The effect of rowing headgear on forced convective heat loss and radiant heat gain on a thermal manikin headform

Abstract

Both radiant and forced convective heat flow were measured for a prototype rowing headgear and white and black cotton caps. The measurements were performed on a thermal manikin headform at a wind speed of 4.0 m · s^?1 (s = 0.1) in a climate chamber at 22.0°C (s = 0.05), with and without radiant heat flow from a heat lamp, coming from either directly above (90°) or from above at an angle of 55°. The effects of hair were studied by repeating selected measurements with a wig. All headgear reduced the radiant heat gain compared with the nude headform: about 80% for the caps and 95% for the prototype rowing headgear (P < 0.01). Forced convective heat loss was reduced more by the caps (36%) than by the prototype rowing headgear (9%) (P < 0.01). The radiant heat gain contributed maximally 13% to the net heat transfer, with or without headgear, showing that forced convective heat loss is the dominant heat transfer parameter under the chosen conditions. The results of the headgear – wig combinations were qualitatively similar, with lower absolute heat transfer.     

Radiant heat transfer of bicycle helmets and visors

Twenty-six bicycle helmets and their associated visors were characterized for radiant heat transfer using a thermal manikin headform in a climate chamber to assess their ability to protect the wearer from heating by the sun. A single configuration for applied radiant flow of 9.3 W was used to assess the roles of the forward and upper vents and the visor. The helmets shielded 50-75% of the radiant heating without a visor and 65-85% with one. Twenty-three visors were shown to result in a relevant reduction of radiant heating of the face (>0.5 W), with 15 reaching approximately 1 W. Heating of the visor and/or helmet and subsequent heating of the air flowing into the helmet was nevertheless found to be a relevant effect in many cases, suggesting that simple measures like reflective upper surfaces could noticeably improve the radiant heat rejection without changing the helmet structure. The forward vents in the helmets that allow the transmission of radiant heat are often important for forced convection, so that minimizing radiant heating geneally reduces the maximization of forced convective heat loss for current helmets.     

Heat transfer variations of bicycle helmets

Bicycle helmets exhibit complex structures so as to combine impact protection with ventilation. A quantitative experimental measure of the state of the art and variations therein is a first step towards establishing principles of bicycle helmet ventilation. A thermal headform mounted in a climate-regulated wind tunnel was used to study the ventilation efficiency of 24 bicycle helmets at two wind speeds. Flow visualization in a water tunnel with a second headform demonstrated the flow patterns involved. The influence of design details such as channel length and vent placement was studied, as well as the impact of hair. Differences in heat transfer among the helmets of up to 30% (scalp) and 10% (face) were observed, with the nude headform showing the highest values. On occasion, a negative role of some vents for forced convection was demonstrated. A weak correlation was found between the projected vent cross-section and heat transfer variations when changing the head tilt angle. A simple analytical model is introduced that facilitates the understanding of forced convection phenomena. A weak correlation between exposed scalp area and heat transfer was deduced. Adding a wig reduces the heat transfer by approximately a factor of 8 in the scalp region and up to one-third for the rest of the head for a selection of the best ventilated helmets. The results suggest that there is significant optimization potential within the basic helmet structure represented in modern bicycle helmets.     

Heat transfer variations of bicycle helmets

Abstract

Bicycle helmets exhibit complex structures so as to combine impact protection with ventilation. A quantitative experimental measure of the state of the art and variations therein is a first step towards establishing principles of bicycle helmet ventilation. A thermal headform mounted in a climate-regulated wind tunnel was used to study the ventilation efficiency of 24 bicycle helmets at two wind speeds. Flow visualization in a water tunnel with a second headform demonstrated the flow patterns involved. The influence of design details such as channel length and vent placement was studied, as well as the impact of hair. Differences in heat transfer among the helmets of up to 30% (scalp) and 10% (face) were observed, with the nude headform showing the highest values. On occasion, a negative role of some vents for forced convection was demonstrated. A weak correlation was found between the projected vent cross-section and heat transfer variations when changing the head tilt angle. A simple analytical model is introduced that facilitates the understanding of forced convection phenomena. A weak correlation between exposed scalp area and heat transfer was deduced. Adding a wig reduces the heat transfer by approximately a factor of 8 in the scalp region and up to one-third for the rest of the head for a selection of the best ventilated helmets. The results suggest that there is significant optimization potential within the basic helmet structure represented in modern bicycle helmets.     

