Final Contacts Research Articles

Mobile Spatiotemporal Gait Segmentation Using an Ear-Worn Motion Sensor and Deep Learning.

Mobile health technologies enable continuous, quantitative assessment of mobility and gait in real-world environments, facilitating early diagnoses of gait disorders, disease progression monitoring, and prediction of adverse events like falls. Traditionally, mobile gait assessment predominantly relied on body-fixed sensors positioned at the feet or lower trunk. Here, we investigate the potential of an algorithm utilizing an ear-worn motion sensor for spatiotemporal segmentation of gait patterns. We collected 3D acceleration profiles from the ear-worn sensor during varied walking speeds in 53 healthy adults. Temporal convolutional networks were trained to detect stepping sequences and predict spatial relations between steps. The resulting algorithm, mEar, accurately detects initial and final ground contacts (F1 score of 99% and 91%, respectively). It enables the determination of temporal and spatial gait cycle characteristics (among others, stride time and stride length) with good to excellent validity at a precision sufficient to monitor clinically relevant changes in walking speed, stride-to-stride variability, and side asymmetry. This study highlights the ear as a viable site for monitoring gait and proposes its potential integration with in-ear vital-sign monitoring. Such integration offers a practical approach to comprehensive health monitoring and telemedical applications, by integrating multiple sensors in a single anatomical location.

Understanding the sintering behavior of AlCrFeNiTi high entropy alloy via phase field modeling illustration

In this study, a computational approach is employed to understand the densification behavior of a multi-component alloy system during the sintering process by generating a phase field modeling image. First, a single-phase body-centered cubic (BCC) AlCrFeNiTi high entropy alloy (HEA) is prepared via a mechanical alloying (MA) route, and the powder-processed HEA is shown to exhibit dual BCC phases after spark plasma sintering (SPS). Then, phase field modeling (PFM) is used to generate a generalized image and to understand densification behavior during the sintering process. The results indicate that bulk and grain-boundary diffusion take place during the early stage and grain growth of the powder particles starts when the particles interact with their adjacent grains. Subsequently, in the final sintering stage point contacts and necking were observed. This understanding has been presented based on the phase field simulation to explore the different stages of the sintering during the processing.

Ecological validity of a deep learning algorithm to detect gait events from real-life walking bouts in mobility-limiting diseases.

The clinical assessment of mobility, and walking specifically, is still mainly based on functional tests that lack ecological validity. Thanks to inertial measurement units (IMUs), gait analysis is shifting to unsupervised monitoring in naturalistic and unconstrained settings. However, the extraction of clinically relevant gait parameters from IMU data often depends on heuristics-based algorithms that rely on empirically determined thresholds. These were mainly validated on small cohorts in supervised settings. Here, a deep learning (DL) algorithm was developed and validated for gait event detection in a heterogeneous population of different mobility-limiting disease cohorts and a cohort of healthy adults. Participants wore pressure insoles and IMUs on both feet for 2.5 h in their habitual environment. The raw accelerometer and gyroscope data from both feet were used as input to a deep convolutional neural network, while reference timings for gait events were based on the combined IMU and pressure insoles data. The results showed a high-detection performance for initial contacts (ICs) (recall: 98%, precision: 96%) and final contacts (FCs) (recall: 99%, precision: 94%) and a maximum median time error of -0.02 s for ICs and 0.03 s for FCs. Subsequently derived temporal gait parameters were in good agreement with a pressure insoles-based reference with a maximum mean difference of 0.07, -0.07, and <0.01 s for stance, swing, and stride time, respectively. Thus, the DL algorithm is considered successful in detecting gait events in ecologically valid environments across different mobility-limiting diseases.

Asking about self-harm during risk assessment in psychosocial assessments in the emergency department: questions that facilitate and deter disclosure of self-harm.

