Search

Background: The water deficit equation (WD1 = 0.6Bm[1 - 140/Na+]) is employed in medicine and nutrition to estimate the volume (liters) of water required to correct dehydration during the initial stages of fluid replacement therapy. Several equation assumptions may limit its accuracy, but none have been systematically tested. Objectives: To quantify the potential error in WD1 for estimating free water (FW) and total body water (TBW) losses and to systematically evaluate its assumptions. Design: Thirty-six euhydrated volunteers were dehydrated (2.2 to 5.8% body mass, Bm) via thermoregulatory sweating. Assumptions within WD1 were tested by substituting measured euhydrated values for assumed or unknown values. These included the known (pre-morbid) Bm (WD2), a proposed correction for unknown Bm (WD3), the TBW estimated from body composition (WD4), the actual plasma sodium (WD5), the substitution of plasma osmolality (Posm) for sodium (WD6), and actual Posm (WD7). Results: Dehydration reduced TBW by 3.49 - 0.91 L, 57% of which (2.02 - 0.96 L) was FW loss, and increased plasma sodium from 139 (135 to 143 mmol/L) to 143 (141 to 148 mmol/L). Calculations for WD1-WD7 all underestimated TBW loss by 1.5 to 2.5 L (P0.05). WD1-WD5 underestimated FW by 0.5 L to 1.0 L (P0.05), but WD6 and WD7 estimated FW loss to within 0.06 to 0.16 L (P0.05). Conclusions: WD1 grossly underestimates TBW and FW losses. Corrections for unknowns and assumptions (WD1-WD5) improved estimates little. The use of WD6 = 0.6Bm(1 - 290/Posm) accurately estimates FW, but still underestimates TBW losses by 40%., Published in the American Journal of Clincal Nutrition v97 p79-85, 2013.

Equivocal findings have been reported in the few studies that examined the impact of ambient temperature (Ta) and hypohydration on cognition and dynamic balance. The purpose of this study was to determine the impact of acute exposure to a range of ambient temperatures (Ta 10 40 deg C) in euhydration (EUH) and hypohydration (HYP) states on cognition, mood and dynamic balance. Thirty-two men (age 22 4 years, height 1.80 0.05 m, body mass 85.4 10.8 kg) were grouped into four matched cohorts (n = 8), and tested in one of the four Ta (10, 20, 30, 40 deg C) when EUH and HYP (-4 % body mass via exercise heat exposure). Cognition was assessed using psychomotor vigilance, 4-choice reaction time, matching to sample, and grammatical reasoning. Mood was evaluated by profile of mood states and dynamic postural balance was tested using a Biodex Balance System. Thermal sensation (TS), core (Tcore) and skin temperature (Tsk) were obtained throughout testing. Volunteers lost -4.1 0.4 % body mass during HYP. Tsk and TS increased with increasing Ta, with no effect of hydration. Cognitive performance was not altered by HYP or thermal stress. Total mood disturbance (TMD), fatigue, confusion, anger, and depression increased during HYP at all Ta. Dynamic balance was unaffected by HYP, but 10 deg C exposure impaired balance compared to all other Ta. Despite an increase in TMD during HYP, cognitive function was maintained in all testing environments, demonstrating cognitive resiliency in response to body fluid deficits. Dynamic postural stability at 10 deg C appeared to be hampered by low-grade shivering, but was otherwise maintained during HYP and thermal stress., Published in the European Journal of Applied Physiology, v113 p1027-1034, 2013.

Dehydration (body water deficit) is a physiologic state that can have profound implications for human health and performance. Unfortunately, dehydration can be difficult to assess, and there is no single, universal gold standard for decision making. In this article, we review the physiologic basis for understanding quantitative dehydration assessment. We highlight how phenomenologic interpretations of dehydration depend critically on the type (dehydration compared with volume depletion) and magnitude (moderate compared with severe) of dehydration, which in turn influence the osmotic (plasma osmolality) and blood volume dependent compensatory thresholds for antidiuretic and thirst responses. In particular, we review new findings regarding the biological variation in osmotic responses to dehydration and discuss how this variation can help provide a quantitative and clinically relevant link between the physiology and phenomenology of dehydration. Practical measures with empirical thresholds are provided as a starting point for improving the practice of dehydration assessment.

