Differing Characteristics of Human-Shaped Visual Stimuli Affect Clinicians' Dosage of a Spinal Manipulative Thrust on a Low-Fidelity Model: A Cross-Sectional Study.

OBJECTIVE: The purpose of this study was to determine whether chiropractic clinicians modulate spinal manipulation (SM) thrust characteristics based on visual perception of simulated human silhouette attributes. METHODS: We performed a cross-sectional within-participant design with 8 experienced chiropractors. During each trial, participants observed a human-shaped life-sized silhouette of a mock patient and delivered an SM thrust on a low-fidelity thoracic spine model based on their visual perception. Silhouettes varied on the following 3 factors: apparent sex (male or female silhouette), height (short, average, tall), and body mass index (BMI) (underweight, healthy, obese). Each combination was presented 6 times for a total of 108 trials in random order. Outcome measures included peak thrust force, thrust duration, peak preload force, peak acceleration, time to peak acceleration, and rate of force application. A 3-way repeated measures analysis of variance model was used to for each variable, followed by Tukey's honestly significant difference on significant interactions. RESULTS: Peak thrust force was reduced when apparent sex of the presented silhouette was female (F1,7 = 5.70, P = .048). Thrust duration was largely invariant, except that a BMI by height interaction revealed a longer duration occurred for healthy tall participants than healthy short participants (F4,28 = 4.34, P = .007). Compared to an image depicting obese BMI, an image appearing underweight lead to reduced peak acceleration (F2,5 = 6.756, P = .009). Clinician time to peak acceleration was reduced in short compared to tall silhouettes (t7 = 2.20, P = .032). CONCLUSION: Visual perception of simulated human silhouette attributes, including apparent sex, height, and BMI, influenced SM dose characteristics through both kinetic and kinematic measures. The results suggest that visual information from mock patients affects the decision-making of chiropractic clinicians delivering SM thrusts.

Tactile Perception of Pressure and Volitional Thrust Intensity Modulate Spinal Manipulation Dose Characteristics.

OBJECTIVE: The purpose of this study was to examine clinicians' ability to modulate spinal manipulation (SM) thrust characteristics based on their tactile perception of pressure and volitional intensity. METHODS: In a cross-sectional, within-participants design, 13 doctors of chiropractic delivered SM thrusts of perceived least, appropriate, or greatest intensity of their perceived safe output level for an SM thrust on low-fidelity thoracic spine models of 4 different pressure levels. The participants performed SM over the course of 96 trials in a randomized order on combinations of thrust intensity and pressure. Dependent variables included normalized preload force, thrust force, thrust duration, peak acceleration, time to peak acceleration, and displacement. For all dependent measures, 2-factor within-participants analysis of variance models with repeated measures on both factors were performed. RESULTS: Preload force increased with intensity (F2,24 = 9.72; P < .001) and model pressure (F3,36 = 4.27; P = .011). Participants modulated thrust force and displacement as each also increased with intensity escalation (F2,24 = 22.53, P < .001; F2,18 = 45.20, P < .001). The highest accelerations were observed during the greatest intensity. Increased thrust force was delivered at higher model pressures (F3,36 = 6.43; P < .001). A significant interaction demonstrated that as volitional thrust intensity increased, greater displacement was attained, particularly on low pressure models (F6,54 = 11.06; P < .001). Thrust duration and time to peak acceleration yielded no significant differences. CONCLUSION: Spinal manipulation thrust dosage was modulated by the chiropractors' tactile perception of pressure and volitional intensity.

Acceleration of clinician hand movements during spinal manipulative therapy.

This study used an observational design to examine the kinematics of spinal manipulative therapy (SMT) by determining the acceleration characteristics of the manipulative input at the cervical, thoracic, and lumbar spinal regions. Studies of SMT have been restricted to measuring the forces that result from the manipulative input. Several studies have indicated the rate of force development is a key parameter of clinically delivered SMT. Despite this, the movement strategies employed during SMT, including acceleration, have not been directly measured. Participants (n = 29) were recruited from a private practice chiropractic clinic. A wireless accelerometer attached to the clinician's hand was used to characterize the thrust phase of the SMT treatments. Significant differences were found across each spinal region for acceleration amplitude parameters (p < 0.0001). Post-hoc analysis indicated that amplitudes significantly increased in order from thoracic to cervical to lumbar regions (p < 0.0001). Spinal level was also a significant factor in determining the temporal parameters of hand acceleration during SMT (p < 0.0005). This study provides a description of the acceleration properties of clinically delivered SMT. Consistent with that reported for SMT forces, acceleration amplitudes varied significantly across spinal regions with relatively little differences in acceleration latencies. Notably, acceleration amplitudes and latencies were not associated with each other within spinal regions. These findings indicate that changes in acceleration amplitude, rather than latency, are used to tailor SMT to individuals.