A modelling framework for local thermal comfort assessment related to bicycle helmet use.

Thermal discomfort due to accumulated sweat increasing head skin wettedness may contribute to low wearing rates of bicycle helmets. Using curated data on human head sweating and helmet thermal properties, a modelling framework for the thermal comfort assessment of bicycle helmet use is proposed. Local sweat rates (LSR) at the head were predicted as the ratio to the gross sweat rate (GSR) of the whole body or by sudomotor sensitivity (SUD), the change in LSR per change in body core temperature (Δtre). Combining those local models with Δtre and GSR output from thermoregulation models, we simulated head sweating depending on the characteristics of the thermal environment, clothing, activity, and exposure duration. Local thermal comfort thresholds for head skin wettedness were derived in relation to thermal properties of bicycle helmets. The modelling framework was supplemented by regression equations predicting the wind-related reductions in thermal insulation and evaporative resistance of the headgear and boundary air layer, respectively. Comparing the predictions of local models coupled with different thermoregulation models to LSR measured at the frontal, lateral and medial head under bicycle helmet use revealed a large spread in LSR predictions predominantly determined by the local models and the considered head region. SUD tended to overestimate frontal LSR but performed better for lateral and medial head regions, whereas predictions by LSR/GSR ratios were lower and agreed better with measured frontal LSR. However, even for the best models root mean squared prediction errors exceeded experimental SD by 18-30%. From the high correlation (R > 0.9) of skin wettedness comfort thresholds with local sweating sensitivity reported for different body regions, we derived a threshold value of 0.37 for head skin wettedness. We illustrate the application of the modelling framework using a commuter-cycling scenario, and discuss its potential as well as the needs for further research.

Clothing air gaps in various postures in firefighters' work.

Both the physical properties of the fabric materials used in clothing and the effective design of the clothing, primarily in terms of the air gap thickness, restrict the transmission of the thermal energy from the heat source to the firefighter's body. The air gap distribution over the body in real deployment conditions of firefighters will vary, and is likely to be different from the air gap distribution in standardised manikin tests in standing upright posture. In this study, we investigated differences in the distribution of air layers in firefighters' clothing in three postures reflecting realistic on-duty exposure conditions (crawling, hose-holding, and standing upright used in laboratory tests) using 3D body scanning technology. The body posture induced substantial changes in the air gap thickness on the upper body (chest and back) and lower body. These changes were reflected in both the thermal and evaporative resistance of the ensemble, and consequently, in their potential thermal performance in the field. Therefore, it is recommended to consider body postures during the evaluation of clothing protective performance. Secondly, the knowledge of local clothing properties in real-life exposure provides a true protection mapping and gives design inputs to improve the local protective properties of firefighters' clothing.

Assessment of compression forces in a digitally modified short leg cast for pressure injury risk monitoring in healthy children.

Introduction: Casting is an essential treatment for neuro-orthopedic conditions in children with cognitive, sensory, and communicational disabilities. However, a main side-effect is the development of pressure injuries resulting in additional (wound) therapies and prolongation of the hospital stay. The primary aim of our study was to investigate the potential of objective pressure measurements in casts to assess the risk for pressure injury development. Methods: Five pediatric healthy participants were included in this study. We measured the global and the local compression force at body sites prone to pressure injury development for different body positions and the transfer in-between in a cast equipped with pressure sensors. These conditions resulted in partial or full body weight loading. Results and discussion: The global maximum compression force was affected significantly by body postures with partial and full loading of the cast and during transfer. The local compression force significantly correlated with the global compression force at the heel and instep area. In conclusion, the integration of sensing technologies into casts bears a high potential for early recognition of critical conditions inside the cast and inducing preventive measures in the at-risk population.

How long and effective does a mask protect you from an infected person who emits virus-laden particles: By implementing one-dimensional physics-based modeling.

