Conductive and convective heat flows of exercising humans in cold water.

The apparent conductance (Kss, in W.m-2.degrees C-1) of a given region of superficial shell (on the thigh, fat + skin) was determined on four nonsweating and nonshivering subjects, resting and exercising (200 W) in water [water temperature (Tw) 22-23 degrees C] Kss = Hss/(Tsf-Tsk) where Hss is the skin-to-water heat flow directly measured by heat flow transducers and Tsf and Tsk are the temperatures of the subcutaneous fat at a known depth below the skin surface and of the skin surface, respectively. The convective heat flow (qc) through the superficial shell was then estimated as qc = (Tsf - Tsk).(Kss - Kss,min), assuming that at rest Kss was minimal (Kss,min) and resting qc = 0. The duration of immersion was set to allow rectal temperature (Tre) to reach approximately 37 degrees C at the end of rest and approximately 38 degrees C at the end of exercise. Except at the highest Tw used, Kss at the start of exercise was always Kss,min and averaged 51 W.m-2.degrees C-1 (range 33-57 W.m-2.degrees C-1) across subjects, and qc was zero. At the end of exercise at the highest Tw used for each subject, Kss averaged 97 W.m-2.degrees C-1 (range 77-108 W.m-2.degrees C-1) and qc averaged 53% (range 48-61%) of Hss (mean Hss = 233 W.m-2).(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue heat transfer in water: lessons from the Korean divers.

The factors which influence tissue heat transfer and temperature gradients from body core to skin surface are reviewed in the context of studies on Korean diving women. The resistance to heat transfer imposed by resting muscle is shown to be 2-3 times as great as that imposed by overlying fat and skin. However, exercising muscle imposes very little resistance to heat flux because of the increase in convective heat transfer. Accordingly, the limiting resistance to heat flow is shifted to subcutaneous fat and skin during exercise in cold water. Hypothetical examples are given of how important the subcutaneous fat can be in maintaining a high core-to-water temperature gradient in cold water and the same validated by examples from the literature. Last, hypothetical examples are given of the role cutaneous blood flow must play in controlling heat flux and temperature gradients across the subcutaneous fat layer.

Effect of wearing gloves on the thermal balance of Korean women wet-suit divers in cold water.

Effect of wearing neoprene gloves on the thermal exchanges of wet-suited divers was studied in 8 Korean diving women. Subjects, clad with 5-6-mm-thick neoprene wet suits (jacket, pants, and boots) either with or without wearing 3-mm-thick neoprene gloves, were immersed for 3 h in water of critical temperature (17.3 degrees +/- 0.8 degree C) while the rectal and skin (chest, leg, arm, and hand) temperatures and oxygen consumption were measured. Overall thermal insulation of the subject plus suit was calculated from the rectal-to-water temperature difference divided by the estimated rate of skin heat loss. The skin heat loss was assumed to equal metabolic heat production minus respiratory heat loss, corrected for changes in heat storage when mean body temperature changed. All measurements were carried out in a resting condition. During the 3rd h of immersion, the rectal temperature was lower with gloves (delta Tre = 0.30 degree +/- 0.04 degree C; P less than 0.05) whereas metabolic heat production was not significantly different. Consequently, the total thermal insulation was nearly 16% lower with gloves than without gloves. In both the hands and forearms, the regional heat flux determined directly using a heat flux transducer was higher and the thermal insulation index was lower with gloves than without gloves. These results indicate that in wet-suited subjects resting in cold (17 degrees C) water gloves do not provide additional protection against heat loss, but rather decrease the efficiency of thermoregulatory mechanisms. We suggest that sensory input from cold receptors in the distal extremities is particularly important in thermoregulation during immersion in cold water.

Regional heat flows of resting and exercising men immersed in cool water.