Individuals exercise and work in a wide range of environmental conditions. Depending on environmental conditions and a person's metabolic rate and clothing, exercise can accentuate heat gain or heat loss, causing body temperature to rise or fall. Healthy humans normally regulate body (core) temperatures near 37 deg. C at rest, and with environmental and/or exercise perturbations, body temperatures can fluctuate between 35 deg. C and 41 deg. C without adverse health consequences. Fluctuations outside that range can be associated with morbidity and mortality. In this chapter, the term exercise refers to dynamic exercise, and training refers to repeated days of exercise in a specific modality leading to adaptations. The term stress refers to environmental and/or exercise conditions that tend to influence the body's heat content, and strain refers to the physiologtc consequences of stress. The magnitude of stress and the resulting strain depend on a complex interaction among environmental factors (e.g., ambient conditions) and the individual's biologic characteristics (e.g. acclimatization status and body size) and activity level (e.g., metabolic rate and duration). The term acclimatization refers to adaptations to both natural (acclimatization) and artificial (acclimation) environmental conditions. In this chapter, we examine the effects of both heat stress and cold stress on physiologic responses and exercise capabilities. Human thermoregulation during exercise is addressed, but more detailed reviews on this process during environmental stress can be found elsewhere. This chapter reviews the physiology. needs, and assessmem of human water and electrolyte balance. The extent to which water and electrolyte imbalances affect temperature regulation and exercise performance are also considered. This chapter includes information on the pathogenesis of exertional heat illness and hypothermia, since exercise can increase morbidity and mortality from thermal injury., Book chapter, Human Water and Electrolyte Balance, published in Present Knowledge in Nutrition, Tenth Edition, chapter 32, p493-505, 2012. Journal article, Sweat rate prediction equations for outdoor exercise with transient solar radiation, published in Journal of Applied Physiology, v112 p1300-1310, 12 Jan 2012. Prepared in collaboration with Biology Department, New Mexico State University, Las Cruces,NM; Heller Institute of Medical Research, Sheba Medical Center, Tel Hashomer; and Ariel University Center of Samaria, Israel.

We investigated the validity of employing a fuzzy piecewise prediction equation (PW) defined by sweat rate (msw, g/sq m/h) = 147 + 1.527x(Ereq) - 0.87x(Emax), which integrates evaporation required (Ereq) and the maximum evaporative capacity of the environment (Emax). Heat exchange and physiological responses were determined throughout the trials. Environmental conditions were ambient temperature (Ta) = 16-26 deg C, relative humidity (RH) = 51-55%, and wind speed (V) = 0.5-1.5 m/s. Volunteers wore military fatigues [clothing evaporative potential (im/clo) = 0.33] and carried loads (15-31 kg) while marching 14-37 km over variable terrains either at night (N = 77, trials 1-5) or night with increasing daylight (N = 33, trials 6 and 7). PW was modified (Pw,sol) for transient solar radiation (Rsol, W) determined from measured solar loads and verified in trials 6 and 7. PW provided a valid msw prediction during night trials (1-5) matching previous laboratory values and verified by bootstrap correlation (rbs of 0.81, SE + or - 0.014, SEE = + or - 69.2 g/sq m/h). For trials 6 and 7, Ereq and Emax components included Rsol applying a modified equation Pw,sol, in which msw = 147 + 1.527x(Ereq,sol) - 0.87 x(Emax). Linear prediction of msw = 0.72 x Pw,sol + 135 (N = 33) was validated (R2 = 0.92; SEE = + or -33.8 g/sq m/h) with PW beta-coefficients unaltered during field marches between 16 deg C and 26 deg C Ta for msw or = 700 g/sq m/h. PW was additionally derived for cool laboratory/night conditions (Ta 20 deg C) in which Ereq is low but Emax is high, as: PW,cool (g/sq m/h) = 350 + 1.527xEreq - 0.87xEmax. These sweat prediction equations allow valid tools for civilian, sports, and military medicine communities to predict water needs during a variety of heat stress/exercise conditions., Published in Journal of Applied Physiology, v112 p1300-1310, 2012.

Body fluid balance is controlled by both physiological and behavioral actions. However, when there is lack of fluid availability, exposure to extreme environments, or illness, inability to maintain fluid balance can seriously jeopardize health and the ability to perform. This chapter presents an overview of topics surrounding hydration, dehydration, and rehydration. The terms euhydration, hypohydration, and hyperhydration will be used. Euhydration defines a normal, narrow fluctuation in body water content, whereas the terms hypohydration and hyperhydration define, respectively, a general deficit (hypohydration) and surfeit (hyperhydration) in body water content beyond normal. The term dehydration specifically defines the condition of hypertonic hypovolemia brought about by the net loss of hypotonic body fluids. Isotonic or hypotonic hypovolemia, manifest by large losses of solute and water, is defined simply as hypovolemia. Table 70-1 lists the two principal forms of body water deficit and the physiology and particular circumstances associated with each form of deficit., Published in Wilderness Medicine, chapter 70, 2012.

Human hydration assessment is a key component for the prevention and proper treatment of heat related fluid and electrolyte imbalances within military, sports and clinical medicine communities. Despite the availability of many different methods for assessing hydration status, the need for a valid method or technology that is simple, rapid, non-invasive, universal (detects both hypertonic and isotonic hypovolaemia) and is applicable for static (single point in time) and dynamic (change across time) hydration assessment is widely acknowledged. The eye is one candidate body region that might afford such a measure given the intricate balance between ocular dynamics (tear and aqueous humor formation) and blood (plasma osmolality and volume), which is considered the criterion measure for hydration assessment. The aim of this review is to introduce and discuss the potential for using ocular measurements for non-invasive hydration assessment, including tear fluid osmolarity (Tosm), noninvasive tear break-up time (NITBUT) and intraocular pressure (IOP). There is a relevant physiological basis for testing the merit of ocular measures for human hydration assessment and recent data indicate that Tosm and IOP may have utility. Further investigations are warranted to determine the degree to which ocular measures can act as accurate and reliable non-invasive hydration status markers., Pub. in Journal of Thermal Biology, v37 p111-117, 2012.