SARS-CoV-2 spreads via droplets, aerosols, and smear infection. From the beginning of the COVID-19 pandemic, using a facemask in different locations was recommended to slow down the spread of the virus. To evaluate facemasks' performance, masks' filtration efficiency is tested for a range of particle sizes. Although such tests quantify the blockage of the mask for a range of particle sizes, the test does not quantify the cumulative amount of virus-laden particles inhaled or exhaled by its wearer. In this study, we quantify the accumulated viruses that the healthy person inhales as a function of time, activity level, type of mask, and room condition using a physics-based model. We considered different types of masks, such as surgical masks and filtering facepieces (FFPs), and different characteristics of public places such as office rooms, buses, trains, and airplanes. To do such quantification, we implemented a physics-based model of the mask. Our results confirm the importance of both people wearing a mask compared to when only one wears the mask. The protection time for light activity in an office room decreases from 7.8 to 1.4 h with surgical mask IIR. The protection time is further reduced by 85 and 99% if the infected person starts to cough or increases the activity level, respectively. Results show the leakage of the mask can considerably affect the performance of the mask. For the surgical mask, the apparent filtration efficiency reduces by 75% with such a leakage, which cannot provide sufficient protection despite the high filtration efficiency of the mask. The facemask model presented provides key input in order to evaluate the protection of masks for different conditions in public places. The physics-based model of the facemask is provided as an online application.

Modeling and Prediction of Thermophysiological Comfort Properties of a Single Layer Fabric System Using Single Sector Sweating Torso.

Thermophysiological comfort is known to play a primary role in maintaining thermal balance, which corresponds to a person's satisfaction with their immediate thermal environment. Among the existing test methods, sweating torsos are one of the best tools to provide a combined measurement of heat and moisture transfer using non-isothermal conditions. This study presents a preliminary numerical model of a single sector sweating torso to predict the thermophysiological comfort properties of fabric systems. The model has been developed using COMSOL Multiphysics, based on the ISO 18640-1 standard test method and a single layer fabric system used in sportswear. A good agreement was observed between the experimental and numeral results over different exposure phases simulated by the torso test (R2 = 0.72 to 0.99). The model enables a systematic investigation of the effect of fabric properties (thickness, porosity, thermal resistance, and evaporative resistance), environmental conditions (relative humidity, air and radiant temperature, and wind speed), and physiological parameters (sweating rate) to gain an enhanced understanding of the thermophysiological comfort properties of the fabric system.

Community Masks - from an Emergency Solution to an Innovation Booster for the Textile Industry.

The COVID-19 pandemic resulted in shortages of personal protective equipment and medical devices in the initial phase. Agile small and medium-sized enterprises from regional textile industries reacted quickly. They delivered alternative products such as textile-based community masks in collaboration with industrial partners and research institutes from various sectors. The current mask materials and designs were further improved by integrating textiles with antiviral and antimicrobial properties and enhanced protection and comfort by novel textile/membrane combinations, key factors to increase the acceptance and compliance of mask wearing. The innocuity and sustainability of masks, as well as taking into account particular needs of vulnerable persons in our society, are new fields for textile-based innovations. These innovations developed for the next generation of facemasks have a high adaptability to other product segments, which make textiles an attractive material for hygienic applications and beyond.

Influence of Measurement Location on Reflectance Pulse Oximetry in Sleep Apnea Patients: Wrist vs. Upper Arm.

Peripheral oxygen saturation (SpO2) plays a key role in diagnosing sleep apnea. It is mainly measured via transmission pulse oximetry at the fingertip, an approach less suited for long-term monitoring over several nights.In this study we tested a more patient-friendly solution via a reflectance pulse oximetry device. Having previously observed issues with pulse oximetry at the wrist, we investigated in this study the influence of the location of our device (upper arm vs. wrist) to measure SpO2. Accuracy was compared against state-of-the-art fingertip SpO2 measurements during a full overnight polysomnography in nine patients with suspected sleep apnea.The upper arm location clearly showed a lower root mean square error ARMS = 1.8% than the wrist ARMS = 2.5% and a lower rate of automatic data rejection (19% vs 25%). Irrespective of the measurement location the accuracies obtained comply with the ISO standard and the FDA guidance for pulse oximeters. In contrast to the wrist, the upper arm location seemed to be more resilient to deteriorating influences such as venous blood.Reflectance pulse oximetry at the wrist remains challenging but the upper arm could provide remedy for more robust SpO2 estimates to reliably screen for sleep apnea and other diseases.Clinical Relevance- The performance of reflectance pulse oximetry measured at the upper arm during sleep is superior to measurements at the wrist which are perturbed by undesired large fluctuations suspected to be caused by venous blood. If confirmed, this could also apply to the optical measurement of other vital signs such as blood pressure.