Emergency departments are key settings for suicide prevention. Most people are deemed to be at no or low risk in final contacts before death. To micro-analyse how clinicians ask about suicidal ideation and/or self-harm in emergency department psychosocial assessments and how patients respond. Forty-six psychosocial assessments between mental health clinicians and people with suicidal ideation and/or self-harm were video-recorded. Verbal and non-verbal features of 55 question-answer sequences about self-harm thoughts and/or actions were micro-analysed using conversation analysis. Fisher's exact test was used to test the hypothesis that question type was associated with patient disclosure. (a) Eighty-four per cent of initial questions (N = 46/55) were closed yes/no questions about self-harm thoughts and/or feelings, plans to self-harm, potential for future self-harm, predicting risk of future self-harm and being okay or keeping safe. Patients disclosed minimal information in response to closed questions, whereas open questions elicited ambivalent and information rich responses. (b) All closed questions were leading, with 54% inviting no and 46% inviting yes. When patients were asked no-inviting questions, the disclosure rate was 8%, compared to 65% when asked yes-inviting questions (P < 0.05 Fisher's exact test). (c) Patients struggled to respond when asked to predict future self-harm or guarantee safety. (d) Half of closed questions had a narrow timeframe (e.g. at the moment, overnight) or were tied to possible discharge. Across assessments, there is a bias towards not uncovering thoughts and plans of self-harm through the cumulative effect of leading questions that invite a no response, their narrow timeframe and tying questions to possible discharge. Open questions, yes-inviting questions and asking how people feel about the future facilitate disclosure.

Estimation of running biomechanical parameters using magneto-inertial sensors: a preliminary investigation

Many runners perform training sessions outdoors and on varying surfaces (e.g., track, paved path, trail). Training surface has been shown to influence running spatiotemporal measures and stiffness [1]. However, applied research in understanding training surface influence has been limited by lack of robust methodology to capture biomechanics in-the-field. The increasing availability of wearable magneto- inertial sensors (MIMUs) is now making it possible to perform in-field assessment of running biomechanics [2]. Validation of new inertial-based methods is vital to widespread field use. In this study, we compared inertial-based methods for running biomechanical analysis and against gold-standard stereo-photogrammetric system (SP). Ten recreational male runners (age: 32.3 ± 10.0 years) were enrolled and asked to run on a treadmill at 14 km/hr for 8 trials lasting 6 minutes. We simulated changes in surface in a controlled lab setting by using 8 different footwear conditions. Participants were instrumented with MIMUs (mod: Opal v2, APDM, Portland, USA; fs=200 sample/s) attached on the pelvis (L5) and the instep of both feet, and retroreflective markers on heels, toes, and each MIMU (recorded with a 9-camera Vero system, Vicon, Oxford, UK; fs=200 sample/s). The estimated relevant biomechanical parameters included: stride/stance/swing duration, stride rate, vertical oscillations of the center of mass (CoM), and vertical/leg stiffness. Gait events (initial and final contacts) were estimated using a modified version of the MIMU-based method proposed by Benson et al. [2]. CoM vertical displacement was estimated as the vertical component of the L5 MIMU trajectory. Vertical and leg stiffness were computed starting from CoM displacement, stance interval, and swing interval [3]. For each participant and trial condition, errors with respect to SP were computed (80 values for each parameter) and root mean squared errors (RMSE) across participants and conditions were then calculated. In addition, a Bland-Altman analysis was used to quantify the agreement between MIMU and SP outcomes in terms of 50% limits of agreement interval (LoAI). Differences between MIMU-based and SP-based parameters over all the runners are reported in Table 1. Results showed high accuracy especially in the estimation of stride duration, stride rate and CoM vertical displacement. The level of uncertainty associated to each biomechanical variable, as provided by the LoAIs, can be used to detect differences in surface conditions (footwear conditions). Future analysis and development of field methods will investigate the influence of unconstrained movements (outdoor, no treadmill) in addition to varying surface conditions and the influence of running speed on inertial-based method accuracy.

Validation of temporal parameters within the skating sub-techniques when roller skiing on a treadmill, using inertial measurement units.

The aim of this study was to develop and validate a method using inertial measurements units (IMUs) to determine inner-cycle parameters (e.g., cycle, poles and skis contact, and swing time) and the main sub-techniques (i.e., G2, G3 and G4) in cross-country roller ski skating on a treadmill. The developed method is based on the detection of poles and skis initial and final contacts with the ground during the cyclic movements. Thirteen well-trained athletes skied at different combinations of speed (6–24 km∙h-1) and incline (2–14%) on a treadmill using the three different sub-techniques. They were equipped with IMUs attached to their wrists and skis. Their movements were tracked using reflective markers and a multiple camera infrared system. The IMU-based method was able to detect more than 99% of the temporal events. It calculated the inner-cycle temporal parameters with a precision ranging from 19 to 66 ms, corresponding to 3.0% to 7.8% of the corresponding inner-cycle duration. The obtained precision would likely allow differentiation of skiers on different performance levels and detection of technique changes due to fatigue. Overall, this laboratory validation provides interesting possibilities also for outdoor applications.

