Search

The risk of low back pain and injury during manual materials handling is increased if personnel are not physically capable of safely performing such tasks. To establish predictive relationships and develop a test cut-score, 69 participants performed a critical military lifting task to a 1.5-m platform (pack lift) and two task-related predictive tests (box lift to 1.5 m and 1.3 m). The pack lift was strongly correlated with both the 1.5-m (R2 = 0.85) and 1.3-m box lifts (R2 = 0.82). Both tests had similar sensitivity (range 0.85-0.94) with the 1.3-m test having higher specificity when compared with the 1.5-m lift. Increasing the test cut-score with the application of a safety factor increased the number of false positives and true negatives for both tests. Organisations must carefully assess their risk acceptance when applying safety factors to test cut-scores as the classification (pass/fail) of personnel may be affected.

In this experiment, hand and forearm vasomotor activity was investigated during localised, but stable heating and cooling of the face, hand and thigh, under open-loop (clamped) conditions. It was hypothesised that facial stimulation would provoke the most potent vascular changes. Nine individuals participated in two normothermic trials (mean body temperature clamp: 36.6 °C; water-perfused suit and climate chamber) and two mildly hyperthermic trials (37.9 °C). Localised heating (+5 °C) and cooling (−5 °C) stimuli were applied to equal surface areas of the face, hand and thigh (perfusion patches: 15 min), while contralateral forearm or hand blood flows (venous-occlusion plethysmography) were measured (separate trials). Thermal sensation and discomfort votes were recorded before and during each thermal stimulation. When hyperthermic, local heating induced more sensitive vascular responses, with the combined thermosensitivity of both limb segments averaging 0.011 mL·100 mL−1 ·min−1 ·mmHg−1 ·°C−1 , and 0.005 mL·100 mL−1 ·min−1 ·mmHg−1 ·°C−1 during localised cooling (P < 0.05). Inter-site comparisons among the stimulated sites yielded minimal evidence of variations in local thermal sensation, and no differences were observed for vascular conductance (P > 0.05). Therefore, regional differences in vasomotor and sensory sensitivity appeared not to exist. When combined with previous observations of sudomotor sensitivity, it seems that, during mild heating and cooling, regional representations within the somatosensory cortex may not translate into meaningful differences in thermal sensation or the central integration of thermoafferent signals. It was concluded that inter-site variations in the cutaneous thermosensitivity of these thermolytic effectors have minimal physiological significance over the ranges investigated thus far.

A mismatch between physical ability and task requirements can increase the risk of on-the-job injury. Therefore, understanding key anthropometric characteristics associated with job performance is important in developing targeted training programs and selecting employees in physically demanding occupations. The aims of this study were to understand which anthropometric and demographic (age/sex) characteristics were associated with performance in a unilateral stretcher carry and bilateral jerry can and kettle bell carries. Sixty-seven enlisted Australian Army soldiers (46 men and 21 women) participated in this investigation. Body composition was quantified using dual-energy X-ray absorptiometry. Univariate and multivariable regression techniques were used to quantify correlations between anthropometric characteristics and carry performance. Median carry distance was 650 m (interquartile range [IQR] = 425-1,025 m) in the stretcher carry, 300 m (IQR = 215-445 m) in the jerry can carry, and 265 m (IQR = 200-400 m) in the kettle bell carry. Univariate analyses demonstrated that whole body, trunk, upper arm, forearm, and leg lean mass, as well as stature and body mass were associated with performance across the 3 carry tasks. Of these, leg lean mass was shown to be a key characteristic associated with carry performance. Subsequently, it is suggested that training programs focus on whole-body lean mass with specific emphasis on leg lean mass. Additionally, we demonstrated that age and sex were not significantly associated with carry performance when controlling for leg lean mass, indicating that modifiable factors can be targeted in training programs to improve job performance.

