Muscle testing for lie detection: Grip strength dynamometry is inadequate

Abstract

Introduction: Although DMT is primarily used in the diagnosis of neuromusculoskeletal (NMS) disorders, previous studies have attempted to use other forms of manual muscle testing (MMT) to detect conditions other than NMS. For instance, muscle response testing (MRT) was used to distinguish lies (a known stressor) from truth. Therefore, it is hypothesised that DMT might be used to detect deceit as well, and the aim of this study was to investigate if grip strength via dynamometric muscle testing (DMT) could be used to distinguish lies from truth. Methods: A prospective study of diagnostic test accuracy was carried out. Twenty participants, aged 18-65 years, with healthy hands, were recruited. Participants were given a visual stimulus and followed an auditory instruction to lie or to tell the truth about the stimulus, before recording grip strength with a dynamometer. Testing proceeded in this manner until 20 DMTs were performed, 10 by each hand. We analysed the accuracy of grip strength for detecting lies. Results: The mean grip strength after true statements was found to be 24.9 kg (95% CI 20.3 to 29.6), and after false statements, 24.8 (95% CI 20.2 to 29.5), which were not statistically different (p=0.61). Conclusion: DMT via hand-held grip strength dynamometry failed to distinguish lies from truth. These results seem to suggest that strength as measured by DMT is not impacted by deceit. A limitation of this study is it is not generalisable to other types or applications of MMT or MRT or to other target conditions.

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Investigating the validity of muscle response testing: Blinding the patient using subliminal visual stimuli

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