Associations between gait and isometric lower limb strength following stroke

Abstract

Stroke is a leading cause of disability worldwide. The most commonly stated goal following stroke is to regain the ability to walk independently, resulting in a large amount of rehabilitation time focussed on gait retraining. Identification of key variables that relate to and affect gait function is important in order to understand the factors associated with impaired gait and to guide future intervention strategies. Reduced muscle strength has been proposed as a key contributor to physical limitations after stroke and is commonly assessed in clinical and research settings. The aim of this thesis was to examine the associations between lower limb isometric strength and gait following stroke. A systematic literature review was conducted for Study One in order to collate the results of previous research which reported on the correlations between muscle strength and gait velocity following stroke. The review identified 21 articles that had examined this association with varied results. The majority of the identified studies had a small sample size (n ≤ 30) and received low scores for methodological quality. The studies with a larger sample size and methodological quality revealed a trend which suggested the strength of the ankle dorsiflexors provides the strongest bivariate association with gait velocity. Due to the limitations of the included studies, further research is needed. Another important consideration of muscle function is not only the peak amount of force a muscle group can produce (muscle strength) but how quickly force can be produced (muscle power). The second study of this thesis examined the psychometric properties of a clinically accessible device, hand-held dynamometry, for assessment of isometric muscle strength and power. The results from Study Two showed that hand-held dynamometry demonstrated acceptable reliability across eight lower limb muscle groups for the assessment of isometric strength and power in a healthy and unimpaired cohort. Concurrent validity of hand-held dynamometry also demonstrated acceptable results for the majority of lower limb muscle groups when compared against a laboratory-based fixed dynamometer. The muscle groups of the ankle were found to have lower than expected validity, however this may be due to the ankle attachment used on the fixed dynamometer, which demonstrated larger measurement error. Nevertheless, hand-held dynamometry has shown promising results for assessment of strength and power for the muscles of the lower limb in a sample of adults without impairments. To expand on the results of the systematic review (Study One), Study Three provided a detailed analysis of the relationships between isometric strength and gait velocity following stroke, as well as examining a previously underutilised outcome measure in the stroke population, isometric muscle power. Study Three was undertaken to examine if isometric power provided additional value in the relationship with gait velocity over muscle strength and to determine which muscle group of the lower limb demonstrates the strongest relationship with gait velocity. Results revealed isometric strength provided significant additional value in the relationship with gait velocity over isometric power. Comparison of seven lower limb muscle groups revealed the strength of the ankle plantarflexors and hip flexors to explain the most variance in gait velocity. The final study of this thesis (Study Four) examined the relationship between isometric measures of strength and power, assessed with hand-held dynamometry, and joint power generation during gait following stroke. Ankle plantarflexor strength and power showed a significant relationship with peak ankle joint power generation during gait. Similar to Study Three, comparison between strength and power revealed ankle plantarflexor strength had a stronger relationship over ankle plantarflexor power. The program of research presented in this thesis found hand-held dynamometry provided psychometrically-sound measures of isometric strength and power. The relationship between hand-held dynamometry derived measures of strength and power with gait function revealed isometric strength provided additional value over isometric power. The strength of the ankle plantarflexors demonstrated a strong relationship with gait velocity and ankle power generation during gait. Future research may examine the ankle plantarflexors further to see if improved plantarflexor strength results in improved gait function following stroke. This thesis provides a substantial contribution to the knowledge in this field and may assist clinical decision making when considering gait function post-stroke as well as guiding future research in the design of intervention strategies aimed at improving gait.