Changes in eccrine sweating on the glabrous skin of the palm and finger during isometric exercise

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.     

Psychological sweating from glabrous and nonglabrous skin surfaces under thermoneutral conditions

Recent experiments revealed psychological sweating to be a ubiquitous phenomenon in passively heated individuals. Since heating potentiates sweating, and since most research into psychological sweating was not conducted in this thermal state, these observations required thermoneutral verification. Thermoneutral subjects performed mental arithmetic (at 26^oC) with psychological sweating evaluated from nine sites (ventilated capsules, skin conductance). Discharged sweating was evident from three glabrous sites (P < .05). However, significant sweating was evident from two nonglabrous surfaces (P < .05), and skin conductance increased at the volar and dorsal finger surfaces (P < .05). Each of these changes occurred while core and skin temperatures remained stable (P > .05). These thermoneutral observations further refute the proposition that psychological sweating in humans is restricted to the glabrous skin surfaces.     

Local differences in sweat secretion from the head during rest and exercise in the heat

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.     

Quantification of head sweating during rest and exercise in the heat

The head’s capacity for evaporative heat loss is important for design of protective helmets for use in hot environments. This study quantified head sweating rate (m _sw) in eight males during rest and exercise at three metabolic rates (338 ± 36, 481 ± 24, 622 ± 28 W) in hot-dry (HD: 45 °C, 21 % RH) and hot-wet (HW: 35 °C, 69 % RH) conditions (matched at 31.6 °C WBGT), which were counterbalanced. Heads were shaved, and surface area was (458 ± 61 cm²) measured by 3D scanner. For measurement of head m _sw, dry air was passed through a sealed helmet, whereas for forearm m _sw a capsule (15.9 cm²) was ventilated with ambient air. Evaporation rate was determined from the increase in vapor pressure in the exiting air. Whole-body sweat loss was calculated from the change in nude weight plus fluid intake and corrected for respiratory fluid losses. Head m _sw increased (p = 0.001) with metabolic rate, and was lower (p = 0.018) in HD (0.4 ± 0.2 mg cm^?2 min^?1 at rest to 1.1 ± 0.6 mg cm^?2 min^?1 at 622 W), compared to HW (0.5 ± 0.3–1.4 ± 0.8 mg cm^?2 min^?1). Forearm m _sw increased (p < 0.001) with metabolic rate, but was higher (p = 0.002) in HD (0.4 ± 0.3–1.4 ± 0.7 mg cm^?2 min^?1) than HW (0.1 ± 0.1–1.1 ± 0.3 mg cm^?2 min^?1). Whole-body sweat loss was not significantly different (p = 0.06) between HD (647 ± 139 g m^?2 h^?1) and HW (528 ± 189 g m^?2 h^?1). This study demonstrates the importance of the head for evaporative heat loss, particularly for populations who wear protective clothing which can impair vapor transfer from the skin.     

Lactate kinetics in human tissues at rest and during exercise

Aim: We sought to determine whether pulmonary diffusing capacity for nitric oxide (DLNO), carbon monoxide (DLCO) and pulmonary capillary blood volume (Vc) at rest predict peak aerobic capacity (O_2peak), and if so, to discern which measure predicts better. Methods: Thirty-five individuals with extreme obesity (body mass index or BMI = 50 ± 8 kg m⁻²) and 26 fit, non-obese subjects (BMI = 23 ± 2 kg m⁻²) participated. DLNO and DLCO at rest were first measured. Then, subjects performed a graded exercise test on a cycle ergometer to determine O_2peak. Multivariate regression was used to assess relations in the data. Results: Findings indicate that (i) pulmonary diffusion at rest predicts O_2peak in the fit and obese when measured with DLNO, but only in the fit when measured with DLCO; (ii) the observed relation between pulmonary diffusion at rest and O_2peak is different in the fit and obese; (iii) DLNO explains O_2peak better than DLCO or Vc. The findings imply the following reference equations for DLNO: O_2peak (mL kg⁻¹ min⁻¹) = 6.81 + 0.27 × DLNO for fit individuals; O_2peak (mL kg⁻¹ min⁻¹) = 6.81 + 0.06 × DLNO, for obese individuals (in both groups, adjusted R² = 0.92; RMSE = 5.58). Conclusion: Pulmonary diffusion at rest predicts O_2peak, although a relation exists for obese subjects only when DLNO is used, and the magnitude of the relation depends on gender when either DLCO or Vc is used. We recommend DLNO as a measure of pulmonary diffusion, both for its ease of collection as well as its tighter relation with O_2peak.     

