Warming by immersion or exercise affects initial cooling rate during subsequent cold water immersion

INTRODUCTION: We examined the effect of prior heating, by exercise and warm-water immersion, on core cooling rates in individuals rendered mildly hypothermic by immersion in cold water. METHODS: There were seven male subjects who were randomly assigned to one of three groups: 1) seated rest for 15 min (control); 2) cycling ergometry for 15 min at 70% Vo2 peak (active warming); or 3) immersion in a circulated bath at 40 degrees C to an esophageal temperature (Tes) similar to that at the end of exercise (passive warming). Subjects were then immersed in 7 degrees C water to a Tes of 34.5 degrees C. RESULTS: Initial Tes cooling rates (initial approximately 6 min cooling) differed significantly among the treatment conditions (0.074 +/- 0.045, 0.129 +/- 0.076, and 0.348 +/- 0.117 degrees C x min(-1) for control, active, and passive warming conditions, respectively); however, secondary cooling rates (rates following initial approximately 6 min cooling to the end of immersion) were not different between treatments (average of 0.102 +/- 0.085 degrees C x min(-1)). Overall Tes cooling rates during the full immersion period differed significantly and were 0.067 +/- 0.047, 0.085 +/- 0.045, and 0.209 +/- 0.131 degrees C x min(-1) for control, active, and passive warming, respectively. DISCUSSION: These results suggest that prior warming by both active and, to a greater extent, passive warming, may predispose a person to greater heat loss and to experience a larger decline in core temperature when subsequently exposed to cold water. Thus, functional time and possibly survival time could be reduced when cold water immersion is preceded by whole-body passive warming, and to a lesser degree by active warming.     

Effect of hydrotherapy on recovery from fatigue

The present study investigated the effects of three hydrotherapy interventions on next day performance recovery following strenuous training. Twelve cyclists completed four experimental trials differing only in 14-min recovery intervention: cold water immersion (CWI), hot water immersion (HWI), contrast water therapy (CWT), or passive recovery (PAS). Each trial comprised five consecutive exercise days of 105-min duration, including 66 maximal effort sprints. Additionally, subjects performed a total of 9-min sustained effort (time trial - TT). After completing each exercise session, athletes performed one of four recovery interventions (randomly assigned to each trial). Performance (average power), core temperature, heart rate (HR), and rating of perceived exertion (RPE) were recorded throughout each session. Sprint (0.1 - 2.2 %) and TT (0.0 - 1.7 %) performance were enhanced across the five-day trial following CWI and CWT, when compared to HWI and PAS. Additionally, differences in rectal temperature were observed between interventions immediately and 15-min post-recovery; however, no significant differences were observed in HR or RPE regardless of day of trial/intervention. Overall, CWI and CWT appear to improve recovery from high-intensity cycling when compared to HWI and PAS, with athletes better able to maintain performance across a five-day period.     

Training wearing thermal clothing and training in hot ambient conditions are equally effective methods of heat acclimation

The objective was to compare the efficacy of three different heat acclimation protocols to improve exercise performance in the heat. Thirty four cyclists completed one of three 10-day interventions 1) 50-min cycling per day in 35 °C, 2) 50-min cycling per day wearing thermal clothing, and 3) 50-min cycling wearing thermal clothing plus 25 min hot water immersion per day. Pre- and post-intervention hemoglobin mass, intravascular volumes and core temperature were determined at rest. Heart rate, sweat rate, blood lactate concentration and core temperature were evaluated during 15-min submaximal and 30-min all-out cycling performance conducted in 35.2 ± 0.1 °C and 61 ± 1% relative humidity.There were no significant between-group differences in any of the determined variables. None of the interventions statistically altered any of the parameters investigated as part of the 15-min submaximal trial. However, following the intervention period, heat chamber, thermal clothing and thermal clothing + hot water immersion all improved 30-min all-out average power in the heat (9.5 ± 3.8%, 9.5 ± 3.6 and 9.9 ± 5.2%, respectively, p < 0.001, F = 192.3). At termination of the 30-min all-out test, the increase in blood lactate concentration, rate of perceived exertion and sweat rate were not different between the three interventions.In conclusion, daily training sessions conducted either in ambient 35 °C, while wearing thermal clothing in temperate conditions or while wearing thermal clothing combined with hot water immersion are equally effective for improving exercise performance in the heat.     

