The effects of two nights of sleep deprivation with or without energy restriction on immune indices at rest and in response to cold exposure

The purpose of the study was to determine the effects of two nights of sleep deprivation with or without energy restriction on immune indices at rest and in response to cold exposure. On three randomised occasions ten males slept normally [mean (SD): 436 (21) min night⁻¹; CON], were totally sleep-deprived (SDEP), or were totally sleep-deprived and 90% energy-restricted (SDEP + ER) for 53 h. After 53 h (1200 h) participants performed a seated cold air test (CAT) at 0.0°C until T _re decreased to 36.0°C. Circulating leucocyte counts, neutrophil degranulation, stress hormones and saliva secretory IgA (S-IgA) were determined at 0 h, 24 h, 48 h, pre-CAT, post-CAT, 1-h and 2-h post-CAT. One night on SDEP increased bacterially stimulated neutrophil degranulation (21%, P < 0.05), and two nights on SDEP and SDEP + ER increased S-IgA concentration (40 and 44%; P < 0.01). No other significant effects were observed for immuno-endocrine measures prior to CAT. CAT duration was not different between trials [mean (SD): 133 (53) min] and T _re decreased to 35.9 (0.3)°C. Modest whole-body cooling decreased circulating lymphocyte counts (25%; P < 0.01), S-IgA concentration (36%; P < 0.01) and secretion rate (24%; P < 0.05). A neutrophilia occurred post-CAT on CON and SDEP and 2-h post-CAT on SDEP + ER (P < 0.01). Modest whole-body cooling also decreased neutrophil degranulation on CON (22%) and SDEP (18%; P < 0.05). Plasma cortisol and norepinephrine increased post-CAT (31 and 346%, P < 0.05), but modest whole-body cooling did not alter plasma epinephrine. In conclusion, two nights of SDEP or SDEP + ER did not compromise resting immune indices. However, modest whole-body cooling (T _re 35.9°C) decreased circulating lymphocytes, neutrophil degranulation and S-IgA, but responses were not amplified by prior SDEP or SDEP + ER.     

Quantification of the decay and re-induction of heat acclimation in dry-heat following 12 and 26 days without exposure to heat stress

Compared with the induction of heat acclimation (HA), studies investigating the decay and re-induction of HA (RA) are relatively sparse and have yielded conflicting results. Therefore, 16 semi-nude men were acclimated to dry-heat by undertaking an exercise protocol in a hot chamber (dry-bulb temperature 46.1 ± 0.1°C; relative humidity 17.9 ± 0.1%) on 10 consecutive days (HA1–10) in winter UK. Thereafter, the subjects were divided into two groups and re-exposed to the work-in-heat tests after 12 and 26 days until RA was attained (RA₁₂, n = 8; RA₂₆, n = 8). The exercise protocol consisted of 60 min of treadmill walking (1.53 m s⁻¹) at an incline individually set to induce a rectal temperature (T _re) of ∼38.5°C during HA1 (equating to 45 ± 4% peak oxygen uptake), followed by 10 min of rest and 40 min of further treadmill exercise, the intensity of which was increased across HA to maintain T _re at ∼38.5°C. T _re, mean skin temperature, heart rate and rate of total water loss measured at 60 min did not change after HA7, and HA was taken as the mean of the responses during HA8–10. For both groups, there was no decay in T _re and for all measured variables RA was attained after 2 and 4 days in RA₁₂ and RA₂₆, respectively. It is concluded that once adaptation to heat has been attained, the time that individuals may spend in cooler conditions before returning to a hot environment could be as long as one month, without the need for extensive re-adaptation to heat.     

Differences in rectal temperatures measured at depths of 4–19 cm from the anal sphincter during exercise and rest

The purpose of the present study was to examine the discrepancies in rectal temperature (T _re) at various depths. Nineteen young males performed two bouts of bicycle exercise and recovery. T _re was simultaneously measured at depth of 4, 6, 8, 10, 13, 16, and 19 cm, alongside the measurement of skin temperatures. We found small but statistically significant differences by depth in the absolute T _re, the magnitude of rise in T _re and the lag of response in T _re. During the stabilization stage before exercise, T _re at 4 cm-depth was 0.5°C lower than T _re at 16 cm-depth (p < 0.05). As the depth measured in the rectum was shallower, the rise in T _re during exercise was greater. However the rise in T _re at 10, 13, 16 and 19 cm showed no systemic difference. Among seven depths, T _re at 16 cm-depth had the most stable feature with the longest latent period (3.1 ± 1.3 min) and the smallest rise (0.8 ± 0.3°C), while T _re at 4 cm-depth was the most responsive to the change of exercise and rest with the shortest latent period (1.0 ± 0.6 min) and the greatest rise (1.2 ± 0.5°C). The differences observed in the depths from 4 to 19 cm were offset by exercise to some extent. In summary, T _re appeared in different manners according to the seven depths during the repetition of exercise and rest, but T _re deeper than 10 cm-depth seemed to have no systematic differences.     