A Deep Learning Approach for Gait Event Detection from a Single Shank-Worn IMU: Validation in Healthy and Neurological Cohorts.

Many algorithms use 3D accelerometer and/or gyroscope data from inertial measurement unit (IMU) sensors to detect gait events (i.e., initial and final foot contact). However, these algorithms often require knowledge about sensor orientation and use empirically derived thresholds. As alignment cannot always be controlled for in ambulatory assessments, methods are needed that require little knowledge on sensor location and orientation, e.g., a convolutional neural network-based deep learning model. Therefore, 157 participants from healthy and neurologically diseased cohorts walked 5 m distances at slow, preferred, and fast walking speed, while data were collected from IMUs on the left and right ankle and shank. Gait events were detected and stride parameters were extracted using a deep learning model and an optoelectronic motion capture (OMC) system for reference. The deep learning model consisted of convolutional layers using dilated convolutions, followed by two independent fully connected layers to predict whether a time step corresponded to the event of initial contact (IC) or final contact (FC), respectively. Results showed a high detection rate for both initial and final contacts across sensor locations (recall , precision ). Time agreement was excellent as witnessed from the median time error (0.005 s) and corresponding inter-quartile range (0.020 s). The extracted stride-specific parameters were in good agreement with parameters derived from the OMC system (maximum mean difference 0.003 s and corresponding maximum limits of agreement (−0.049 s, 0.051 s) for a confidence level). Thus, the deep learning approach was considered a valid approach for detecting gait events and extracting stride-specific parameters with little knowledge on exact IMU location and orientation in conditions with and without walking pathologies due to neurological diseases.

A method for gait events detection based on low spatial resolution pressure insoles data

The accurate identification of initial and final foot contacts is a crucial prerequisite for obtaining a reliable estimation of spatio-temporal parameters of gait. Well-accepted gold standard techniques in this field are force platforms and instrumented walkways, which provide a direct measure of the foot–ground reaction forces. Nonetheless, these tools are expensive, non-portable and restrict the analysis to laboratory settings. Instrumented insoles with a reduced number of pressure sensing elements might overcome these limitations, but a suitable method for gait events identification has not been adopted yet. The aim of this paper was to present and validate a method aiming at filling such void, as applied to a system including two insoles with 16 pressure sensing elements (element area = 310 mm2), sampling at 100 Hz. Gait events were identified exploiting the sensor redundancy and a cluster-based strategy. The method was tested in the laboratory against force platforms on nine healthy subjects for a total of 801 initial and final contacts. Initial and final contacts were detected with low average errors of (about 20 ms and 10 ms, respectively). Similarly, the errors in estimating stance duration and step duration averaged 20 ms and <10 ms, respectively. By selecting appropriate thresholds, the method may be easily applied to other pressure insoles featuring similar requirements.

How early should you brake during a 180° turn? A kinetic comparison of the antepenultimate, penultimate, and final foot contacts during a 505 change of direction speed test

ABSTRACT The aim of the study was to compare ground reaction force (GRF) characteristics between the antepenultimate foot contact (APFC), penultimate foot contact (PFC), and final foot contact (FFC), and to examine the relationships between APFC, PFC, and FFC GRF characteristics with 505 change of direction (COD) speed performance. Twenty university male soccer players performed three COD trials, whereby GRFs were collected over the aforementioned foot contacts. Greater peak braking forces in shorter ground contact times were demonstrated over the APFC compared to the PFC and FFC (p ≤ 0.011, d = 0.96–7.82), while APFC mean GRFs were greater than the PFC (p ≤ 0.001, d = 1.86–7.57). Faster 505 performance was associated with greater APFC peak and mean vertical, horizontal, and resultant braking GRFs (r2 = 21.6–54.5%), greater FFC mean HGRFs (r2 = 38.8%), more horizontally orientated peak resultant APFC and PFC GRFs (r2 = 22.8–55.4%), and greater APFC, PFC, and FFC mean horizontal to vertical GRF ratios (r2 = 32.0–61.9%). Overall, the APFC plays a more pivotal role in facilitating deceleration compared to the PFC for effective 505 performance. Practitioners should develop their athletes’ technical ability to express force horizontally across all foot contacts and coach braking strategies that emphasise greater magnitudes of posteriorly directed APFC GRFs to facilitate faster 505 performance.

