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Purpose: Torso loads restrict chest-wall movement and ventilation, particularly during heavy exercise. Therefore, the differential impact of load carriage and chest-wall restriction was investigated during progressive treadmill exercise. In addition, acceptable work durations were derived across a wide range of submaximal, loaded exercise intensities., Methods: Twelve males participated in two research phases. Phase 1: Three incremental treadmill tests until exhaustion [control (clothing only), load carriage (clothing plus 22-kg vest), and clothing with chest strapping]. Phase 2: Five steady-state exercise trials (clothing plus 22-kg vest) at intensities from 30 to 80 % of peak aerobic power to determine maximal acceptable work durations., Results: Maximal work tolerance [control 17.21 min (±0.93); loaded 13.44 min (±0.68); strapped 17.00 min (±0.83)] and the mass-specific peak aerobic power [control 61.61 mL kg(-1) min(-1) (±2.28); loaded 45.42 mL kg(-1) min(-1) (±1.41); strapped 59.99 mL kg(-1) min(-1) (±1.61)] were reduced only when loaded (P < 0.05). Peak minute ventilation was retained, although loading and chest strapping reduced the breathing reserve. The lower and upper acceptable work duration derivations when working at the 30 % intensity were 133.40 min (±23.77) and 220.10 min (±48.69), but at 80 % intensity, both durations were reduced to <7 min., Conclusion: Thoracic loading significantly reduced exercise tolerance and the breathing reserve, but did not modify peak minute ventilation or the absolute peak aerobic power. Chest strapping, as used herein, exerted minimal impact. However, the projected maximal acceptable work durations were much less than derived using previously published methods.

Aim: Few investigators have considered the possibility that skeletal muscles might contain thermosensitive elements capable of modifying thermoeffector responses. In this experiment, the temporal relationships between dynamic changes in deep-body and intramuscular temperatures and eccrine sweat secretion were explored during rhythmical and reproducible variations in heat production., Methods: Eight subjects performed semi-recumbent cycling (25 °C) at a constant load to first establish whole-body thermal and sudomotor steady states (35 min), followed by a 24-min block of sinusoidal workload variations (three, 8-min periods) and then returning to steady-state cycling (20 min). Individual oesophageal, mean skin and intramuscular (vastus lateralis) temperatures were independently cross-correlated with simultaneously measured forehead sweat rates to evaluate the possible thermal modulation of sudomotor activity., Results: Both intramuscular and oesophageal temperatures showed strong correlations with sinusoidal variations in sweating with respective maximal cross-correlation coefficients of 0.807 (±0.044) and 0.845 (±0.035), but these were not different (P = 0.40). However, the phase delay between intramuscular temperature changes and sweat secretion was significantly shorter than the delay between oesophageal temperature and sweating [25.6 s (±12.6) vs. 46.9 s (±11.3); P = 0.03]., Conclusion: The temporal coupling of eccrine sweating to intramuscular temperature, combined with a shorter phase delay, was consistent with the presence of thermosensitive elements within skeletal muscles that appear to participate in the modulation of thermal sweating., (© 2014 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.)

Objective: The influence of variations in exercise mode, thermal state, and load carriage on cardiac and ventilatory predictors of metabolic rate were investigated., Methods: Fifteen males were studied at rest and during whole-, upper-, and lower-body exercise (unloaded and loaded) under thermoneutral and hot conditions., Results: Ventilatory predictions were superior in thermoneutral (residual mean square error range: 0.04 to 0.17 L·min(-1) vs 0.21 to 0.36 L·min(-1)) and hot conditions (0.03 to 0.07 L·min(-1) vs 0.21 to 0.24 L·min(-1)). Predictions derived from whole- or lower-body exercise, and unloaded or loaded exercise could be interchanged without significant error. Nevertheless, a mode-specific prediction was required for upper-body work, and mild hyperthermia significantly reduced the precision of cardiac predictions., Conclusion: Ventilatory predictions were more precise, but errors from heart-rate predictions could be minimized by using thermal-state and exercise mode-specific predictions.