This paper reviews the roles of hot skin (35 deg C) and body water deficits (2% body mass; hypohydration) in impairing submaximal aerobic performance. Hot skin is associated with high skin blood flow requirements and hypohydration is associated with reduced cardiac filling, both of which act to reduce aerobic reserve. In euhydrated subjects, hot skin alone (with a modest core temperature elevation) impairs submaximal aerobic performance. Conversely, aerobic performance is sustained with core temperatures 40 deg C if skin temperatures are coolwarm when euhydrated. No study has demonstrated that high core temperature ( -40 deg C) alone, without coexisting hot skin, will impair aerobic performance. In hypohydrated subjects, aerobic performance begins to be impaired when skin temperatures exceed 27 deg C, and even warmer skin exacerbates the aerobic performance impairment (-1.5% for each 1 deg C skin temperature). We conclude that hot skin (high skin blood flow requirements from narrow skin temperature to core temperature gradients), not high core temperature, is the 'primary' factor impairing aerobic exercise performance when euhydrated and that hypohydration exacerbates this effect ., Pub in Experimental Physiology v97 n3 pp327-332 2012

Appropriate quantification of analytical and biological variation of thermoregulatory sweating has important practical utility for research design and statistical analysis. We sought to examine contributors to variability in local forearm sweating rate (SR) and sweating onset (SO) and to evaluate the potential for using bilateral measurements. Two women and eight men (26 +/- 9 yr; 79 +/- 12 kg) completed 5 days of heat acclimation and walked (1.8 1/min VO2) on three occasions for 30 min in 40 deg C, 20% RH, while local SR and SO were measured. Local SR measures among days were not different (2.14 +/- 0.72 vs. 2.02 +/- 0.79 vs. 2.31 +/- 0.72 mg x sq cm x min(-1), P = 0.19) nor was SO (10.47 +/- 2.54 vs. 10.04 +/- 2.97 vs. 9.87 +/- 3.44 min, P = 0.82). Bilateral SR (2.14 +/- 0.72 vs. 2.16 +/- 0.71 mg x sq cm x min(-1), P = 0.56) and SO (10.47 +/- 2.54 vs. 10.83 +/- 2.48 min, P = 0.09) were similar and differences were 1 SD of day-to-day differences for a single forearm. Analytical imprecision (CVa), within (CVi)-, and between (CVg)-subjects' coefficient of variation for local SR were 2.4%, 22.3%, and 56.4%, respectively, and were 0%, 9.6%, and 41%, respectively, for SO. We conclude: 1) technologically, sweat capsules contribute negligibly to sweat measurement variation; 2) bilateral measures of SR and SO appear interchangeable; 3) when studying potential factors affecting sweating, changes in SO afford a more favorable signal-to-noise ratio vs. changes in SR. These findings provide a quantitative basis for study design and optimization of power/sample size analysis in the evaluation of thermoregulatory sweating., Published in American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, v302 n2 pr252-258, 15 Jan 2012.

Insect repellents (e.g. N,N-diethyl-m-toluamide or DEET) applied to the skin can potentially interfere with sweat production and evaporation, thus increasing physiological strain during exercise-heat stress. The purpose was to determine the impact of 33% DEET lotion on sweating responses, whole body thermoregulation and thermal sensation during walking exercise in the heat. Nine volunteers (2 females, 7 males; 22.1 + or - 4.9 years; 176.4 + or - 10.0 cm; 79.9 + or - 12.9 kg) completed 5 days of heat acclimation (45 deg C, 20% rh; 545 watts; 100 min/day) and performed three trials: control (CON); DEET applied to forearm (DEETLOC, 12 sq cm); and DEET applied to 13% body surface area (DEETWB,). Trials consisted of 30 min walking (645 watts) in 40 deg C, 20% rh environment. Local sweat rate (SR), onset and skin wettedness were measured in DEETLOC, and heart rate (HR), rectal temperature (Tre), skin temperature (Tsk), RPE, and thermal sensations (TS) were measured during DEETWB. No differences (p0.05) were observed between DEETLOC versus CON, respectively, for steady state SR (1.89 + or - 0.44 vs. 2.09 + or - 0.84 mg/sq cm/min), SR area under the curve (46.9 + or - 11.7 vs. 55.0 + or - 20.8 mg/sq cm), sweating onset, or skin wettedness. There were no differences (p0.05) in HR, Tre, Tsk, Physiological Strain Index, RPE or TS between DEETWB versus CON. DEET did not impact measures of local forearm sweating and when applied according to military doctrine, did not adversely impact physiological responses during exercise-heat stress. DEET can be safely worn during military, occupational and recreational activities in hot, insect infested environments., Published in European Journal of Applied Physiology, v111 n12 p3061-3068, 2011.