Male and female soccer players exhibit different knee joint mechanics during pre-planned change of direction

ABSTRACT Change of direction manoeuvres is important in soccer and associated with non-contact anterior cruciate ligament injury, yet it is not known how the mechanics differentiate between males and females during 180° turns. Twenty-eight soccer players (14 males and 14 females) performed 180° turns with ground reaction forces collected over penultimate and final contacts. A two-way (contact × limb) multivariate analysis of variance (MANOVA) were run to examine differences between contact (penultimate and final) or limb (dominant and non-dominant) for sagittal plane hip, knee and ankle peak angles and moments, and frontal plane knee abduction moments and angles between sexes. Average horizontal GRF was increased on the dominant limb, compared to non-dominant and for the final contact compared to the penultimate contact. Knee abduction angles were increased in females compared to males, while the opposite was true for knee abduction moments. Statistically significant differences were evident, with increases in peak vertical GRF, peak hip flexion angle, peak knee flexion angle, peak knee extensor moment, and peak ankle dorsiflexion angle observed in the penultimate contact compared to final contact. The results indicate the penultimate contact during turns helps reduce loading on the final contact, yet male and female soccer players exhibit different knee joint mechanics during pre-planned change of direction.

Effect of Asymmetry on Biomechanical Characteristics During 180° Change of Direction.

Thomas, C, Dos'Santos, T, Comfort, P, and Jones, PA. Effect of asymmetry on biomechanical characteristics during 180° change of direction. J Strength Cond Res 34(5): 1297-1306, 2020-The aim of this study was to explore the effect of asymmetry on biomechanical characteristics during two 180° change of direction (CoD) tasks (505 and modified 505 [505mod]). Fifty-two male (n = 24; age = 22.1 ± 4.8 years; height = 1.78 ± 0.06 m; body mass = 76.9 ± 10.8 kg) and female (n = 28; age = 19.1 ± 1.7 years; height = 1.67 ± 0.06 m; body mass = 60.4 ± 7.4 kg) team-sport players were recruited for this investigation. Three-dimensional motion data using 10 Qualisys Oqus 7 infrared cameras (240 Hz) and ground reaction force (GRF) data from 2 AMTI force platforms (1,200 Hz) were collected to analyze penultimate contacts (PEN) and final foot contacts. A series of repeated-measures analysis of variance were used to examine for differences in each dependent variable. Significant differences existed between dominant (D) and nondominant (ND) limbs for knee abduction angle (KAA) during 505mod (p = 0.048), while significant differences existed for peak horizontal and vertical GRF (vGRF) (p < 0.001) during 505. For both tasks, the PEN involved significantly greater peak vGRF, hip flexion angles, hip extensor moments, knee flexion angles, and knee extensor moments, but lower average vGRF, horizontal GRF, and peak ankle extensor moments. For 505, the ND limb involved significantly greater peak vGRF, but the opposite was revealed for peak horizontal GRF. For 505mod, the D limb involved significantly greater KAAs. Finally, there was a significant interaction (group × limb) for peak horizontal GRF ratio during 505. For both tasks, there was no interaction or main effects for time to completion. Therefore, it appears asymmetry influences GRFs and KAAs, but not completion time during 180° CoD in team-sport players.

Deep Learning Techniques for Improving Digital Gait Segmentation.

Wearable technology for the automatic detection of gait events has recently gained growing interest, enabling advanced analyses that were previously limited to specialist centres and equipment (e.g., instrumented walkway). In this study, we present a novel method based on dilated convolutions for an accurate detection of gait events (initial and final foot contacts) from wearable inertial sensors. A rich dataset has been used to validate the method, featuring 71 people with Parkinson's disease (PD) and 67 healthy control subjects. Multiple sensors have been considered, one located on the fifth lumbar vertebrae and two on the ankles. The aims of this study were: (i) to apply deep learning (DL) techniques on wearable sensor data for gait segmentation and quantification in older adults and in people with PD; (ii) to validate the proposed technique for measuring gait against traditional gold standard laboratory reference and a widely used algorithm based on wavelet transforms (WT); (iii) to assess the performance of DL methods in assessing high-level gait characteristics, with focus on stride, stance and swing related features. The results showed a high reliability of the proposed approach, which achieves temporal errors considerably smaller than WT, in particular for the detection of final contacts, with an inter-quartile range below 70 ms in the worst case. This study showes encouraging results, and paves the road for further research, addressing the effectiveness and the generalization of data-driven learning systems for accurate event detection in challenging conditions.