Aim: The goals of this study were to investigate changes in the sweating and cutaneous vascular responses on the palm and the volar aspect of the index finger during sustained static exercise of increasing intensity and to determine whether the former can be attributed to altered sweat gland activity., Methods: Five male and five female subjects performed maximal voluntary handgrip contractions (MVC: right hand) for 60 s at 20, 35 and 50% MVC (ambient temperature 25 °C, relative humidity 50%)., Results: The sweat rate and the number of activated sweat glands on the non-exercised hand showed intensity-dependent increases (P < 0.05). At 35 and 50% MVC, finger sweat secretion was significantly higher than on the palm, which was primarily associated with the number of activated sweat glands (P < 0.05). In addition, there was a marked simultaneous decrease in the cutaneous vascular conductance for the finger at 35 and 50% MVC (P < 0.05), but not for the palm., Conclusion: Our results suggest that a difference exists between intensity-dependent increases of sudomotor responses within more than one glabrous skin site. Specifically, markedly greater sweating occurs on the volar finger than on the palmar surface during sustained static exercise. These differences in sweat rate mainly resulted from changes in the number of activated sweat glands. In addition, intra-segment variations in cutaneous blood flow on the glabrous hand are shown., (© 2011 The Authors. Acta Physiologica © 2011 Scandinavian Physiological Society.)

Objective: This project was aimed at evaluating the impact of combat armor on physiological and cognitive functions during low-intensity exercise in hot-humid conditions (36 degrees C and 60% relative humidity)., Methods: Nine males participated in three trials (2.5 hours), walking at two speeds and wearing different protective equipment: control (combat uniform and cloth hat); torso armor with uniform and cloth hat; and full armor (uniform, torso armor, and helmet)., Results: As time progressed, core temperatures increased and deviated significantly among trials, rising at 0.37 degrees C h(-1) (control), 0.41 degrees C h(-1) (torso armor), and 0.51 degrees C h(-1) (full armor). Heart rates also progressively diverged, and subjects lost significantly more sweat during the two armored trials. However, cognitive-function tests revealed neither significant main effects nor time by treatment interactions., Conclusion: The combat armor and helmet significantly increased thermal and cardiovascular strain, but these were unlikely to lead to either exertional heat illness or impaired cognitive function during uneventful urban, military patrols in hot-humid conditions.

Introduction: It is generally accepted that the palmar (volar) and dorsal surfaces of human hands display different sudomotor responses to mental or thermal stimuli. We tested the hypothesis that, during thermal stimulation, secretion from the dorsal surfaces would always exceed that from the volar aspect of the hand., Methods: Sweat secretion from 10 hand sites and the forehead was examined (ventilated capsules) in 10 subjects during passive heating (climate chamber: 36 degrees C, 60% relative humidity, water-perfusion suit: 40 degrees C) immediately followed by incremental cycling to volitional fatigue., Results: This treatment significantly increased core temperature (39.3 degrees C), heart rate (178 bpm), and sweat rate at all sites. Mean sweat secretion during exercise was greater at the forehead (2.90 mg x cm(-2) x min(-1); +/- 0.19) than the hand (1.49 mg x cm(-2) min(-1); +/- 0.27). While no significant differences in sweating were observed among dorsal sites, a nonuniform secretion pattern was observed across the volar surface, with sweating at the palm being the lowest, and that from the volar aspect of the distal phalanges being equivalent to the dorsal hand. These differences became more evident as exercise progressed. Mean hand sweat rate during exercise was 41.7 ml x h(-1), with sweating from the palm accounting for only about 6% of sweat secretion., Conclusion: Sweat secretion from both the palmar and dorsal surfaces of the hand increases during exercise in the heat, although this occurs in a nonuniform fashion. It is possible that a greater sweat gland density on the fingers may account for variations across the volar surface. However, higher dorsal sweating with lower gland counts (high glandular flow) may be attributable to either larger sweat glands, or to a greater cholinergic sensitivity of these glands.

Thermal sweating from the human torso accounts for about half of the whole-body sweat secretion, yet its intra-segmental distribution has not been thoroughly examined. Therefore, the aim of the current study was to provide a detailed description of the distribution of eccrine sweating within the torso during passively-induced (water-perfusion garment: 40 degrees C) and progressively increasing, exercise-related thermal strain (36 degrees C, 60% relative humidity). Sudomotor function was measured in ten males using ventilated sweat capsules (3.16 cm(2)) attached to twelve sites on the ventral (four), lateral (three) and dorsal (four) torso, and upper shoulder surfaces. Sweating increased asymptotically in all sites, with the final core temperature averaging 39.7 degrees C (+/-0.1) and heart rates being 181 b min(-1) (+/-2). During exercise, the mean torso sweat rate averaged 1.35 mgcm(-2)min(-1), with sweating from the lateral torso surfaces generally being the lowest. Each of the between-site comparisons with the lateral torso differed significantly (P < 0.05), except for comparisons with the chest (P = 0.051) and shoulder (P > 0.05). The intra-segmental differences between the lateral torso and the chest, abdomen, upper- and lower-back areas were significantly accentuated during exercise. From these data, it is evident that the torso is another region that does not have a uniform distribution of thermally-induced sweating. Thus, it is no longer acceptable for researchers, modellers, sweating manikins engineers or clothing manufacturers to assume that the sweat rates for all local sites within any body segment are equivalent.