Effect of recovery modality on 4-hour repeated treadmill running performance and changes in physiological variables

The purpose of this study was to compare the effectiveness of three different recovery modalities--active (ACT), passive (PAS) and contrast temperature water immersion (CTW)--on the performance of repeated treadmill running, lactate concentration and pH. Fourteen males performed two pairs of treadmill runs to exhaustion at 120% and 90% of peak running speed (PRS) over a 4-hour period. ACT, PAS or CTW was performed for 15-min after the first pair of treadmill runs. ACT consisted of running at 40% PRS, PAS consisted of standing stationary and CTW consisted of alternating between 60-s cold (10 degrees C) and 120-s hot (42 degrees C) water immersion. Run times were converted to time to cover set distance using critical power. Type of recovery modality did not have a significant effect on change in time to cover 400 m (Mean +/- SD; ACT 2.7 +/- 3.6 s, PAS 2.9 +/- 4.2 s, CTW 4.2 +/- 6.9 s), 1000 m (ACT 2.2 +/- 4.0 s, PAS 4.8 +/- 8.6 s, CTW 2.1 +/- 7.2 s) or 5000 m (ACT 1.4 +/- 29.0 s, PAS 16.7 +/- 58.5 s, CTW 11.7 +/- 33.0 s). Post exercise blood lactate concentration was lower in ACT and CTW compared with PAS. Participants reported an increased perception of recovery in the CTW compared with ACT and PAS. Blood pH was not significantly influenced by recovery modality. Data suggest both ACT and CTW reduce lactate accumulation after high intensity running, but high intensity treadmill running performance is returned to baseline 4-hours after the initial exercise bout regardless of the recovery strategy employed.     

Effects of kinesio taping on anaerobic power recovery after eccentric exercise

The aim of the study was to evaluate the effectiveness of kinesio taping (KT) in anaerobic power recovery after eccentric exercise. The study was carried out on 10 healthy men. The participants performed two 60-min downhill runs with a constant intensity. Peak anaerobic power (PP) and mean power (MP) were measured before and five times after eccentric exercise. Anaerobic power was evaluated with the Maximal Cycling Sprint Test. After the downhill run, passive recovery (PR) and KT (lymphatic application) were applied in random order. A significant decrease in PP and MP was observed at least for 24 h after PR, compared to baseline. After the KT application 24 h after eccentric exercises, anaerobic power was already similar to the baseline measurement. The application of KT significantly improved anaerobic power recovery time after eccentric exercise compared to the period of passive rest immediately prior to testing.     

Ascending aortic blood flow dynamics following intense exercise

The purpose of this study was to compare and contrast aortic blood flow kinetics during recovery from intense aerobic (maximal oxygen uptake test) and anaerobic (Wingate anaerobic power test) exercise. Fifteen healthy male subjects (VO2max = 56.1 +/- 5.8 mk/kg/min) participated in this study. Beat-to-beat peak aortic blood flow velocity (pkV) and acceleration (pkA) measurements were obtained by placing a 3.0 MHz continuous-wave ultrasonic transducer on the suprasternal notch at rest and during recovery (immediately post-exercise, 2.5 min, and 5.0 min) following the two exercise conditions. Peak velocity and acceleration significantly increased (p less than 0.01) from rest to immediately post-exercise and remained elevated throughout the 5-min recovery period. No differences were observed between the aerobic and anaerobic tests. Stroke distance significantly declined (p less than 0.01) immediately following exercise and progressively rose during the 5-min recovery period. The results indicate that: 1) aortic blood flow kinetics remained elevated during short-term recovery, and 2) intense aerobic and anaerobic exercise exhibit similar post-exercise aortic blood flow kinetics.     