Limitations of Salivary Osmolality as a Marker of Hydration Status. Med. Sci. Sports Exerc., Vol. 43, No. 6, pp. 1080-1084, 2011. Salivary osmolality (Sosm) is a potentially useful hydration marker but may be confounded by oral artifacts. Purpose: This study aimed to determine the efficacy of Sosm for detecting hypohydration and evaluate the effect of a simple mouth rinse. Methods: Eight healthy volunteers (six males and two females; age = 22 +/- 7 yr, body mass = 83.7 +/- 14.9 kg, height = 176.9 +/- 9.2 cm) were measured for nude body mass (BM), plasma osmolality (Posm), and Sosm when euhydrated (EUH) and again when hypohydrated (HYP) by exercise-heat exposure with fluid restriction. After the initial saliva sample during HYP, a 10-s mouth rinse with 50 mL of water was provided, and saliva samples were obtained 1 min (RIN01), 15 min (RIN15), and 30 min (RIN30) after rinse. The ability of S(sub osm) to detect HYP was compared with P(sub osm). Results: Volunteers were hypohydrated by -4.0% +/-1.2% of BM (range = -2.2% to -5.3%). S(sub osm) was elevated above EUH after hypohydration (EUH 58 +/- 8 mmol-kg(exp -1) vs HYP 96 +/- 28 mmol-kg(exp -1), P < 0.05). S(sub osm) baseline and change values displayed more variability than P(sub osm) based on ANOVA and regression analyses. After the oral rinse, saliva decreased in concentration (RIN01 = 61 +/- 17 mmol-kg(exp -1), P < 0.05) but returned to prerinse values within 15 min (RIN15 = 101 +/- 25 mmol-kg(exp -1)) and remained similar 30 min after (RIN30 = 103 +/- 33 mmol-kg(exp -1). Conclusions: Sosm was remarkably altered 1 min after a brief water mouth rinse. Fifteen minutes proved an adequate recovery time, indicating that the timing of oral artifacts and saliva sample collection is critical when considering Sosm for hydration assessment., Pub. in Journal of the Medicine and Science in Sports and Exercise, v43 n6, p.1080-1084 and 1080-1084, 2011.

The Shapiro sweat prediction equation (OSE) was formulated more than two decades ago as: msw (g m[expn -2] h[expn -1]) = 27.9 E(sub req) (Emax)[expn -0.455], where Ereq is required evaporative heat loss and Emax is maximum evaporative power of the environment. Although OSE was developed for a limited set of conditions, in practice it is often used outside its boundaries to estimate fluid requirements and generate guidance in military, public health, occupational and sports medicine settings. Military (NATO) and public health (IOM) reports have expressed a need for improved sweating rate prediction models that calculate hourly and daily water needs., See also ADA564696. Human Modelling for Military Application (Applications militaires de la modelisation humaine). RTO-MP-HFM-202

Environmental heat stress can challenge the limits of human cardiovascular and temperature regulation, body fluid balance, and thus aerobic performance. This minireview proposes that the cardiovascular adjustments accompanying high skin temperatures (Tsk), alone or in combination with high core body temperatures (Tc), provide a primary explanation for impaired aerobic exercise performance in warm-hot environments. The independent (Tsk) and combined (Tsk + Tc) effects of hyperthermia reduce maximal oxygen uptake (VO2max), which leads to higher relative exercise intensity and an exponential decline in aerobic performance at any given exercise workload. Greater relative exercise intensity increases cardiovascular strain, which is a prominent mediator of rated perceived exertion. As a consequence, incremental or constant-rate exercise is more difficult to sustain (earlier fatigue) or requires a slowing of self-paced exercise to achieve a similar sensation of effort., Published in Journal of Applied Physiology, v109 p1989-1995, 2010.

Hypoxia often causes body water deficits (hypohydration, HYPO); however, the effects of HYPO on aerobic exercise performance and prevalence of acute mountain sickness (AMS) at high altitude (ALT) have not been reported. We hypothesized that 1) HYPO and ALT would each degrade aerobic performance relative to sea level (SL)-euhydrated (EUH) conditions, and combining HYPO and ALT would further degrade performance more than one stressor alone; and 2) HYPO would increase the prevalence and severity of AMS symptoms. Seven lowlander men (25 +/- 7 yr old; 82 +/- 11 kg; mean SD) completed four separate experimental trials. Trials were 1) SL-EUH, 2) SL-HYPO, 3) ALT-EUH, and 4) ALT-HYPO. In HYPO, subjects were dehydrated by 4% of body mass. Subjects maintained hydration status overnight and the following morning entered a hypobaric chamber (at SL or 3,048 m, 27 deg C) where they completed 30 min of submaximal exercise immediately followed by a 30-min performance time trial (TT). AMS was measured with the Environmental Symptoms Questionnaire-Cerebral Score (AMS-C) and the Lake Louise Scoring System (LLS)., Published in Journal of Applied Physiology, v109 p1792-1800, 2010.

