Correlation between the strength of muscle actions of the paretic lower-limb and gait speed after stroke: Results of a meta-analysis of six studies

Abstract

BACKROUND AND OBJECTIVE:

Lower limb strength after stroke, particularly of the more paretic side, is known to correlate with comfortable gait speed. This meta-analysis sought to determine the relative value of 6 muscle group strengths as explanators of comfortable gait speed.

METHODS:

Relevant literature was sought using PubMed, CINAHL Scopus, and a hand search. Information on samples, measurements, and correlations were extracted. Correlational data were subjected to meta-analysis.

RESULTS:

Results from 6 studies were consolidated. The summary correlations between paretic lower limb strength and comfortable gait speed ranged from 0.45 to 0.61. Data were highly heterogeneous but did not show publication bias.

CONCLUSIONS:

The correlation between the lower limb strength and comfortable gait speed strength was moderate. However, it does not provide an adequate explanation to guide clinical practice.

Keywords

Muscle strength measurement clinimetrics

1. Introduction

Muscle strength, primarily on the side contralateral to a brain lesion, is a body function commonly impaired after stroke [1]. These impairments are often accompanied by gait limitations, which are of particular concern to patients who have experienced a stroke [2]. Among the gait performance variables measured, comfortable gait speed has realized particularly widespread use [3]. Not surprisingly, therefore, many studies have investigated the relationship between paretic lower limb strength [most often that of the knee extensors] and gait speed after stroke [4]. These investigations and findings notwithstanding, uncertainty remains regarding the relative magnitude of association between the strength of different paretic lower limb muscle actions and comfortable gait speed. Acknowledging that correlations do not prove cause and effect, the relative magnitude of association between the strength of different lower limb muscle actions and comfortable gait speed may help identify the most appropriate targets for intervention after stroke. The purpose of this meta-analysis, therefore, was to describe and compare the association of the strength of paretic lower limb muscle actions with comfortable gait speed following stroke. The focus was on 6 muscle groups acting in the sagittal plane as they were the most often measured.

Table 1
Summary statistics of articles describing the relationship between the strength of 6 paretic lower limb muscle actions and comfortable gait speed

Study	Sample	Strength measurement	Gait measurement	Correlations
Aguiar et al. (2018)	Brazilians with subacute stroke ( $n=$ 39 to 41)	MicroFET2 HHD Single isometric force of each action	“Comfortable & habitual speed” over 10 m	$r=$ 0.37 (ankle dorsiflexors) to $r=$ 0.49 (hip flexors)
Bohannon (1989)	Americans with subacute stroke ( $n=$ 33)	Chatillon HHD Single isometric force of each action normalized against body weight	“Comfortable pace” over 8 m	$r_{s}=$ 0.77 (ankle dorsiflexors) to $r_{s}=$ 0.83 (ankle plantarflexors)
Bohannon (1986)	Americans with subacute or chronic stroke ( $n=$ 20)	Chatillon HHD Single isometric force of each action normalized against body weight	“Most comfortable speed” over 8 m	$r=$ 0.25 (hip flexors) to $r=$ 0.59 (hip extensors)
Dorsch et al. (2012)	Australians with chronic stroke ( $n=$ 60)	Nonspecified HHD Best of 2 isometric forces of each action	“Comfortable walking speed” over 10 m	$r=$ 0.27 (knee extensors) to $r=$ 0.50 (ankle dorsiflexors)
Kim and Eng (2003)	Canadians with chronic stroke ( $n=$ 20)	Kin-Com IKD Average isokinetic torque of 60 ${}^{\circ}$ /s or 30 ${}^{\circ}$ /s for action	“Most comfortable speed” over 8 m	$r=$ 0.33 (ankle dorsiflexion) to $r=$ 0.85 (ankle plantarflexion)
Nasciutti-Prudente et al. (2009)	Brazilians with chronic stroke ( $n=$ 12)	MicroFET2 HHD Single isometric torques for each action corrected for gravity	“Self-selected speed” over10 m	$r=$ 0.34 (knee extensors) to $r=$ 0.80 (knee flexors)

${}^{*}$ HHD $=$ hand-held dynamometry; IKD $=$ isokinetic dynamometry.

Table 2

Correlational data summarizing the relationship between the strength of paretic lower-limb muscle actions and comfortable gait speed ${}^{*}$

Muscle action ( $n$ )	Range of correlations for individual studies	Summary correlations (95% CI)	Heterogeneity (I ${}^{2}$ )
Hip flexion (186)	0.30 to 0.81	0.58 (0.36 to 0.73)	66.0
Hip extension (184)	0.25 to 0.67	0.45 (0.28 to 0.59)	29.5
Knee flexion (185)	0.25 to 0.80	0.54 (0.31 to 0.71)	67.2
Knee extension (186)	0.27 to 0.81	0.48 (0.21 to 0.69)	73.9
Ankle dorsiflexion (185)	0.27 to 0.72	0.49 (0.29 to 0.64)	51.1
Ankle plantarflexion (184)	0.29 to 0.85	0.61 (0.37 to 0.78)	76.3

${}^{*}$ Only the correlations of plantarflexion and hip extension strength with comfortable gait speed were significantly different.