Contrast water immersion hastens plasma lactate decrease after intense anaerobic exercise

The benefits of rapid recovery after intense exercise are widely recognised, and lactate elimination is one indicator of recovery rate. This study examined the effect of contrast (alternating hot and cold) water immersion (CWI) on the rate of plasma lactate decrease during recovery after intense anaerobic exercise. Eleven subjects on each of two occasions undertook four successive 30-s Wingate tests separated by 30-s rest periods. On each occasion, plasma lactate concentration during recovery was measured 5 min post-exercise and thereafter at 5 min intervals for 30 min. On one occasion (determined randomly), the subjects recovered passively (PR) on a recovery bed and, on the other, they alternated partial body immersion in hot (36 °C) and cold (12 °C) water baths. Plasma lactate concentrations were analysed by repeated measures analysis of variance and by fitting a linear regression model, allowing for both gender and recovery mode differences. The rate of decrease in plasma lactate concentration over the 30-min recovery period was significantly higher (p < 0.001) in CWI; 0.28(±0.02) mmol L⁻¹ min⁻¹ (CWI) compared to 0.22(±0.02) mmol L⁻¹ min⁻¹ (PR). These values do not differ significantly between males and females. Contrast water immersion is a valid method of hastening plasma lactate decrease during recovery after intense anaerobic exercise for both males and females. An approximately 1.8 mmol L⁻¹ difference between the two conditions may be expected after 30 min. With differences among elite competitors as little as 1–2%, this reduction may be of practical significance.     

Cooling hyperthermic firefighters by immersing forearms and hands in 10 degrees C and 20 degrees C water

INTRODUCTION: Firefighters experience significant heat stress while working with heavy gear in a hot, humid environment. This study compared the cooling effectiveness of immersing the forearms and hands in 10 and 20 degrees C water. METHODS: Six men (33 +/- 10 yr; 180 +/- 4 cm; 78 +/- 9 kg; 19 +/- 5% body fat) wore firefighter 'turn-out gear' (heavy clothing and breathing apparatus weighing 27 kg) in a protocol including three 20-min exercise bouts (step test, 78 W, 40 degrees C air, 40% RH) each followed by a 20-min rest/cooling (21 degrees C air); i.e., 60 min of exercise, 60 min of cooling. Turn-out gear was removed during rest/cooling periods and subjects either rested (Control), immersed their hands in 10 or 20 degrees C water (H-10, H-20), or immersed their hands and forearms in 10 or 20 degrees C water (HF-10, HF-20). RESULTS: In 20 degrees C water, hand immersion did not reduce core temperature compared with Control; however, including forearm immersion decreased core temperature below Control values after both the second and final exercise periods (p < 0.001). In 10 degrees C water, adding forearm with hand immersion produced a lower core temperature (0.8 degrees C above baseline) than all other conditions (1.1 to 1.4 degrees C above baseline) after the final exercise period (p < 0.001). Sweat loss during Control (1458 g) was greater than all active cooling protocols (1146 g) (p < 0.001), which were not different from each other. DISCUSSION: Hand and forearm immersion in cool water is simple, reduces heat strain, and may increase work performance in a hot, humid environment. With 20 degrees C water, forearms should be immersed with the hands to be effective. At lower water temperatures, forearm and/or hand immersion will be effective, although forearm immersion will decrease core temperature further.     

Effects of active vs. passive recovery on work performed during serial supramaximal exercise tests

The current investigation was undertaken to determine the effects of active versus passive recovery on work performance during repeated bouts of supramaximal exercise. Six healthy sedentary subjects and 9 moderately trained healthy hockey players performed serial 30-second Wingate anaerobic power tests (WAnT) on a bicycle ergometer interposed with 4 minutes of active recovery at a work rate corresponding to 28 % of VO(2)max or passive recovery at rest. Peak power, mean power, total work achieved, and fatigue index were calculated for the serial WAnT. Capillary blood lactate was determined at 5-minute intervals after the last WAnT during 30 minutes of active or passive recovery. Mean power was significantly greater during active recovery in sedentary subjects when compared with passive recovery (388 +/- 42 vs. 303 +/- 37 W, p < 0.05), but did not differ according to recovery mode in moderately trained hockey players (589 +/- 22 W active vs. 563 +/- 26 W passive, p = 0.14). Total work achieved significantly increased during active when compared with passive recovery in sedentary subjects (34 890 +/- 3768 vs. 27 260 +/- 3364 J, p < 0.02) and moderately trained hockey players (86 763 +/- 9151 vs. 75 357 +/- 8281 J, p < 0.05). Capillary blood lactate levels did not differ during active when compared with passive recovery in sedentary subjects but were significantly lower during active when compared with passive recovery in moderately trained hockey players. These data demonstrate that active recovery at a work rate corresponding to 28 % of VO(2)max increases total work achieved during repeated WAnT when compared with passive recovery in sedentary subjects and moderately trained hockey players.     