Well-recognized markers for static (one time) or dynamic (monitoring over time) dehydration assessment have not been rigorously tested for their usefulness in clinical, military, and sports medicine communities. This study evaluated the components of biological variation and the accuracy of potential markers in plasma, urine, saliva, and body mass (Bm) for static and dynamic dehydration assessment. Design: We studied 18 healthy volunteers (13 men and 5 women) while carefully controlling hydration and numerous preanalytic factors. Biological variation was determined over 3 consecutive days by using published methods. Atypical values based on statistical deviations from a homeostatic set point were examined. Measured deviations in body fluid were produced by using a separate, prospective dehydration experiment and evaluated by receiver operating characteristic (ROC) analysis to quantify diagnostic accuracy. Results: All dehydration markers displayed substantial individuality and one-half of the dehydration markers displayed marked heterogeneity of intraindividual variation. Decision levels for all dehydration markers were within one SD of the ROC criterion values, and most levels were nearly identical to the prospective group means after volunteers were dehydrated by 1.8-7.0% of Bm. However, only plasma osmolality (Posm) showed statistical promise for use in the static dehydration assessment. A diagnostic decision level of 301 plus or minus 5 mmol/kg was proposed. Reference change values of 9 mmol/kg (Posm), 0.010 [urine specific gravity (Usg)], and 2.5% change in B(m) were also statistically valid for dynamic dehydration assessment at the 95% probability level., Published in The American Journal of Clinical Nutrition, p565-573, 2010.

This study examined vertical jump performance using a force platform and weighted vest to determine why hypohydration (~4% body mass) does not improve jump height. Jump height and other measures of functional performance from a force platform were determined for 15 healthy and active males when euhydrated (EUH), hypohydrated (HYP) and hypohydrated while wearing a weighted vest (HYPv) adjusted to precisely match water mass losses. HYP produced a significant loss of body mass [- 3.2 +/- 0.5 kg (- 3.8 +/- 0.6%); P<0.05], but body mass in HYPv was not different from EUH. There were no differences in absolute or relative peak force or power among trials. Jump height was not different between EUH (0.380 +/- 0.048 m) and HYP (0.384 +/- 0.050 m), but was 4% lower (P<0.05) in HYPv (0.365 +/- 0.52 m) than EUH due to a lower jump velocity between HYPv and EUH only (P<0.05). However, vertical ground reaction impulse (VGRI) was reduced in both HYP and HYPv (2-3%) compared with EUH (P<0.05). This study demonstrates that the failure to improve jump height when hypohydrated can be explained by offsetting reductions in both VGRI and body mass., Published in the European Journal of Applied Physiology 2010.

Many athletes seeking a competitive edge rely on nutritional ergogenic aids to improve performance. Carbohydrate (CHO) and caffeine (CAF) supplementation appear efficacious at enhancing endurance exercise performance when studied under ideal circumstances, but the unique challenges imposed by environmental stressors such as heat may minimize or negate these effects. Similar to findings in temperate or cool environments, CHO intake during endurance exercise in hot environments produces a consistent performance benefit. But in contrast to the benefits observed in moderate environments. CAF affords no apparent performance advantage in the heat. These findings raise interesting questions about nutritional ergogenic mechanisms of action and offer direction for future research., Published in Current Topics in Nutraceutical Research, v8 n1 p1-6, 2010. ISSN 1540-7535.

Environmental heat stress degrades aerobic performance; however, little research has focused on performance when the selected task elicits modest elevations in core body temperature (<38.5 deg C). Purpose: To determine the effect of environmental heat stress, with modest hyperthermia, on aerobic performance and pacing strategies. Methods: After a 30-min cycling preload at 50% VO sub 2peak, eight euhydrated men performed a 15-min time trial on a cycle ergometer in temperate (TEMP; 21 deg C, 50% RH) and hot (HOT; 40 deg C, 25% RH) environments. Core and skin temperature (Tc and Tsk, respectively) and HR were continuously monitored. Performance was assessed by the total work (kJ) completed in 15 min. Pacing was quantified by comparing the percent difference in actual work performed in each of five 3-min blocks normalized to the mean work performed per 3-min block. Pace over the final 2 min was compared with the average pace from minutes 0 to 13 for end spurt analysis. Results: Tc and HR rose continually throughout both time trials. Peak Tc remained modestly elevated in both environments [mean (range): HOT = 38.20 deg C (37.97-38.42 deg C); TEMP = 38.11 deg C (38.07-38.24 deg C)], whereas Tsk was higher in HOT (36.19 + or - 0.40 deg C vs 31.14 + or - 1.14 deg C), and final HR reached ~ 95% of age-predicted maximum in both environments. Total work performed in HOT (147.7 + or - 23.9 kJ) was ~17% less (P < 0.05) than TEMP (177.0 + or - 25.0 kJ). Pace was evenly maintained in TEMP, but in HOT, volunteers were unable to maintain initial pace, slowing progressively over time. A significant end spurt was produced in both environments. Conclusions: During a brief aerobic exercise time trial where excessive hyperthermia is avoided, total work is significantly reduced by heat stress because of a gradual slowing of pace over time. These findings demonstrate how aerobic exercise performance degrades in hot environments without marked hyperthermia., Published in Medicine & Science in Sports & Exercise, v42 n1 p135-141, 2010.