Trunk (HT), limb (HL), and whole-body (HDIR = HT + HL + Hforehead) skin-to-water heat flows were measured by heat flow transducers on nine men immersed head out in water at critical temperature (TCW = 30 +/- 2 degrees C) and below [overall water temperature (TW) range = 22-32 degrees C] after up to 3 h at rest and exercise. Body heat flow was also determined indirectly (HM) from metabolic rate corrected for changes in heat stores. At rest at TCW [O2 uptake (VO2) = 0.33 +/- 0.07 l/min, n = 7], HT = 52.3 +/- 14.2 (SD) W, HL = 56.4 +/- 14.6 W, HDIR = 120 +/- 27 W, and HM = 111 +/- 29 W (significantly different from HDIR). TW markedly affected HDIR but only slightly affected HM (n = 22 experiments at TW different from TCW plus 7 experiments at TCW). During light exercise (3 MET) at TCW (VO2 = 1.06 +/- 0.26 l/min, n = 9), HT = 122 +/- 43 W, HL = 130 +/- 27 W, HDIR = 285 +/- 69 W, and HM = 260 +/- 60 W. During severe exercise (7 MET) at TCW (VO2 = 2.27 +/- 0.50 l/min, n = 4), HT = 226 +/- 100 W, HL = 262 +/- 61 W, HDIR = 517 +/- 148 W, and HM = 496 +/- 98 W. Lowering TW at 7-MET exercise (n = 9, plus 4 at TCW) had no effect on HDIR and HM. In conclusion, resting HL and HT are equal. At TW less than TCW at rest, HDIR greater than HM, showing that unexpectedly the shell was still cooling. During exercise, HL increases more than HT but less than expected from the heat production of the working limbs. Therefore some heat produced by the limbs is probably transported by blood to the trunk. During heavy exercise, HDIR is constant at all considered TW; apparently it is regulated by some thermally dependent mechanism, such as a progressive cutaneous vasodilation occurring as TW increases.

Changes in thermal insulation during underwater exercise in Korean female wet-suit divers.

The present work was undertaken to examine the effect of wet suits on the pattern of heat exchange during immersion in cold water. Four Korean women divers wearing wet suits were immersed to the neck in water of critical temperature (Tcw) while resting for 3 h or exercising (2-3 met on a bicycle ergometer) for 2 h. During immersion both rectal (Tre) and skin temperatures and O2 consumption (VO2) were measured, from which heat production (M = 4.83 VO2), skin heat loss (Hsk = 0.92 M +/- heat store change based on delta Tre), and thermal insulation were calculated. The average Tcw of the subjects with wet suits was 16.5 +/- 1.2 degrees C (SE), which was 12.3 degrees C lower than that of the same subjects with swim suits (28.8 +/- 0.4 degrees C). During the 3rd h of immersion, Tre and mean skin temperatures (Tsk) averaged 37.3 +/- 0.1 and 28.0 +/- 0.5 degrees C, and skin heat loss per unit surface area 42.3 +/- 2.66 kcal X m-2 X h. The calculated body insulation [Ibody = Tre - Tsk/Hsk] and the total shell insulation [Itotal = (Tre - TW)/Hsk] were 0.23 +/- 0.02 and 0.5 +/- 0.04 degrees C X kcal-1 X m2 X h, respectively. During immersion exercise, both Itotal and Ibody declined exponentially as the exercise intensity increased. Surprisingly, the insulation due to wet suit (Isuit = Itotal - Ibody) also decreased with exercise intensity, from 0.28 degrees C X kcal-1 X m2 X h at rest to 0.12 degrees C X kcal-1 X m2 X h at exercise levels of 2-3 met.(ABSTRACT TRUNCATED AT 250 WORDS)

Decrease in body insulation with exercise in cool water.

Steady-state body insulation was measured in 7 healthy male subjects during rest and exercise for 3 h in water of 28 degrees C - 32 degrees C. At rest, maximal body insulation increased as a linear function of mean subcutaneous fat thickness by an amount approximately 4-fold what would be predicted from the physical insulation of fat alone. With arm plus leg exercise, body insulation declined as an exponential function of the exercise intensity, reaching approximately 25% of the resting value at work loads above VO2 = 1.2 liters.min-1. During exercise the relationship between overall body insulation and mean subcutaneous fat thickness was almost identical to that predicted from fat insulation and mean subcutaneous fat thickness was almost identical to that predicted from fat insulation alone. These results suggest that 75% of maximal body insulation in resting subjects is achieved by use of skeletal muscle as an insulative barrier and that the muscle component is increased with increasing fat thickness. This muscle insulation shell is lost during exercise. As a practical consequence, heat generated by muscular exercise in water colder than critical water temperature cannot offset cooling unless the exercise intensity is great.