The effect of training on the norepinephrine response at rest and during exercise in 5 degrees and 20 degrees C environments

Eleven males were examined at rest and during submaximal exercise in 5 degrees C and 20 degrees C environments to determine if the norepinephrine (NE) and other physiological responses in the cold would be altered by eight weeks of training. Blood samples were obtained at the end of 15 minutes of rest and submaximal exercise, and were assayed for NE. Pretraining resting NE levels in the 5 degrees C condition were significantly higher than those found in the 20 degrees C environment (684 +/- 89 vs 491 +/- 48 pg/ml). A significant training effect reduced resting NE levels in the 5 degrees C (502 +/- 77 pg/ml) but not the 20 degrees C (392 +/- 45 pg/ml) condition. Pre and posttraining exercise NE levels were elevated above resting in both the 5 degrees C (1477 +/- 136 vs 1559 +/- 208) and the 20 degrees C environments (1623 +/- 176 pg/ml vs 1444 +/- 224 pg/ml), but were not significantly different between conditions. Skin temperatures were significantly lower, and resting blood pressure was significantly higher in the 5 degrees C condition. These data suggest that both cold and exercise act as stimulators of NE release, but an additive effect on NE of cold and exercise does not occur. The resting NE levels pre and posttraining in the 5 degrees C condition suggest that a cross tolerance to cold stress was present.     

A 2.5 min cold water immersion improves prolonged intermittent sprint performance

ObjectivesWe investigated if cold water immersion (CWI) affects exercise performance during a prolonged intermittent sprint test (IST), designed to mimic activity patterns of team-sports.DesignRandomized-crossover design.MethodsTen male team-sport players completed 3 IST protocols (two 40-min “halves” of repeated 2-min blocks consisting of a 8-s “all-out” sprint, 100-s active recovery and 12-s rest) on a cycle ergometer at normothermic conditions. Each “half” was separated by a 15 min recovery period of either: (i) passive rest, (ii) 5-min CWI at 8 °C (CWI-5) or (iii) 2.5-min CWI at 8 °C (CWI-2.5), in a random counterbalanced order.ResultsPhysical performance, core temperature (T_core) and heart rate were not different among conditions in the first half. In the passive rest trial, total work (TW) and peak power (PP) were lower during the second half (TW: 5.04 ± 1.11 kJ; PP: 929 ± 286 W) than the first half (TW: 5.66 ± 1.02 kJ; PP: 1009 ± 266 W); while TW and PP were not different between halves following CWI-5 (first half, TW: 5.34 ± 1.02 kJ, PP: 1016 ± 283 W; second half, TW: 5.19 ± 1.38 kJ; PP: 996 ± 318 W) and CWI-2.5 (first half, TW: 5.47 ± 1.19 kJ, PP: 966 ± 261 W; second half, TW: 5.25 ± 1.17 kJ; PP: 952 ± 231 W). T_core was lower until the 20^th minute of the second half after CWI-5 and CWI-2.5 compared with passive rest.ConclusionsA post-exercise 2.5–5-min CWI attenuates the reductions in prolonged sprint performance that occur in the second half of team sports, due, at least partly, to reductions in core temperature and associated increase in heat storage.     