Effect of water ingestion on cardiovascular and thermal responses to prolonged cycling and running in humans: a comparison

The aim of this investigation was to examine the effect of water ingestion on physiological responses to prolonged cycling (CYC) and running (RUN). A group of 11 men with mean (SEM) maximal oxygen uptake (V˙O_2max) 48.5 (1.8) ml·kg^–1·min^–1 on a cycle-ergometer and 52.1 (2.2) ml·kg^–1·min^–1 on a treadmill (P<0.01) exercised for 90 min on four occasions, twice on each ergometer, at 60% of mode specific V˙O_2max. No fluid was taken (D) in one trial on each ergometer, whereas 60% of fluid losses were replaced by drinking water in the other trial (W). In CYC, water ingestion attenuated the change in cardiac output ( ) and the reduction in stroke volume (ΔSV) [ΔSV: –22.7 (3.8) in D, –10.7 (2.9) ml·beat^–1 in W, P<0.01; : –1.9 (0.5) in D, –0.2 (0.4) l·min^–1 in W at 85 min, P<0.01], but did not affect rectal temperature [T _re at 90 min: 38.8 (0.1)°C in D, 38.7 (0.1)°C in W]. In contrast, fluid replacement reduced hyperthermia in RUN [T _re at 90 min: 39.6 (0.2) in D, 39.1 (0.2)°C in W, P<0.01], and this was linked with a higher skin blood flow [RUN-W 88.9 (8.5), RUN-D 70.7 (8.4)%, P<0.05]. The and ΔSV were also attenuated with water ingestion in this mode of exercise (P<0.05). It is concluded that water ingestion improves physiological function in both cycling and running, but that the underlying mechanism is different in the two modes of exercise. Electronic Publication     

The impact of different cooling modalities on the physiological responses in firefighters during strenuous work performed in high environmental temperatures

This study investigated the impact of ice vests and hand/forearm immersion on accelerating the physiological recovery between two bouts of strenuous exercise in the heat [mean (SD), 49.1(1.3)°C, RH 12 (1)]. On four occasions, eight firefighters completed two 20-min bouts of treadmill walking (5 km h, 7.5% gradient) while wearing standard firefighter protective clothing. Each bout was separated by a 15-min recovery period, during which one of four conditions were administered: ice vest (VEST), hand/forearm immersion (W), ice vest combined with hand/forearm immersion (VEST + W) and control (CON). Core temperature was significantly lower at the end of the recovery period in the VEST + W (37.97 ± 0.23°C) and W (37.96 ± 0.19°C) compared with the VEST (38.21 ± 0.12°C) and CON (38.29 ± 0.25°C) conditions and remained consistently lower throughout the second bout of exercise. Heart rate responses during the recovery period and bout 2 were similar between the VEST + W and W conditions which were significantly lower compared with the VEST and CON which did not differ from each other. Mean skin temperature was significantly lower at the start of bout 2 in the cooling conditions compared with CON; these differences reduced as exercise progressed. These findings demonstrate that hand/forearm immersion (~19°C) is more effective than ice vests in reducing the physiological strain when firefighters re-enter structural fires after short rest periods. Combining ice vests with hand/forearm immersion provides no additional benefit.     

Effects of brief leg cooling after moderate exercise on cardiorespiratory responses to subsequent exercise in the heat

