Whole-body fluid distribution in humans during dehydration and recovery, before and after humid-heat acclimation induced using controlled hyperthermia

Patterson, Mark J.; Stocks, Jodie M.; Taylor, Nigel A.S.

doi:10.1111/apha.12214

Cited by 41 publications

(55 citation statements)

References 55 publications

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“…In this state, and depending upon the ambient conditions, heat storage can approximate heat production , imposing a significant impediment to viable work durations (McLellan et al 2013;Taylor 2015;Taylor and Patterson 2016). Moreover, continued physiological attempts to lose heat can actually exacerbate the problem, with excessive sweating leading to rapid dehydration, and the depletion of body fluids and electrolytes (Patterson et al 2014), whilst cutaneous vascular engorgement (Rowell et al 1970;Fogarty et al 2004) can challenge blood pressure regulation (Taylor and Patterson 2016).…”

Section: Thermoregulatory Consequencesmentioning

confidence: 99%

Load carriage, human performance, and employment standards

Taylor

Peoples

Petersen

2016

Appl. Physiol. Nutr. Metab.

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Abstract:The focus of this review is on the physiological considerations necessary for developing employment standards within occupations that have a heavy reliance on load carriage. Employees within military, fire fighting, law enforcement, and search and rescue occupations regularly work with heavy loads. For example, soldiers often carry loads >50 kg, whilst structural firefighters wear 20-25 kg of protective clothing and equipment, in addition to carrying external loads. It has long been known that heavy loads modify gait, mobility, metabolic rate, and efficiency, while concurrently elevating the risk of muscle fatigue and injury. In addition, load carriage often occurs within environmentally stressful conditions, with protective ensembles adding to the thermal burden of the workplace. Indeed, physiological strain relates not just to the mass and dimensions of carried objects, but to how those loads are positioned on and around the body. Yet heavy loads must be borne by men and women of varying body size, and with the expectation that operational capability will not be impinged. This presents a recruitment conundrum. How do employers identify capable and injury-resistant individuals while simultaneously avoiding discriminatory selection practices? In this communication, the relevant metabolic, cardiopulmonary, and thermoregulatory consequences of loaded work are reviewed, along with concomitant impediments to physical endurance and mobility. Also emphasised is the importance of including occupation-specific clothing, protective equipment, and loads during work-performance testing. Finally, recommendations are presented for how to address these issues when evaluating readiness for duty.Key words: backpacks, firefighter, load carriage, oxygen cost, military, employment standards, ventilation, work of breathing.Résumé : Cette analyse documentaire traite principalement des aspects physiologiques essentiels à l'élaboration de normes d'emploi pour des postes dont la fonction majeure est le transport de charges. Les employés dans l'armée, les pompiers, la police, les membres de recherche et sauvetage travaillent régulièrement avec de lourdes charges. Par exemple, les soldats transportent souvent des charges de >50 kg et les pompiers de bâtiments portent un vêtement de protection pesant de 20 à 25 kg et déplacent aussi des charges externes. On sait depuis longtemps que le port de charges lourdes modifie la démarche, la mobilité, le taux métabolique et le rendement tout en augmentant le risque de fatigue musculaire et de blessure. De plus, le déplacement des charges est effectué fréquemment dans des conditions environnementales stressantes et les vêtements de protection accroissent la charge thermique dans cet endroit. En outre, la contrainte physiologique ne dépend pas seulement de la masse et des dimensions des objets à déplacer, mais aussi de leur positionnement sur et autour du corps. Pourtant, il faut que ces charges soient déplacées par des hommes et des femmes de gabarit divers dont les capacités opérationnell...

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Section: Thermoregulatory Consequencesmentioning

confidence: 99%

Load carriage, human performance, and employment standards

Taylor

Peoples

Petersen

2016

Appl. Physiol. Nutr. Metab.

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“…Isothermic heat acclimation (also known as controlled hyperthermia) is imposed based upon endogenous (internal) criteria (Castle et al, 2012;Garrett et al, 2014Garrett et al, , 2012Garrett et al, , 2009Hom et al, 2012;Machado-Moreira et al, 2006;Magalhães et al, 2010aMagalhães et al, , 2010bPatterson et al, 2014Patterson et al, , 2004, and might provide sustained targeting and attainment of specific and individualised internal temperatures through a combination of active and passive heat acclimation (Fox et al, 1963). The balance between work and rest to target and maintain specific core temperatures ensures a consistency, or a progression of endogenous heat strain to induce adaptation, albeit requiring alterations in administration throughout each session.…”

Section: Introductionmentioning

confidence: 99%

Isothermic and fixed intensity heat acclimation methods induce similar heat adaptation following short and long-term timescales