Effects of leg massage on recovery from high intensity cycling exercise

BACKGROUND: The effect of massage on recovery from high intensity exercise is debatable. Many studies on massage suffer from methodological flaws such as poor standardisation of previous exercise, lack of dietary control, and inappropriate massage duration. OBJECTIVE: To examine the effects of leg massage compared with passive recovery on lactate clearance, muscular power output, and fatigue characteristics after repeated high intensity cycling exercise, with the conditions before the intervention controlled and standardised. METHODS: Nine male games players participated. They attended the laboratory on two occasions one week apart and at the same time of day. Dietary intake and activity were replicated for the two preceding days on each occasion. After baseline measurement of heart rate and blood lactate concentration, subjects performed a standardised warm up on the cycle ergometer. This was followed by six standardised 30 second high intensity exercise bouts, interspersed with 30 seconds of active recovery. After five minutes of active recovery and either 20 minutes of leg massage or supine passive rest, subjects performed a second standardised warm up and a 30 second Wingate test. Capillary blood samples were drawn at intervals, and heart rate, peak power, mean power, and fatigue index were recorded. RESULTS: There were no significant differences in mean power during the initial high intensity exercise bouts (p = 0.92). No main effect of massage was observed on blood lactate concentration between trials (p = 0.82) or heart rate (p = 0.81). There was no difference in the maximum power (p = 0.75) or mean power (p = 0.66) in the subsequent Wingate test, but a significantly lower fatigue index was observed in the massage trial (p = 0.04; mean (SD) fatigue index 30.2 (4.1)% v 34.2 (3.3)%). CONCLUSIONS: No measurable physiological effects of leg massage compared with passive recovery were observed on recovery from high intensity exercise, but the subsequent effect on fatigue index warrants further investigation.     

Effect of combined active recovery from supramaximal exercise on blood lactate disappearance in trained and untrained man

The purpose of this study was to determine the effect of different modalities of individualized active recovery on blood lactate disappearance after supramaximal exercise in subjects with different levels of aerobic fitness. Fourteen healthy subjects (7 trained and 7 untrained subjects mean age 20 +/- 1.5 and 19.5 +/- 1.5, respectively) participated in this study. They performed three supramaximal intermittent exercises at 60 % of the time to exhaustion at 120 % of the maximum aerobic power (MAP) with 5-min recovery periods (2 x 5 min). The third exercise was followed by 20 min of recovery. The effects of four types of recovery were compared in trained and untrained subjects: passive recovery (PR), an active recovery at an intensity corresponding to the first anaerobic ventilatory threshold minus 20 % (VT1), an active recovery at an intensity corresponding to the second anaerobic ventilatory threshold minus 20 % (VT2) and a combined active recovery (CR) which consisted of 7 min at VT2 followed by 13 min at VT1. Blood lactate levels were measured at rest and during the recovery periods. Peak blood lactate after supramaximal exercise was observed significantly earlier with VT2 and CR (4th min) than VT1 and PR (7th min) in trained and in untrained subjects. Combined active recovery (CR) showed a significantly faster lactate disappearance than did PR, VT1, or VT2 from the 7th min of recovery in trained subjects (p < 0.05) and at the 20th min in untrained subjects (p < 0.05). CR and VT2 conditions showed earlier peak blood lactate (4th min) than PR or VT1 (7th min). Blood lactate disappearance was faster in trained than untrained subjects during combined active recovery. This result suggests that the level of physical fitness plays an important role mainly in the pattern of blood lactate decrease during combined active recovery.     

Leg heating and cooling influences running stride parameters but not running economy

To evaluate the effect of temperature on running economy (RE) and stride parameters in 10 trained male runners (VO2peak 60.8 +/- 6.8 ml . kg (-1) . min (-1)), we used water immersion as a passive temperature manipulation to contrast localised pre-heating, pre-cooling, and thermoneutral interventions prior to running. Runners completed three 10-min treadmill runs at 70 % VO2peak following 40 min of randomised leg immersion in water at 21.0 degrees C (cold), 34.6 degrees C (thermoneutral), or 41.8 degrees C (hot). Treadmill runs were separated by 7 days. External respiratory gas exchange was measured for 30 s before and throughout the exercise and stride parameters were determined from video analysis in the sagittal plane. RE was not affected by prior heating or cooling with no difference in oxygen cost or energy expenditure between the temperature interventions (average VO2 3rd-10th min of exercise: C, 41.6 +/- 3.4 ml . kg (-1) . min (-1); TN, 41.6 +/- 3.0; H, 41.8 +/- 3.5; p = 0.94). Exercise heart rate was affected by temperature (H > TN > C; p < 0.001). During minutes 3 - 5 of running the respiratory-exchange and minute ventilation/oxygen consumption ratios were greater in cold compared with thermoneutral (p < 0.05). Averaged over the full 10 min of exercise, stride length was shorter and stride frequency higher for the C trial compared to TN and H (p < 0.01). Leg temperature manipulation did not influence running economy despite changes in stride parameters that might indicate restricted muscle-tendon elasticity after pre-cooling. Larger changes in stride mechanics than those produced by the current temperature intervention are required to influence running economy.     