Aim: Static muscle activation elicits intensity-dependent, non-thermal sweating that is presumably controlled by feedforward (central command) mechanisms. However, it is currently unknown how the size of the recruited muscle mass interacts with that mechanism. To investigate the possible muscle-size dependency of that non-thermal sweating, the recruitment of two muscle groups of significantly different size was investigated in individuals within whom steady-state thermal sweating had been established and clamped. Methods: Fourteen passively heated subjects (climate chamber and water-perfusion garment) performed 60-s, static handgrip and knee-extension activations at 30% and 50% of maximal voluntary force, plus a handgrip at 40% intensity (143.4 N) and a third knee extension at the same absolute force. Local sweating from four body segments (averaged to represent whole-body sudomotor activity), three deep-body and eight skin temperatures, heart rates and perceptions of physical effort were measured continuously, and analyzed over the final 30 s of exercise. Results: In the presence of thermal clamping and low-level, steady-state sweating, static muscle activation resulted in exercise-intensity dependent changes in the whole-body sudomotor response during these handgrip and knee-extension actions (P < 0.05). However, there was no evidence of a dependency on the size of the recruited muscle mass (P > 0.05), yet both dependencies were apparent for heart rate, and partially evident for the sensations of physical effort. Conclusion: These observations represent the first evidence that exercise-related sudomotor feedforward is not influenced by the size of the activated muscle mass, but is instead primarily dictated by the intensity of the exercise itself.

Aim The inter-relationships between mean body and local skin temperatures have previously been established for controlling hand and foot blood flows. Since glabrous skin contains many arteriovenous anastomoses, it was important to repeat those experiments on non-glabrous regions using the same sample and experimental conditions. Methods Mild hypothermia (mean body temperature 31.4 °C), normothermia (control: 36.0 °C) and moderate hyperthermia (38.3 °C) were induced and clamped (climate chamber and water-perfusion garment) in eight males. Within each condition, five localised thermal treatments (5, 15, 25, 33, 40 °C) were applied to the left forearm and right calf. Steady-state forearm and calf blood flows were measured (venous occlusion plethysmography) for each of the resulting 15 combinations of clamped mean body and local skin temperatures. Results Under the normothermic clamp, cutaneous blood flows averaged 4.2 mL 100 mL−1 min−1 (±0.28: forearm) and 5.4 mL 100 mL−1 min−1 (±0.27: calf). When mildly hypothermic, these segments were unresponsive to localised thermal stimuli, but tracked those changes when normothermic and moderately hyperthermic. For deep-body (oesophageal) temperature elevations, forearm blood flow increased by 5.1 mL 100 mL−1 min−1 °C−1 (±0.9) relative to normothermia, while the calf was much less responsive: 3.3 mL 100 mL−1 min−1 °C−1 (±1.5). Three-dimensional surfaces revealed a qualitative divergence in the control of calf blood flow, with vasoconstrictor tone apparently being released more gradually. Conclusion These descriptions reinforce the importance of deep-tissue temperatures in controlling cutaneous perfusion, with this modulation being non-linear at the forearm and appearing linear for the calf.

Carrying a casualty on a stretcher is a critical task within military and emergency service occupations. This study evaluated the impact of manipulating carry speed and the object type in bilateral carries on the ability to predict performance and reflect the physical and physiological requirements of a unilateral stretcher carry. We demonstrated that three task-related predictive tests; a jerry can carry performed at 4.5 km h-1or 5.0 km h-1 and a kettle-bell carry performed at 5.0 km h-1 were strongly predictive of the physical and physiological demands of an individual participating as part of a four-person stretcher carry team. Therefore, bilateral predictive assessments have the utility for predicting the suitability of employees to effectively and safely conduct a four-person unilateral stretcher carry.

Carrying a casualty on a stretcher is a critical task conducted in a range of occupations. To ensure that personnel have the requisite physical capacity to conduct this task, two bilateral jerry can carries were used to predict individual performance in a four-person stretcher carry. Results demonstrated a bilateral 22-kg jerry can carry (R2 = 0.59) had superior predictive ability of stretcher carry performance than a bilateral 15-kg jerry can carry (R2 = 0.46). Pre- to post-carry changes in grip endurance (p > 0.05), back-leg isometric strength (p > 0.05) and leg power (p > 0.05) were not significantly different between carry tasks. There was no significant difference in heart rate (p > 0.05) and oxygen consumption (p > 0.05) between the stretcher carry and either jerry can carry. Thus, on the basis of performance correlations and physiological measures, the 22-kg jerry can carry is an appropriate predictive assessment of four-person stretcher carriage. Practitioner Summary: This study investigated the ability of a jerry can carry to predict individual performance on a four-person stretcher carry. Performance correlations were substantiated with physiological measures to demonstrate similar physical requirements between task and test. These results can be used to set physical employment standards to assess stretcher carriage.

