Physiological Strain Research Articles

Comparison of the Impact of an Optimized Ice Cooling Vest and a Paraffin Cooling Vest on Physiological and Perceptual Strain.

BackgroundIce cooling vests can cause tissue damage and have no flexibility. Therefore, these two undesirable properties of ice cooling vest were optimized, and the present study was aimed to compare the impact of the optimized ice cooling vest and a commercial paraffin cooling vest on physiological and perceptual strain under controlled conditions.MethodsFor optimizing, hydrogel was used to increase the flexibility and a layer of the ethylene vinyl acetate foam was placed into the inside layer of packs to prevent tissue damage. Then, 15 men with an optimized ice cooling vest, with a commercial paraffin cooling vest, and without a cooling vest performed tests including exercise on a treadmill (speed of 2.8 km/hr and slope of %0) under hot (40°C) and dry (40 %) condition for 60 min. The physiological strain index and skin temperature were measured every 5 and 15 minutes, respectively. The heat strain score index and perceptual strain index were also assessed every 15 minutes.ResultsThe mean values of the physiological and perceptual indices differed significantly between exercise with and without cooling vests (P < 0.05). However, the difference of the mean values of the indices except the value of the skin temperature during the exercises with the commercial paraffin cooling vest and the optimized ice cooling vest was not significant (P > 0.05).ConclusionsThe optimized ice cooling vest was as effective as the commercial paraffin cooling vest to control the thermal strain. However, ice has a greater latent heat and less production cost.

Subjective thermal strain impairs endurance performance in a temperate environment

PurposeThe aim of this study was to test the hypothesis that subjective thermal strain can reduce endurance performance independently from the general physiological strain normally associated with impaired endurance performance in the heat. MethodsIn 20 °C and 44% relative humidity, 12 endurance-trained athletes (1♀ 11♂; mean ± SD; age: 27 ± 6 y; VO2max: 61 ± 6 ml/kg/min) performed a time to exhaustion (TTE) test in two different experimental conditions: with an electric heat pad applied to the subjects' upper back (HP) and control (CON: without heat pad). In both conditions, subjects cycled to volitional exhaustion at 70% of their VO2max. Cardiorespiratory, metabolic, thermoregulatory and perceptual responses were measured throughout the TTE test and compared at 0%, 50% and 100% isotime and at exhaustion. ResultsTTE was reduced by 9% in HP (2092 ± 305 s) compared to CON (2292 ± 344 s; p = .023). The main effect of condition on thermal discomfort at isotime (p = .002), the effect of condition on thermal sensation at 0% isotime (p = .004) and the condition by isotime interaction on rating of perceived exertion (p = .036) indicated higher subjective thermal strain in HP compared to CON. None of the measured cardiorespiratory, metabolic and thermoregulatory variables differed significantly between conditions. ConclusionOur novel experimental manipulation (HP) was able to induce significant subjective thermal strain and reduce endurance performance in a temperate environment without inducing the general physiological strain normally associated with impaired endurance performance in the heat. These results suggest that subjective thermal strain is an important and independent mediator of the heat-induced impairment in endurance performance.

Fuzzy comprehensive evaluation of human physiological state in indoor high temperature environments

Quantification of physiological state is a key issue for human physiological safety in high temperature environments. In this study, the fuzzy comprehensive evaluation method is introduced into the physiological state evaluation in indoor high temperature environments. Five physiological parameters (skin temperature, rectal temperature, heart rate, systolic pressure and sweat rate) are selected as the evaluation indexes, then the membership functions of the evaluation indexes are proposed to determine their membership degrees related to the evaluation grades. Based on the sensitivity analysis method, the sensitivity weights of above physiological parameters are determined. Then a comprehensive evaluation model for quantifying the physiological state is established. And physiological state score (PSS) is proposed to rank the safety level of the physiological state. Finally, the evaluation model is applied and verified in a case study. The results indicate that the weights of each physiological index change with the ambient temperature. The weights of the skin temperature and the rectal temperature account for a relatively large proportion, ranging from 81.8% to 88.5%. The safety levels ranked by the physiological state score are similar to the heat strain levels ranked by the physiological strain index values. The comparison results demonstrate the effectiveness and reliability of the proposed approach. The application of fuzzy comprehensive evaluation and sensitivity analysis provides a new scientific method for quantifying the human physiological state. This study can provide guidance for the physiological state evaluation and safety protection of relevant people in indoor high temperature environments.

