The concurrent validity and intrarater reliability of a hand-held dynamometer for the assessment of neck strength in semi-professional rugby union players.

OBJECTIVES: The main objective of this study was to determine the concurrent validity between a hand-held (HHD) and mounted hand-held dynamometer (MHHD) for assessing isometric neck strength. DESIGN: Observational design. SETTING: Semiprofessional rugby club. PARTICIPANTS: Nineteen semi-professional rugby players (age = 26 ± 5 years, stature = 186.5 ± 6.5 cm, body mass = 98.7 ± 12.8 kg). MAIN OUTCOME MEASURES: Concurrent validity (limits of agreement, correlation) between HHD and MHHD, the intrarater reliability (intra-class correlation, ICC) and comparison between playing positions. RESULTS: Absolute peak and mean peak force were systematically lower when using the HHD compared to MHHD, with the mean bias ranging from -1.8 to -3.8 kgf (P < 0.05). Differences were not evident for flexion when applying the correction equations (-0.5 to 2.1 kgf, P > 0.05) but remained for extension. Correlations between methods were large-to-very large; the ICCs for both methods were good (ICC = 0.72-0.89), with no difference between positions (P < 0.05). CONCLUSION: The concurrent validity of HHD was considered acceptable when compared to the MHHD and the correction equation applied. Both methods are reliable and useful for assessing neck strength in rugby players, though, caution is needed when determining strength during neck extension.

Assessment of Interrater and Intrarater Reliability of Cervical Range of Motion (CROM) Goniometer.

PURPOSE: The current study was designed to assess interrater and intrarater validity of cervical range of motion measurements performed with a CROM goniometer. Material and Methods. The study involved 95 healthy university students (31 males and 64 females) aged 20-24 years. Two examiners performed measurements of cervical range of motion using a CROM goniometer. The same subjects were examined again after two weeks, in the same conditions. The results acquired by one rater during the first and the second examination were compared for reproducibility, while the results obtained by the two examiners were compared to assess validity and reliability of the tool. Cronbach's alpha was applied to determine intrarater reliability, and the values of correlations were used to assess the interrater agreement. RESULTS: Analysis of the results showed both intrarater and interrater agreement in all the measures of cervical range of motion. The highest intrarater and interrater concordance was observed in the measure of extension. Intrarater agreement for Examiner 1 was reflected by Cronbach's alpha = 0.85, and for Examiner 2 by Cronbach's alpha = 0.89. As for the interrater agreement in the measure of extension, the value of correlation in both the first and the second measurement amounted to r = 0.89. CONCLUSIONS: Measurements performed with the CROM goniometer show interrater and intrarater agreement in assessments of cervical range of motion. The CROM goniometer can be recommended for use in daily clinical practice.

Assessment of the cervical spine mobility by immersive and non-immersive virtual reality.

INTRODUCTION: Despite many devices are helpful for motion analysis, there is still no established standard technique for the assessment of cervical spine mobility. OBJECTIVE: To compare differences in using immersive or non-immersive virtual reality (VR) for the assessment of the sensorimotor movement of the cervical spine in healthy subjects. METHODS: Thirty-five healthy adults were asked to perform head rotation, flexion, extension, lateral flexion, reaching and repositioning tasks with the head. The same tasks were performed interacting with both non-immersive and immersive virtual reality. Random sequence determined which of the environments was used as first assessment. Range of motion and kinematics i.e. number of completed targets, time of execution (seconds), spatial length (cm), angle distance (°), jerk of the cervical spine, were automatically computed by a 6D electromagnetic motion tracking system. RESULTS: The following variables were significantly larger in immersive than non-immersive VR: head right rotation (p = 0.027), extension (p = 0.047), flexion (p = 0.000), time (p = 0.001), spatial length (p = 0.004), jerk target (p = 0.032), trajectory repositioning (p = 0.003), jerk target repositioning (p = 0.007). A regression model showed that assessment in both VR environments can be influenced by dependent and independent variables. CONCLUSIONS: Immersive VR provided more accurate measurement of cervical spine than non-immersive VR in healthy adults.

Assessment of the gait-related acceleration patterns in adults with autism spectrum disorder.