Meeting abstract.

Meeting abstract

Meeting abstract.

The purpose of this review is to describe the unique anatomical and physiological features of the hands and feet that support heat conservation and dissipation, and in so doing, highlight the importance of these appendages in human thermoregulation. For instance, the surface area to mass ratio of each hand is 4-5 times greater than that of the body, whilst for each foot, it is ~3 times larger. This characteristic is supported by vascular responses that permit a theoretical maximal mass flow of thermal energy of 6.0 W (136 W m2) to each hand for a 1 °C thermal gradient. For each foot, this is 8.5 W (119 W m2). In an air temperature of 27 °C, the hands and feet of resting individuals can each dissipate 150-220 W m2 (male-female) of heat through radiation and convection. During hypothermia, the extremities are physiologically isolated, restricting heat flow to <0.1 W. When the core temperature increases ~0.5 °C above thermoneutral (rest), each hand and foot can sweat at 22-33 mL h−1, with complete evaporation dissipating 15-22 W (respectively). During heated exercise, sweat flows increase (one hand: 99 mL h−1; one foot: 68 mL h−1), with evaporative heat losses of 67-46 W (respectively). It is concluded that these attributes allow the hands and feet to behave as excellent radiators, insulators and evaporators.

The purpose of this project was to design, construct and validate water-displacement plethysmographs for the forearm, hand and foot that could clamp segmental skin temperature whilst simultaneously measuring cutaneous blood flow. Two experiments were performed. In the first, the forearm plethysmograph was validated against a mercury-in-silastic plethysmograph under thermoneutral conditions, with and without forearm heating. Cutaneous vascular conductance was elevated almost three-fold by this treatment, however, there were no significant differences between the two forms of plethysmography in either state (P > 0.05). In study two, hand and foot blood flows were measured under clamped thermoneutral conditions, but with three local skin temperature treatments (5, 25, 40 °C). The hand had significantly higher blood flows than the foot at both 25 °C (4.07 versus 2.20 mL.100 mL( - 1).min( - 1); P < 0.05) and 40 °C (8.20 versus 4.47 mL.100 mL( - 1).min( - 1); P < 0.05). The foot was maximally constricted during the two lower temperatures, yet the cutaneous thermal sensitivity of the hand was almost two-fold greater (P < 0.05). This evidence supports the significant role played by these appendages in heat loss and conservation, and these plethysmographs will now be used to map cutaneous vascular responses (forearm, hand, calf, foot) across combinations of core and local skin temperatures.

Purpose Much is known about the control of blood flow, yet gaps remain concerning the interactions of deep-body and peripheral thermal feedback. In this experiment, changes in the vascular tone of the hands and feet were mapped to demonstrate the separate and combined influences of mean body and local skin temperature changes. Methods Eight males participated in three trials. Three pre-experimental conditions were established via water immersion (oesophageal temperatures: 36.1, 37.0, 38.5 °C), with core and mean skin temperatures then clamped (water-perfusion garment) whilst five thermal treatments were applied to the right hand and left foot (5, 15, 25, 33, 40 °C). This yielded 15 thermal combinations under which hand and foot blood flows were measured (displacement plethysmography). Results Lower volume-specific blood flows were observed at the foot for almost all temperature combinations. When thermoneutral and moderately hyperthermic, the cutaneous thermosensitivity of the hand was significantly greater: thermoneutral: 0.2 vs. 0.1 (foot) mL 100 mL−1 min−1 °C−1 (P < 0.05); moderate hyperthermia: 0.4 vs. 0.2 (foot) mL 100 mL−1 min−1 °C−1 (P < 0.05). The hand was 13 times more responsive to core temperature elevations than an equivalent local skin temperature change. For the foot, this thermosensitivity differed by a factor of 26. Conclusion These observations identified the hands as heat radiators, with the feet resisting heat loss, and reinforce the dominance of central thermal feedback, particularly in controlling foot blood flow. However, thermosensitivity to local skin temperature changes was highly plastic, site-specific and dictated by thermal and regional variations in vaso- and venoconstrictor tone.