The acute effect of training fire exercises on fire service instructors

Fire service instructors (FSI) regularly experience different types of fire exercises, however the strain experienced from these scenarios is not well understood. This study aims to identify the physiological and perceptual strain of Fire Service Instructors (FSI) to three training exercises: DEMO, ATTACK, COMPARTMENT, and the different roles performed: SETTER, INSTRUCTOR. The study also aims to assess the effect that different exercise patterns over a day (BOX, MULTI, COMBINATION) have on immunological responses. Sixteen FSI (age: 41 ± 8 years, body mass: 83.7 ± 6.7 kg, height: 177.0 ± 6.7 cm) were recruited, with 10 FSI completing the three exercises. Physiological and perceptual measures were collected prior to and immediately post each exercise. Venous blood samples were collected at the beginning and end of each day. One-way analysis of variance (ANOVA) were conducted to assess differences in physiological variables between exercise types, independent samples t-tests were conducted between roles. Day changes in hematological variables were assessed by paired sample t-tests and analyzed by one-way ANOVAs to identify differences between exercise patterns. The COMPARTMENT exercise resulted in a greater change in rectal temperature (ΔTre) (0.49 ± 0.28 °C) than both the DEMO (0.23 ± 0.19 °C, p = 0.045) and ATTACK (0.27 ± 0.22 °C, p = 0.016). Within the COMPARTMENT exercise, the SETTER resulted in a greater ΔTre and rating of perceived exertion than the INSTRUCTOR (0.67 ± 0.29 °C vs. 0.43 ± 0.18 °C, p = 0.027 and 14 ± 2 vs. 11 ± 2, p = 0.001, respectively). Following a day of fire exercises white blood cells (WBC), neutrophils, lymphocytes (LYMPH), monocytes (MONO), platelets (PLT), mean platelet volume (MPV), Interleukin (IL)-6, and cardiac troponin T (cTnT) all increased (p < 0.05). Exercise patterns containing a COMPARTMENT exercise resulted in greater PLT, MPV, and IL-6. Total daily variation in ΔTre was correlated with post-exercise WBC, MONO, and LYMPH. COMPARTMENT exercises produce the greatest physiological strain, with the SETTER role within this exercise causing the greatest ΔTre. Although predominately physiological responses remain within safe limits. Exercise patterns that include a COMPARTMENT exercise also generate a greater inflammatory response.

The physiological demands of elite epée fencers during competition

ABSTRACTThe aim of this study was to determine the physiological demands of epée fencing performance. Eight elite male epée fencers competed in a competition consisting of 7 Poule and 7 Direct Elimination (DE) fights. Core temperature (TC), heart rate (HR), movement patterns, training load, and differentiated ratings of perceived exertion (RPE) were collected for all Poule and DE fights. Expired gas, and energy expenditure (EE) were measured using breath-by-breath gas analysis during selected fights, along with blood lactate concentration. Maximal HR and RPE were greater in DE than Poule fights. There was a tendency for greater increases in TC in DE compared to Poule fights (p = 0.052). Blood lactate concentration decreased during the competition from Poule to DE suggesting reliance on phosphocreatine and aerobic energy sources during fencing. High oxygen consumption (~50 ml.kg−1.min−1) and EE (~13 kcal.min−1) were recorded in both Poule and DE. Fencers covered 3 times more distance in DE than Poule fights. High training load scores were also recorded. This is the first study to show an increased physiological strain, with high aerobic and anaerobic demands, as fencing competition progressed from Poule to DE. Additionally, there was a considerable energy demand exhibited during epée competition.