Individuals with autism spectrum disorder (ASD) can exhibit a range of movement issues, which are often characterized by a general slowing of movement responses that can extend to walking speed. The current study was designed to examine the spatio-temporal features and pattern of acceleration for the trunk, neck and head during walking for a cohort of adults with ASD compared to neurotypical individuals. Twenty young adults with ASD and 20 age-matched neurotypical adults participated in this study. Participants performed five walking trials across a 20ft Protokinetics pressure sensitive surface at their preferred walking speed. Accelerations were collected using three triaxial accelerometers affixed to the head, neck, and lower trunk. Comparisons of acceleration amplitude (i.e., RMS), frequency, segmental gain and regularity (i.e., SampEn) during the walking tasks were performed. Results revealed that the adults with ASD walked slower than the neurotypical persons with a greater proportion of time spent in double stance. Despite walking at a slower pace overall, the adults with ASD exhibited a decreased ability to attenuate gait-related oscillations from the trunk to the head. Overall, these findings suggest that adults with ASD exhibited a decreased ability to accommodate and dampen those accelerations related to walking. As declines in gait speed are often linked with loss of head control, one suggestion is that the inability to appropriately compensate for gait-related oscillations may, in part, explain why persons with ASD walk slower.

Correlation and Similarity between Cerebral and Non-Cerebral Electrical Activity for User's States Assessment.

Human tissues own conductive properties, and the electrical activity produced by human organs can propagate throughout the body due to neuro transmitters and electrolytes. Therefore, it might be reasonable to hypothesize correlations and similarities between electrical activities among different parts of the body. Since no works have been found in this direction, the proposed study aimed at overcoming this lack of evidence and seeking analogies between the brain activity and the electrical activity of non-cerebral locations, such as the neck and wrists, to determine if i) cerebral parameters can be estimated from non-cerebral sites, and if ii) non-cerebral sensors can replace cerebral sensors for the evaluation of the users under specific experimental conditions, such as eyes open or closed. In fact, the use of cerebral sensors requires high-qualified personnel, and reliable recording systems, which are still expensive. Therefore, the possibility to use cheaper and easy-to-use equipment to estimate cerebral parameters will allow making some brain-based applications less invasive and expensive, and easier to employ. The results demonstrated the occurrence of significant correlations and analogies between cerebral and non-cerebral electrical activity. Furthermore, the same discrimination and classification accuracy were found in using the cerebral or non-cerebral sites for the user's status assessment.

Experimental assessment of cervical ranges of motion and compensatory strategies.

Background: Literature is still limited regarding reports of non-invasive assessment of the cervical range of motion in normal subjects. Investigations into compensatory motions, defined as the contribution of an additional direction to the required motion, are also limited.The objectives of this work were to develop and assess a reliable method for measuring the cervical range of motion in order to investigate motion and compensatory strategies. Methods and data collection: Ninety-seven no neck-related pain subjects (no severe cervical pathology, 57 women, age: 28.3 ± 7.5y. old, BMI: 22.5 ± 3.2 kg/m2) underwent a non-invasive cervical range of motion assessment protocol. In-vivo head's motion relative to the thorax was assessed through the measurement of the main angular amplitudes in the 3 directions (flexion/extension, axial rotations and lateral inclinations) and associated compensatory motions using an opto-electronic acquisition system. Results: The principal motion reproducibility resulted in intra-class correlation coefficients ranging from 0.81 to 0.86. The following maximum ranges of motion were found: 127.4 ± 15.1° of flexion/extension, 89.3 ± 12° of lateral inclinations and 146.4 ± 13° of axial rotations after 6 outlier exclusions. Compensatory motions highly depend on the associated principal motion: for flexion/extension: (3.5 ± 7.6;-2.1 ± 7.8°), for rotation: (25.7 ± 17.9°;0.4 ± 4.7)°, for inclination: (22.9 ± 34.7°;-0.04 ± 8.7°). Age, BMI and weight significantly correlated with flexions (p < 0.032). Motion patterns were identified through clustering. Conclusions: This kinematic analysis has been proven to be a reliable diagnostic tool for the cervical range of motion. The non-unicity and variability of motion patterns through the clustering of motion strategy identification have been shown. Compensatory motions contributed to such motion pattern definition despite presenting significant intra-individual variability.

Estimating carotid pulse and breathing rate from near-infrared video of the neck.