Personal protective equipment (PPE) markedly increases heat strain, reduces work performance, and increases the incidence of heat casualties. Microclimate cooling (MCC) technologies have been successfully used to alleviate this heat strain in mounted soldiers, but cooling limitations, power and weight restrictions do not currently make this technology applicable to dismounted soldiers. This composite of studies investigated the potential for intermittent-regional cooling and skin temperature feedback approaches to better enable MCC systems for the dismounted soldier. PURPOSE: The purposes of this study were to 1) determine, using a variety of intermittent cooling paradigms, the optimal skin temperature for maximizing thermoregulatory efficiency, and 2) examine the potential power savings associated with using biofeedback to maintain optimal skin temperature. METHODS: Two studies were conducted using the same facilities and test equipment. In study one, 5 male soldiers exercised moderately (500W) in a warm environment (30 deg C, 30%rh) while wearing PPE (clo: 2.1; im/clo: .32) over a water-perfused (21 deg C) liquid MCC garment covering the head, chest, back, and legs (72% of body surface area, BSA). All four body regions were independently controlled. A matrix of six randomized trials was conducted in which conventional MCC (constant perfusion, CP), no MCC (NC), or 4 trials of intermittent and regional (IR1-4) MCC was provided. IR1-4 was time-activated and on:off cooling ratios and the % BSA cooled were systematically varied. In study two, 8 male soldiers were subjected to the same conditions as study one, but only three trials were performed to include CP, IR2 (2 min on: 2 min off, 72% BSA), and skin temperature feedback (STF, 72% BSA) using a skin temperature range of 33-35 deg C. Heart rate (HR), body core (Tc) and skin temperatures (Tsk) were measured at regular intervals in both studies., See also ADA562561. RTO-MP-HFM-181 Human Performance Enhancement for NATO Military Operations (Science, Technology and Ethics) (Amelioration des performances humaines dans les operations militaires de l'OTAN (Science, Technologie et Ethique)). RTO Human Factors and Medicine Panel (HFM) Symposium held in Sofia, Bulgaria, on 5-7 October 2009., The original document contains color images.

Sweating threshold temperature and sweating sensitivity responses are measured to evaluate thermoregulatory control. However, analytic approaches vary, and no standardized methodology has been validated. This study validated a simple and standardized method, segmented linear regression (SReg), for determination of sweating threshold temperature and sensitivity. Archived data were extracted for analysis from studies in which local arm sweat rate (m'sw; ventilated dew-point temperature sensor) and esophageal temperature (Tes) were measured under a variety of conditions. The relationship m'sw/Tes from 16 experiments was analyzed by seven experienced raters (Rater), using a variety of empirical methods, and compared against SReg for the determination of sweating threshold temperature and sweating sensitivity values. Individual interrater differences (n=324 comparisons) and differences between Rater and SReg (n=110 comparisons) were evaluated within the context of biologically important limits of magnitude (LOM) via a modified Bland-Altman approach. The average Rater and SReg outputs for threshold temperature and sensitivity were compared (n=16) using inferential statistics., Published in Journal Applied Physiology, v107 p69-75, 2009.

Persons exercising in cold weather can incur substantial fluid losses and are advised to maintain hydration to sustain performance. Body water deficits or hypohydration (HYP) in excess of 2% body mass impairs endurance exercise performance in hot and temperate environments and HYP may also degrade cognitive performance in hot-temperature conditions. However the extent to which these performance decrements occur in cold environments with HYP is unknown. This study investigated whether HYP degrades physical and cognitive performance during cold exposure and if physical exercise could mitigate any cold-induced cognitive performance decline. On four occasions, eight volunteers (6 men, 2 women) were exposed to 3 h of passive heat stress, with or without fluid replacement. Later in the day, volunteers sat in a cold or temperate environment for 1 hour before performing 30 min of cycle ergometry followed immediately by a 30-min performance time trial. Performance was assessed by the total amount of work completed during the 30-min performance time trial., Presented at the Symposium on Human Factors and Medicine (HFM), held in Helsinki, Finland, on 20-22 Apr 2009. Published in the proceedings of the symposium, p35-1 through 35-18, 2009. Sponsored in part by NATO/RTO-MP-HFM-168.