A synthetic undergarment increases physiological strain

Our aim was to examine the effect of a synthetic material undergarment on heat stress during exercise in a hot environment. Ten active males completed two trials of intermittent (50min walking, 10min sitting) treadmill walking over 3h in 35°C and 30% relative humidity. Subjects wore wildland firefighter flame-resistant meta-aramid blend pants and shirt with either a 100% cotton (C) or flame-retardant modacrylic undergarment (S), while carrying a 16-kg pack, helmet and leather gloves. Exercise was followed by a 30-min rest period without pack, helmet, gloves, and outerwear shirt. Rectal temperature and physiological strain were greater in S than C (P=0.04). No significant differences were found for heart rate, rating of perceived exertion, energy expenditure or skin temperature between C and S. Skin blood flow increased significantly in S following the second hour of exercise, resulting in a time×trial interaction (P=0.001). No significant differences for skin blood flow were found post exercise. Sweat rate and percent dehydration were not different between C and S. These data indicate that, of the two undergarments investigated, the synthetic undergarment negatively affected physiological factors that have been shown to indicate an increased risk of heat-related injuries.

The Physiological Strain Index Modified for Trained Heat-Acclimatized Individuals in Outdoor Heat.

Purpose: To determine if the Physiological Strain Index (PSI), in original or modified form, can evaluate heat strain on a 0-10 scale, in trained and heat-acclimatized men undertaking a competitive half-marathon run in outdoor heat. Methods: Core (intestinal) temperature (TC) and heart rate (HR) were recorded continuously in 24 men (mean [SD] age = 26 [3]y, VO2peak = 59 [5]mL·kg·min-1). A total of 4 versions of the PSI were computed: original PSI with upper constraints of TC 39.5°C and HR 180beats·min-1 (PSI39.5/180) and 3 modified versions of PSI with each having an age-predicted maximal HR constraint and graded TC constraints of 40.0°C (PSI40.0/PHRmax), 40.5°C (PSI40.5/PHRmax), and 41.0°C (PSI41.0/PHRmax). Results: In a warm (26.1-27.3°C) and humid (79-82%) environment, all runners finished the race asymptomatic in 107 (10) (91-137) min. Peak TC and HR were 39.7°C (0.5°C) (38.5-40.7°C) and 186 (6) (175-196) beats·min-1, respectively. In total, 63% exceeded TC 39.5°C, 71% exceeded HR 180beats·min-1, and 50% exceeded both of the original PSI upper TC and HR constraints. The computed heat strain was significantly greater with PSI39.5/180 than all other methods (P < .003). PSI >10 was observed in 63% of runners with PSI39.5/180, 25% for PSI40.0/PHRmax, 8% for PSI40.5/PHRmax, and 0% for PSI41.0/PHRmax. Conclusions: The PSI was able to quantify heat strain on a 0-10 scale in trained and heat-acclimatized men undertaking a half-marathon race in outdoor heat, but only when the upper TC and HR constraints were modified to 41.0°C and age-predicted maximal HR, respectively.

Post-exercise Hot Water Immersion Elicits Heat Acclimation Adaptations in Endurance Trained and Recreationally Active Individuals.