OBJECTIVE: Non-contact physiological measurement is a growing research area that allows capturing vital signs such as heart rate (HR) and breathing rate (BR) comfortably and unobtrusively with remote devices. However, most of the approaches work only in bright environments in which subtle photoplethysmographic and ballistocardiographic signals can be easily analyzed and/or require expensive and custom hardware to perform the measurements. APPROACH: This work introduces a low-cost method to measure subtle motions associated with the carotid pulse and breathing movement from the neck using near-infrared (NIR) video imaging. A skin reflection model of the neck was established to provide a theoretical foundation for the method. In particular, the method relies on template matching for neck detection, principal component analysis for feature extraction, and hidden Markov models for data smoothing. MAIN RESULTS: We compared the estimated HR and BR measures with ones provided by an FDA-cleared device in a 12-participant laboratory study: the estimates achieved a mean absolute error of 0.36 beats per minute and 0.24 breaths per minute under both bright and dark lighting. SIGNIFICANCE: This work advances the possibilities of non-contact physiological measurement in real-life conditions in which environmental illumination is limited and in which the face of the person is not readily available or needs to be protected. Due to the increasing availability of NIR imaging devices, the described methods are readily scalable.

Laboratory Evaluation of Low-Cost Wearable Sensors for Measuring Head Impacts in Sports.

Advances in low-cost wearable head impact sensor technology provide potential benefits regarding sports safety for both consumers and researchers. However, previous laboratory evaluations are not directly comparable and do not incorporate test conditions representative of unhelmeted impacts. This study addresses those limitations. The xPatch by X2 Biosystems and the SIM-G by Triax Technologies were placed on a National Operating Committee on Standards for Athletic Equipment (NOCSAE) headform with a Hybrid III neck which underwent impact tests using a pendulum. Impact conditions included helmeted, padded impactor to bare head, and rigid impactor to bare head to represent long- and short-duration impacts seen in helmeted and unhelmeted sports. The wearable sensors were evaluated on their kinematic accuracy by comparing results to reference sensors located at the headform center of gravity. Statistical tests for equivalence were performed on the slope of the linear regression between wearable sensors and reference. The xPatch gave equivalent measurements to the reference in select longer-duration impacts, whereas the SIM-G had large variance leading to no equivalence. For the short-duration impacts, both wearable sensors underpredicted the reference. This error can be improved with increases in sampling rate from 1 to 1.5 kHz. Follow-up evaluations should be performed on the field to identify error in vivo.

Camera-based assessment of arterial stiffness and wave reflection parameters from neck micro-motion.

The feasibility of a camera-based extraction of carotid distension waveforms offers the prospect of a user-friendly alternative to laser Doppler velocimetry (LDV) or accelerometry-based systems. Upon supplementary calibration of vessel wall displacement to arterial pressure, our system may also be an appealing alternative to applanation tonometry for extracting cardiac-related features from the central pulse pressure waveform. OBJECTIVE: This paper describes the application of camera-based micro-motion imaging to extract health-related features from the contour of the carotid displacement waveform. APPROACH: We build on the assumption that the cardiac-related frequency components of the skin motion (sMOT) waveform, as acquired at the vicinity of the carotid artery under uneven illumination, receive a dominant contribution from the carotid wall displacement. We propose a two-step approach at which sMOT signals are queried based on the local amplitude of remote-photoplethysmography sensors spanning the neck's skin and then ensemble-averaged for cardiovascular health assessment. MAIN RESULTS: The feasibility of the system is demonstrated for assessing stiffness index, augmentation pressure, augmentation index and reflection magnitude on a dataset comprising 28 participants (ages 23 to 62 yrs; 22 males). SIGNIFICANCE: Although presented here as a standalone system, micro-motion imaging can be an auxiliary technique for improving sensor placement and signal quality of tonometric or LDV technologies.

Neck motion kinematics: an inter-tester reliability study using an interactive neck VR assessment in asymptomatic individuals.

