Objectives: Speckle tracking analysis (STA) of ultrasound (US) images quantifies the longitudinal deformation of a region of muscle tissue to provide a mechanical measure of muscle activity. As the validity and reliability of this method has not yet been adequately assessed, the aim of this study was to determine the validity and reliability of STA in the dorsal neck muscles during isometric neck extension contractions.
Methods: Twenty volunteers performed 3 repetitions of isometric neck extension in a dynamometer at 10%, 20%, 40%, 60%, and 80% of maximal voluntary torque while US and surface electromyography (EMG) data were recorded. Speckle tracking analysis was then used to calculate measurements of muscle deformation. The relationship among torque, muscle deformation (separate for each muscle and summed), and EMG was evaluated using linear regressions and Spearman's correlation coefficients. The reliability of EMG and muscle deformation was determined using intraclass correlation coefficients (ICCs).
Results: Muscle deformation in 4 of the 5 muscles when examined separately and collectively was significantly related to torque (P < .05); however, the relationship was weak (r2 = 0.03-0.18). In contrast, a strong linear relationship was observed between torque and EMG (P < .001, r2 = 0.83). Poor to moderate reliability of muscle deformation measures (ICC: 0.02-0.69) was found compared with EMG, which was highly reliable (ICC: 0.67-0.90).
Conclusion: These results suggest that the validity of US STA measurements for isometric contractions of the dorsal neck muscles is questionable. Further investigation into this method is required before it can be used as a tool to measure muscle activity.
Author keywords: Reproducibility of Results
Author affiliations: KFM: National Health and Medical Research Council Centres for Clinical Research Excellence (Spinal Pain, Injury, and Health), The University of Queensland, Brisbane, Australia; School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Australia; SPO: School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Australia; Department of Physiotherapy, Royal Brisbane and Women's Hospital, Queensland Health, Queensland, Australia; KJT: University of Queensland, School of Biomedical Sciences, University of Queensland, Australia; SMM: Clinical Informatics Directorate, Metro South Health, Brisbane, Australia; Australian Centre for Health Services Innovation and Centre for Healthcare Transformation, School of Public Health & Social Work, Queensland University of Technology, Brisbane, Australia; AP: National Health and Medical Research Council Centres for Clinical Research Excellence (Spinal Pain, Injury, and Health), The University of Queensland, Brisbane, Australia; Department of Health, Medicine and Caring Sciences, Physiotherapy, Linköping University, Linköping, Sweden
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