Hot water immersion (HWI) after exercise on 6 consecutive days in temperate conditions has been shown to provide heat acclimation adaptations in a recreationally active population. Endurance athletes experience frequent, sustained elevations in body temperature during training and competition; as a consequence, endurance athletes are considered to be partially heat acclimatized. It is therefore important to understand the extent to which endurance trained individuals may benefit from heat acclimation by post-exercise HWI. To this end, we compared the responses of eight endurance trained and eight recreationally active males (habitual weekly endurance exercise: 9 h vs. 3 h) to a 6-day intervention involving a daily treadmill run for 40 min (65% O2max) in temperate conditions followed immediately by HWI (≤40 min, 40°C). Before (PRE) and after the intervention (POST), hallmark heat acclimation adaptations were assessed during a 40-min treadmill run at 65% O2max in the heat (33°C, 40% RH). The 6 day, post-exercise HWI intervention induced heat acclimation adaptations in both endurance trained and recreationally active individuals. Training status did not significantly influence the magnitude of heat acclimation adaptations from PRE to POST (interactions P > 0.05) for: the reduction in end-exercise rectal core temperature (Tre, mean, endurance trained -0.36°C; recreationally active -0.47°C); the reduction in resting Tre (endurance trained -0.17°C; recreationally active -0.23°C); the reduction in Tre at sweating onset (endurance trained -0.22°C; recreationally active -0.23°C); and, the reduction in mean skin temperature (endurance trained -0.67°C; recreationally active -0.75°C: PRE to POST P < 0.01). Furthermore, training status did not significantly influence the observed reductions in mean O2, mean metabolic energy expenditure, end-exercise physiological strain index, perceived exertion or thermal sensation (PRE to POST P < 0.05). Only end-exercise heart rate was influenced by training status (P < 0.01, interaction); whereby, recreationally active but not endurance trained individuals experienced a significant reduction in end-exercise heart rate from PRE to POST (P < 0.01). In summary, these findings demonstrate that post-exercise HWI presents a practical strategy to reduce thermal strain during exercise-heat-stress in endurance trained and recreationally active individuals.

Agonistic and antagonistic roles of fibroblasts and cardiomyocytes on viscoelastic stiffening of engineered human myocardium

Cardiomyocyte and stroma cell cross-talk is essential for the formation of collagen-based engineered heart muscle, including engineered human myocardium (EHM). Fibroblasts are a main component of the myocardial stroma. We hypothesize that fibroblasts, by compacting the surrounding collagen network, support the self-organization of cardiomyocytes into a functional syncytium. With a focus on early self-organization processes in EHM, we studied the molecular and biophysical adaptations mediated by defined populations of fibroblasts and embryonic stem cell-derived cardiomyocytes in a collagen type I hydrogel. After a short phase of cell-independent collagen gelation (30 min), tissue compaction was progressively mediated by fibroblasts. Fibroblast-mediated tissue stiffening was attenuated in the presence of cardiomyocytes allowing for the assembly of stably contracting, force-generating EHM within 4 weeks. Comparative RNA-sequencing data corroborated that fibroblasts are particularly sensitive to the tissue compaction process, resulting in the fast activation of transcription profiles, supporting heart muscle development and extracellular matrix synthesis. Large amplitude oscillatory shear (LAOS) measurements revealed nonlinear strain stiffening at physiological strain amplitudes (>2%), which was reduced in the presence of cells. The nonlinear stress-strain response could be characterized by a mathematical model. Collectively, our study defines the interplay between fibroblasts and cardiomyocytes during human heart muscle self-organization in vitro and underscores the relevance of fibroblasts in the biological engineering of a cardiomyogenesis-supporting viscoelastic stroma. We anticipate that the established mathematical model will facilitate future attempts to optimize EHM for in vitro (disease modelling) and in vivo applications (heart repair).