Direct Observation of Activated Kinetics and Downhill Dynamics in DNA Dehybridization.

We have studied two model DNA oligonucleotide sequences that display contrasting degrees of heterogeneous melting using an optical temperature jump to trigger dehybridization and a nonlinear infrared (IR) spectroscopy probe to track the response of the helix ensemble. This approach offers base-sensitive structural insight through the unique vibrational fingerprint characteristic of each nucleobase as well as time resolution capable of following unfolding across nanoseconds to milliseconds. We observe predissociation unzipping of the helical termini, loss of final dimer contacts, and rehybridization of the dissociated strands all in a single measurement. Complete dissociation of the dimer is found to be well described by Arrhenius kinetics for both sequences, with dissociation barriers in the range of 160-190 kJ/mol. A sequence with terminal adenine-thymine (AT) base pairs and a guanine-cytosine core returns a large-amplitude fast response ranging from 70 to 170 ns, originating only from the AT base pairs. Variable temperature jump ( T-jump) experiments in which the final temperature ( Tf) is fixed and the initial temperature ( Ti) is varied such that different starting ensembles all evolve on the same final free-energy surface were employed to explore the features of the underlying potential that dictates hybridization. These experiments reveal that the unzipping of the AT termini is an essentially barrierless process and that both activated and downhill events are necessary to describe the dehybridization mechanism. Although our results are largely consistent with the classic nucleation-zipper picture, new insights regarding the nature of base pair zippering refine the mechanistic details of the fastest DNA hybridization dynamics.

Accuracy, sensitivity and robustness of five different methods for the estimation of gait temporal parameters using a single inertial sensor mounted on the lower trunk

In the last decade, various methods for the estimation of gait events and temporal parameters from the acceleration signals of a single inertial measurement unit (IMU) mounted at waist level have been proposed. Despite the growing interest for such methodologies, a thorough comparative analysis of methods with regards to number of extra and missed events, accuracy and robustness to IMU location is still missing in the literature. The aim of this work was to fill this gap. Five methods have been tested on single IMU data acquired from fourteen healthy subjects walking while being recorded by a stereo-photogrammetric system and two force platforms. The sensitivity in detecting initial and final contacts varied between 81% and 100% across methods, whereas the positive predictive values ranged between 94% and 100%. For all tested methods, stride and step time estimates were obtained; three of the selected methods also allowed estimation of stance, swing and double support time. Results showed that the accuracy in estimating step and stride durations was acceptable for all methods. Conversely, a statistical difference was found in the error in estimating stance, swing and double support time, due to the larger errors in the final contact determination. Except for one method, the IMU positioning on the lower trunk did not represent a critical factor for the estimation of gait temporal parameters. Results obtained in this study may not be applicable to pathologic gait.

Comparison of the effects of modified and full-coverage thermoplastic retainers on occlusal contacts

The purpose of this prospective study was to determine the number of contacts in centric occlusion during retention with modified and full-coverage thermoplastic Essix retainers. This research was based on 36 patients who were randomly assigned to wear either modified (18 patients) or full-coverage (18 patients) Essix retainers. Silicone-based bite registrations were used to record occlusal contacts at the beginning (T1), end of full-time (6 months; T2), and end of night-time (3 months; T3) wear of retainers. The occlusal contacts determined in treated patients were compared with the values of 18 untreated "normal" Class I subjects. Bonferroni-adjusted Wilcoxon and Kruskal-Wallis tests were used to evaluate intra- and intergroup differences. Total posterior contacts increased significantly at T3 compared to T1 and T2 only in the modified Essix group. Non-ideal and total contacts on premolars, non- ideal and actual contacts on first molars, and actual contacts on second molars increased significantly at T3 in the modified Essix group. No significant increase was determined in the final total posterior contacts in the full-coverage Essix group. Actual contacts on premolars and first molars and total posterior actual contacts were significantly greater at T3 in the modified Essix group compared to the full-coverage Essix Group. Also the number of final posterior ideal contacts in the modified Essix group was greater than in the normal sample. Total anterior contacts decreased significantly in the modified Essix group, whereas they increased significantly in the full-coverage Essix group. Increase in posterior contacts was achieved only during night-time wear of modified Essix retainers.