Human temperature regulation during exercise after oral pyridostigmine administration

Four healthy males exercised in two experiments at ambient temperatures of 22, 29, and 36 degrees C with the relative humidity at 30% in all environments (Tdp = 3.9, 9.9, and 15.8 degrees C). One experiment in each environment was done 150 min after 30 mg oral pyridostigmine bromide (PYR) administration, and the second experiment was done on a separate day with no medication (CON). Red blood cell cholinesterase was 39 +/- 7% lower after PYR (11.8 vs 7.2 micromol.ml-1.min-1). Esophageal (Tes) and mean skin temperature (Tsk), forearm blood flow (FBF), forearm sweating, and skin blood flow (SkBF) were measured twice each minute during a 15-min rest period and during 30-min of seated cycle exercise at approximately 58% Vo2peak. Whole body sweating was determined from weight changes before and after exercise. PYR decreased heart rate at rest and during exercise at 29 degrees C and 36 degrees C (8bpm, p less than 0.05). Resting SkBF was 40% lower at 29 degrees C and 30% lower at 36 degrees C after PYR compared to CON (p less than 0.05). There was no effect of PYR on heat production at rest or during exercise. Tsk was different in the three conditions by design, but was unchanged by PYR. Tes was not different at rest in any condition, but was elevated during exercise at 36 degrees C (0.1 degree C, p less than 0.05) in PYR compared to CON. These data suggest that pyridostigmine ingestion decreased skin blood flow, which may limit exercise thermoregulation in more severe environments.     

Protection provided against the initial responses to cold immersion by a partial coverage wet suit

The protection provided against the initial responses to cold water immersion by a partial coverage wet suit was assessed. Eighteen subjects performed three 2-min immersions into water at 5 degrees C. During each immersion, the subjects wore either: a) cotton overall, b) trunk and arms "wet" immersion suit, or c) "dry" immersion suit. Results showed that the dry suit provided significantly (p less than 0.05) greater protection against the initial cardiac and ventilatory responses to immersion than either the wet suit or cotton overall assemblies. The responses recorded in the wet suit were similar to, and in some cases did not differ from, the cotton overall. We conclude that immersion suit design and tests should consider all of the responses associated with accidental cold water immersion and not just those resulting in a fall in core temperature.     

Effect of precooling on high intensity cycling performance

OBJECTIVE: To examine the effects of precooling skin and core temperature on a 70 second cycling power test performed in a warm and humid environment (29 degrees C, 80% relative humidity). METHODS: Thirteen male national and international level representative cyclists (mean (SD) age 24.1 (4.1) years; height 181.5 (6.2) cm; weight 75.5 (6.4) kg; maximal oxygen uptake (VO2peak) 66.1 (7.0) ml/kg/min) were tested in random order after either 30 minutes of precooling using cold water immersion or under control conditions (no precooling). Tests were separated by a minimum of two days. The protocol consisted of a 10 minute warm up at 60% of VO2peak followed by three minutes of stretching. This was immediately followed by the 70 second power test which was performed on a standard road bicycle equipped with 172.5 mm powermeter cranks and mounted on a stationary ergometer. RESULTS: Mean power output for the 70 second performance test after precooling was significantly (p<0.005) increased by 3.3 (2.7)% from 581 (57) W to 603 (60) W. Precooling also significantly (p<0.05) decreased core, mean body, and upper and lower body skin temperature; however, by the start of the performance test, lower body skin temperature was no different from control. After precooling, heart rate was also significantly lower than control throughout the warm up (p<0.05). Ratings of perceived exertion were significantly higher than the control condition at the start of the warm up after precooling, but lower than the control condition by the end of the warm up (p<0.05). No differences in blood lactate concentration were detected between conditions. CONCLUSIONS: Precooling improves short term cycling performance, possibly by initiating skin vasoconstriction which may increase blood availability to the working muscles. Future research is required to determine the physiological basis for the ergogenic effects of precooling on high intensity exercise.     