A Thermal Skin Model for Comparing Contact Skin Temperature Sensors and Assessing Measurement Errors.

To improve the measurement and subsequent use of human skin temperature (Tsk) data, there is a need for practical methods to compare Tsk sensors and to quantify and better understand measurement error. We sought to develop, evaluate, and utilize a skin model with skin-like thermal properties as a tool for benchtop Tsk sensor comparisons and assessments of local temperature disturbance and sensor bias over a range of surface temperatures. Inter-sensor comparisons performed on the model were compared to measurements performed in vivo, where 14 adult males completed an experimental session involving rest and cycling exercise. Three types of Tsk sensors (two of them commercially available and one custom made) were investigated. Skin-model-derived inter-sensor differences were similar (within ±0.4 °C) to the human trial when comparing the two commercial Tsk sensors, but not for the custom Tsk sensor. Using the skin model, all surface Tsk sensors caused a local temperature disturbance with the magnitude and direction dependent upon the sensor and attachment and linearly related to the surface-to-environment temperature gradient. Likewise, surface Tsk sensors also showed bias from both the underlying disturbed surface temperature and that same surface in its otherwise undisturbed state. This work supports the development and use of increasingly realistic benchtop skin models for practical Tsk sensor comparisons and for identifying potential measurement errors, both of which are important for future Tsk sensor design, characterization, correction, and end use.

Body Temperature Is Associated With Cognitive Performance in Older Adults With and Without Mild Cognitive Impairment: A Cross-sectional Analysis.

Wearable devices for remote and continuous health monitoring in older populations frequently include sensors for body temperature measurements (i.e., skin and core body temperatures). Healthy aging is associated with core body temperatures that are in the lower range of age-related normal values (36.3 ± 0.6°C, oral temperature), while patients with Alzheimer's disease (AD) exhibit core body temperatures above normal values (up to 0.2°C). However, the relation of body temperature measures with neurocognitive health in older adults remains unknown. This study aimed to explore the association of body temperature with cognitive performance in older adults with and without mild cognitive impairment (MCI). Eighty community-dwelling older adults (≥65 years) participated, of which 54 participants were cognitively healthy and 26 participants met the criteria for MCI. Skin temperatures at the rib cage and the scapula were measured in the laboratory (single-point measurement) and neuropsychological tests were conducted to assess general cognitive performance, episodic memory, verbal fluency, executive function, and processing speed. In a subgroup (n = 15, nine healthy, six MCI), skin and core body temperatures were measured continuously during 12 h of habitual daily activities (long-term measurement). Spearman's partial correlation analyses, controlled for age, revealed that lower median body temperature and higher peak-to-peak body temperature amplitude was associated with better general cognitive performance and with better performance in specific domains of cognition; [e.g., rib median skin temperature (single-point) vs. processing speed: rs = 0.33, p = 0.002; rib median skin temperature (long-term) vs. executive function: rs = 0.56, p = 0.023; and peak-to-peak core body temperature amplitude (long-term) vs. episodic memory: rs = 0.51, p = 0.032]. Additionally, cognitively healthy older adults showed lower median body temperature and higher peak-to-peak body temperature amplitude compared to older adults with MCI (e.g., rib median skin temperature, single-point: p = 0.035, r = 0.20). We conclude that both skin and core body temperature measures are potential early biomarkers of cognitive decline and preclinical symptoms of MCI/AD. It may therefore be promising to integrate body temperature measures into multi-parameter systems for the remote and continuous monitoring of neurocognitive health in older adults.

Fatigue Monitoring Through Wearables: A State-of-the-Art Review.