Cutaneous blood flow manipulation supports body temperature regulation. Whilst deep tissue temperature has the greatest influence on this flow, local skin temperature influences flow independently of the sympathetic nervous system. Furthermore, the neural control of cutaneous blood vessels differs between acral and non-acral skin, with the former also containing arteriovenous anastomoses. These interactions are well known and have previously been explored. However, the interactions of core and local skin temperatures on cutaneous blood flow have not been studied in mildly hypothermic and hyperthermic individuals over a range of local skin temperatures, and certainly not within both the acral and non-acral skin regions. This was the primary focus of this study.

Thermally induced eccrine sweating is cholinergically mediated, but other neurotransmitters have been postulated for psychological (emotional) sweating. However, we hypothesized that such sweating is not noradrenergically driven in passively heated, resting humans. To test this, nine supine subjects were exposed to non-thermal stimuli (palmar pain, mental arithmetic and static exercise) known to evoke sweating. Trials consisted of the following four sequential phases: thermoneutral rest; passive heating to elevate (by ∼1.0◦C) and clamp mean body temperature and steady-state sweating (perfusion garment and footbath); an atropine sulphate infusion (0.04mg kg−1)with thermal clamping sustained;andfollowingclamp removal. Sudomotor responses from glabrous (hairless) and non-glabrous skin surfaces were measured simultaneously (precursor and discharged sweating).When thermoneutral, these non-thermal stimuli elicited significant sweating only from the palm (P 0.05). However, when the thermal clamp was removed, core and skin temperatures became further elevated and sweating was restored (P <0.05), indicating that the blockade had been overcome, presumably through elevated receptor competition. These observations establish the dependence of both thermal and non-thermal eccrine sweating from glabrous and non-glabrous surfaces on acetylcholine release, and challenge theories concerning the psychological modulation of sweating. Furthermore, no evidence existed for the significant participation of non-cholinergic neurotransmitters during any of these stimulations.

Individuals exposed to extreme heat may experience reduced physiological and cognitive performance, even during very light work. This can have disastrous effects on the operational capability of aircrew, but such impairment could be prevented by auxiliary cooling devices. This hypothesis was tested under very hot-dry conditions, in which eight males performed 2 h of low-intensity exercise (similar to 30 W) in three trials, whilst wearing biological and chemical protective clothing: temperate (control: 20A degrees C, 30% relative humidity) and two hot-dry trials (48A degrees C, 20% relative humidity), one without (experimental) and one with liquid cooling (water at 15A degrees C). Physiological strain and six cognitive functions were evaluated (MiniCog Rapid Assessment Battery), and participants drank to sustain hydration state. Maximal core temperatures averaged 37.0A degrees C (+/- 0.1) in the control trial, and were significantly elevated in the experimental trial (38.9A degrees C +/- A 0.3; P < 0.05). Similarly, heart rates peaked at 92 beats min(-1) (+/- 7) and 133 beats min(-1) (+/- 4; P < 0.05), respectively. Liquid cooling reduced maximal core temperatures (37.3A degrees C +/- A 0.1; P < 0.05) and heart rates 87 beats min(-1) (+/- 3; P < 0.05) in the heat, such that neither now differed significantly from the control trial (P > 0.05). However, despite inducing profound hyperthermia and volitional fatigue, no cognitive degradation was evident in the heat (P > 0.05). Since extensive dehydration was prevented, it appears that thermal strain in the absence of dehydration may have minimal impact upon cognitive function, at least as evaluated within this experiment.

