Elsevier

Journal of Biomechanics

Volume 75, 25 June 2018, Pages 171-175
Journal of Biomechanics

Short communication
Assessment of isometric muscle strength and rate of torque development with hand-held dynamometry: Test-retest reliability and relationship with gait velocity after stroke

https://doi.org/10.1016/j.jbiomech.2018.04.032Get rights and content

Abstract

Isometric rate of torque development examines how quickly force can be exerted and may resemble everyday task demands more closely than isometric strength. Rate of torque development may provide further insight into the relationship between muscle function and gait following stroke. Aims of this study were to examine the test-retest reliability of hand-held dynamometry to measure isometric rate of torque development following stroke, to examine associations between strength and rate of torque development, and to compare the relationships of strength and rate of torque development to gait velocity. Sixty-three post-stroke adults participated (60 years, 34 male). Gait velocity was assessed using the fast-paced 10 m walk test. Isometric strength and rate of torque development of seven lower-limb muscle groups were assessed with hand-held dynamometry. Intraclass correlation coefficients were calculated for reliability and Spearman’s rho correlations were calculated for associations. Regression analyses using partial F-tests were used to compare strength and rate of torque development in their relationship with gait velocity. Good to excellent reliability was shown for strength and rate of torque development (0.82–0.97). Strong associations were found between strength and rate of torque development (0.71–0.94). Despite high correlations between strength and rate of torque development, rate of torque development failed to provide significant value to regression models that already contained strength. Assessment of isometric rate of torque development with hand-held dynamometry is reliable following stroke, however isometric strength demonstrated greater relationships with gait velocity. Further research should examine the relationship between dynamic measures of muscle strength/torque and gait after stroke.

Introduction

Evidence suggests that muscle weakness is a key impairment limiting gait following stroke (Bohannon, 1989). Previous studies have examined the associations between maximal strength and gait velocity after stroke (Mentiplay et al., 2015a), however, there is limited evidence that strength training improves gait in neurological rehabilitation (Salter et al., 2016, Williams et al., 2014). Rate of torque development (RTD) is defined as the change in torque over change in time during an isometric contraction (Maffiuletti et al., 2016) and indicates how quickly muscles generate force. Compared with traditional measures of strength, RTD may provide greater insight into the relationship between weakness and gait velocity. Research in other clinical populations, such as those with cerebral palsy (Moreau et al., 2012), anterior cruciate ligament reconstruction (Pua et al., 2017) and knee osteoarthritis (Winters and Rudolph, 2014), has shown isometric RTD to provide larger associations compared to isometric strength with various measures of physical function including gait. One previous study in stroke found isometric RTD demonstrated a superior relationship with gait velocity compared to strength (Pohl et al., 2002). This study by Pohl et al. (2002) only assessed the knee extensors which are not prime movers during gait (Olney et al., 1991). The ankle plantar flexors are more affected compared to proximal muscle groups post-stroke (Adams et al., 1990), and provide the majority of power generation during gait (Winter, 1983). It is possible that the isometric RTD of other muscle groups, such as the plantar flexors, may demonstrate greater relationships with gait velocity compared to the knee extensors.

To aid clinical implementation, recent iterations of hand-held dynamometry (HHD) have allowed raw data to be exported and isometric RTD processed post-assessment. Good to excellent reliability and validity has been shown for isometric RTD measures assessed with HHD in a healthy cohort (Mentiplay et al., 2015b). Additionally, isometric strength assessed with HHD in neurological populations has shown excellent reliability (Bohannon, 1986, Riddle et al., 1989). However, the properties of HHD for assessment of RTD are currently unknown following stroke. Therefore, the aim of the current study was to firstly examine the test-retest reliability of isometric strength and RTD measures using HHD, secondly to examine the associations between measures of isometric strength and RTD, and thirdly to compare the relationships of muscle strength and RTD with gait velocity after stroke. Based on similar previous research in clinical cohorts, it was hypothesised that RTD would demonstrate greater relationships with gait velocity compared to muscle strength.

Section snippets

Participants

A convenience sample of adults 21 years or older were recruited from two major hospitals in Australia and Singapore. Inclusion criteria were: (1) confirmed stroke >3 months prior; and (2) ability to walk >10 m without gait aids or orthoses. Exclusion criteria were: (1) cerebellar stroke; (2) cognitive impairment; and (3) other diagnosed comorbidities that would impact physical participation. Ethics approval was obtained from the hospitals and all participants provided written informed consent.

Results

Characteristics of the 63 recruited participants are provided in Table 1.

Discussion

Assessment of isometric strength and RTD using HHD showed good to excellent test-retest reliability. Strong to very strong correlations were shown between isometric strength and RTD, indicating potential redundancy between measures (i.e. strength and RTD predicted each other easily). Both measures of strength and RTD provided significant predictive value to gait velocity over a covariates-only model. However, strength had significantly greater relationships with gait velocity compared to RTD.

Conflict of interest

The authors declare that they have no conflict of interest.

Acknowledgements

The authors wish to thank Ms Laura Di Nicolantonio and Dr Bok Chek Wai for their generous assistance in participant recruitment. This work was supported by an Endeavour Research Fellowship (author BFM), a National Health and Medical Research Council RD Wright Biomedical Fellowship (grant ID 1090415; author RAC), and a National Health and Medical Research Council Translating Research Into Practice Fellowship (grant ID 1110837; author GW). None of the funding bodies had any involvement in the

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