The objective measurement of fatigue is of critical relevance in areas such as occupational health and safety as fatigue impairs cognitive and motor performance, thus reducing productivity and increasing the risk of injury. Wearable systems represent highly promising solutions for fatigue monitoring as they enable continuous, long-term monitoring of biomedical signals in unattended settings, with the required comfort and non-intrusiveness. This is a p rerequisite for the development of accurate models for fatigue monitoring in real-time. However, monitoring fatigue through wearable devices imposes unique challenges. To provide an overview of the current state-of-the-art in monitoring variables associated with fatigue via wearables and to detect potential gaps and pitfalls in current knowledge, a systematic review was performed. The Scopus and PubMed databases were searched for articles published in English since 2015, having the terms "fatigue," "drowsiness," "vigilance," or "alertness" in the title, and proposing wearable device-based systems for non-invasive fatigue quantification. Of the 612 retrieved articles, 60 satisfied the inclusion criteria. Included studies were mainly of short duration and conducted in laboratory settings. In general, researchers developed fatigue models based on motion (MOT), electroencephalogram (EEG), photoplethysmogram (PPG), electrocardiogram (ECG), galvanic skin response (GSR), electromyogram (EMG), skin temperature (Tsk), eye movement (EYE), and respiratory (RES) data acquired by wearable devices available in the market. Supervised machine learning models, and more specifically, binary classification models, are predominant among the proposed fatigue quantification approaches. These models were considered to perform very well in detecting fatigue, however, little effort was made to ensure the use of high-quality data during model development. Together, the findings of this review reveal that methodological limitations have hindered the generalizability and real-world applicability of most of the proposed fatigue models. Considerably more work is needed to fully explore the potential of wearables for fatigue quantification as well as to better understand the relationship between fatigue and changes in physiological variables.

Heart Rate Variability Mainly Relates to Cognitive Executive Functions and Improves Through Exergame Training in Older Adults: A Secondary Analysis of a 6-Month Randomized Controlled Trial.

Heart rate variability (HRV) mirrors autonomic nervous system activities and might serve as a parameter to monitor health status in older adults. However, it is currently unknown which functional health measures, including cognitive, physical, and gait performance parameters, are most strongly related to HRV indices. This knowledge would enable implementing HRV assessments into health monitoring routines and training planning for older adults. Simultaneous cognitive-motor and exergame training may be effective to improve HRV indices but has not been investigated yet. Eighty-nine healthy older adults (≥70 years of age) were randomized into three groups: (1) virtual reality video game dancing, i.e., exergaming (DANCE); (2) treadmill walking with simultaneous verbal memory training (MEMORY); or (3) treadmill walking only (PHYS). Strength and balance exercises complemented each program. Over 6 months, two weekly 1-h training sessions were performed. HRV indices (standard deviation of N-N intervals, SDNN; root mean square of successive R-R interval differences, RMSSD; and absolute power of high-frequency band (0.15-0.4 Hz), HF power) and various measures of cognitive, physical, and gait performance were assessed at baseline and after 3 months and 6 months. Multiple linear regression analyses with planned comparisons were calculated. At baseline, 8-12% of HRV variance was significantly explained by cognitive executive functions and leg strength (inversely related). Verbal long-term memory, aerobic and functional fitness, and gait performance did not contribute to the model (SDNN: R2 = 0.082, p = 0.016; RMSSD: R2 = 0.121, p = 0.013; HF power: R2 = 0.119, p = 0.015). After 6 months, DANCE improved HRV indices, while MEMORY and PHYS did not (time × intervention interactions: first-contrast DANCE/MEMORY vs. PHYS: SDNN p = 0.014 one-tailed, ΔR 2 = 0.020 and RMSSD p = 0.052 one-tailed (trend), ΔR 2 = 0.007; second-contrast DANCE vs. MEMORY: SDNN p = 0.002 one-tailed, ΔR 2 = 0.035, RMSSD p = 0.017 one-tailed, ΔR 2 = 0.012, and HF power p = 0.011 one-tailed, ΔR 2 = 0.013). We conclude that mainly cognitive executive functions are associated with HRV indices and that exergame training improves global and parasympathetic autonomic nervous system activities in older adults. Periodic assessments of HRV in older citizens could be particularly beneficial to monitor cognitive health and provide indications for preventative exercise measures.

Classification of Sleep Apnea Severity by Electrocardiogram Monitoring Using a Novel Wearable Device.