The widely accepted, though not unequivocal, opinion concerning thermal and psychological (psychogenic) seating is tha the former is cholinergically mediated (Dale & Feldberg, 1934), while the latter is of noradrenergic origin (Robertshaw, 1977). Moreover, psychological sweating is thought to be elicited by a different neural centre (Ogawa, 1975), possibly through separate pathways (Chalmers & Keele, 1952) that exclusively innervate the glabrous (non-hairy) skin of the hands and feet (Darow, 1937, Kuno, 1956, Ogawa, 1975). Evidence for the cholinergic modulation of thermal sweating is incontrovertible. However, evidence supporting the theoretical control of psychological sweating is less than convincing. Following observations of Chalmers & Keele (1952) and Kuno (1956) first Ogawa (1975), and then Ogawa et al. (1977) hypothesised the existence of separate non-thermal pathways, and this was further developed by lwase et al (1997). Their hypothetical model, in addition to assigning thermal seating to the non-glabrous (hairy) sites and psychological sweating to glabrous skin surfaces, proposed the existence of inhibitory affects of thermal loading upon psychological sweating, and of psychological stress upon thermal sweating. Two recently completed projects were designed to test the underlying assumptioins of this model, and this research is summarised below.

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°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 signifi cantly among trials, rising at 0.37°C h −1 (control), 0.41°C h −1 (torso armor), and 0.51°C h −1 (full armor). Heart rates also progressively diverged, and subjects lost signifi cantly more sweat during the two armored trials. However, cognitive-function tests revealed neither signifi cant main effects nor time by treatment interactions. Conclusion: The combat armor and helmet signifi cantly 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.

A significant number of military personnel suffer from exertional heat illness, with some extreme cases resulting in death. These illnesses may occur without warning, they are often characterised by a rapid onset and can occur even in experienced personnel. Various field treatments for hyperthermia have been developed, and one of particular interest is the use of cold-water immersion. Not surprisingly, immersion in ice-cold water (0-2oC) has been shown to be an effective means of rapidly reducing body core temperature (Proulx et al., 2003, 2006).

Extensive research into the physiological impact of wearing thermal protective clothing has been conducted for many years. However, the current literature does not provide a consensus concerning the interaction of heat strain and cognitive function. This project sought to investigate the problems associated with personnel working in uncompensable environmental conditions while wearing Australian Defence Force (ADF) protective clothing. Four separate investigations were conducted. The first was a field based study evaluating the thermal influences of operating a helicopter simulator. The second was a laboratory study evaluating the impact of wearing body armour on physiological and cognitive function. Thirdly, a theoretical evaluation of, the problems associated with performing work in an uncompensable heat stress environment and, the physical characteristics of various coolants and cooling systems were investigated. Finally, a laboratory investigation on the physiological and cognitive consequences of wearing a personal protective ensemble while performing exercise with and without an activated liquid-cooling garment. A significant reduction in flying performance was evident when pilots were heated to a mean skin temperature (TGsk) of~39EC compared to the other two conditions (~33EC and 37EC, P less than 0.05), using a water perfusion garment to achieve these target TGsk. However no obvious detriments in cognitive performancewere observed for the two laboratory based studies even though subjects were exposed to a significant thermal load, as determined by increases in TC, TGsk and fc (P less than 0.05). For the final study, where thermal strain was significantly higher in the hot-dry trial without cooling (P less than 0.05), resulting in a terminal rectal temperature that was 1.6EC higher than the thermoneutral condition, the liquid-cooling garment (water temperature 15EC) successfully prevented all detriments in physiological function observed during the hot-dry tr

The hottest months encountered on northern Australian cattle stations are from September to November, where the climate is both hot and dry, and it is during these months that horseback cattle mustering occurs. Stockmen wear clothing that restricts heat loss (collared shirts and long trousers), yet protective helmets have recently been introduced into the cattle industry (AS/NZS 3838:2006), as part of the increasing occupational health and safety responsibilities of pastoral companies. Anecdotal evidence points to the possibility that protective helmets may increase the probability of stockmen developing heat illness, or experiencing reduced workplace performance. Herein, we describe the working and thermal environment on these cattle stations, and provide an overview of the metabolic demands, and the concurrent physiological and cognitive strain encountered during horseback mustering in a hot-dry environment, whilst stockmen wore an equestrian helmet (Taylor and Caldwell, 2007). In subsequent investigations, we evaluated heat penetration through various forms of headwear (Caldwell and Taylor, 2007), and completed laboratory-based trials in which the physiological impact of an equestrian helmet, relative to the traditional felt hat, was evaluated (Caldwell et al., 2007).