High-intensity intermittent running and field hockey skill performance in the heat

Nine well-trained, unacclimatized female hockey players performed the Loughborough Intermittent Shuttle Test (LIST) interspersed with three field hockey skill tests in hot (30 degrees C, 38% relative humidity) and moderate (19 degrees C, 51% relative humidity) environmental conditions. Field hockey skill performance declined in both the hot and moderate conditions following 30 and 60 min of the LIST compared with pre-LIST values (P < 0.01). This decrement in performance was compounded in the hot environment with a 6% poorer performance in the heat recorded for the second skill test at 30?min (P < 0.05, hot 101.7 +/- 3.6 vs moderate 95.7 +/- 2.9 s; mean +/- s(x)). However, no difference was found in the decision-making element of the skill test. Fifteen-metre sprint times were slower in the hot condition (P < 0.01). In the hot environment, rectal temperature (P < 0.01), perceived exertion (P < 0.05), perceived thirst (P < 0.01), blood glucose concentration (P < 0.05) and serum aldosterone concentration (P < 0.01) were higher. Estimated mean ( +/- s(x)) sweat rate was higher in the hot trial (1.27 +/- 0.10 l.h(-1)) than in the moderate trial (1.05 +/- 0.12 l.h(-1)) (P < 0.05). Body mass was well maintained in both trials. No differences in serum cortisol, blood lactate, plasma volume or plasma ammonia concentrations were found. These results demonstrate that field hockey skill performance is decreased following intermittent high-intensity shuttle running and that this decrease is greater in hot environmental conditions. The exact mechanism for this decrement in performance remains to be elucidated, but is unlikely to be due to low glycogen concentration or dehydration.     

Compressive properties of helmet materials subjected to dynamic impact loading of various energies

Abstract

Many helmet safety standards require children's helmets to be tested using adult-weighted headforms of approximately 5 kg and impact velocities representative of adult anatomy. The purpose of this study was to test the individual and combined effect of variable headform mass and inbound headform velocity on helmet test results. Testing was conducted on sample sections of helmet liner materials commonly used in multi- and single-impact helmets. Three densities of expanded polystyrene and expanded polypropylene were moulded into 2.54-cm thick foam blocks and cut into circular samples with a 5-cm diameter. Each sample was impacted once using an EN 960 magnesium K1A headform of variable mass on a monorail apparatus in the crown position. A total of 25 impact conditions were used: 5 headform masses and 5 inbound velocities. A PCB 203B force sensor collected force data at 20 kHz in the y-axis of the impact and a 1000-Hz low-pass Butterworth filter was applied during analysis. A three-way analysis of variance revealed significant main effects for headform mass, inbound velocity, and material density on peak linear acceleration (P<0.01). Inbound velocity and headform mass played a significant role in material performance. It is proposed that the headform mass and inbound velocity used in helmet testing protocols be representative of the intended age group to improve the performance range and safety of sport helmets.     

Does extensive on-water rowing increase muscular strength and endurance?

The purpose of this study was to compare changes in aerobic condition, strength, and muscular endurance following 8 weeks of endurance rowing alone or in combination with weight-training. Twenty-two elite rowers were assigned to (1) rowing (n = 10, 250-270 km · week?1) or (2) rowing (n = 12, 190-210 km · week?1) plus four weight-training sessions each week. Pre and post mean and standardized effect-size (ES) differences in aerobic condition (watts at 4 mmol · L?1) and strength (isometric pull, N), prone bench-pull (6-repetition maximum, 6-RM), 5- and 30-repetition leg-press and 60-repetition seated-arm-pull (J, performed on a dynamometer) normalized by body mass and log-transformed were analysed, after adjusting for gender. The standardized differences between groups were trivial for aerobic condition (ES [±90% CI] = 0.15; ±0.28, P = 0.37) and prone bench-pull (ES = 0.27; ±0.33, P = 0.18), although a moderate positive benefit in favour of rowing only was observed for the seated-arm-pull (ES = 0.42; ±0.4, P = 0.08). Only the weight-training group improved isometric pull (12.4 ± 8.9%, P < 0.01), 5-repetition (4.0 ± 5.7%, P < 0.01) and 30-repetition (2.4 ± 5.4%, P < 0.01) leg-press. In conclusion, while gains in aerobic condition and upper-body strength were comparable to extensive endurance rowing, weight-training led to moderately greater lower-body muscular-endurance and strength gains.     