Differences in regional sweating responses during exercise between athletes trained on land and in water

We investigated whether there are any differences in regional sweating responses during exercise between athletes trained on land and in water. We measured the local sweating rates on the left forearm (m_swf) and the left scapula (m_sws), body temperatures (mean skin temperature, and rectal temperature T _re) in eight athletes trained on land (five soccer players, one distance runner and two baseball players, L group) and seven athletes trained in water (seven swimmers, W group) during cycle ergometer exercise at 50% maximal oxygen uptake for 40 min. The heart rate and oxygen uptake in the two groups during exercise showed nearly the same pattern of change. The T _re at the end of the exercise were 38.13 (SEM 0.19)°C in the L group and 38.26 (SEM 0.34)°C in the W group. Although the m_swf in the two groups were similar, m_sws were significantly higher in L than in W at 30, 35 and 40 min of exercise. The m_sws at any given mean body temperature tended to be greater in L than in W. These results showed that a difference in regional sweating rate during exercise between the athletes trained on land and in water was present on the scapula.     

Elimination of breathing artefacts from impedance cardiograms at rest and during exercise

A signal processing technique was developed by which breathing artefacts can be eliminated from impedance cardiograms. The breathing component of the transthoracic impedance signal is identified by a moving-window technique using linear regression analysis, the window span being determined by the current R-R interval of the ECG. Satisfactory beat-by-beat stroke volume measurements were obtained when the method was applied to eliminate simulated breathing artefacts superimposed on distortion-free impedance signals from human subjects. In subjects performing moderate to heavy exercise the potential capability of the method to retrieve the cardiogenic impedance signal in the presence of severe interference caused by exercise hyperpnoea was demonstrated, permitting distortion-free beat-by-beat stroke volume estimations.     

Sudomotor responses from glabrous and non-glabrous skin during cognitive and painful stimulations following passive heating

Aim: It is widely accepted that thermal and psychological sweating are independently controlled and respectively restricted to non‐glabrous (hairy) and glabrous skin. These assumptions were evaluated in six experiments conducted across eight body segments, in which 38 glabrous and non‐glabrous skin surfaces were investigated. Methods: Sweating was measured in 30 passively heated individuals using ventilated sweat capsules, with passive heating used to first establish steady‐state sweating, averaging 0.30 mg cm^?2 min^?1 (±0.03) across all sites, prior to the application of cognitive and painful stimuli. Results: These non‐thermal (psychological) stimulations significantly increased sweat secretion at more than 70% of the sites investigated [cognitive: 28 of 38 sites (P < 0.05); pain: 23 of 32 sites (P < 0.05)], eliciting peak sweat rates averaging 0.51 mg cm^?2 min^?1 (±0.05) and 0.47 mg cm^?2 min^?1 (±0.4 respectively) across all sites. Furthermore, non‐thermal sweating was evident from both the glabrous and non‐glabrous surfaces and occurred without mean body or local skin temperatures changes (P > 0.05). Indeed, neither thermal nor psychological sweating was restricted to discrete skin surfaces, and there were no consistent sudomotor differences between these two skin classifications. Finally, at no site was thermal sweating inhibited during a non‐thermal stimulation. Conclusion: These generalized sudomotor responses challenge the hypotheses that glabrous skin sweating is driven by psychological stimuli, and that thermal sweating is a phenomenon restricted to the non‐glabrous skin surfaces.     

Thermoregulation at rest and during exercise in prepubertal boys

Summary Thermal balance was studied in 11 boys, aged 10–12 years, with various values for maximal oxygen uptake ( ), during two standardized sweating tests performed in a climatic chamber in randomized order. One of the tests consisted in a 90-min passive heat exposure [dry bulb temperature (T _db) 45° C] at rest. The second test was represented by a 60-min ergocycle exercise at 60% of individual (T _db 20° C). At rest, rectal temperature increased during heat exposure similar to observations made in adults, but the combined heat transfer coefficient reached higher values, reflecting greater radiative and convective heat gains in the children. Children also exhibited a greater increase in mean skin temperature, and a greater heat dissipation through sweating. Conversely, during the exercise sweating-test, although the increase in rectal temperature did not differ from that of adults for similar levels of exercise, evaporative heat loss was much lower in children, suggesting a greater radiative and convective heat loss due to the relatively greater body surface area. Thermophysiological reactions were not related to in children, in contrast to adults.     