On multiscale boundary conditions in the computational homogenization of an RVE of tendon fascicles

Present study provides a numerical investigation on multiscale boundary conditions in the computational homogenization of a representative volume element (RVE) of tendon fascicles. A three-dimensional hexagonal-helicoidal finite element RVE composed of two material phases (collagen fibers and cells) and three finite strain viscoelastic models (collagen fibrils, matrix of fibers and cells) compose the multiscale model. Due to the unusual helical geometry of the RVE, the performance of four multiscale boundary conditions is evaluated: the linear boundary displacements model, the minimally constrained model and two mixed boundary conditions allying characteristics of both, linear and minimal models. Numerical results concerning microscopic kinematic fields and macroscopic stress-strain curves point out that one of the mixed models is able to predict the expected multiscale mechanics of the RVE, presenting sound agreement with experimental facts reported in literature, for example: characteristic non-linear shape of the stress-strain curves; macroscopic energy loss by hysteresis; axial rotation of fascicles observed in tensile tests; collagen fibrils are the main load-bearing components of tendons; cells contribute neither to the stiffness nor to the macroscopic energy loss. Moreover, the multiscale model provides important insights on the micromechanics of tendon fascicles, predicting a non-homogeneous and relevant strain localization on cells, even under physiological macroscopic strain amplitudes.

Cardiopulmonary-induced deformations of the thoracic aorta following thoracic endovascular aortic repair.

Thoracic endovascular aortic repair has become a preferred treatment strategy for thoracic aortic aneurysms and dissections. Yet, it is not well understood if the performance of endografts is affected by physiologic strain due to cyclic aortic motion during cardiac pulsation and respiration. We aim to quantify cardiac- and respiratory-induced changes of the postthoracic endovascular aortic repair thoracic aorta and endograft geometries. Fifteen thoracic endovascular aortic repair patients (66 ± 10 years) underwent cardiac-resolved computed tomography angiographies during inspiratory/expiratory breath holds. The computed tomography angiography images were utilized to build models of the aorta, and lumen centerlines and cross-sections were extracted. Arclength and curvature were computed from the lumen centerline. Effective diameter was computed from cross-sections of the thoracic aorta. Deformation was computed from the mid-diastole to end-systole (cardiac deformation) and expiration to inspiration (respiratory deformation). Cardiac pulsation induced significant changes in arclength, mean curvature, maximum curvature change, and effective diameter of the ascending aorta, as well as effective diameter of the stented aortic segment. Respiration, however, induced significant change in mean curvature and effective diameter of the ascending aorta only. Cardiac-induced arclength change of the ascending aorta was significantly greater than respiratory-induced arclength change. Deformations are present across the thoracic aorta due to cardiopulmonary influences after thoracic endovascular aortic repair. The geometric deformations are greatest in the ascending aorta and decline at the stented thoracic aorta. Additional investigation is warranted to correlate aortic deformation to endograft performance.

Reviewing the Effects of Integrated Lean Six Sigma Methodologies with Ergonomics Principles in an Industrial Workstation

This work presents the importance of a combination of three approaches: the Lean idea of waste to be eliminated, the Six Sigma concept of variance to be reduced, and Ergonomics approaches that play an important role in maintaining workers’ productivity. Improper workstation layout conditions lead to excessive stress, reduced performance, and physical burdens. This leads to increases in waste indicators such as loss of time, poor space, and low quality levels. A single-minded focus on productivity may neglect health and safety issues and, worse, changes introduced by Lean may lead to additional risks. Muda is a term in Lean referring to any action or process that doesn’t add value within processes, such as physical waste of time or safety violations. Job Rotation as a problem-solving tool refers to the structured interchange of workers between different jobs that are recognised as problem or high-risk jobs. The methodology of this research work proposes an integrated model combining Lean as represented by reducing Muda or waste that does not add value to both process and workers, previewed by means of the DMAIC Six Sigma stages, with job rotation used as an efficient measurement tool to observe jobs that may be identified as overly stressful. A computerised worksheet tool was used to perform a semi-quantitative assessment process for rating a job’s Exertion Index (IE), which can be used to determine the best arrangement of Job Rotation schedules. The work aims were: I) Rearrangement of jobs according to risk level of producing non-well-being to reduce additional psychological stress on workers and to II) reflect this by achieving continuous improvement by eliminating waste, decreasing activities that are Non-Values Add, and thereby creating good quality levels. The findings showed enhancement of current safety and productivity levels from evaluating the Exertion Index and swapping some workstations with unacceptable indices. This offered a reduction in physiological strain, stress, and fatigue on various muscle sets. The case study for this research work was implemented in the General Company for Hydraulic Industries/Damper factory.