Energetics of wet-suit diving in Korean women breath-hold divers.

Contemporary Korean women divers wear wet suits during diving work to avoid the cold water stress. The present study was undertaken to evaluate the effect of wearing wet suits on the daily thermal balance of divers and on the duration of diving work. Rectal (TR) and skin temperatures and O2 consumption (VO2) were measured in four divers before and during diving work in summer (22.5 degrees C water) and winter (10 degrees C water). Subjects wore either wet suits (protected) or cotton suits (unprotected) for comparison. TR decreased 0.4 degrees C in summer and 0.6 degrees C in winter after 2 h of diving work in protected divers, while it decreased to 35 degrees C in 60 min in summer and in 30 min in winter in unprotected divers. Mean skin temperature of protected divers decreased to 31 degrees C in summer and 28 degrees C in winter, while that of unprotected divers decreased to 24 degrees C in summer and 13 degrees C in winter. VO2 toward the end of the diving work period increased by 80 (summer) and 140% (winter) in protected divers and by 160 (summer) and 250% (winter) in unprotected divers. From these values total thermal cost of diving work was estimated to be 260 and 370 kcal . day-1 in summer and winter, respectively.

Time course of deacclimatization to cold water immersion in Korean women divers.

Seasonal basal metabolic rates (BMR), critical water temperature (Tcw), maximal body insulations (Imax), and finger blood flow during hand immersion in 6 degrees C water (Q finger) were measured periodically during the course of a 3-yr longitudinal study (1980-1982) of modern Korean diving women (ama), who have been wearing wet suits since 1977 to avoid cold stress during work. Methods and protocols were identical to previous studies of cotton-suited ama from 1961-1974. The BMR of modern ama did not undergo seasonal fluctuation (1980-1981) and was within the DuBois standard and comparable to nondivers year around Tcw of ama was still reduced by 2-3 degrees C in 1980 but increased progressively to equal that of nondivers in 1982, when compared at comparable subcutaneous fat thickness (SFT). Since modern ama and nondivers have 2.4 times thicker SFT (i.e., 4-13 mm) than in 1962 the absolute Tcw is significantly reduced. Q finger of ama was also significantly lower than controls in 1980 but in 1981-1982 was identical to controls. Imax of modern ama was identical to controls of comparable SFT in 1980-1982. The time course of cold deacclimatization thus was BMR, 3 yr; Imax, 3 yr; Q finger, 4 yr; and Tcw, 5 yr. This longitudinal study provides further evidence that acclimatization to cold did at one time exist in these diving women.

Dynamic and steady-state metabolic changes in running dogs.

Dynamic and steady-state changes of VO2, VE, VCO2, PaO2 and blood lactate concentration (Lab) were studied in 4 intact (I) and in the same tracheostomized (T) dogs walking or running uphill (+ 10%) on a treadmill at speeds up to 12 km X h-1. A) Non-steady state results: The half times of the VO2 on-response (t1/2 VO2 on-) to rectangular work loads were 18.9 sec +/- 1.2 (SE) in I and 15.6 sec +/- 1.0 in T dogs (P less than 0.05), independent of work intensity and similar to those found for isolated perfused dog gastrocnemii (15-17 sec). Lab during the rest to work transient was almost unchanged. B) Steady-state results: VO2 and VE increased with increasing speed up to 8 km X h-1 (+ 10%) then levelled off both in I and T. Asymptotic VO2, and VE values were higher for I than for T (VO2 = 93 and 83 ml X kg-1 X min-1; VE = 2.6 and 1.75 l X kg-1 X min-1, respectively). Calculated delta VO2/delta VE ratios for equal external work loads indicate that the energy cost of breathing was about 12 ml O2 per liter VE. From (A) it is concluded that the adjustment of oxidative reactions upon work onset is as fast for the whole animal as for isolated gastrocnemius and can be assessed from gas exchange in the upper airways. From (B) it appears that, in the absence of glycolysis, the cost of running per unit distance decreases with increasing speed while the cost of VE becomes a sizeable part of the overall energy expenditure.