Thirst sensations and AVP responses at rest and during exercise-cold exposure

PURPOSE: The purpose of this study was to 1) determine the effect of hypohydration (HYPO) on thirst sensations during moderate exercise in the cold and 2) determine a possible mechanism for a cold-induced decline in thirst. METHODS: In the first phase of the study, eight males walked on four occasions, in T-shirts, shorts, and shoes, at 50% VO2max, for 60 min in either a 4 degrees C (cold) or 27 degrees C (temperate) environment in a state of HYPO or euhydration (EU). In the second phase, nine males in states of EU or HYPO randomly performed four trials consisting of 30 min standing at 27 degrees C, followed by 30 min of standing and 30 min of treadmill exercise at 50% of VO2max, in either 4 degrees C or 27 degrees C air. RESULTS: In phase 1, thirst sensations were lower throughout 60 min of exercise (P < 0.05) in both HYPO and EU conditions during the cold trials. In phase 2, despite elevated plasma osmolality (P < 0.05), perception of thirst and plasma arginine vasopressin [AVP] similarly decreased (P < 0.05) after 30-min standing rest and 30-min exercise in the HYPO-cold trial, compared with the HYPO-temperate, EU-cold, and EU-temperate trials. CONCLUSIONS: When either euhydrated or hypohydrated, cold exposure attenuated thirst by up to 40% at rest and during moderate-intensity exercise. The attenuated thirst when hypohydrated during cold exposure was associated with lower plasma [AVP] despite an elevated plasma osmolality. This decline in thirst and AVP in the cold may be the result of peripheral vasoconstriction, mediating an increase in central blood volume and stimulation of central volume receptors.     

The influence of regional insulation on the initial responses to cold immersion

Twelve healthy male subjects performed three 10-min head-out immersions in water at 10 degrees C. The responses of the subjects to immersion were recorded under three conditions: a) Control condition (CC)--torso and limbs exposed; b) Torso protected/limbs exposed condition (TPC); and c) Limbs protected/torso exposed condition (LPC). Results showed that the LPC significantly reduced the heart rate (p less than 0.01), minute ventilation (p less than 0.05), and respiratory frequency (p less than 0.05) during the first minute of immersion compared to the CC. Subjects also found the LPC the most comfortable. The TPC significantly reduced minute ventilation (p less than 0.01) and respiratory frequency (p less than 0.01) on immersion compared to the CC, but did not significantly lower the heart rate response. A comparison of the LPC and TPC revealed no significant difference in minute ventilation and respiratory frequency recorded on immersion. The LPC however, produced significantly lower heart rates on immersion (p less than 0.05) than the TPC. It was concluded that the limbs may be more important than the torso for the initiation of cardiac response to cold water immersion.     

Prediction of human thermoregulatory responses and endurance time in water at 20 and 24 degrees C

A multi-compartmental mathematical model for predicting human thermoregulatory responses was applied to immersion in moderately cold water. Data were used from experiments where eight healthy male volunteers were immersed nude and up to the neck for 1 h in water at 20 and 24 degrees C under conditions of rest and exercise. Rectal temperature and metabolic rate were measured before and during immersion. Once agreement between the model prediction and experimental observation was obtained, the model was used for prediction beyond the duration of the experiment. Stabilization of core temperature was predicted after 4-5 h of immersion for rest and after 2-4 h for exercise. Stabilization for resting individuals has been observed in other experiments under similar conditions. These results suggest that linear extrapolations based on linear body cooling rates are inadequate for predicting endurance times in moderately cold water. In this study, predicted endurance times were based on the concept of relative exercise intensity and are in agreement with the limited data available.