Sleep apnea (SA) is a prevalent disorder diagnosed by polysomnography (PSG) based on the number of apnea-hypopnea events per hour of sleep (apnea-hypopnea index, AHI). PSG is expensive and technically complex; therefore, its use is rather limited to the initial diagnostic phase and simpler devices are required for long-term follow-up. The validity of single-parameter wearable devices for the assessment of sleep apnea severity is still debated. In this context, a wearable electrocardiogram (ECG) acquisition system (ECG belt) was developed and its suitability for the classification of sleep apnea severity was investigated using heart rate variability analysis with or without data pre-filtering. Several classification algorithms were compared and support vector machine was preferred due to its simplicity and overall performance. Whole-night ECG signals from 241 patients with a suspicion of sleep apnea were recorded using both the ECG belt and patched ECG during PSG recordings. 65% of patients had an obstructive sleep apnea and the median AHI was 21 [IQR: 7-40] h - 1 . The classification accuracy obtained from the ECG belt (accuracy: 72%, sensitivity: 70%, specificity: 74%) was comparable to the patched ECG (accuracy: 74%, sensitivity: 88%, specificity: 61%). The highest classification accuracy was obtained for the discrimination between individuals with no or mild SA vs. moderate to severe SA. In conclusion, the ECG belt provided signals comparable to patched ECG and could be used for the assessment of sleep apnea severity, especially during follow-up.

Changes in skin-physiology after local heat application using two different methods in individuals with complete paraplegia: a feasibility and safety trial.

STUDY DESIGN: Interventional feasibility study. OBJECTIVES: To evaluate safety and effects of local heat preconditioning on skin physiology using water-filtered infrared-A radiation (wIRA) or warm water therapy (wWT) in individuals with spinal cord injury (SCI). SETTING: Acute and rehabilitation center, specialized in SCI. METHODS: A convenience sample of 15 individuals (3 women, 12 men) with complete paraplegia from thoracic levels ranging between T2 and T12 received local heat applications either with wIRA or wWT on the thigh (paralyzed area) and on the upper arm (non-paralyzed area). Local heat was applied during three 30-min cycles, each separated by 30 min rest; thus, the treatment lasted for 180 min. Temperature, blood perfusion, and skin redness were measured at baseline, before and after heat application and 24 h after the last application. RESULTS: Heat applications with wIRA and wWT were well-tolerated. No burns or any other side effects were detected. Skin temperature (p ≤ 0.008) and blood perfusion (p ≤ 0.013) significantly increased after heat application. Local skin temperature (arm p = 0.004/leg p < 0.001) and blood perfusion (arm p = 0.011/leg p = 0.001) after the first and the second application cycle, respectively, were significantly higher during heat application with wIRA than with wWT. However, skin redness did not change significantly (p = 0.1). No significant differences were observed between the paralyzed and non-paralyzed areas for all parameters immediately, as well as 24 h after the treatment. CONCLUSIONS: Although both heating methods have been confirmed as safe treatments in this study, further investigations with regard to their efficacy in the context of preconditioning are warranted. SPONSORSHIP: The use of the instruments Hydrosun® 750 Irradiator (Hydrosun Medizintechnik, Germany) and Hilotherm-Calido 6 (Hilotherm GmbH, Germany) was sponsored by the Dr. med. h. c. Erwin Braun Foundation and by Hilotherm GmbH, respectively.

Applicability of a Textile ECG-Belt for Unattended Sleep Apnoea Monitoring in a Home Setting.

Sleep monitoring in an unattended home setting provides important information complementing and extending the clinical polysomnography findings. The validity of a wearable textile electrocardiography (ECG)-belt has been proven in a clinical setting. For evaluation in a home setting, ECG signals and features were acquired from 12 patients (10 males and 2 females, showing an interquartile range for age of 48-59 years and for body mass indexes (BMIs) of 28.0-35.5) over 28 nights. The signal quality was assessed by artefacts detection, signal-to-noise ratio, and Poincaré plots. To assess the validity, the data were compared to previously reported data from the clinical setting. It was found that the artefact percentage was slightly reduced for the ECG-belt from 9.7% ± 14.7% in the clinical setting, to 7.5% ± 10.8% in the home setting. The signal-to-noise ratio was improved in the home setting and reached similar values to the gel electrodes in the clinical setting. Finally, it was found that for artefact percentages above 3%, Poincaré plots are instrumental to evaluate the origin of artefacts. In conclusion, the application of the ECG-belt in a home setting did not result in a reduction in signal quality compared to the ECG-belt used in the clinical setting, and thus provides new opportunities for patient pre-screening or follow-up.

Evaluation of the effect of cooling strategies on recovery after surgical intervention.

