Estimating the accuracy of muscle response testing: two randomised-order blinded studies

Abstract

Background: Manual muscle testing (MMT) is a non-invasive assessment tool used by a variety of health care providers to evaluate neuromusculoskeletal integrity, and muscular strength in particular. In one form of MMT called muscle response testing (MRT), muscles are said to be tested, not to evaluate muscular strength, but neural control. One established, but insufficiently validated, application of MRT is to assess a patient's response to semantic stimuli (e.g. spoken lies) during a therapy session. Our primary aim was to estimate the accuracy of MRT to distinguish false from true spoken statements, in randomised and blinded experiments. A secondary aim was to compare MRT accuracy to the accuracy when practitioners used only their intuition to differentiate false from true spoken statements.

Methods: Two prospective studies of diagnostic test accuracy using MRT to detect lies are presented. A true positive MRT test was one that resulted in a subjective weakening of the muscle following a lie, and a true negative was one that did not result in a subjective weakening of the muscle following a truth. Experiment 2 replicated Experiment 1 using a simplified methodology. In Experiment 1, 48 practitioners were paired with 48 MRT-naïve test patients, forming unique practitioner-test patient pairs. Practitioners were enrolled with any amount of MRT experience. In Experiment 2, 20 unique pairs were enrolled, with test patients being a mix of MRT-naïve and not-MRT-naïve. The primary index test was MRT. A secondary index test was also enacted in which the practitioners made intuitive guesses ("intuition"), without using MRT. The actual verity of the spoken statement was compared to the outcome of both index tests (MRT and Intuition) and their mean overall fractions correct were calculated and reported as mean accuracies.

Results: In Experiment 1, MRT accuracy, 0.659 (95% CI 0.623 - 0.695), was found to be significantly different (p < 0.01) from intuition accuracy, 0.474 (95% CI 0.449 - 0.500), and also from the likelihood of chance (0.500; p < 0.01). Experiment 2 replicated the findings of Experiment 1. Testing for various factors that may have influenced MRT accuracy failed to detect any correlations.

Conclusions: MRT has repeatedly demonstrated significant accuracy for distinguishing lies from truths, compared to both intuition and chance. The primary limitation of this study is its lack of generalisability to other applications of MRT and to MMT.

Study registration: The Australian New Zealand Clinical Trials Registry (ANZCTR; www.anzctr.org.au ; ID # ACTRN12609000455268 , and US-based ClinicalTrials.gov (ID # NCT01066312 ).

Keywords: Kinesiology; Lie detection; Muscle weakness; Sensitivity; Specificity.

Figures

Fig. 1

An example of a practitioner performing MRT using a patient's right deltoid muscle

Fig. 2

Testing Scenario Layout: a Experiment 1. The Test Patient (TP; red) viewed a monitor (also red) which the Practitioner could not see, had an ear piece in his ear through which he received instructions, and used a mouse to advance his computer to the next picture/statement. The Practitioner (blue) also viewed a monitor (also blue) which the Test Patient could not see and entered his results on a keyboard. Note that the Practitioner was presented with the same picture as the Test Patient or a blank, black screen. Also note that the Principal Investigator (PI) was present in the room and observing during all assessments. b Experiment 2. The TP (red) viewed a monitor (also red) which the Practitioner could not see, had an ear piece in his ear through which he received instructions, and used a mouse to advance his computer to the next picture/statement. In this Experiment, the Practitioner did not view a monitor, and still entered his results on a keyboard. Note that the Principal Investigator (PI) was absent during this Experiment