Improvements in heat tolerance induced by interval running training in the heat and in sweat clothing in cool conditions

To compare the effectiveness of training in heat and in sweat clothing in cool conditions on improving heat tolerance, two groups of active subjects (n = 6 in each) performed an interval running heat-tolerance test before and after a 7-day experimental treatment. On each treatment day the subjects attempted to complete 4 x 15 min interval treadmill running periods (a 7.5 s effort every 30 s, on 15 km h-1, 15% grade; the same exercise format as the heat-tolerance test), which were interspersed with 5-min recovery periods (total time each day = 80 min). Group 1 (heat) ran in shorts, socks and shoes in hot humid conditions, and Group 2 (sweat clothing) ran in cool conditions dressed in shorts, socks and T-shirt covered by a polyester-cotton tracksuit, over which was worn 100% nylon spray-proof pants and jacket (cotton lined) with an acrylic cloth bobble hat (beanie) on the head. Both groups displayed changes typical of heat acclimatization over the 7-day period, with significant decreases in final rectal temperature (Tr) and heart rate (HR) being evident, but no change in sweat loss. Mean skin temperature (Tsk) was similar in both groups during the training sessions (heat group: 34.8-35.7 degrees C; sweat clothing group 34.9-35.5 degrees C). After the heat-tolerance test, both groups had significantly lower Tr, Tsk and HR values than before, and sweating sensitivity (g m-2 h-1 degrees C rise in Tr) was significantly increased. There was only one significant difference between the two groups (Tsk, 20th min value). It was concluded that training in sweat clothing in cool conditions can provide the same improvements in heat tolerance as training in hot humid conditions where a fixed exercise intensity and duration are used.     

The influence of drink temperature on thermoregulatory responses during prolonged exercise in a moderate environment

Nine males cycled at 53% (s = 2) of their peak oxygen uptake (VO(2peak)) for 90 min (dry bulb temperature: 25.4 degrees C, s = 0.2; relative humidity: 61%, s = 3). One litre of flavoured water at 10 (cold), 37 (warm) or 50 degrees C (hot) was ingested 30 - 40 min into exercise. Immediately after the 90 min of exercise, participants cycled at 95%VO(2peak) to exhaustion to assess exercise capacity. Rectal and mean skin temperatures and heart rate were recorded. The gradient of rise in rectal temperature was influenced (P < 0.01) by drink temperature. Mean skin temperature was highest in the hot trial (cold trial: 34.2 degrees C, s = 0.5; warm trial: 34.4 degrees C, s = 0.5; hot trial: 34.7 degrees C, s = 0.6; P < 0.01). Significant differences were observed in heart rate (cold trial: 132 beats . min(-1), s = 13; warm trial: 134 beats . min(-1), s = 12; hot trial: 139 beats . min(-1), s = 13; P < 0.05). Exercise capacity was similar between trials (cold trial: 234 s, s = 69; warm trial: 214 s, s = 52; hot trial: 203 s, s = 53; P = 0.562). The heat load and debt induced via drinking resulted in appropriate thermoregulatory reflexes during exercise leading to an observed heat content difference of only 33 kJ instead of the predicted 167 kJ between the cold and hot trials. These results suggest that there may be a role for drink temperature in influencing thermoregulation during exercise.     

Recovery of pulmonary diffusing capacity after maximal exercise.