Practical Torso Cooling During Soccer-Specific Exercise in the Heat.

Precooling and midevent cooling of the torso using cooling vests can improve exercise performance in the heat with or without physiological changes; however, the effects of such cooling during intermittent exercise in the heat are unknown. To investigate the effects of torso cooling during intermittent exercise in the heat (35°C, 50% relative humdity) on sprint performance and the physiological and perceptual responses to the exercise. Crossover study. Walk-in environmental chamber. Ten non-heat-acclimated, male soccer players (age = 25 ± 2 years, height = 1.77 ± 0.06 m, mass = 72.9 ± 7.6 kg). Two 90-minute bouts of soccer-specific intermittent running in the heat: 1 trial with a cooling vest worn during the exercise and 1 trial without a cooling vest. Each trial comprised two 45-minute periods separated by approximately 15 minutes of seated rest in cool conditions (approximately 23°C, 50% relative humdity). Peak sprint speed, rectal temperature (Tr), mean-weighted skin temperature (Tsk), heart rate (HR), rating of perceived exertion (RPE), and thermal sensation (TS) were measured every 5 minutes. Peak sprint performance was largely unaffected by the cooling vest. The Tr, Tsk, HR, RPE, and TS were unaffected in the cooling-vest trial during the first 45 minutes, but Tr rose at a slower rate in the cooling-vest trial (0.026°C.min-1 ± 0.008°C.min-1) than in the no-vest trial (0.032°C.min-1 ± 0.009°C.min-1). During the second 45-minute period, Tr, Tr rate of rise, Tsk, RPE, and TS were lower in the cooling-vest trial (Hedges g range, 0.55-0.84), but mean HR was unaffected. Wearing a cooling vest during soccer-specific intermittent running in the heat reduced physiological and perceptual strain but did not increase peak sprint speed.

Analysis of Cartilage Creep Recovery Using a Highly Dynamic Closed-loop Test System

The aim of this study was to analyze cartilage creep and creep recovery after static and cyclic loading. Up to now technical limitations have hindered the measurement of creep recovery. For this reason, we developed a closed loop micro creep and creep-recovery indentation test system with active force control. Bovine osteochondral explants were tested under static (110 kPa) and cyclic (100 cycles, 350 kPa/35 kPa, 1 Hz) loading conditions and subsequently creep recovery was measured. The cartilage thickness was determined using needle indentation. For static loading, the creep and creep-recovery rates were significantly different during the first 60 seconds (p < 0.05). Cyclic loading was assessed for the medial and lateral patella and resulted in a physiological patellar cartilage strain of 7.7% ± 2.6% and 8.2% ± 2.7%, respectively. We recorded a creep recovery of 97.8% ± 2.1% for the medial and 98.3% ± 2.4% for the lateral patella. The advantage of this study over earlier in vitro studies is that we recorded creep-recovery profiles with an actively controlled setup. This allowed us to analyze creep recovery immediately after removing the creep load, in contrast to MRI-based in vivo studies. In future, the presented method will enable us to quantify spatial variations within articular joints.

Deception of cycling distance on pacing strategies, perceptual responses, and neural activity.

