PSYCHOMETRIC PROPERTIES OF HAND-HELD DYNAMOMETRY FOR THE MEASUREMENT OF TRUNK MUSCLE STRENGTH IN PEOPLE WITH CHRONIC LOW BACK PAIN

Abstract

Low back pain, a common source of morbidity and the leading cause of disability, not only affects physical ability but can have a tremendous impact on patients' psychological and social well-being. People with chronic low back pain (CLBP) often present with reduced range of motion, increased fatigue, changes in muscle activation, in addition to decreased trunk muscle strength. Trunk muscle strength is one of the most frequently evaluated outcome measures in CLBP research and is measured using isokinetic dynamometry as the gold standard. However, owing to the cost and operational complexity associated with isokinetic dynamometry measurements, more portable and clinically feasible tools are needed. The overarching aim of this thesis is to comprehensively investigate the measurement properties of the hand-held dynamometer (HHD) to evaluate trunk muscle strength and to explore the influence of multiple outcomes on trunk isometric strength variability. Three studies were undertaken to address each specific aim of this thesis. The first study (systematic review), aimed to explore the measurement properties (reliability, validity, and responsiveness) of current practicable performance-based outcome measures (PerFOMs) of trunk muscle strength. The results of the systematic review found few studies that investigated the reliability and validity of practicable PerFOMs in people with CLBP and a lack of studies exploring the responsiveness of these measures. Overall, the evidence was of very low quality. The second study aimed to examine the intra-rater reliability (within-day and between-days) and criterion validity of HHD for assessing trunk strength in people with CLBP and asymptomatic individuals. In this study, good to excellent intra-rater reliability was observed for people with CLBP and asymptomatic individuals for the measurements of trunk flexion, extension, and rotation strength. In addition, the HHD measurements moderately correlated with trunk strength measured using a isokinetic dynamometer, indicating adequate criterion validity. Building on these findings, the third study i aimed to investigate the responsiveness of HHD to detect changes in trunk strength following 6- weeks of progressive resistance exercises in people with CLBP. The findings suggested that HHD has adequate internal responsiveness, however, inadequate external responsiveness was reported as indicated by the poor correlation between measures using the HHD and an isokinetic dynamometer. The fourth study was an exploratory study, which evaluated the influence of several demographics, patient-reported and performance-based outcome variables on trunk isometric flexion and extension strength variability. Findings supported the major influence of gender, physical function level and performance-based outcomes including baseline strength and muscle activity, on isometric trunk strength variability. In conclusion, as a portable, easy-to-use tool for obtaining objective measurements, this thesis has determined that hand-held dynamometry is a reliable and valid assessment tool for trunk muscle strength measurement in people with CLBP. In this thesis, it was shown that a HHD can be used to detect changes in trunk strength following 6 weeks of strength training (internal responsiveness), however, future work needs to focus on examining the external responsiveness of the HHD to facilitate it is clinical applicability to monitor change in trunk strength in people with CLBP.