Effect of exercise to rest ratio on plasma lactate concentration at work rates above and below maximum oxygen uptake

Summary The metabolic and physiological responses to different exercise to rest ratios (E: R) (2:1, 1: l, 1:2) of eight subjects exercising at work rates approximately 10% above and below maximum oxygen uptake ( ) were assessed. Each of the six protocols consisted of 15 1-min-long E : R intervals. Total work (kJ), oxygen uptake ( ), heart rate (f _c and plasma lactate concentrations were monitored. With increases in either E : R or work rate, andf _c increased (P <0.05). The average (15 min) andf _c ranged from 40 to 81 %, and from 62 to 91% of maximum, respectively. Plasma lactate concentrations nearly doubled at each E : R when work rate was increased from 90 to 110% of and ranged from a low of 1.8 mmol -I^–1 (1: 2–90) to a high of 10.7 mmol·1^–1 (2:1–110). The 2:1–110 protocol elicited plasma lactate concentrations which were approximately 15 times greater than that of rest. These data suggest that plasma lactate concentrations during intermittent exercise are very sensitive to both work rate and exercise duration.     

Plasma vasopressin,neurophysin, renin and aldosterone during a 4-day head-down bed rest with and without exercise

Summary The purpose of this study was to investigate the main renal and hormonal responses to head-down bed rest, which is curently considered a reliable experimental model for the simulation of weightlessness. Urinary output and electrolytes, plasma renin activity (PRA), aldosterone (PA), antidiuretic hormone (ADH) and immunoreactive neurophysin-I (Np) were measured in eight adult volunteers submitted to a 4-day head-down bed rest (–6) after a 24-h control period in the horizontal position (day 0). Four of the eight subjects were submitted to two 1-h periods of controlled muscular exercise (50% ) from day 1 to day 4. Throughout the head-down bed rest period, urinary output remained stable, although lower than in the control period (day 0), but the urinary Na/K ratio decreased. Plasma electrolytes and osmolality, and creatinine clearance remained unchanged. There was no significant difference between exercising and non-exercising subjects. At the hormonal level, PRA and PA increased during the head-down bed rest. This increase was more pronounced in the group with exercise. At the end of the tilt period, PRA and PA were about 3 times higher than on day 1. No significant changes could be observed for ADH and Np. It is concluded that a 4-day head-down bed rest results in no apparent changes in neurohypophyseal secretory activity, and in a progressive secondary hyperaldosteronism.Presented in part at the 35^th Congress of the International Astronautical Federation, Lausanne, October 1984     

Regional differences in the effect of exercise intensity on thermoregulatory sweating and cutaneous vasodilation

To investigate regional body differences in the effect of exercise intensity on the thermoregulatory sweating response, nine healthy male subjects (23.2 ± 0.4 year) cycled at 35, 50 and 65% of their maximal O₂ uptake (V˙O _2max) for 30 min at an ambient temperature of 28.3 ± 0.2 °C and a relative humidity of 42.6 ± 2.4%. Local sweating rate ( m˙_sw) on the forehead, chest, back, forearm and thigh increased significantly with increases in the exercise intensity from 35 to 50% V˙O _2max and from 50 to 65% V˙O _2max (P < 0.05). The mean values for the density of activated sweat glands (ASG) at 50 and 65% V˙O _2max at the five sites were significantly greater than at 35% V˙O _2max. The mean value of the sweat output per gland (SGO) also increased significantly with the increase in exercise intensity (P < 0.05). The patterns of changes in ASG and SGO with an increase in exercise intensity differed from one region of the body to another. Although esophageal temperature (T_es) threshold for the onset of sweating at each site was not altered by exercise intensity, the sensitivity of the sweating response on the forehead increased significantly from 35 to 50 and 65% V˙O _2max (P < 0.05). The threshold for cutaneous vasodilation tend to increase with exercise intensity, although the exercise intensity did not affect the sensitivity (the slope in the relationship T_es vs. percentage of the maximal skin blood flow) at each site. T_es threshold for cutaneous vasodilation on the forearm was significantly higher at 65% V˙O _2max than at either 35 or 50% V˙O _2max, but this was not observed at the other sites, such as on the forehead and chest. These results suggest that the increase in m˙_sw seen with an increasing intensity of exercise depends first on ASG, and then on SGO, and the dependence of ASG and SGO on the increase in m˙_sw differs for different body sites. In addition, there are regional differences in the T_es threshold for vasodilation in response to an increase in exercise intensity.     