The importance of the head in dissipating body heat under hot conditions is well recognised, although very little is known about local differences in sweat secretion across the surface of the head. In this study, we focused on the intra-segmental distribution of head sweating. Ten healthy males were exposed to passive heating and exercise-induced hyperthermia (36 degrees C, 60% relative humidity, water-perfusion suit: 46 degrees C), with ventilated sweat capsules (3.16 cm(2)) used to measure sweat rates from the forehead and nine sites inside the hairline. Sweat secretion from both non-hairy (glabrous) and hairy areas of the head increased linearly with increments in work rate and core temperature, with heart rate and core temperature peaking at 175 b min(-1) (+/-6) b min(-1) and 39.2 degrees C (+/-0.1). The mean sweat rate during exercise for sites within the hairline was 1.95 mg cm(-2) min(-1). However, the evolution of this secretion pattern was not uniformly distributed within the head, with the average sweat rate for the top of the head being significantly lower than at the anterior lateral aspect of the head (P < 0.05), and representing only 30% of the forehead sweat rate (P < 0.05). It is hypothesised that these intra-segmental observations may reflect variations in the local adaptation of eccrine glands to differences in local evaporation associated either with bipedal locomotion, which will influence forehead sweating, or the hidromeiotic suppression of sweating, which impacts upon sweat glands within the hairline.

The hottest months on northern Australian cattle stations are from September to November, and it is during these months that horseback cattle mustering occurs. Stockmen wear clothing that restricts heat loss, and protective helmets have recently been introduced. Anecdotal evidence points to the possibility that helmets may increase the probability of developing heat illness, or reducing workplace performance. In this project, we quantified the working (thermal) environment on such cattle stations, and measured the metabolic demands on, and concurrent physiological strain in stockmen during mustering, whilst wearing an equestrian helmet. During horseback work, the average heart rate was 102.0 beats min(-1) (SD 14.0), with almost 90% of the time (238 min) spent working at intensities <50% of the heart rate reserve. The projected metabolic heat production during mustering ranged between 178 and 333 W (women), and between 212 and 542 W (men). The average core temperature was 37.6 degrees C, while the mean skin temperature averaged 34.1 degrees C. It was concluded that the working environment is, on average, thermally uncompensable during the mustering season. However, horseback mustering per se is a relatively low-intensity activity, interspersed with short periods of high-intensity work. This activity level was reflected within core temperatures, which rarely climbed above values associated with light-moderate exercise. Thus, whilst the climatic state was uncompensable, stockmen used behavioural strategies to minimise the risk of heat illness. Finally, it was observed that the helmet, though unpleasant to wear, did not appear to increase thermal strain in a manner that would disadvantage stockmen.

Introduction: Little is known regarding local differences in foot sweat secretion. Since such information is important to our understanding of sweat gland control for thermoregulatory modeling and for the design of footwear we explored this topic., Methods: Local sweat rates were investigated across core temperatures from 37-39 degrees C, achieved using endogenous (cycling) and exogenous heat (water-perfusion garment: 46 degrees C). Six healthy adults (three men, three women) performed one-legged, incremental cycling in a heated, climate-controlled chamber (36 degrees C, 60% relative humidity). Sweat rates were measured at the forehead and stationary (left) foot (capsules 3.16 cm2): three dorsal sites (base of toes, second metatarsal, and mid point), the lateral, and the central plantar surfaces., Results: Terminal core temperatures ranged between 38.3-39.1 oC, with peak heart rates of 155-187 bpm. Most foot sweat rates were < 50% of that observed at the forehead: dorsal 1 (38%); dorsal 2 (54%); dorsal 3 (37%); lateral (24%); and plantar surfaces (18%). When averaged across the trial, local sweat rates were: 2.61 (forehead); 0.98 (dorsal 1); 1.39 (dorsal 2); 0.95 (dorsal 3); 0.62 (lateral); and 0.47 mg cm2 2 min-1 (plantar)., Conclusion: Two key observations emerged. First, sweat secretion from the experimental foot averaged 30 ml x h(-1), peaking in the last 5 min at 50 ml x h(-1). Second, approximately 70% of the measured sweat flow emanated from the upper skin surfaces, with only 30% coming from the plantar surface.