2. Method

This review involved an electronic search of 3 bibliographic databases (Scopus, CINAHL, and PubMed) as well as a hand search. The electronic searches used the string “(leg OR “lower limb” OR hip OR knee OR ankle) AND (strength) AND (“gait speed” OR “walking speed”) AND “stroke.” As should be apparent from the search string, inclusion required that an article addressed paretic lower limb muscle strength, gait speed, and the correlation between them in patients with stroke. Articles were excluded if they failed to address the individual strength of all 6 paretic muscle groups of interest (i.e., hip flexors and extensors, knee flexors and extensors, and ankle plantarflexors and dorsiflexors). Articles were also excluded if they reported only fast or maximum speed gait. Articles in languages other than English were disallowed.

Potentially relevant articles were selected and abstracted by the author for information on the study sample, strength and gait measures, and correlations between lower limb strength and gait speed. The MedCalc statistical program (version 20) was used for all analysis [5]. The “meta-analysis: correlation” subprogram used random effects models to calculate summary correlations between the strength of each muscle action and gait speed and I ${}^{2}$ to determine heterogeneity of study data. The magnitudes of summary correlations were compared using the “comparison of correlation coefficients” subprogram.

3. Results

The electronic searches yielded 1166 potentially relevant nonduplicative articles. Three additional potentially relevant articles were identified by hand searches. After examination, 6 of the potentially relevant articles were found to meet all inclusion and exclusion criteria [6, 7, 8, 9, 10, 11].

Table 1 summarizes the 6 included studies. The participants of the studied samples resided in 4 different countries and included from 12 to 60 patients with subacute or chronic stroke. Strength was measured with a hand-held dynamometer in 5 studies and an isokinetic dynamometer in 1 study. Four studies measured force whereas 2 measured torque. Two studies normalized strength measures against body weight. Walking speed was measured over distances of 8 or 10 meters. The correlations between strength and gait speed were highly variable- ranging from 0.25 to 0.85 depending on the study and muscle group. Summary correlations ranging from 0.45 (hip extension) to 0.61 (ankle plantarflexion) were of only moderate magnitude [12]. The correlations between comfortable gait speed and hip extension and ankle plantarflexion were the only 2 which were significantly different from one another. The heterogeneity of the correlations, as indicated by I ${}^{2}$ , ranged from 29.5 to 76.3.

4. Discussion

This consolidation of correlational data using meta-analysis suggests that comfortable walking speed can be explained in part by the strength of each of 6 lower limb muscle actions. As the summary correlations were of only moderate magnitude, however, correlations between other strength and gait variables warrant investigation. These variables may be other strength measures of the paretic side not addressed in many analyses (e.g., hip abduction) [13] strength measures of the nonparetic lower limb [e.g., knee extension] [14], or composite measures of multiple muscle actions of either one or both lower limbs after stroke [15].

In any case, the clear superiority of certain muscle action strengths as correlates with gait speed was not established in this meta-analysis. With the possible exception of the ankle plantarflexors [10, 16, 17], no specific muscle group was identified in the literature as particularly notable across studies summarized by meta-analysis.

This study had several limitations. First, it was restricted to 6 studies addressing weakness of 6 muscle groups of the paretic lower limb of patients with stroke. This limitation was driven by the lack of studies reporting data for other muscle groups of the paretic side. It was also influenced by the lack of studies reporting impairments of the nonparetic side. The literature typically shows measurements of strength of the paretic side to have higher correlations with gait speed than measurements of strength of the nonparetic side [7]. Second, the summary correlations calculated were between lower limb strength and comfortable gait speed. Correlations of paretic limb strength with maximum speed gait tend to be higher [18]. Third, only one researcher abstracted the included article and no quality assessment was applied. As any investigators are free to repeat my search and selection process, I do not see this as a limitation of consequence. Finally, the data contributing to the meta-analysis was rather heterogeneous. Consequently, their consolidation must be interpreted with caution.

In conclusion, this review and meta-analysis provides limited support for the measurement of paretic lower limb strength as an explanator of comfortable gait speed after stroke. The measures described herein, however, are insufficient to guide clinical practice.

Ethical considerations

This study, as a literature review, is exempt from Institutional Review Board approval.

Funding

The author reports no funding.

Footnotes

Acknowledgments

The author has no acknowledgments.

Conflict of interest

Given his role as an Editorial Board Member, Richard W. Bohannon had no involvement nor access to information regarding the peer review of this article.

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Correlation between the strength of muscle actions of the paretic lower-limb and gait speed after stroke: Results of a meta-analysis of six studies

Abstract

BACKROUND AND OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

Table 1 Summary statistics of articles describing the relationship between the strength of 6 paretic lower limb muscle actions and comfortable gait speed

3. Results

4. Discussion

Ethical considerations

Funding

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Summary statistics of articles describing the relationship between the strength of 6 paretic lower limb muscle actions and comfortable gait speed