Superficial shell insulation in resting and exercising men in cold water.

From measurements of subcutaneous fat temperature (Tsf) at known depths below the surface, skin surface temperature (Tsk), and direct skin heat flux (H), the superficial shell isulation (Iss) of the thigh (fat + skin) was calculated as Iss (degrees C.m2.w-1) = (Tsf - Tsk)/H in nine male subjects immersed head out in a well-stirred water bath. Also, at critical water temperature (CWT = 28-33 degrees C), eight of the subjects rested for 3 h, enabling overall maximal tissue insulation (It,max) to be calculated as It,max (degrees C.m2.W-1) = (Tre - Tw)/(0.92 M +/- delta S), where Tre is rectal temperature, Tw is water temperature, M is metabolic rate, and s is loss or gain of body heat. Five subjects performed up to 2 h of mild leg cycling, preceded and followed by 60 min of rest, and both thigh Iss and overall It were measured during exercise. Iss increased from minimal values in Tw greater than 33 degrees C to maximal values (Iss,max) at CWT or below. Iss,max was linearly related to tissue thickness (d) in millimeters of fat plus skin, Iss,max (degrees C.m2.W-1) = 0.0048d-0.0052; r = 0.95, n = 37, and was not influenced by leg exercise up to a metabolic rate of 150 W.m-2 in CWT despite large increases in Tsf and H and large decreases in overall It. The slope of Iss,max vs. depth, 0.0048 degrees C.m2.W-1.mm-1, is almost identical to thermal resistivity of fat in vitro, suggesting that the superficial shell is unperfused in CWT at rest or during mild exercise. When maximal superficial shell insulation (It,ss,max) for the whole body was calculated with allowance for differing fat thicknesses and surface areas of body regions, it could account for only 10-15% of overall It,max at rest and 35-40% of overall It in mild exercise. We suggest that the poorly perfused muscle shell plays a more important role as a defense against cooling at CWT than does the superficial shell (fat + skin), particularly at rest.

Thermal insulation and shivering threshold in Greek sponge divers.

Sublingual temperature (Tor), average skin temperature (Tsk), and skin heat flow (Hsk) were determined in a field study for six Greek sponge divers and seven nondiving controls during head-out immersions at water temperature of 21 degrees C. Wetsuits kept Tsk at 22-28 degrees C for 1-3 h until Tor fell to 36.5-35.5 degrees C and violent shivering [metabolic rate (M) = 100-150 W . m-2] ended the test. At a steady Tsk, immediately before shivering, overall tissue insulation (It), calculated as (Tor--Tsk)/Hsk, was linearly related to mean subcutaneous fat thickness (MFT) in both groups without statistical difference between them. The onset of shivering, as detected by a sharp increase of M, occurred at the same Tor for a Tsk of about 26 degrees C, and the relationship of M vs. Tor (i.e., metabolic sensitivity) was the same for both groups. Contrary to other groups accustomed to diving in cold water, the use of a wetsuit for a long time has evidently prevented cold adaptation in these divers.

Aerobic and glycolytic metabolism in arm exercise.

Eight kayakers (K) and 3 sedentary subjects (S) performed arm cranking and pedaling while erect or supine at each of several work loads from submaximal to the highest they could sustain for 2 min and for intervals varying from 10 s to 5 min. From measurements of VO2 and blood lactate concentration, the aerobic and glycolytic energy release in arm work was assessed. For steady-state aerobic work all subjects had a mechanical efficiency averaging 0.24 independent of posture or exercise mode. Per unit fat-free limb volume, arm VO2max of group K was 1.5-fold that of group S, whereas leg VO2max was the same in each group. Compared to group S, glycolytic arm work in group K was characterized by: 1) higher thresholds for release of lactate at the onset of submaximal work, 2) lower blood lactate concentrations during comparable absolute or relative submaximal work, 3) higher conventional anaerobic thresholds for absolute, but not relative work loads, 4) higher maximal rates of lactate release, and 5) the same maximal blood lactate concentrations. Measurement of the early lactate threshold, which occurred at considerably lower arm work loads than did anaerobic threshold, but which was greatly increased by specific muscle training, may provide a simple, sensitive, and nontraumatic evaluation of muscle training.