Cardiac output measured by acetylene rebreathing technique at rest and during exercise

Cardiac output ( ) was measured by a rebreathing technique, using acetylene and a mass-spectrometer for analyzing. In addition the rate of pulmonary uptake of O₂ ( ) during the rebreathing period and during a preceding steady-state period were determined. Measurements were made on 8 adult humans at rest and at different levels of exercise up to maximum at two occasions. The ratio ( ) during steady-state/ during rebreathing) was found to be significantly below 1 when the was below about 21·min^–1 and to be about 0.55 for subjects at rest. This indicates that , and hence is increased by the rebreathing procedure when this involves deeper and more frequent respirations than those of the preceding period. Accordingly, when was below about 21·min^–1, the value, calculated exclusively from acetylene concentrations recorded during rebreathing, was multiplied by the above-mentioned -ratio. It is shown that this correcting procedure gives more reasonable values than those obtained by acetylene data alone. It is pointed out in what respects this correcting procedure of calculation deviates from that originally used by Grollman, and it is shown that there are only moderate differences between the results obtained by the two procedures.List of Symbols Ac Acetylene - _Ac ^B Bunsen solubility coefficient for Ac in blood (0.700 ml·ml^–1·atm^–1, Chapman et al. 1950) - _PT ^Ac Solubility coefficient for Ac in pulmonary tissue (0.768 ml·ml^–1·atm^–1, Cander and Forster 1959) - Mixed end-capillary to mixed venous oxygen difference per ml blood - F _AC Fractional (dry) concentration of a gas (Ac) in the gas mixture during rebreathing (s) or in the initial mixture in the bag (b) - Alveolar oxygen tension (mm Hg) - pB Barometric pressure (mm Hg) - Pulmonary capillary blood flow (cardiac output), (ml·min^–1) - t Time (s) - V ^b Initial gas volume (ml STPD) in the rebreathing bag (b) - V ^L Initial gas volume in lungs and airways after a deep expiration - V ^PT Volume of pulmonary tissue and blood in the pulmonary capillaries - V _Ac ^s (t _O) Distribution compartment (system volume) of a gas (Ac) at timet _O - Oxygen uptake (ml·min^–1) during rebreathing (RB) or steady-state (SS)     

Effects of blood-volume distribution on the characteristics of the carotid baroreflex in humans at rest and during exercise

Seven supine subjects were studied at rest and during mild to moderate dynamic leg exercise with and without unloading of the cardiopulmonary baroreceptors accomplished by exposing the lower portion of the body to a subatmospheric pressure of 20 mmHg (Lower Body Negative Pressure, LBNP). The function of the cardiac branch of the carotid baroreflex was studied over its full operational range by measuring R-R intervals during application of pulse synchronous graded pressures (40 to – 65 mmHg) in a neck-chamber device. Raising the carotid transmural pressure (systolic arterial pressure minus neck-chamber pressure) induced increasing R-R intervals in all conditions. In conformity with previous results from our laboratories it was found that the maximal rate of change in relative R-R intervals and the corresponding transmural pressure were higher during exercise than at rest, indicating that exercise increased the carotid baroreflex sensitivity and shifted its optimal buffering range to higher arterial pressures. LBNP did not affect the characteristics of the reflex at rest nor during exercise. It is concluded that reduced central venous pressure with consequent selective cardiopulmonary receptor disengagement exerts no influence on the carotid baroreflex control of heart rate (HR), as tested over the entire arterial pressure-effector response relation, either at rest or during mild-moderate exercise.     

The effect of diurnal variation on the regional differences in sweating and skin blood flow during exercise

The aim of the present study was to examine changes in the control of heat-dissipation responses to exercise associated with the diurnal variation in core temperature from the viewpoint of the regional response patterns. We studied seven men during exercise on a cycle ergometer at 100 W for 40 min at 25°C at 0630 (morning) 1630 (evening) hours on 2 separate days. Oesophageal temperature (T _oes), local skin temperature, local sweating rate ( ) on the forehead, back, forearm and thigh, and skin blood flow by laser Doppler flowmeter (LDF) on the back and forearm were measured continuously. TheT _oes at rest was significantly higher in the evening than in the morning, the difference averaging approximately 0.4°C (P < 0.05). TheT _oes thresholds for each site in and that for back in LDF were significantly different between the two times of day (P < 0.05). The change inT _oes thresholds for sweating and vasodilatation for morning and evening were similar toT _oes at rest. Although on the forehead was significantly higher in the morning than in the evening, on the back was significantly higher in the evening than in the morning (P < 0.05). Total local sweating rate ( ) for each site during exercise was significantly higher on the forehead than on the forearm in the morning, and on the back than on the forearm in the evening, respectively (P < 0.05). The results would suggest that the diurnal variation of heat-dissipation responses to exercise is influenced not only by a central controlling mechanism but also by changes in the regional differences.     