Gibson

Mee

Tuttle

et al. 2015

Journal of Thermal Biology

103

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Heat acclimation requires the interaction between hot environments and exercise to elicit thermoregulatory adaptations. Optimal synergism between these parameters is unknown. Common practise involves utilising a fixed workload model where exercise prescription is controlled and core temperature is uncontrolled, or an isothermic model where core temperature is controlled and work rate is manipulated to control core temperature. Following a baseline heat stress test; 24 males performed a between groups experimental design performing short term heat acclimation (STHA; five 90 min sessions) and long term heat acclimation (LTHA; STHA plus further five 90 min sessions) utilising either fixed intensity (50% VO2peak), continuous isothermic (target rectal temperature 38.5 °C for STHA and LTHA), or progressive isothermic heat acclimation (target rectal temperature 38.5 °C for STHA, and 39.0 °C for LTHA). Identical heat stress tests followed STHA and LTHA to determine the magnitude of adaptation. All methods induced equal adaptation from baseline however isothermic methods induced adaptation and reduced exercise durations (STHA = -66% and LTHA = -72%) and mean session intensity (STHA = -13% VO2peak and LTHA = -9% VO2peak) in comparison to fixed (p < 0.05). STHA decreased exercising heart rate (-10 b min(-1)), core (-0.2 °C) and skin temperature (-0.51 °C), with sweat losses increasing (+0.36 Lh(-1)) (p<0.05). No difference between heat acclimation methods, and no further benefit of LTHA was observed (p > 0.05). Only thermal sensation improved from baseline to STHA (-0.2), and then between STHA and LTHA (-0.5) (p<0.05). Both the continuous and progressive isothermic methods elicited exercise duration, mean session intensity, and mean T(rec) analogous to more efficient administration for maximising adaptation. Short term isothermic methods are therefore optimal for individuals aiming to achieve heat adaptation most economically, i.e. when integrating heat acclimation into a pre-competition taper. Fixed methods may be optimal for military and occupational applications due to lower exercise intensity and simplified administration.

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“…Hypovolemia and hyperosmolality due to thermal dehydration also suppress thermoregulatory responses of sweating and cutaneous vasodilation, resulting in increased risk of heat illness (18). It has been often observed that non-acclimatized individuals tend to consume inadequate fluid leading to hypohydration, which can quickly result in dehydration with increased risk of heat illness / injury (27). Heat acclimatization induced effective adaptations are more pronounced after fluid-regulatory strain from permissive dehydration (11).…”

Section: Research Articlementioning

confidence: 99%

“…It was further observed by Patterson et al that plasma volume was not defended more vigorously following humid-heat acclimatization. Rather a greater fluid loss may well underlie the mechanisms for enhancing plasma volume recovery when heat acclimation is induced using controlled-hyperthermia (26,27). Sufficient body water is required to sustain thermoregulatory function, thus losses in total body water can challenge the thermoregulatory system (18).…”

Section: Research Articlementioning

confidence: 99%

Profiling of Body Hydration and Related Blood Parameters under Hot-Arid Conditions among Indian Population doing Graded Physical Activity

Bharadwaj¹,

Baburaj²,

Bajaj³

et al. 2017

IJCRR

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This study highlights the effect of extreme heat stress exposure (WBGT Index 36.24°C) on hematological variables while performing graded physical activity (sedentary, moderate and heavy). Total 30 participants were involved in the study and were randomly distributed into batches of 10 under three categories of physical activity. Volunteers performed physically strenuous work while being exposed to ambient heat stress (hot -arid conditions). White Blood Corpuscles (WBC) count in heavy work group [506 kcal/ hr energy expenditure] showed significant increase from pre to post exposure (p < 0.01). No other group showed significant change in WBC count. Haematocrit % (Hct %) was significantly increased among heavy work group (p < 0.01) whereas Red Blood Corpuscles (RBC) count and Red Blood Cell Distribution Width (RDW) showed no significant increase. Blood viscosity showed increase among moderate work group [412kcal / hr energy expenditure] (p<0.05) and heavy work group (p< 0.001). These alterations indicate that participants exposed to high ambient temperature while doing graded physical activity underwent considerable hypo-hydration (sweat loss upto 4% of body weight) which got reflected in hematological parameters. This depletion of body fluid got reflected on blood viscosity and WBC count at a stage when the condition was not subjectively perceived. Data may be beneficial to identify such hypo hydration status before the condition is manifested visibly or symptomatically.

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Whole-body fluid distribution in humans during dehydration and recovery, before and after humid-heat acclimation induced using controlled hyperthermia

Abstract: It is concluded that the plasma volume was not defended more vigorously following humid-heat acclimation. Indeed, a greater fluid loss may well underlie the mechanisms for enhancing plasma volume recovery when heat acclimation is induced using the controlled-hyperthermia technique.

Cited by 41 publications

References 55 publications

Load carriage, human performance, and employment standards

Load carriage, human performance, and employment standards

Isothermic and fixed intensity heat acclimation methods induce similar heat adaptation following short and long-term timescales

Profiling of Body Hydration and Related Blood Parameters under Hot-Arid Conditions among Indian Population doing Graded Physical Activity

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