Purpose: The validity and the reliability of using intestinal temperature (Tint) via ingestible temperature sensors (ITS) to measure core body temperature have been demonstrated. However, the effect of elapsed time between ITS ingestion and Tint measurement has not been thoroughly studied. Methods: Eight volunteers (six men and two women) swallowed ITS 5 h (ITS-5) and 29 h (ITS-29) before 4 h of varying intensity activity. Tint was measured simultaneously from both ITS, and Tint differences between the ITS-5 and the ITS-29 over the 4 h of activity were plotted and compared relative to a meaningful threshold of acceptance (+ or - 0.25 deg C). The percentage of time in which the differences between paired ITS (ITS-5 vs ITS-29) were greater than or less than the threshold of acceptance was calculated. Results: Tint values showed no systematic bias, were normally distributed, and ranged from 36.94 deg C to 39.24 deg C. The maximum Tint difference between paired ITS was 0.83 deg C with a minimum difference of 0.00 deg C. The typical magnitude of the differences (SE of the estimate) was 0.24 deg C, and these differences were uniform across the entire range of observed temperatures. Paired Tint measures fell outside of the threshold of acceptance 43.8% of the time during the 4 h of activity. Conclusions: The differences between ITS-5 and ITS-29 were larger than the threshold of acceptance during a substantial portion of the observed 4-h activity period. Ingesting an ITS more than 5 h before activity will not completely eliminate confounding factors but may improve accuracy and consistency of core body temperature., Published in Medicine & Science in Sports & Exercise, v41 n3 p597-602, 2009.

Exercise alone or in combination with environmental heat stress can elevate blood S-100 beta protein concentrations. However, the explanatory power of exercise with marked environmental heat stress on the appearance of S-100 beta is questionable. It is possible that the process of heat acclimation might afford additional insight. Purpose: Determine the S-100 beta response to moderate intensity exercise with heat strain before and after heat acclimation. Methods: Nine healthy male volunteers completed 10 consecutive days of heat acclimation consisting of up to 100 minutes of treadmill walking 91.56 m/s, 4% grade) in the heat (45 deg C, 20% relative humidity). Changes in heart rate (HR), rectal temperature (Tre), and sweat rate (SR) were examined to determine successful acclimation. Area under the curve (AUC) for Tre > 38.5 deg C was calculated to assess cumulative hyperthermia. Blood samples were taken before and after exercise on days 1 and 10 and analyzed for serum osmolality and S-100 beta concentration. Results: All subjects displayed physiological adaptations to heat acclimation, including a significant (P< 0.05) reduction in final HR (161 to 145 b/mm) and Tre (39.0 to 38.4 C), as well as a modest (approx. 10%) increase in SR (1.10 to 1.20 L/hr; p=0.09). No differences were observed in pre-to-post exercise serum S-100 beta concentrations on day 1 or day 10, nor were differences observed in S-100 beta values between days 1 and 10. No significant correlations were found between S-100 beta values and any variable of interest. Conclusions: S-100 beta concentrations do not necessarily increase in response to exercise heat strain and no effect of heat acclimation on S-100 beta could be observed despite other quantifiable physiological adaptations., Published in Medicine & Science in Sports & Exercise, v p1477-1482, 2008.

This study determined whether a torso-vest forced ambient air body ventilation system (BVS) reduced physiological strain during exercise-heat stress. Seven heat-acclimated volunteers attempted nine, 2-h treadmill walks at 200 W/sq m in three environments, -40 C, 20% rh (HD), 35 C, 75% rh (HW), and 30 C, 50% rh, (WW) wearing the Army Combat Uniform, interceptor body armor (IBA) and Kevlar helmet. Three trials in each environment were BVS turned on (BVS (On)), BVS turned off (BVS(Off)), and no BVS (IBA). In HD, BVS(On) significantly lowered core temperature (T(ak)), mean torso skin temperature (T(torso)), thermal sensation (TS), heat storage (S), and physiological strain index (PSI), versus BVS(off) and IBA (P < 0.05). For HW (n = 6), analyses were possible only through 60 min. Exercise tolerance time (min) during HW was significantly longer for BVS(On) (116 +/- 10 min) versus BVS(off) (95 +/- 22 min) and IBA (96 +/- 18 min) (P < 0.05). During HW, BVS(On) lowered HR at 60 min versus IBA T(sk) from 30 to 60 min. versus BVS(Off) and IBA, and PSI from 45 to 60 min versus BVS(Off) and at 60 min versus IBA (P < 0.05). BVS(On) changes in T(re) and HR were lower in HD and HW. During WW, BVS(On) significantly lowered HR, T( sk) and T(torso) versus BVS(Off) and IBA (P < 0.05) during late exercise. Sweating rates were significantly lower for BVS(On) versus BVS(Off) and IBA in both HD and WW (P < 0.05), but not HW. These results indicate that BVS(On) reduces physiological strain in all three environments by a similar amount; however, in hot-dry conditions the BVS(Off) increases physiological strain., Published in European Journal of Applied Physiology, v103 p307-314, 2008.