Myocardial lactate extraction and release at rest and during heavy exercise in healthy men

The relationship between myocardial lactate extraction and blood lactate concentration and the possibility that simultaneous uptake and release of lactate occur in the normal human heart was investigated by measuring arterial-coronary sinus differences of lactate and of labelled lactate during infusion of ¹⁴C lactate in 13 healthy young male volunteers. Measurements were done at rest, during increased cardiac work with unaltered arterial lactate concentration achieved by atrial pacing and during increased cardiac work and increased arterial lactate concentration achieved by supine cycle ergometer exercise. There was on no occasion a significant difference in ¹⁴C lactate specific activity between arterial and coronary sinus blood, i.e. no significant admixture of non-labelled lactate occurred in the coronary sinus indicating that on no occasion was there any sign of lactate release. The myocardial extraction of lactate seemed to be a linear function of arterial lactate concentration. During exercise with an arterial lactate concentration of 6 mmol l^-1 and above, lactate could have covered approximately 75–100% of the oxidative metabolism. Thus, during short-term heavy work myocardial lactate extraction dominates over other substrates (mainly free fatty acids and glucose) taken up by the heart, and used for oxidation by the heart muscle cells.     

Near-infrared monitoring of tissue oxygenation during application of lower body pressure at rest and during dynamical exercise in humans

During the application of a wide range of graded lower body pressures (LBP) (–50 to 50 mmHg), we examined how (1) the tissue oxygenation in the lower and upper parts of the body changes at rest, and (2) how tissue oxygenation changes in the lower extremities during dynamical leg exercise. We used near-infrared spectroscopy (NIRS) to measure the changes induced by LBP in total Hb content and Hb oxygenation in seven subjects. At rest, total Hb increased and Hb oxygenation decreased in the thigh muscles during –25 and –50 mmHg LBP, while both decreased during +25 and +50 mmHg LBP. However, in the forearm muscles during graded LBP, the pattern of change in total Hb was the reverse of that in the thigh. Measurements from the forehead showed changes only during +50 mmHg LBP. These results demonstrated that the pattern of change in total Hb and Hb oxygenation differed between upper and lower parts with graded LBP at rest. During dynamical leg exercise, total Hb and Hb oxygenation in the thigh muscles decreased during stepwise increases in LBP above –25 mmHg, Hb oxygenation decreasing markedly during +50 mmHg LBP. These results suggest that during dynamical exercise (i) LBP at +25 mmHg or more causes a graded decline in blood volume and/or flow in the thigh muscles, and (ii) especially at +50 mmHg LBP, the O₂ content may decrease markedly in active muscles. Our results suggest that NIRS can be used to monitor in a non-invasive and continuous fashion the changes in oxygenation occurring in human skeletal muscles and head during the graded changes in blood flow and/or volume caused by changes in external pressure and secondary reflexes both at rest and during dynamical exercise.     

The effect of menthol application to the skin on sweating rate response during exercise in swimmers and controls

We tested the hypothesis that menthol application would reduce the magnitude and initiation of sweating via excitation of cold-sensitive afferent pathways and concurrently via a cross-inhibition of heat loss pathways in acclimatized (swimmers, SW) and non acclimatized (control, CON) subjects in cool water. It was expected this effect to be exaggerated in SW subjects. Eight SW and eight CON subjects cycled at 60% of their [(V)\dot] \dot{V} O₂max, as long as to reach 38°C in rectal temperature (Tre), without or with (4.6 g per 100 ml of water) all-body application of menthol sediment. Heart rate (HR), Tre, sweating rate (SwR), the proximal–distal skin temperature gradient (TSk_f–f), and oxygen consumption ([(V)\dot] \dot{V} O₂) were measured continuously. [(V)\dot] \dot{V} O₂ and HR were similar between groups and conditions. Menthol increased TSk_f–f, Tre threshold for SwR [+0.32 (0.01)°C] and Tre gain, while menthol reduced exercise time by 8.1 (4.1) min. SW group showed higher changes in Tre threshold for SwR [+0.50 (0.01)°C for SW vs. +0.13 (0.03)°C for CON], higher Tre gain, lower time for Tre increase and shorter exercise time [−10.7 (7) min for SW vs. −4.9 (4) min for CON] in menthol condition. Upon exercise initiation, previously applied menthol on the skin seems to induce vasoconstriction, results in a delayed sweating, which in turn affects the rectal temperature. Acclimatized subjects showed higher delay in SwR and earlier rise in Tre, which most probably is due to the inter-group differences in cold receptors activity.