BACKGROUND AND PURPOSE: The use of virtual reality (VR) for assessment and intervention of neck pain has previously been used and shown reliable for cervical range of motion measures. Neck VR enables analysis of task-oriented neck movement by stimulating responsive movements to external stimuli. Therefore, the purpose of this study was to establish inter-tester reliability of neck kinematic measures so that it can be used as a reliable assessment and treatment tool between clinicians. METHODS: This reliability study included 46 asymptomatic participants, who were assessed using the neck VR system which displayed an interactive VR scenario via a head-mounted device, controlled by neck movements. The objective of the interactive assessment was to hit 16 targets, randomly appearing in four directions, as fast as possible. Each participant was tested twice by two different testers. RESULTS: Good reliability was found of neck motion kinematic measures in flexion, extension, and rotation (0.64-0.93 inter-class correlation). High reliability was shown for peak velocity globally (0.93), in left rotation (0.9), right rotation and extension (0.88), and flexion (0.86). Mean velocity had a good global reliability (0.84), except for left rotation directed movement with moderate reliability (0.68). Minimal detectable change for peak velocity ranged from 41 to 53 °/s, while mean velocity ranged from 20 to 25 °/s. CONCLUSIONS: The results suggest high reliability for peak and mean velocity as measured by the interactive Neck VR assessment of neck motion kinematics. VR appears to provide a reliable and more ecologically valid method of cervical motion evaluation than previous conventional methodologies.

A comparison of neck bending and flexion measurement methods for assessment of ergonomic risk.

Head movements of workers were measured in the sagittal plane in order to establish a precise and accurate assessment method to be used in real work situations. Measurements were performed using two inclinometers connected to an embedded recording system. Two quantitative analysis methods were tested, i.e., measurement of bending with an inclinometer attached to the head, and measurement of flexion/extension by using an additional inclinometer located at C7/T1. The results were also compared with a video observation method (qualitative). The results showed that bending measurements were significantly different from those of flexion/extension for angles between 0° and 20°, and angles >45°. There were also significant differences between workers for flexion >45°, reflecting individual variability. Additionally, several limitations of observational methods were revealed by this study.

A system for predicting musculoskeletal disorders among dental students.

OBJECTIVE: This study aimed to develop a system for predicting work-related musculoskeletal disorders (WMSD) among dental students. MATERIALS AND METHODS: The system comprised 2 accelerometer sensors to register neck and upper back postures and movements, and software developed to collect and process the data. Hidden Markov models (HMMs) were used to predict the likelihood of WMSD in dental students by comparing their neck and upper back movement patterns with WMSD and non-WMSD HMMs learned from previous data. To evaluate the performance of the system, 16 participants were randomly assigned into a 2 × 2 crossover trial scheduled for each sequence of working: receiving feedback or no-feedback from the system. The primary outcome measure was the extension of the neck and upper back, before (pre-test) and after (posttest) receiving feedback or no-feedback from the system. The secondary outcome measure was the log likelihood of classifying the movements as WMSD. RESULTS AND DISCUSSION: The results showed that in the group that received feedback, the extension of the neck in the y axis and of the upper back in the y axis decreased significantly (t test, p < .05) on the post-test. CONCLUSION: The system for predicting and preventing WMSD aids the correction of the extension of the neck and upper back in the y axis.

Sonography assessment of the median nerve during cervical lateral glide and lateral flexion. Is there a difference in neurodynamics of asymptomatic people?

There is clinical evidence that cervical lateral glide (CLG) improves neurodynamics and alleviates pain in patients who suffer from neurogenic arm pain. Cervical lateral flexion (CLF) is also a treatment method and a means of testing neurodynamics. However, for both techniques nerve movement has not yet been investigated using ultrasound imaging (US). The purpose of this study was to quantify median nerve movement in the arm during CLG and CLF. For this study 27 healthy participants were recruited. Longitudinal movement of the median nerve was measured using US during CLG and CLF with the shoulder in 30° abduction in the middle and distal forearm (Fad). Data could be obtained from 11 participants (6 women and 5 men, average age 25.6 years, ± 2.25) at the middle forearm (Fam) and from 9 participants (5 women and 4 men, average age 27.2 years, ± 2.75) at the Fad. When applying CLF, the median nerve moved 2.3 mm (SEM ± 0.1 mm) at the Fam. At the same measuring point the median nerve moved 3.3 mm (SEM ± 0.3 mm, p = 0.005) by applying CLG. At the Fad the difference between CLF and CLF amounted to 0.6 mm (CLF: 1.9 mm (SEM ± 0.2 mm, CLG: 2.5 mm (SEM ± 0.2 mm, p ≤ 0.05). The movements during CLG are larger than during CLF. This difference is statistically significant. However, the statistical relevance cannot be extrapolated to a clinical relevance.