The objective of this project was to cross validate the original Shapiro equation (OSE) which was developed to predict rate of sweat loss over wide environmental conditions, clothing systems, and metabolic activities. activities. Within the limits of the data, the equation has been shown to be a valid estimator of sweating rate for a variety of heat stress exposures up to 2 h and work rates limited to less than 450 W. The second objective was to develop a new prediction algorithm or correct the previous one so that reliable fluid replacement guidelines using such equations can be constructed in the future for more extended work times greater than just 2 h, the exposure time in the original study. The need to develop a new prediction equation stems from results of recent studies at USARIEM that revealed that the original equation embedded in a Heat Strain Decision Aide (HSDA) computer model over predicts actual sweating responses over wide environmental extremes, work rates, and work periods. Overpredictions of sweating rate (and the required fluid intake to fully replace the expected sweat loss) can lead to over-hydration problems. A USARIEM database was secured consisting of 101 volunteer subjects who completed experiments at various activity levels over wide environmental ambient conditions. Subjects wore various military clothing systems including chemical protective clothing and body armor. Each element of the comprehensive heat balance equation was analyzed. Data were analyzed using fuzzy piecewise linear and nonlinear regression analyses to establish appropriate change points in sweat loss per time points. It was established that the original Shapiro algorithm predicts markedly high values in sweating rates. The most important finding of the current study and recommendation is to substitute or modify the current HSDA program with a corrected algorithm., The original document contains color images.

Protective vests worn by global security personnel, and weighted vests worn by athletes, may increase physiological strain due to added load, increased clothing insulation and vapor resistance. The impact of protective vest clothing properties on physiological strain, and the potential of a spacer garment to reduce physiological strain, was examined. Eleven men performed 3 trials of intermittent treadmill walking over 4 h in a hot, dry environment (35 C, 30% rh). Volunteers wore the US Army battle dress uniform (trial B), B + protective vest (trial P), and B + P + spacer garment (trial S). Biophysical clothing properties were determined and found similar to many law enforcement, industry, and sports ensembles. Physiological measurements included core (T sub c), mean skin (T sub sk) and chest (T sub chest) temperatures, heart rate (HR), and sweating rate (SR). The independent impact of clothing was determined by equating metabolic rate in all trials. In trial P, HR was +7 b/min higher after 1 h of exercise and +19 b/min by the fourth hour compared to B (P<0.05). T sub c (+0.30 C), T sub sk (+1.0 C) and Physiological Strain Index were all higher in P than B (P<0.05). S did not abate these effects except to reduce T sub sk (P>S) via a lower T sub chest (-0.40 C) (P<0.05). SR was higher (P<0.05) in P and S versus B, but the magnitude of differences was small. A protective vest increases physiological strain independent of added load, while a spacer garment does not alter this outcome., Published in European Journal of Applied Physiology, v102 p577-583, 2008.

Purpose: This study examined the impact of 10 days of exercise-heat acclimation on sweat mineral concentrations. Methods: Eight male subjects walked on a treadmill at 3.5 mph, 4% grade for 100 continuous minutes or until rectal temperature reached 39.5 C on 10 consecutive days in an environmental chamber set at 45 C, 20% relative humidity. Arm sweat samples were collected during the first 30 min of exercise-heat stress on days 1 and 10 using a polyethylene arm glove. Results: Final core temperature and HR values were significantly lower (P < 0.05) on day 10 versus day 1. Whole-body sweating rates increased by approximately 6% (P = 0.12). Sweat sodium concentration on day 10 (36.22 + or - 7.22 mM) was significantly lower than day 1 (54.49 + or - 16.18 mM) (P < 0.05). Sweat mineral concentrations of calcium (~29%), copper (~50%), and magnesium (~43%) were also significantly lower on day 10 versus day 1 of heat acclimation (P < 0.05). A trend for lower sweat iron (~75%; P = 0.07) and zinc (~23%; P = 0.10) concentrations were observed from day 1 to day 10. The estimated hourly sweat mineral losses (arm concentration x whole-body sweat rate) were reduced for calcium (~27%), copper (~46%), and magnesium (~42%) (P < 0.05), but not iron (75%) or zinc (~16%) (P > 0.05), from day 1 to day 10. Conclusion: Exercise-heat acclimation conserves arm sweat mineral concentrations and possibly whole-body sweat losses of calcium, copper, and magnesium, and may reduce sweat iron and zinc concentrations., Pub. in Medicine & Science in Sports & Exercise, v40 n5 p886-891, 2008.

Marathon races are performed over a broad range of environmental conditions. Hyperthermia is a primary challenge for runners in temperature and warm weather, but hypothermia can be a concern during cool-wet or cold conditions. Body temperature during the marathon is a balance between metabolic heat production and exchange with the environment described by the heat balance equation. During exercise, core temperature is proportional to the metabolic rate and largely independent of a wide range of environmental conditions., Pub in Proceedings of the Conference on Sports Med, v37 p312-315, 2007.

The USARIEM Heat Strain Decision Aid (HSDA) is an empirically developed tool for mission planning and prevention of heat injury. HSDA uses information about the individual, their environment, clothing, and activity to estimate core temperature (Tc) and calculate recommended safe work times. Data from a recent series of experiments was used to validate the performance of HSDA for the conditions studied.