A method for calculating vector forces at human-mattress interface during sleeping positions utilizing image registration.

The vector forces at the human-mattress interface are not only crucial for understanding the distribution of vertical and shear forces exerted on the human body during sleep but also serves as a significant input for biomechanical models of sleeping positions, whose accuracy determines the credibility of predicting musculoskeletal system loads. In this study, we introduce a novel method for calculating the interface vector forces. By recording indentations after supine and lateral positions using a vacuum mattress and 3D scanner, we utilize image registration techniques to align body pressure distribution with the mattress deformation scanning images, thereby calculating the vector force values for each unit area (36.25 mm × 36.25 mm). This method was validated through five participants attendance from two perspectives, revealing that (1) the mean summation of the vertical force components is 98.67% ± 7.21% body weight, exhibiting good consistency, and mean ratio of horizontal component force to body weight is 2.18% ± 1.77%. (2) the predicted muscle activity using the vector forces as input to the sleep position model aligns with the measured muscle activity (%MVC), with correlation coefficient over 0.7. The proposed method contributes to the vector force distribution understanding and the analysis of musculoskeletal loads during sleep, providing valuable insights for mattress design and evaluation.

Influence of shoe upper structure on shoe microclimate and human physiological characteristics during running.

BACKGROUND: Shoes upper has been shown to affect the shoe microclimate (temperature and humidity). However, the existing data on the correlation between the microclimate inside footwear and the body's physical factors is still quite limited. OBJECTIVE: This study examined whether shoes air permeability would influence foot microclimate and spatial characteristics of lower limb and body. METHODS: Twelve recreational male habitual runners were instructed to finish an 80 min experimental protocol, wearing two running shoes with different air permeability. RESULTS: Participants wearing CLOSED upper structure shoe exhibited higher in-shoe temperature and relative humidity. Although there was no significant difference, shank temperature and metabolism in OPEN upper structure shoes were lower. CONCLUSIONS: This indicates that the air permeability of shoes can modify the microclimate of the feet, potentially affecting the lower limb temperature. This study provides relevant information for the design and evaluation of footwear.

Modification and verification of the PMV model to improve thermal comfort prediction at low pressure.

The human body's thermal physiology changes due to atmospheric pressure, which significantly impacts the perception of thermal comfort. To quantify this effect, an improved version of the Predicted Mean Vote model (PMVp), was developed in this study to predict human thermal sensation under low atmospheric pressure conditions. The study employed environmental conditions of 0km/26°C, 3km/26°C, 4km/26°C, and 4km/21°C. Thirteen subjects were continuously monitored for exhaled CO2, inhaled O2, ambient temperature (ta), relative humidity (RH), air velocity (V), black globe temperature (tg), and altitude (H). The predictive performance of PMVp was evaluated by comparing the experimental results from this study with previous experiments. The findings demonstrate that PMVp exhibits lower root-mean-square errors (RMSE) than the original PMV model. Under the four experimental conditions, the RMSE values for PMVp were 0.311, 0.408, 0.123, and 0.375, while those for PMV were 1.251, 1.367, 1.106, and 1.716, respectively. Specifically, at a temperature range of 21∼27°C (altitude: 941m), the RMSE of PMVp (0.354) was smaller than PMV's. Furthermore, the study analyzed the sensitivity of PMVp to input parameters at an altitude of 4 km. PMVp exhibited considerable sensitivity to the metabolic rate (M) and thermal insulation of clothing (ICL). Consequently, a simple sensitivity scale was established: M>ICL>Ta≈V>Tr>H≈RH, indicating the relative importance of these parameters in influencing PMVp's response. The research findings provide comprehensive knowledge and a useful reference for developing a standard to design and evaluate indoor thermal environments in the plateau region.

Effects of simulated high altitude on body temperature and heart rate in pilot reserves during the hot-dry exposure.

Recent research has primarily focused on human thermoregulatory responses at high altitudes, but investigations involving extremely high-temperature and hypobaric compound environments are currently lacking. To address this gap in knowledge, this study aimed to enhance the prediction of human heat sensation for pilot reserves while operating in extremely hot cabins with decompression. To achieve this, an improved Predicted Heat Strain (PHS) model was developed by incorporating the influence of air pressure on metabolic rate. The model's validity was assessed through experiments conducted at different altitudes (0m, 5000m, and 8000m) and varying environmental conditions (26°C and 45 °C, 10% RH and 40% RH) within an environmental simulation cabin. During these experiments, local skin temperature, core temperature, heart rate, and blood oxygen saturation were measured. The findings revealed distinct variations in the skin temperature of the hand and foot segments across different experimental stages, and significant correlations were observed between heart rate, core temperature, and local skin temperatures. Furthermore, regression models were established to explore the relationship between heart rate and local skin temperatures. By comparing simulated and experimental core and local skin temperatures, the enhanced PHS model was successfully validated. The conclusions drawn from this study provide valuable insights for predicting thermal physiological indices accurately and conveniently in hot-dry and hypobaric environments.

Thermal response of human body with immersion suit in cold environment.

Hypothermia caused by cold water immersion is one of the main causes of death in marine accidents. Immersion suit is a kind of protective clothing when implementing flying tasks over the sea in cold seasons, with the main function to slow down the loss of human heat in water and prolong the survival time. In this study, the thermal properties and wearing types of immersion suit and underwear were analyzed. The subjects with internal- and external-wear immersion suit exposed to the experimental environments for 2 h in five working conditions. The core temperature, weighted average skin temperature, and average body temperature were measured and calculated. Both internal- and external-wear immersion suits could fulfil the cold protection requirements under the experimental conditions. The results of clothing parameter tests and physiological experiments both exhibit that the external-wear immersion suit has better thermal insulation effect. And the tolerance time in low-temperature water was predicted, which is crucial for effective and efficient rescue during shipwreck in adverse thermal scenarios. In future research, a comprehensive evaluation and analysis of the thermal insulation performance of immersion suit could be completed in combination with the water ingress of the clothing, the subjects' thermal comfort, and flexibility of the clothing.