Pulmonary diffusing capacity (DICO), together with spirometric variables, arterial oxygen tension (paO2) and cardiac output were determined before and at intervals after maximal arm cranking, treadmill running and ergometer rowing. Independent of the type of exercise, D1CO increased immediately post-exercise from a median 13.6 (range 7.3-16.3) to 15.1 (9.3-19.6) mmol min-1 kPa-1 (P < 0.01). However, it decreased to 11.6 (6.9-15.5) mmol min-1 kPa-1 (P < 0.01) after 24 h with cardiac output and paO2 at resting values, and D1CO normalized after 20 h. Thoracic electrical impedance at 2.5 and 100 kHz increased slightly post-exercise, indicating a decrease in thoracic fluid balance, and there were no echocardiographic signs of left ventricular failure at the time of the decrease in D1CO. Also, active muscle (limb) circumference and volume, and an increase in haematocrit from 43.8 (38.0-47.0) to 47.1 (42.7-49.8) (P < 0.01), had normalized at the time of the decrease in D1CO. Vital capacity, forced vital capacity, forced expiratory volume in 1 s, peak and peak mid-expiratory flows did not change. However, total lung capacity increased from 6.8 (5.0-7.6) to 7.0 (5.1-7.8) litres (P < 0.05) immediately after exercise and remained elevated at 6.9 (5.1-8.7) litres (P < 0.05) when a decrease in D1CO was noted. The results demonstrate that independent of the type of maximal exercise, an approximate 15% reduction in D1CO takes place 2-3 h post-exercise, which normalizes during the following day of recovery.     

Effects of radiant heat exposure on pacing pattern during a 15-km cycling time trial

Abstract

The goal of this study was to investigate the effects of different durations of skin temperature manipulation on pacing patterns and performance during a 15-km cycling time trial. Nineteen well-trained men completed three 15-km cycling time trials in 18°C and 50% relative humidity with 4.5-km (short-heat), 9.0-km (long-heat) or without (control) radiant heat exposure applied by infrared heaters after 1.5 km in the time trial. During the time trials, power output, mean skin temperature, rectal temperature, heart rate and rating of perceived exertion were assessed. The radiant heat exposure resulted in higher mean skin temperature during the time trial for short-heat (35.0 ± 0.6°C) and long-heat (35.3 ± 0.5°C) than for control (32.5 ± 1.0°C; P < 0.001), whereas rectal temperature was similar (P = 0.55). The mean power output was less for short-heat (273 ± 8 W; P = 0.001) and long-heat (271 ± 9 W; P = 0.02) than for control (287 ± 7 W), but pacing patterns did not differ (P = 0.55). Heart rate was greatest in control (177 ± 9 beats · min^?1; P < 0.001), whereas the rating of perceived exertion remained similar. We concluded that a radiant heat exposure and associated higher skin temperature reduced overall performance, but did not modify pacing pattern during a 15-km cycling time trial, regardless of the duration of the exposure.     

Prediction of 2000 m indoor rowing performance using a 30 s sprint and maximal oxygen uptake

The aim of this study was to predict indoor rowing performance in 12 competitive female rowers (age 21.3 +/- 3.6 years, height 1.68 +/- 0.54 m, body mass 67.1 +/- 11.7 kg; mean +/- s) using a 30 s rowing sprint, maximal oxygen uptake and the blood lactate response to submaximal rowing. Blood lactate and oxygen uptake (VO2) were measured during a discontinuous graded exercise test on a Concept II rowing ergometer incremented by 25 W for each 2 min stage; the highest VO2 measured during the test was recorded as VO2max (mean = 3.18 +/- 0.35 l.min-1). Peak power (380 +/- 63.2 W) and mean power (368 +/- 60.0 W) were determined using a modified Wingate test protocol on the Concept II rowing ergometer. Rowing performance was based on the results of the 2000 m indoor rowing championship in 1997 (466.8 +/- 12.3 s). Laboratory testing was performed within 3 weeks of the rowing championship. Submitting mean power (Power), the highest and lowest five consecutive sprint power outputs (Maximal and Minimal), percent fatigue in the sprint test (Fatigue), VO2max (l.min-1), VO2max (ml.kg-1.min-1), VO2 at the lactate threshold, power at the lactate threshold (W), maximal lactate concentration, lactate threshold (percent VO2max) and VEmax (l.min-1) to a stepwise multiple regression analysis produced the following model to predict 2000 m rowing performance: Time2000 = -0.163 (Power) -14.213.(VO2max l.min-1) +0.738.(Fatigue) 7.259 (R2 = 0.96, standard error = 2.89). These results indicate that, in the women studied, 75.7% of the variation in 2000 m indoor rowing performance time was predicted by peak power in a rowing Wingate test, while VO2max and fatigue during the Wingate test explained an additional 12.1% and 8.2% of the variance, respectively.     

