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 m
2
) to each hand for a 1 °C thermal gradient. For each foot, this is 8.5 W (119 W m
2
). In an air temperature of 27 °C, the hands and feet of resting individuals can each dissipate 150–220 W m
2
(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.
Purpose
To determine the impact of altering dietary sodium intake for 3 days preceding exercise on sweat sodium concentration Na
+
, and cardiovascular and thermoregulatory variables.
Methods
Fifteen ...male endurance athletes (runners
n
= 8, cyclists
n
= 7) consumed a low (LNa, 15 mg kg
−1
day
−1
) or high (HNa, 100 mg kg
−1
day
−1
) sodium diet, or their usual free-living diet UDiet, 46 (37–56) mg kg
−1
day
−1
for 3 days in a double-blind, randomized cross-over design, collecting excreted urine (UNa) and refraining from exercise. On day 4, they completed 2 h running at 55%
V
˙
O
2max
or cycling at 55% maximum aerobic power in
T
amb
35 °C. Pre- and post-exercise blood samples were collected, and sweat from five sites using absorbent patches along the exercise protocol.
Results
UNa on days 2–3 pre-exercise mean (95% CI) LNa 16 (12–19) mg kg
−1
day
−1
, UDiet 46 (37–56) mg kg
−1
day
−1
, HNa 79 (72–85) mg kg
−1
day
−1
;
p
< 0.001 and pre-exercise aldosterone LNa 240 (193–286) mg kg
−1
day
−1
, UDiet 170 (116–224) mg kg
−1
day
−1
, HNa 141 (111–171) mg kg
−1
day
−1
;
p
= 0.001 reflected sodium intake as expected. Pre-exercise total body water was greater following HNa compared to LNa (
p
< 0.05), but not UDiet. Estimated whole-body sweat Na
+
following UDiet was 10–11% higher than LNa and 10–12% lower than HNa (
p
< 0.001), and correlated with pre-exercise aldosterone (1st h
r
= − 0.568, 2nd h
r
= − 0.675;
p
< 0.01). Rectal temperature rose more quickly in LNa vs HNa (40–70 min;
p
< 0.05), but was similar at the conclusion of exercise, and no significant differences in heart rate or perceived exertion were observed.
Conclusions
Three day altered sodium intake influenced urinary sodium excretion and sweat Na
+
, and the rise in rectal temperature, but had no effect on perceived exertion during moderate-intensity exercise in hot ambient conditions.
To investigate the disparity in the specification and physiological demand of a task simulation when developed by two independent panels of experiential experts.
Independent groups design.
Two groups ...of experiential experts from the Royal Australian Air Force (RAAF) worked independently to design, and then complete a simulation of a generic occupational task; the establishment of a security control point. Task duration, oxygen consumption, and cardiac frequency were measured whilst each panel completed the task simulation. Maximal acceptable work duration (MAWD) and the percentage of MAWD (%MAWD) were also calculated. Independent t-tests were used to determine differences (P < 0.05) between the measured variables.
No differences were observed in the average oxygen consumption (1.26 ± 0.25 L min−1 and 1.28 ± 0.29 L min−1 respectively; P = 0.84), or cardiac frequency (134 ± 16.4 beats·min−1 and 125 ± 8.5 beats·min−1 respectively; P = 0.12) between Panel 1 and Panel 2. However, there was a significant difference between panels with respect to task duration (Panel 1: 15.5 ± 3.68 min; Panel 2: 34.20 ± 9.60 min; P < 0.01), and the %MAWD (Panel 1: 5.32 ± 3.17%, Panel 2: 12.15 ± 9.40%, P = 0.04).
The physiological demand of a task simulation is dependent upon the group of experts consulted to develop the simulation. It is critical that input from a wide representation of experiential experts is considered when developing task simulations to avoid bias towards the perceptions of the experts consulted.
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 (0.04 mg kg−1) with thermal clamping sustained; and following clamp 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). Passive heating induced steady‐state sweating ranging from 0.20 ± 0.04 (volar hand) to 1.40 ± 0.14 mg cm−2 min−1 (forehead), with each non‐thermal stimulus provoking greater secretion (P < 0.05). Atropine suppressed thermal sweating, and it also eliminated the sudomotor responses to these non‐thermal stimuli when body temperatures were prevented from rising (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.
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.
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 (R
2
= 0.59) had superior predictive ability of stretcher carry performance than a bilateral 15-kg jerry can carry (R
2
= 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.
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.
To better understand the relationships between changes in body temperature and displacements of the thermoeffector thresholds (critical temperatures), the passive cooling (and heating) of pre-heated ...(and pre-cooled) individuals was investigated. Such experiments are necessary to understand the inter-dependence of those thresholds, and may possibly yield human evidence for the existence of separate central controllers. Eight males participated in four trials; two when normothermic, one following pre-experimental heating and the fourth following pre-cooling. Subjects were exposed to passive, whole-body cooling and heating when normothermic (the control trials), and again following pre-heating and pre-cooling (respectively). Cutaneous vasomotor, thermogenic, as well as precursor and discharged sudomotor thresholds from different body segments were compared across those dynamic thermal states. Following pre-heating, the critical mean body temperatures for vasoconstriction (0.37 °C ± 0.10) and thermogenesis (0.67 °C ± 0.20) were significantly elevated during passive cooling, relative to the corresponding control trial (both P < 0.05). When passive heating followed pre-cooling, the thresholds for vasodilatation were reduced (0.37 °C ± 0.07; P < 0.05). Conversely, but with the exception of forehead precursor sweating, the sudomotor thresholds were elevated (averaging 0.16 °C ± 0.02; P < 0.05). Most thermoeffectors revealed unique and adjustable activation thresholds, with the threshold displacements for thermogenesis and vasomotion appearing to be linked to the change in mean body temperature. Following pre-cooling, the critical temperatures for vasodilatation and sudomotor activation varied independently, with the exception of forehead precursor sweating. Collectively, those observations are consistent with the presence of independent central controllers for thermally dependent vasomotor and sudomotor responses, and perhaps also for shivering thermogenesis.
•Thermoeffector thresholds were determined during passive heating and cooling.•Subjects were normothermic, pre-heated or pre-cooled.•Six vasomotor, one thermogenic and six sudomotor thresholds were determined.•After pre-cooling, the vasodilatation and sudomotor thresholds varied independently.•Support was provided for independent thermoeffector controllers in humans.
Beck, B, Carstairs, GL, Billing, DC, Caldwell, JN, and Middleton, KJ. Modifiable anthropometric characteristics are associated with unilateral and bilateral carry performance. J Strength Cond Res ...31(2): 489-494, 2017-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.
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