Assessment of follow-up sonography and clinical improvement among infants with congenital muscular torticollis.

BACKGROUND AND PURPOSE: Infants grow rapidly, which causes the SCM to thicken physiologically. Therefore some cases of physiologically-thickened SCM can be confused with a poor response to physical therapy. There have been only a few quantitative ultrasonographic studies on the clinical outcome of rehabilitation for CMT. Our aim was to evaluate whether a new sonographic assessment method that uses the muscular thickness ratio of the SCM can help quantify the outcome of rehabilitation therapy for patients with CMT. MATERIALS AND METHODS: We evaluated 48 patients (male/female, 17:31; mean age, 3.9 months) who were diagnosed with CMT and who underwent initial and follow-up sonography. The ratio of the thickness of the involved SCM to the thickness of the intact SCM (SCM thickness ratio) was calculated. A scoring system based on the range of motion of the neck was used to assess clinical improvement. The correlations between clinical improvement and the thickness of the involved muscle, the difference in involved muscle thickness, the SCM thickness ratio, and the difference in the SCM thickness ratio were evaluated with Spearman rank correlations. RESULTS: Follow-up Cheng scores were higher than initial scores; this difference indicates clinical resolution (follow-up, 4.90; initial, 3.38). The SCM thickness ratio at follow-up was lower than that at the initial evaluation (follow-up, 1.29-1.34; initial, 1.65-1.77). Intra- and interobserver agreements were excellent. Most variables were moderately correlated with clinical improvement (correlation coefficients, 0.36-0.509). R1 showed the highest correlation with clinical improvement (0.481 and 0.509), followed by the initial maximal thickness of the SCM (0.434 and 0.488). ΔP (P1-P2) and ΔR showed similar correlation coefficients with clinical improvement. CONCLUSIONS: Measurement of the SCM thickness ratio appears to overcome the problem of a false-positive diagnosis of clinical aggravation of CMT resulting from physiologic growth. R1 and ΔR are accurate objective measurements, which can be used in the management of CMT.

Validated assessment scale for neck volume.

BACKGROUND: Sagging of the neck aesthetic area is an important indicator of age. The development of complex and globally accepted tools for proper assessment of the change in neck volume is an essential contribution to aesthetic research and the routine clinical setting. OBJECTIVE: To develop a grading scale for the objective assessment of the neck volume and to establish the reliability of this scale for clinical research and practice. MATERIALS AND METHODS: A 5-point rating scale was developed to assess neck volume objectively. Twelve experts rated frontal and lateral neck photographs of 50 subjects in two separate rating cycles using the neck volume scale. Responses of raters were analyzed to assess inter- and intrarater reliability. RESULTS: Interrater reliability for the neck volume scale was almost perfect, with intraclass correlation coefficients for the first and second rating cycles of 0.85 and 0.84, respectively. Intrarater reliability for the neck volume scale was high (0.90) and Pearson correlation coefficients ranged between 0.88 and 0.95 and were statistically significant. CONCLUSION: The neck volume scale demonstrates optimal reliability for clinical research and practice.

Postural assessment of school children: an input for the design of furniture.

During the last decades of the previous century, school desks with a tilt top have disappeared. The chairs have been designed for sitting upright, with the hip, knees and ankles all at right angles. However, the erect posture cannot be maintained for more than one or two minutes, after which it will result in fatigue, discomfort or poor posture. The main aim of project is to identify the type of furniture that most effectively contribute to adequate neck and back postures of the school children, by carrying out a postural analysis of a sample of school pupils when using three different types of furniture. The postures adopted by school pupils were monitored by video during several activities, such as reading, writing and painting tasks, copying from a blackboard and listening the teacher. Additionally, the characteristics of the adopted postures were assessed by registering the head tilt, flexion of the neck, trunk and hips position. All these aspects were classified and the results were recorded for future analysis. The obtained results seem to point out that the use of a school desk with a tilted table surface resulted in a reduction in trunk and neck flexion, preserving the natural lordosis in the lumbar and cervical regions. Accordingly, it can be concluded that there are alternatives to consider in the furniture design in order to eliminate tensions and, consequently, to improve children's wellbeing.

Augmentative communication based on realtime vocal cord vibration detection.