Prediction of 2000 m indoor rowing performance using a 30 s sprint and maximal oxygen uptake

The aim of this study was to predict indoor rowing performance in 12 competitive female rowers (age 21.3 - 3.6 years, height 1.68 - 0.54 m, body mass 67.1 - 11.7 kg; mean - s ) using a 30 s rowing sprint, maximal oxygen uptake and the blood lactate response to submaximal rowing. Blood lactate and oxygen uptake ( V O 2 ) were measured during a discontinuous graded exercise test on a Concept II rowing ergometer incremented by 25 W for each 2 min stage; the highest V O 2 measured during the test was recorded as V O 2max (mean = 3.18 - 0.35 l· min -1 ). Peak power (380 - 63.2 W) and mean power (368 - 60.0 W) were determined using a modified Wingate test protocol on the Concept II rowing ergometer. Rowing performance was based on the results of the 2000 m indoor rowing championship in 1997 (466.8 - 12.3 s). Laboratory testing was performed within 3 weeks of the rowing championship. Submitting mean power (Power), the highest and lowest five consecutive sprint power outputs (Maximal and Minimal), percent fatigue in the sprint test (Fatigue), V O 2max (l· min -1 ), V O 2max (ml·kg -1 ·min -1 ), V O 2 at the lactate threshold, power at the lactate threshold (W), maximal lactate concentration, lactate threshold (percent V O 2max ) and V E max (l·min -1 ) to a stepwise multiple regression analysis produced the following model to predict 2000 m rowing performance: Time 2000 =- 0.163 (Power)14.213 ·( V O 2max l· min -1 ) + 0.738· (Fatigue) + 567.259 ( R 2 = 0.96, standard error = 2.89). These results indicate that, in the women studied, 75.7% of the variation in 2000 m indoor rowing performance time was predicted by peak power in a rowing Wingate test, while V O 2max and fatigue during the Wingate test explained an additional 12.1% and 8.2% of the variance, respectively.     

Is three-dimensional anthropometric analysis as good as traditional anthropometric analysis in predicting junior rowing performance?

Abstract With the use of three-dimensional whole body scanning technology, this study compared the 'traditional' anthropometric model [one-dimensional (1D) measurements] to a 'new' model [1D, two-dimensional (2D), and three-dimensional (3D) measurements] to determine: (1) which model predicted more of the variance in self-reported best 2000-m ergometry rowing performance; and (2) what were the best anthropometric predictors of ergometry performance, for junior rowers competing at the 2007 and 2008 Australian Rowing Championships. Each rower (257 females, 16.3?±?1.4 years and 243 males, 16.6?±?1.5 years) completed a performance and demographic questionnaire, had their mass, standing and sitting height physically measured and were landmarked and scanned using the Vitus Smart? 3D whole body scanner. Absolute and proportional anthropometric measurements were extracted from the scan files. Partial least squares regression analysis, with anthropometric measurements and age as predictor variables and self-reported best 2000-m ergometer time as the response variable, was used to first compare the two models and then to determine the best performance predictors. The variance explained by each model was similar for both male [76.1% (new) vs. 73.5% (traditional)] and female [72.3% (new) vs. 68.6% (traditional)] rowers. Overall, absolute rather than proportional measurements, and 2D and 3D rather than 1D measurements, were the best predictors of rowing ergometry performance, with whole body volume and surface area, standing height, mass and leg length the strongest individual predictors.     