Pacing during exercise performance is well-established; however, little is known about the neural responses associated with changes in power output and the effect of exercise end-point knowledge. Therefore, the aim of this study was to examine the effect of deception of cycling distance on pacing, cerebral oxy- (O2Hb) and deoxy-haemoglobin concentrations, and alpha (α) wave activity. Ten well-trained male cyclists (23.7 ± 6.6years) completed three cycling time trials (TT) on a stationary air-braked cycle ergometer and were informed the study was to examine the reliability of 3 × 30-km TT. Participants unknowingly completed three distances (24, 30, and 36km) in a randomised order. Performance (power output; PO), physiological (heart rate; HR), perceptual (rating of perceived exertion; RPE), and neurological (O2Hb, HHb, and α activity) measures were recorded throughout each TT. Data were converted to a percentage relative to the total distance covered. At 100% completion, HR and PO were lower during the 36km compared to the 30km trial (P ≤ 0.01). Compared to the 24km trial, α waves were reduced at 100% (effect size; ES = 1.01), while O2Hb was greater at 70% of completion in the 36km trial (ES = 1.39). RPE was also higher for 36km compared to 30-km trial at 80% and the 24-km trial at 10% and 40-100% of completion (P ≤ 0.02). We conclude that the increase in O2Hb and RPE during the 36-km trial, while a reduction in HR and PO is present, may indicate that the pre-frontal cortex may influence the regulation of exercise performance when deceived of the duration end-point by increasing perception of effort to reduce premature onset of physiological strain.

Short term heat acclimation reduces heat stress, but is not augmented by dehydration

Heat acclimation lowers physiological strain when exercising in the heat, and may be enhanced by promoting dehydration during acclimation. The purpose was to compare fluid intake during heat acclimation by promoting dehydration (DEH=0.5 mL kg−1 15 min−1, ~2.4% dehydration per acclimation session) compared to euhydration (EUH=2.0 mL kg−1 15 min−1, ~1.4% dehydration per acclimation session) following four heat acclimation bouts on thermal strain, and exercise performance.Thirteen males completed 90 min heat stress tests (HST) at 50% VO2max (40 °C, 30%RH) before and after three 90 min heat acclimation trials, involving consecutive bouts with 4-fold less fluid (DEH) or EUH. DEH and EUH trials were separated by 48 h and assigned in a random crossover design separated by a 5 week washout. Wildland firefighter (WLFF) Nomex: shirt, pants, and a cotton T-shirt baselayer were worn.Peak core temperature (Tc) from the HST significantly decreased following both DEH (39.5 ± 0.1–39.0 ± 0.1 °C: P < 0.001) and EUH acclimation (39.5 ± 0.1–38.9 ± 0.1 °C: P < 0.001). HR, RPE, physiological strain index (PSI), and total work (J) completed in a graded exercise test to exhaustion were improved (P < 0.001) in effect for acclimation, but not different when comparing DEH or EUH fluid delivery. SBF was unchanged (P = 0.313). Sweat rate increased greater following DEH (1.52 ± 0.06–1.89 ± 0.09 L h−1) compared to EUH acclimation (1.57 ± 0.06–1.79 ± 0.08 L h−1: P = 0.015). Resting plasma volume increased in effect for acclimation (P = 0.002). Aldosterone decreased in effect for acclimation (P < 0.001) at rest and following exercise, and total protein was unaffected (P = 0.83).In conclusion, short-term heat acclimation (~360 min) attenuates heat stress, and improves exercise capacity in the heat, and was not impaired nor improved by promoting DEH during acclimation.

The Hexoskin physiological monitoring shirt does not impair whole-body heat loss during exercise in hot-dry conditions.

Using direct calorimetry, we determined if the Hexoskin shirt (Carré Technologies Inc., Que., Canada), a wearable device for monitoring physiological strain, would compromise whole-body heat loss and exacerbate body heat storage during moderate-intensity activity in hot-dry conditions. The shirt did not impair heat dissipation and resulted in similar body heat storage when worn alone relative to a semi-nude condition (214 vs. 211 kJ) or when worn underneath a work uniform compared with a cotton undershirt (307 vs. 318 kJ).

Workplace Heat Exposure Management in Indian Construction Workers Using Cooling Garment.

