux personnes Handicapées (ANAH-Rotary Belgium and Luxemburg), the Fondation du patrimoine (Université catholique de Louvain, Brussels) and the Fonds National de la Recherche Scientifique (FNRS).

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The reasons why stroke patients expend so much energy to walk slowly

Abstract

Background

Objective

Methods

Results

Conclusions

Introduction

Section snippets

Study population

Results

Discussion

Conclusion

Conflict of interest statement

Acknowledgments

Gait & Posture

Gait & Posture

Neurophysiologie Clinique

Gait & Posture

Clinical Biomechanics

Gait & Posture

Journal of Biomechanics

Gait & Posture

Gait & Posture

Archives of Physical Medicine and Rehabilitation

Archives of Physical Medicine and Rehabilitation

Archives of Physical Medicine and Rehabilitation

Gait & Posture

NeuroRx

Archives of Physical Medicine and Rehabilitation