Effect of cold water immersion on repeat cycling performance and thermoregulation in the heat

To assess the effect of cold water immersion and active recovery on thermoregulation and repeat cycling performance in the heat, ten well-trained male cyclists completed five trials, each separated by one week. Each trial consisted of a 30-min exercise task, one of five 15-min recoveries (intermittent cold water immersion in 10 degrees C, 15 degrees C and 20 degrees C water, continuous cold water immersion in 20 degrees C water or active recovery), followed by 40 min passive recovery, before repeating the 30-min exercise task. Recovery strategy effectiveness was assessed via changes in total work in the second exercise task compared with that in the first. Following active recovery, a mean 4.1% (s = 1.8) less total work (P = 0.00) was completed in the second than in the first exercise task. However, no significant differences in total work were observed between any of the cold water immersion protocols. Core and skin temperature, blood lactate concentration, heart rate, rating of thermal sensation, and rating of perceived exertion were recorded. During both exercise tasks there were no significant differences in blood lactate concentration between interventions; however, following active recovery blood lactate concentration was significantly lower (P < 0.05; 2.0 +/- 0.8 mmol . l(-1)) compared with all cold water immersion protocols. All cold water immersion protocols were effective in reducing thermal strain and were more effective in maintaining subsequent high-intensity cycling performance than active recovery.     

Impact attenuation of protective boxing and taekwondo headgear

This study aimed to compare the impact attenuation performance of boxing and taekwondo headgear in terms of peak linear and rotational acceleration. To measure the impact attenuation of headgear, a standardized (American Society for Testing and Materials (ASTM) F-2397) martial arts headgear striker was used to impart impacts to a 50th Percentile Male Hybrid III Crash Test Dummy head and neck complex. Two boxing (Adidas and Greenhill) and two taekwondo (Adidas and Nike) headgear, approved by the Association Internationale de Boxe Amateur and the World Taekwondo Federation (WTF), were selected. Each of the selected headgear was fitted to the Hybrid III head and subsequently subjected to five impacts at the front and side with a maximum impact interim time of 60 seconds by the rotating striker at 8?±?0.3?m/s. Linear and rotational acceleration were recorded at 10,000?Hz. There were significant interactions of the impact location and brand on the rotational acceleration, F(3,40)?=?6.7, p?F(1,40)?=?9.07, p?F(3,40)?=?9.9, p?相似文献   

Practical precooling: effect on cycling time trial performance in warm conditions

The purpose of this study was to compare the effects of two practical precooling techniques (skin cooling vs. skin + core cooling) on cycling time trial performance in warm conditions. Six trained cyclists completed one maximal graded exercise test (VO2(peak) 71.4 +/- 3.2 ml x kg(-1) x min(-1)) and four approximately 40 min laboratory cycling time trials in a heat chamber (34.3 degrees C +/- 1.1 degrees C; 41.2% +/- 3.0% rh) using a fixed-power/variable-power format. Cyclists prepared for the time trial using three techniques administered in a randomised order prior to the warm-up: (1) no cooling (control), (2) cooling jacket for 40 min (jacket) or (3) 30-min water immersion followed by a cooling jacket application for 40 min (combined). Rectal temperature prior to the time trial was 37.8 degrees C +/- 0.1 degrees C in control, similar in jacket (37.8 degrees C +/- 0.3 degrees C) and lower in combined (37.1 degrees C +/- 0.2 degrees C, P < 0.01). Compared with the control trial, time trial performance was not different for jacket precooling (-16 +/- 36 s, -0.7%; P = 0.35) but was faster for combined precooling (-42 +/- 25 s, - .8%; P = 0.009). In conclusion, a practical combined precooling strategy that involves immersion in cool water followed by the use of a cooling jacket can produce decrease in rectal temperature that persist throughout a warm-up and improve laboratory cycling time trial performance in warm conditions.     