INTRODUCTION: Different cooling strategies exist for emergency treatments immediately after sports trauma or after surgery. The aim of this study was to investigate the effects of three cooling regimen during the immediate postoperative phase as well as in the rehabilitation phase. METHODS: 36 patients undergoing anterior cruciate ligament reconstruction received either no cooling (control-group, Con, N=12), were cooled with a menthol-containing cooling bandage (Mtl, N=12) or cooled with an ice containing cold pack (CP, N=12). During a 12-week physiotherapy treatment the cross section of the vastus medialis muscle was examined (day-1; 30; 60; 90) and painkiller consumption was documented. RESULTS: A significant reduction in the cross section area 30 days after surgery was observed in CP and Con (Mtl: -3.2±1.7%, p=0.14, CP: -8.8±4.3%, p<0.01, Con: -7.2±8.1%, p<0.05). After 90 days of therapy, a significant increase in muscle cross section area was observed in Mtl (Mtl: 4.6%±6.1%, p<0.05, CP: 1.9%± 8.1%, p=0.29, Con: 3.3%±9.4%, p=0.31). The absolute painkiller consumption was lower for Mtl (25.5±3.7 tablets) than for CP (39.5±6.9 tablets) or Con (34.8±4.2 tablets). CONCLUSION: We observed a beneficial effect of cooling by a menthol-containing bandage during the rehabilitation phase. Reduction of muscle cross section within 30 days after surgery was prevented which highly contributed to rehabilitation success after 90 days of therapy. Painkiller consumption was reduced with Mtl.

Clinical Applicability of a Textile 1-Lead ECG Device for Overnight Monitoring.

Even for 1-lead electrocardiography (ECG), single-use gel conductive electrodes are employed in a clinical setting. However, gel electrodes show limited applicability for long-term monitoring due to skin irritation and detachment. In the present study, we investigated the validity of a textile ECG-belt suitable for long-term measurements in clinical use. In order to assess the signal quality and validity of the ECG-belt during sleep, 242 patients (186 males and 56 females, age 52 (interquartile range 42-60) years, body mass index 29 (interquartile range 26-33) kg·m-2) with suspected sleep apnoea underwent overnight polysomnography including standard 1-lead ECG recording. The single intervals between R-peaks (RR-intervals) were calculated from the ECG-signals. We found a mean difference for average RR-intervals of -2.9 ms, a standard error of estimate of 0.39%, as well as a Pearson r of 0.91. Furthermore, we found that the validity of the ECG-belt decreases when lying on the side, which was potentially due to the fitting of the belt. In conclusion, the validity of RR-interval measurements using the ECG-belt is high and it may be further improved for future applications by optimizing wear fitting.

Validity of contact skin temperature sensors under different environmental conditions with and without fabric coverage: characterisation and correction.

Contact skin temperature (Tsk) sensors are calibrated under uniform thermal conditions but used in the presence of a skin-to-environment temperature gradient. We aimed to characterise the validity of contact Tsk sensors when measuring surface temperature under a range of environmental and fabric coverage conditions, to estimate practical temperature limits for a given measurement bias and to explore correcting for bias. Using two types of contact Tsk sensors (thermistors, n = 5; iButtons, n = 5), we performed experiments in three phases: (1) conventional calibration (uniform thermal environment) over 15-40 °C in 5 °C steps (at t = 0, and 24 h, 12 weeks later), (2) surface temperature measurements of a purpose-made aluminium plate (also 15-40 °C) at different environmental temperatures (15, 25, 35 °C) with different sensor attachments and fabric coverings to assess measurement bias and calculate correction factors that account for the next-to-surface microclimate temperature and (3) surface measurements (33.1 °C in 20 °C environment) for assessing generated corrections. The main results were as follows: (1) after initial calibration, Tsk sensors were valid under uniform thermal conditions [mean bias < 0.05 °C, typical error of the estimate < 0.1 °C]. (2) For the surface measurements, bias increased with increasing surface-to-microclimate temperature difference for both sensor types. The range of surface temperatures possible to remain within given bias limits could be estimated for the various conditions. (3) For a given measurement, using corrections encompassing the microclimate temperature (mean difference - 0.1 to 0.5 °C) performed better than conventional calibration alone (mean difference - 2.1 to - 0.3 °C). In conclusion, the bias of Tsk sensors is influenced by the microclimate temperature and, therefore, body coverings. Where excessive bias is expected, the validity can be improved through sensor and attachment selection and by applying corrections that account for the local temperature gradient.