We investigated the effects of aging on the elastic properties of lung tissue and the chest wall, simultaneously quantifying the contribution of each component to static inspiratory muscle work in resting and exercising adults. We further evaluated the interaction of aging and habitual physical activity on respiratory mechanics. Static lung volumes and elastic properties of the lung and chest wall (pressure-volume relaxation maneuvers) in 29 chronically sedentary and 29 habitually active subjects, grouped by age, were investigated: young (Y, 20-30 years), middle-aged (M, 40-50 years), and older (O, >60 years). Using static pressure-volume data, we computed the elastic work of breathing (joules per liter, J.l(-1)), including inspiratory muscle work, over resting and exercising tidal volume excursions. Elastic work of the lung (Y = 0.79 +/- 0.05; M = 0.47 +/- 0.05; O = 0.43 +/- 0.05 J.l(-1)) and chest wall (Y = -0.49 +/- 0.06; M = -0.12 +/- 0.07; O = 0.04 +/- 0.05 J.l(-1) ) changed significantly with age (P < 0.05). With aging, a parallel displacement of the chest wall pressure-volume curve resulted in a shift from energy being stored primarily during expiration to energy storage during inspiration, and driving expiration, both at rest and during exercise. Although deviating significantly from young adults, this did not significantly elevate static inspiratory muscle work but resulted in a redistribution of the tissues on which this work was performed and the phase of the respiratory cycle in which it occurred. Nevertheless, static inspiratory muscle work remained similar across age groups, at rest and during exercise, and habitual physical activity failed to influence these changes.

This project examined the effects of repeated, resting cold-water immersion on metabolic heat production and core temperature defence during subsequent rest and exercising immersions. Seven males undertook 15 days of cold-water adaptation, immersed to the fourth intercostal space, with cold-water stress tests (CWST) on days 1, 8 and 15 (18.1 SD 0.1 degree C: 60 min seated, followed by 30 min cycling (1 W.kg-1)), and 90-min resting immersions (18.4 SD 0.4 degree C) on each of the intervening days. Adaptation elicited an habituated thermogenic response during the rest phase of CWST3 beyond 20 min, compared to CWST1 (P < 0.05), with oxygen consumption averaging 11.15 (+/- 0.25) ml.kg-1.min-1 and 8.61 (+/- 0.90) ml.kg-1.min-1 by 50 min, for CWST1 and CWST3, respectively. During exercise, this metabolic blunting was only apparent over the first 10-min period (60-70 min). No significant differences were observed during either the rest or exercise phases of the CWSTs for oesophageal temperature (Tes). While repeated cold-water exposures produced an habituated-thermogenic response, for an equivalent drop in Tes during rest, neither this response, nor an elevated thermogenesis, were apparent during subsequent cold-water exercise.

Using a simultaneous-dilution technique, we investigated body-fluid volume changes during exercise in seven males, during 50 min of cycling (50% maximal work rate) in hot (36.2 degrees C), temperate (22.0 degrees C) and cool conditions (14.4 degrees C). Total body water (TBW), extracellular fluid (ECFV), plasma (PV) and erythrocyte volumes (RCV) were measured, while blood volume (BV), interstitial fluid volume (IFV), extracellular water (ECW) and intracellular water volumes (ICW) were derived. During the initial 10 min of cycling, BV decreased in all environments (P .01), primarily because of a PV reduction (P = 0.01), while IFV, ECFV and ICW were not significantly changed. By 30 min, BV recovered in the temperate and cool conditions, despite mass losses of 563 and 520 mL (respectively), but remained depleted in the hot condition (P = 0.01). The 50-min volume changes revealed that, throughout exercise, body-fluid losses appeared to be drawn primarily from the extracellular space, regardless of air temperature. In the hot condition, the PV change represented 63% of the TBW loss, with the ICW contributing 23%. It was concluded that, during cycling, progressive dehydration mainly affected the extracellular space, with the intravascular and intracellular spaces being defended in less stressful conditions.