A binary switch based on the detection of periodic vocal cord vibrations is proposed for individuals with multiple and severe disabilities. The system offers three major advantages over existing speech-based access technologies, namely, insensitivity to environment noise, increased robustness against user-generated artifacts such as coughs, and reduced exertion during prolonged usage periods. The proposed system makes use of a dual-axis accelerometer placed noninvasively in proximity of the vocal cords by means of a neckband. Periodic vocal cord vibrations are detected using the normalized cross-correlation function computed from anterior-posterior and superior-inferior accelerometry signals. Experiments with a participant with hypotonic cerebral palsy show the proposed system outperforming a popular commercial sound-based system in terms of sensitivity, task time, and user-perceived exertion.

Ergonomic assessment of neck posture in the minimally invasive surgery suite during laparoscopic cholecystectomy.

BACKGROUND: With the expanding implementation of minimally invasive surgery, the operating team is confronted with challenges in the field of ergonomics. Visual feedback is derived from a monitor placed outside the operating field. This crossover trial was conducted to evaluate and compare neck posture in relation to monitor position in a dedicated minimally invasive surgery (MIS) suite and a conventional operating room. METHODS: Assessment of the neck was conducted for 16 surgeons, assisting surgeons, and scrub nurses performing a laparoscopic cholecystectomy in both types of operating room. Flexion and rotation of the cervical spine were measured intraoperatively using a video analysis system. A two-question visual analog scale (VAS) questionnaire was used to evaluate posture in relation to the monitor position. RESULTS: Neck rotation was significantly reduced in the MIS suite for the surgeon (p = 0.018) and the assisting surgeon (p < 0.001). Neck flexion was significantly improved in the MIS suite for the surgeon (p < 0.001) and the scrub nurse (p = 0.018). On the questionnaire, the operating room team scored their posture significantly higher in the MIS suite and also indicated fewer musculoskeletal complaints. CONCLUSIONS: The ergonomic quality of the neck posture is significantly improved in the MIS suite for the entire operating room team.

Assessment of age-related morphological and functional changes of selected structures of the head and neck by computed tomography, magnetic resonance imaging, and positron emission tomography.

The head and neck is a complex anatomical region that can be evaluated using many imaging modalities. It is important to discern normal structures from ones that are affected by disease and to study how these structures change in their morphological and functional properties with aging. Therefore, using magnetic resonance imaging (MRI), we retrospectively evaluated volumes of the parotid glands, submandibular glands, thyroid gland, tongue, soft palate, and lingual tonsils in 64 subjects ages 13 to 81 years. Volume, attenuation (HU), and metabolic activity (maximum SUV) of the parotid, submandibular, and thyroid glands were assessed retrospectively using positron emission tomography/computed tomography (PET/CT) imaging in 35 subjects ages 10 to 76 years. Metabolic activity (maximum SUV) of the parotid, submandibular, and sublingual glands; tongue; adenoids; and tonsils (lingual and palatine) were evaluated retrospectively using PET imaging in 15 subjects ages 6 to 20 years. Metabolic volumetric products of the parotid, submandibular, and thyroid gland were calculated and analyzed with increasing age in subjects who underwent PET/CT imaging. Structures that exhibited statistically significant changes (P < 0.05) with increasing age included the submandibular glands, thyroid gland, soft palate, and adenoids. The CT volume of the submandibular glands increased with age, and the attenuation decreased with age with statistical significance. The thyroid gland volume, as measured using MRI, showed a statistically significant decrease with aging. The volume of the soft palate and lingual tonsils, as measured by MRI, exhibited a statistically significant decrease in volume with aging. The maximum SUV of the adenoids demonstrated a statistically significant decrease with aging. In conclusion, CT, MRI, and PET may be used to quantitatively and qualitatively assess structures of the head and neck and are useful in the assessment of structural and functional changes of these structures with aging.

[Cervical, thoracic and upper limb load assessment in dental professionals]. / Studio del carico posturale cervico-dorsale e dell'arto superiore nell'attività dell'odontoiatra.

In order to analyze the effect of working posture on the level of neck, back and shoulder muscular activity, a clinico-anamnestic, electromyographic and postural study of 34 dentistry was undertaken. Using surface electrodes, the level of muscular activity was recorded. The results showed that neck flexed working posture is prevalent: using stereomicroscope gave lower levels than with or without enlarging systems, such as glasses.