The Influence of Backpack Weight and Hip Belt Tension on Movement and Loading in the Pelvis and Lower Limbs during Walking.

The introduction of hip belts to backpacks has caused a shift of loading from the spine to the hips with reported improvements in musculoskeletal comfort. Yet the effects of different hip belt tensions on gait biomechanics remain largely unknown. The goal of this study was to assess the influence of backpack weight and hip belt tension on gait biomechanics. Data from optical motion capture and ground reaction forces (GRF) during walking were acquired in nine healthy male subjects (age 28.0 ± 3.9 years). Six configurations of a commercial backpack were analyzed, that is, 15 kg, 20 kg, and 25 kg loading with 30 N and 120 N hip belt tension. Joint ranges of motion (ROM), peak GRF, and joint moments during gait were analyzed for significant differences by repeated measures of ANOVA with Bonferroni post hoc comparison. Increased loading led to a significant reduction of knee flexion-extension ROM as well as pelvis rotational ROM. No statistically significant effect of hip belt tension magnitudes on gait dynamics was found at any backpack weight, yet there was a trend of increased pelvis ROM in the transverse plane with higher hip belt tension at 25 kg loading. Further research is needed to elucidate the optimum hip belt tension magnitudes for different loading weights to reduce the risks of injury especially with higher loading.

Contact skin temperature measurements and associated effects of obstructing local sweat evaporation during mild exercise-induced heat stress.

OBJECTIVE: Locally increasing evaporative resistance is one mechanism by which contact skin temperature (T sk) sensors and their attachments may disturb the temperature of the skin site being measured. We aimed to determine the extent to which an obstruction of evaporation affects local T sk during exercise-induced sweating and how this compares to the T sk measured using a conventional contact T sk sensor. APPROACH: Twelve adult males each completed one experimental session (~24 °C, ~46% relative humidity) involving seated rest and exercise (cycle ergometer). Air velocity was ~0.5 m · s-1 during rest and ~1 m · s-1 during exercise. T sk of the right posterolateral forearm was measured using fine-wire thermocouples (0.125 mm diameter; chosen for minimal sensor-related disturbance) under two concurrent experimental conditions: uncovered or directly covered by a moisture-impermeable matte-black aluminium foil (thickness 0.08 mm, area 15 mm × 22 mm). The adjacent T sk was also measured using an iButton attached with a nonwoven medical tape. Changes in next-to-skin absolute vapour pressure were used to estimate the onset of sweating. MAIN RESULTS: During exercise, covered thermocouple temperatures were consistently warmer than those uncovered. These differences were small before the onset of sweating (0.1 °C, p = 0.16), but increased thereafter (0.6 and 1.0 °C by minutes 15 and 30 of exercise, respectively; p ⩽ 0.03). For change scores from baseline rest, the iButton-measured T sk was as much as 0.7 °C warmer than uncovered and -0.4 °C cooler than covered thermocouples during sweating, but differences were not statistically supported and with wide 95% limits of agreement (up to ±3.1 °C). SIGNIFICANCE: When delineated, a small obstruction of evaporation itself caused an overestimation of T sk during exercise although, while demonstrable, these effects were less clear in the context of using a conventional contact T sk sensor and attachment.

Local air gap thickness and contact area models for realistic simulation of human thermo-physiological response.

To evaluate the quality of new energy-saving and performance-supporting building and urban settings, the thermal sensation and comfort models are often used. The accuracy of these models is related to accurate prediction of the human thermo-physiological response that, in turn, is highly sensitive to the local effect of clothing. This study aimed at the development of an empirical regression model of the air gap thickness and the contact area in clothing to accurately simulate human thermal and perceptual response. The statistical model predicted reliably both parameters for 14 body regions based on the clothing ease allowances. The effect of the standard error in air gap prediction on the thermo-physiological response was lower than the differences between healthy humans. It was demonstrated that currently used assumptions and methods for determination of the air gap thickness can produce a substantial error for all global, mean, and local physiological parameters, and hence, lead to false estimation of the resultant physiological state of the human body, thermal sensation, and comfort. Thus, this model may help researchers to strive for improvement of human thermal comfort, health, productivity, safety, and overall sense of well-being with simultaneous reduction of energy consumption and costs in built environment.