Construction workers are at high risk of heat-related illnesses during summer months in India. The personal cooling garment (PCG) is a microclimate assistive device that provides protection from heat stress. The applicability and efficacy of wearing PCG for the physiological and subjective responses were tested on 29 healthy construction workers at actual field worksites. During the test, the climatic conditions were 103.64 ± 38.3°F dry bulb temperature, 41.2 ± 13.4% relative humidity, and wet bulb globe temperature 91.43 ± 39.92°F. Mean weighted skin temperature was significantly lowered by 38.66 ± 33.98°F when wearing PCG as compared with wearing habitual clothing (HC), 32.36 ± 33.44°F ( p < .05). Mean sweat loss was also significantly lower when wearing PCG: 0.365 ± 0.257 kg as compared with wearing HC: 0.658 ± 0.342 kg ( p < .05). Heart rate, along with back and chest skin temperatures were significantly reduced with wearing PCG. The present study suggests that PCG provides an affordable way of alleviating the discomfort and physiological strain caused by environmental heat exposure.

A variational homogenization approach applied to the multiscale analysis of the viscoelastic behavior of tendon fascicles

This work presents a variational homogenization approach based on representative volume elements (RVE) in order to investigate the macro- and microviscoelastic behavior of tendon fascicles. A three-dimensional hexagonal–helicoidal finite element RVE is proposed to properly account for the morphology of tendon fascicles observed in serial block-face scanning electron microscopy. Two material phases (collagen fibers and cells) comprising three finite strain variational viscoelastic models (fibrils, matrix of fibers and cells) compose the proposed multiscale model. The material parameters of the micromechanical models were identified with the aid of atomic force microscopy experiments extracted from the literature. A set of multiscale simulations of tensile tests under physiological strain amplitudes were performed, providing the following results. Firstly, numerical predictions corroborate experimental findings: collagen fibrils are the main load-bearing structures of tendons; the cellular matrix contributes neither to the stiffness nor to the energy dissipation of tendons. Secondly, the model brings insights about microscale mechanics of tendon fascicles not completely understood: prediction of uncoiling of fibers during axial loads which may explain the large apparent Poisson ratios and fluid loss, and significant strain localization in cells, which may lead to important mechanotransduction mechanisms. Moreover, the distribution of dissipated power became available, pointing out the fibrils as the main source of dissipation of fascicles under high macroscopic strain rates and during the unloading phase in cyclic regimes.

Concurrent exercise circuit protocol performed in public fitness facilities meets the American College of Sports Medicine guidelines for energy cost and metabolic intensity among older adults in Rio de Janeiro City

The current study investigated whether a single bout of concurrent exercise (Ex Rx) at Third Age Academies (TAAs) in Rio de Janeiro City meets the American College of Sports Medicine (ACSM) guidelines for energy cost and metabolic intensity in older adults. Nine subjects (5 males and 4 females, 63-80 years of age) visited the laboratory for clinical screening and for anthropometrical, resting, and maximal oxygen uptake assessments. Thereafter, subjects performed an Ex Rx circuit consisting of a single circuit alternating aerobic and resistance exercises with outdoor exercise equipment using body mass as the load (total of 9 exercises, 1-2 sets of 15 repetitions). Expired gases were collected via a metabolic cart during exercise bouts. The mean observed energy cost value of 169.1 kcal was slightly greater than the minimum value of 150 kcal reported in the ACSM guidelines (p = 0.018). Like energy cost, all the intensity markers adopted to analyze the physiological strain induced by the Ex Rx circuit significantly exceeded their reference values for moderate intensity (reference values: 3.2 METs (mean observed value = 4.6 METs, p = 0.002); 40% of oxygen uptake reserve (mean observed value = 51.5%, p = 0.040); 40% of heart rate reserve (mean observed value = 64.1%, p < 0.001)), according to the ACSM guidelines. In conclusion, a single bout of Ex Rx circuit performed at TAAs in Rio de Janeiro City was able to induce a physiological strain (i.e., energy cost and intensity) compatible with ACSM recommendations for eliciting health benefits among older adults.