女运动员月经周期中性激素变化与运动成绩的研究

通过对３６ 名不同项目女运动员,在月经周期中血清雌二醇（Ｅ２） 、促卵泡激素（ＦＳＨ） 、促黄体生成素（ＬＨ） 、孕激素（Ｐ） 的测定,观察女运动员月经周期不同时相性激素变化与不同项目运动成绩的关系。受试者必须在卵泡期和黄体期分别按规定项目测试两次全速力竭运动成绩。赛艇队员测试５００ｍ 及２０００ｍ 成绩,田径队员测定１００ｍ 、２００ｍ 成绩,游泳队员测试每人专项成绩后统一评分。结果显示除赛艇运动员２０００ｍ 测试成绩无显著性差异外,其它各项成绩黄体期均优于卵泡期（Ｐ＜ ０ ．０５ 或Ｐ＜ ０ ．０１） ,且黄体期Ｐ的浓度也较高（Ｐ＜ ０ ．０５） 。     

The influence of serial feeding of drinks at different temperatures on thermoregulatory responses during cycling

In this study, we examined thermoregulatory responses to ingestion of separate aliquots of drinks at different temperatures during low-intensity exercise in conditions of moderate heat stress. Eight men cycled at 50% (s = 3) of their peak oxygen uptake (VO2peak) for 90 min (dry bulb temperature: 25.3 degrees C, s = 0.5; relative humidity: 60%, s = 5). Four 400-ml aliquots of flavoured water at 10 degrees C (cold), 37 degrees C (warm) or 50 degrees C (hot) were ingested after 30, 45, 60, and 75 min of exercise. Immediately after the 90 min of exercise, participants cycled at 95% VO2peak to exhaustion to assess exercise capacity. There were no differences between trials in rectal temperature at the end of the 90 min of exercise (cold: 38.11 degrees C, s = 0.30; warm: 38.10 degrees C, s = 0.33; hot: 38.21 degrees C, s = 0.30; P = 0.765). Mean skin temperature between 30 and 90 min tended to be influenced by drink temperature (cold: 34.49 degrees C, s = 0.64; warm: 34.53 degrees C, s = 0.69; hot: 34.71 degrees C, s = 0.48; P = 0.091). Mean heart rate from 30 to 90 min was higher in the hot trial (129 beats . min(-1), s = 7; P < 0.05) than on the cold (124 beats . min(-1), s = 9) and warm trials (126 beats . min(-1), s = 8). Ratings of thermal sensation were higher on the hot trial than on the cold trial at 35 and 50 min (P < 0.05). Exercise capacity was similar between trials (P = 0.963). The heat load and debt induced by periodic drinking resulted in similar body temperatures during low-intensity exercise in conditions of moderate heat stress due to appropriate thermoregulatory reflexes.     

Plasma testosterone and cortisol responses to prolonged sculling in male competitive rowers.

In this study, we examined anabolic and catabolic hormone responses to a single endurance rowing training session in 12 male competitive single scull rowers. A work intensity eliciting a blood lactate concentration of 4 mmol(-1) was determined on a rowing ergometer during an endurance rowing training session lasting about 2 h (7891+/-761 s; distance covered 22.6+/-2.5 km; heart rate 136+/-7 beats x min(-1); intensity 77.4+/-3.8% of anaerobic threshold; mean +/- s). Venous blood samples were obtained before and after on-water rowing. Cortisol, testosterone and sex hormone binding globulin were measured and free testosterone and the free testosterone: cortisol ratio calculated. Blood lactate concentration did not change significantly during training (from 1.7+/-0.4 to 1.9+/-0.4 mmol x l(-1)); however, body mass was reduced (from 82.0+/-10.8 to 80.6+/-11.2 kg) and was related to the distance covered (r = -0.75). The concentrations of cortisol and testosterone did not change significantly during rowing or in the first 2 h of recovery. Free testosterone was reduced in the first 2 h of recovery, but no significant changes were observed in the free testosterone: cortisol ratio. Immediately after rowing, the concentrations of cortisol (r = 0.49) and free testosterone (r = -0.58) were related to the distance covered. Our findings indicate that a prolonged low-intensity training session results in a similar anabolic and catabolic hormone stimulus for trained rowers.