The hand is one of the most closely studied body segments with respect to sweat secretion, with previous research focussing on its neural control, secretion differences between glabrous and non-glabrous (hairy) skin surfaces, and upon the impact of thermal and non-thermal stimuli on sudomotor function. It is generally considered that the glabrous palmar surfaces are adrenergically activated during times of mental or emotional stress, while the non-glabrous dorsal surfaces are cholinergically innervated, and respond to thermal stimuli (Wolf and Maibach, 1974). However, surprisingly little is known concerning the regional distribution of sweating within the palmar and dorsal surfaces of the hand. Therefore, in this project, we investigated the distribution of sweating within the hand, and measured sweat rates from ten sites on the dorsal and palmar surfaces during mild hyperthermia.

Metabolic and external heat sources are equally capable of elevating body core temperature in individuals working in hot environments. When heat loss avenues are impeded by clothing and protective equipment, the risk of exertional heat stress is further increased. There are various work-rest guidance tables available within the literature, some of these have correction factors for variations in clothing insulation, such that rest periods are lengthened and work periods shortened when clothing insulation is increased (TBMED 507). However, there is a paucity of experimental data upon which such modifications may be based. An absence of such empirical data may result either in an increased risk of exertional heat illness, or compromised operational capability, if physiological strain is over-estimated (Danielsson and Bergh, 2005). Therefore, the aim of this project was to assess the impact of wearing such body armour on physiological and cognitive function in hot-humid conditions.

When exposed to environmental heat stress, one’s ability to perform physical and mental tasks can be compromised. In relation to a helicopter pilot, a slight decrement in flight performance can result in devastating consequences. Previously, Froom et al. (1993) found environmental heat stress elevated pilot error, whilst Caldwell et al. (2005) have described impaired flight simulator performance during progressive hyperthermia. Such changes can reflect reduced cognitive function, and Faerevik and Reinertsen (2003) have shown that heat stress can contribute to deficits in both vigilance and multi-choice reaction time. Presumably, the use of biological and chemical (BC) protective clothing will exacerbate this state.

Within environments that pose either a chemical or a biological threat to workers, the ability to regulate body temperature is adversely affected by the need to wear personal protective ensembles. These chemical and biological (CB) protective ensembles impede the loss of metabolically-generated heat, the wicking of sweat and the removal of water vapour resulting from the evaporation of sweat. The design objective of most newly-developed materials is to facilitate heat loss, whilst retaining the appropriate chemical and biological protection. In this project, the focus was upon the physiological impact of exercising in a hot-dry environment, whilst wearing CB protective ensembles made from various combinations of these materials.

It is well known that elevations in body temperature can impair both physical and cognitive performance. For helicopter pilots, the major heat source during flight originates from solar radiation. However, when nuclear, biological and chemical (NBC) protective clothing is worn, metabolic heat generated during the pre-flight period, and during the mission, is trapped, exacerbating thermal strain. In this project, the hypothesis that elevations in body heat content would degrade flight performance was tested. Helicopter pilots completed three, two-hour flight simulations under three levels of thermal strain, administered in a balanced order. Thermal strain was induced using a water-perfusion gannent, worn under flight and NBC clothing, and supplied with water that would elicit skin temperatures of 33°C (control), 37°C (moderate) and 39°C (hot). Each sortie was programmed and controlled by the simulator flight officer (blind to treatment order), and was comprised of eight flight circuits, each involving takeoff and landing exercises. During each circuit, the pilots were required to identify and solve two operational problems, graded as "easy", "moderate" and "hard". In this report, we present preliminary data from four pilots. Terminal core temperatures for each trial were: 37.5°C (±0.17; control), 38.6°C (±0.14; moderate) and 38.8°C (±0.19; hot). This strain was also reflected within the terminal heart rates: 87.8 b.min-1 (±9.6; control), 127.8 b.min-1 (±9.1; moderate) and 150.8 b.min-1 (±6.1; hot). The simulator officer independently graded pilot performance, and while the moderate trial resulted in slightly reduced performance scores, relative to control (P>0.05), scores were significantly lower in the hot trials (P<0.05). Strong correlations existed between the thermal load and both the effort needed to sustain the appropriate flight performance, and the pilots' own assessment of performance quality. From these data, it appears that mean body temperature has the mo