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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.

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.