This project sought to evaluate the importance of skin temperature during heat acclimation, using an isothermal-strain model. Two groups of seven matched males, participated (1 h per day, 10 days) in one of two conditions: (i) temperate physical training (TEMP: 22.4 +/- 0.7 degrees C, relative humidity (r.h.) 41.0 +/- 0.9%); or (ii) combined physical training and heat acclimation (HEAT: 38.2 +/- 0.7 degrees C, r.h. 39.7 +/- 1.3%). Isothermal strain was induced in both groups by rapidly elevating rectal temperature by 1 degree C (cycling), then holding it constant by manipulating external work. Subjects completed two three-phase heat stress tests (39.8 +/- 0.1 degrees C, r.h. 38.6 +/- 1.2), consisting of 20 min rest, then 20 min cycling at each of 30% and 45% of peak power, before and after each regimen. While there was a difference of 4.2 degrees C in mean skin temperature between treatments, both regimens elicited a similar peripheral sudomotor increase, indicating a core temperature dependent adaptation. However, based on significant pre- vs. post-acclimation decreases in average auditory canal temperature (0.4 +/- 0.1 degree C), average forehead skin blood flow (26%), average perceived exertion (11%), and a 5% increase in average forehead sweat rate (0.1 +/- 0.04 mg cm-2 min-1), the HEAT regimen elicited a more complete acclimation. While elevation in core temperature is critical to acclimation, it also appears necessary to expose subjects to an external thermal stress. This observation has not been previously demonstrated under conditions of isothermal strain, and verifies the importance of skin temperature elevation in the acclimation process.

Background: The influence of forehead and mean skin temperature on thermal sensation during exercise in hot, cool, and thermoneutral environments is unclear., Hypothesis: We hypothesized that forehead temperature, in contrast to other skin sites, would contribute significantly to thermal sensation during exercise in hot, cool, and thermoneutral environments., Method: Volunteer males (N = 14) performed 30 min of constant load exercise on a cycle ergometer during which thermal sensation, skin and rectal temperatures, and heart rate were collected. Each subject participated in a control (24 degrees C), hot (40 degrees C), and cool (8 degrees C) condition., Results: Significantly higher mean skin temperatures occurred during exercise in the hot condition (M = 37.22 +/- 0.20 degrees C) compared to exercise in the neutral (M = 33.34 +/- 0.51 degrees C) and cool conditions (M = 27.92 +/- 0.22 degrees C). Forehead skin temperature in the neutral and cool conditions was significantly greater than forearm, hand, thigh, and calf skin temperatures (p < 0.05). In the hot condition, forehead temperature was significantly greater than back, chest, upper arm, and hand skin temperatures (p < 0.05). In contrast to the neutral and hot conditions, forehead skin temperature was significantly associated with thermal sensation during exercise in the cool condition (r consistently > 0.67)., Conclusions: We conclude that forehead skin temperature, in contrast to other skin sites, contributed significantly to thermal sensation during exercise in the cool.

Skin blood flow (SkBF) was measured in six male subjects using laser-Doppler velocimetry, with zero-gradient auditory canal temperature (Tac) used as an index of body core temperature (Tc). Subjects performed incremental, upright cycling commencing at 40% peak power (Wpeak: 10 min), increasing every 4 min by 5% Wpeak thereafter. Trials were conducted in hot (ambient temperature (Ta) 36.7 +/- 0.2 degree C, relative humidity (rh) 46.1 +/- 3.2%; mean +/- S.D.), and neutral environments (Ta 19.6 +/- 0.3 degree C, rh 50.2 +/- 1.4%). SkBF increased with Tac in all subjects. Attenuation of SkBF occurred at the same Tac, relative SkBF and cardiac frequency (fc) between environments, but at a lower exercise intensity (40.8 +/- 0.8% versus 55.8 +/- 3.0% Wpeak) in the hot environment (p < 0.05). Data indicate that Tc thresholds for SkBF attenuation may exist. However, it is suggested that attenuation thresholds coincided with a reduced central blood volume, which may occur at a critical level of cutaneous blood pooling.

The purpose of this study was to evaluate the effects of age on dynamic muscle attributes of the knee extensors and flexors in postmenopausal women. Young healthy women (3rd decade, n = 15; 4th decade, n = 5) and older healthy women (6th decade, n = 9; 7th decade, n = 6) were tested at six angular velocities from 60 degrees.s-1 to 400 degrees.s-1. The 3rd and 4th decade groups produced greater extensor and flexor values for strength related variables at all angular velocities (peak torque, angle specific torque, work, power) than both the 6th and 7th decade groups (P < 0.05). However, relative changes in these variables, with increments in angular velocity, were equivalent among the groups. Analysis of the flexor: extensor ratios for these variables demonstrated a differential loss in flexor function with increased age, perhaps indicative of type II motor unit loss or muscle fibre atrophy. It is suggested that such changes may be present even within 4th decade subjects.