Effects of specific muscle training on VO2 on-response and early blood lactate.

The relationship between half time of the O2 uptake on-response (t1/2 VO2on, seconds) and early blood lactate accumulation (delta Lab, mmol.1(-1) at the onset of submaximal arm and/or leg exercise was the object of a cross-sectional study of sedentary subjects (S,n = 3), and kayakers (K, n = 8), and of a longitudinal study on 11 untrained subjects of specific arm vs. leg training. In supine arm cranking (W = 125 watts) S had an average t1/2 VO2on of 82 s and a delta Aab of 9.2 mmol.1(-1) compared to 47 +/- 7 s and 4 +/- 1.4 mmol.1(-1), respectively, for K. In longitudinal trainees shorter t1/2 VO2on was accompanied by lower Lab for the trained limbs. Specific limb conditioning in swimmers and runners resulted in shorter t1/2 VO2on. A linear relationship was observed between delta Lab and t1/2 VO2on having an intercept on the time axis at congruent to 20 s and a slope proportional to muscle mass. Trained muscles were grouped closest to the intercept indicating local acceleration of the rate of O2 transfer approaching the t1/2 VO2on for isolated perfused muscle at the onset of work. Since t1/2 VO2on, we conclude that factors distal to the capillary are specifically involved in the local training response.

Quantitative analysis of the front crawl in men and women.

Body drag, D, and the overall mechanical efficiency of swimming, e, were measured from the relationship between extra oxygen consumption and extra drag loads in 42 male and 22 female competitive swimmers using the front crawl at speeds ranging from 0.4 to 1.2 m/s. D increased from 3.4 (1.9) kg at 0.5 m/s to 8.2 (7.0) kg at 1.2 m/s, with D of women (in brackets) being significantly less (P less than 0.05) than that of men. Mechanical efficiency increased from 2.9% at 0.5 m/s to 7.4% at 1.2 m/s for men, the values for women being somewhat greater than those for men. The ratio, D/e was shown to be identical to the directly measured energy cost of swimming one unit distance, V02/d, and was independent of the velocity up to 1.2 m/s. It averaged 52 and 37 l/km for men and women respectively (P less than 0.05). When corrected for body surface area the values were 27 and 22 l/km-m2 for men and women, respectively (P less than 0.05). The underwater torque, T, a measure of the tendency of the feet to sink, was 1.44 kg-m for men and 0.70 kg-m for women (P less than 0.05). VO2/d increased linearly with T for both men and women of similar competitive experience. However, the proportionality constant delta VO2/d-delta T was significantly less for competitive than noncompetitive swimmers. The analysis of the relationship VO2/d vs. T provides a valuable approach to the understanding of the energetics of swimming.

Oxygen uptake transients at the onset and offset of arm and leg work.

The halftimes (t1/2) of the VO2 on-and off-responses have been determined on 4 moderately active subjects (1) in arm cranking (VO2 congruent to 1 1/min). (2) in leg pedaling at 4 graded submaximal (VO2 congruent to 0.8 to 2.51/min) work loads, and (3) when superimposing arm cranking on preexisting leg pedaling, both in the supine and in the upright position. In supine experiments the mean t1/2 of the VO2 on-response was longer for arm cranking than for leg pedaling (64 vs 44-49 sec) at equal VO2; however, at the same percentage of arm and leg VO2 max the respective t1/2 were similar. In sitting experiments all t1/2 of the VO2 on-response were shorter than when supine, but the t1/2 for the arms were still slightly longer than those for the legs. When arm cranking was superimposed on preexisting leg pedaling, the t1/4 for arms was reduced both in supine (from 64 to 35-38 sec) and in the sitting position (from 44 to 40 sec). The halftime of the VO2 off-response were much shorter (20-32 sec) than those of the on-response and similar in all experiments. In all conditions the O2 deficits at work onset were considerably larger than the fast component of the corresponding O2 debts during the first minutes of recovery. The difference was totally accounted for by anaerobic glycolysis occurring early during the VO2 on-response, particularly in arm exercise. It is concluded that at submaximal work loads the O2 deficit is accounted for the fast component of the O2 debt plus the O2 equivalent of the early lactate production.