The influence of intraoperative microelectrode recordings and clinical testing on the location of final stimulation sites in deep brain stimulation for Parkinson’s disease

The goal of our study was to investigate the influence of intraoperative microelectrode recordings and clinical testing on the location of the final stimulation site in deep brain stimulation in Parkinson's disease. In 22 patients with Parkinson's disease we compared magnetic resonance imaging (MRI)-based and atlas-based targets with the adjusted stimulation sites after intraoperative, multitrack microelectrode recording (MER) and intraoperative and postoperative clinical testing. The investigation included 176 target/stimulation sites in 44 subthalamic nuclei (STNs), which were related to a standardised three-dimensional, MRI-defined STN. Atlas-based targets were positioned more superior and more medial than the MRI-based targets, which were located in the centre of the MRI-STN. The optimal stimulation sites, found intraoperatively after MER and clinical testing, were located more lateral and slightly more superior than both planned targets. In the majority of the cases the location of the active contact was the most superior and most lateral of all target sites. The differences in the distributions of those four targets reached statistical significance. However, final active contacts were distributed throughout the MRI-defined STN and its immediate surroundings. The adoption of microelectrode recordings and extensive clinical testing allows the adjustment of anatomical targeting even to unexpected stimulation sites in and around the MRI-defined STN.

An enhanced estimate of initial contact and final contact instants of time using lower trunk inertial sensor data

This study introduces a new method of extracting initial and final contact gait time events from vertical acceleration, measured with one waist mounted inertial measurement unit, by means of continuous wavelet transforms. The method was validated on 18 young healthy subjects and compared to two others available in the literature. Of the three methods investigated, the new one was the most accurate at identifying the existence and timing of initial and final contacts with the ground, with an average error of 0.02±0.02s and 0.03±0.03s (approximately 2% and 3% of mean stride duration), respectively.

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Impact of a 12-month exercise program on the temporal parameters of the foot rollover during walking in postmenopausal women

A randomized controlled trial was undertaken to determine the impact of a 12-month exercise program on the temporal characteristics of the foot rollover during walking, based on plantar pressure data. One hundred twenty one postmenopausal women aged 41 to 77 years comprised the sample and were randomly recruited from the community. Exercise and control women were tested before and at the end of the trial. The temporal characteristics were assessed with the women walking barefoot at a self-selected speed over a 9-meter-long walking track having a built-in pressure platform. The initial and final contacts at the lateral and medial heel, metatarsal heads I to V, and the hallux (medial and lateral) were measured. Women from the exercise group presented a latter time of making contact in the relative metatarsal 4, metatarsal 5 (absolute and relative), and medial heel (absolute and relative) and earlier relative initial contact in toe 1. In the modification rates, postmenopausal women from the exercise group presented (1) latter final contact (absolute and relative) in metatarsal 5, (2) latter relative final contact in metatarsal 4, and (3) earlier relative initial contact in toe 1. Postmenopausal women from the control group presented an earlier initial contact in metatarsal 3 (absolute and relative). Repeated-measures analysis of variance demonstrated a time effect in most variables considered. The exercise program is effective in improving the gait pattern in postmenopausal women who adhere, and time has the main effect.

Effect of experimental jaw muscle pain on occlusal contacts

The aim of the study was measuring the effect of experimental jaw muscle pain on number and position of posterior occlusal contacts. Eleven adult voluntary subjects were enrolled. A lower impression was taken for each subject and two dental casts were obtained from each impression. The study was carried out in a randomised cross-over fashion. Each subject participated in two experimental sessions (30-day interval) in which he/she received an injection in the central part of the right masseter muscle consisting of 0·5 mL of either hypertonic or isotonic saline. Each subject was asked to rate pain intensity on a visual analogue scale. Three occlusal bite checks (polyvinylsiloxane) at the maximal intercuspal position were obtained during the experimental session: the first before the injection, the second between 60 and 90 s after the injection and the third 15 min after the injection. Evaluation of contacts was performed on dental casts with the use of different colours (black for baseline, red for intermediate and green for final contacts). Repeated-measures analysis of variance was used to compare the overall number of contacts among groups and the number of contacts of different colours. No significant difference was found between the overall number of occlusal contacts (P>0·05), but significant differences were found between contacts according to different colours: confirmed (P=0·006), disappeared (P=0·007) and new (P<0·001). Assuming different colours as change in contact position, the overall number of contacts did not change, but the position did. Experimentally induced jaw muscle pain affected the pattern of posterior occlusal contacts.