We investigated the effects of brief leg cooling after moderate exercise on the cardiorespiratory responses to subsequent exercise in the heat. Following 40 min of ergometer cycling [65% peak oxygen uptake (O_2peak)] at 35°C (Ex. 1), seven male subjects [21.9 (1.1) years of age; 170.9 (1.9) cm height; 66.0 (2.0) kg body mass; 46.7 (2.0) ml kg^–1 min^–1 O_2peak] immersed their legs in 35°C (control condition, CONT) or 20°C (cooling condition, COOL) water for 5 min and then repeated the cycling (as before, but for 10 min) (Ex. 2). Just before Ex. 2, esophageal temperature (T _es) was lower in COOL than in CONT [36.9 (0.2) vs 37.5 (0.1)°C] (P<0.01), as also were both mean skin temperature [33.9 (0.2) vs 35.2 (0.2)°C] (P<0.01), and heart rate (HR) [93.2 (6.0) vs 102.7 (4.9) beats min^–1] (P<0.05). During Ex. 2, no differences between CONT and COOL were observed in oxygen uptake, arterial blood pressure, blood lactate concentration, or ratings of perceived exertion; however, T _es, skin temperature, and HR were lower in COOL than in CONT. Further, during the first 5 min of Ex. 2, minute ventilation was significantly lower in COOL than in CONT [50.3 (2.0) vs 53.4 (2.6) l min^–1] (P<0.01). These results suggest that brief leg cooling during the recovery period may be effective at reducing thermal and cardiorespiratory strain during subsequent exercise in the heat.     

DEET insect repellent: effects on thermoregulatory sweating and physiological strain

Insect repellents (e.g. N,N-diethyl-m-toluamide or DEET) applied to the skin can potentially interfere with sweat production and evaporation, thus increasing physiological strain during exercise-heat stress. The purpose was to determine the impact of 33% DEET lotion on sweating responses, whole body thermoregulation and thermal sensation during walking exercise in the heat. Nine volunteers (2 females, 7 males; 22.1 ± 4.9 years; 176.4 ± 10.0 cm; 79.9 ± 12.9 kg) completed 5 days of heat acclimation (45°C, 20% rh; 545 watts; 100 min/day) and performed three trials: control (CON); DEET applied to forearm (DEET_LOC, 12 cm²); and DEET applied to ~13% body surface area (DEET_WB,). Trials consisted of 30 min walking (645 watts) in 40°C, 20% rh environment. Local sweat rate (SR), onset and skin wettedness were measured in DEET_LOC, and heart rate (HR), rectal temperature (T _re), skin temperature (T _sk), RPE, and thermal sensations (TS) were measured during DEET_WB. No differences (p > 0.05) were observed between DEET_LOC versus CON, respectively, for steady state SR (1.89 ± 0.44 vs. 2.09 ± 0.84 mg/cm²/min), SR area under the curve (46.9 ± 11.7 vs. 55.0 ± 20.8 mg/cm²), sweating onset, or skin wettedness. There were no differences (p > 0.05) in HR, T _re, T _sk, Physiological Strain Index, RPE or TS between DEET_WB versus CON. DEET did not impact measures of local forearm sweating and when applied according to military doctrine, did not adversely impact physiological responses during exercise-heat stress. DEET can be safely worn during military, occupational and recreational activities in hot, insect infested environments.     

Thermal face protection delays finger cooling and improves thermal comfort during cold air exposure

When people dress for cold weather, the face often remains exposed. Facial cooling can decrease finger blood flow, reducing finger temperature (T _f). This study examined whether thermal face protection limits finger cooling and thereby improves thermal comfort and manual dexterity during prolonged cold exposure. T _f was measured in ten volunteers dressed in cold-weather clothing as they stood for 60 min facing the wind (−15°C, 3 m s⁻¹), once while wearing a balaclava and goggles (BAL), and once with the balaclava pulled down and without goggles (CON). Subjects removed mitts, wearing only thin gloves to perform Purdue Pegboard (PP) tests at 15 and 50 min, and Minnesota Rate of Manipulation (MRM) tests at 30 and 55 min. Subjects rated their thermal sensation and comfort just before the dexterity tests. T _f decreased (p < 0.05 for time × trial interaction) by 15 min of cold exposure during CON (33.6 ± 1.4–28.7 ± 2.0°C), but not during BAL (33.2 ± 1.4–30.6 ± 3.2°C); and after 30 min T _f remained warmer during BAL (23.3 ± 5.9°C) than CON (19.2 ± 3.5); however, by 50 min, T _f was no different between trials (14.1 ± 2.7°C). Performance on PP fell (p < 0.05) by 25% after 50 min in both trials; MRM performance was not altered by cold on either trial. Subjects felt colder (p < 0.05) and more uncomfortable (p < 0.05) during CON, compared to BAL. Thermal face protection was effective for maintaining warmer T _f and thermal comfort during cold exposure; however, local cooling of the hands during manual dexterity tests reduced this physiological advantage, and performance was not improved.     

Thermoregulatory responses to ice-slush beverage ingestion and exercise in the heat

We compared the effects of an ice-slush beverage (ISB) and a cool liquid beverage (CLB) on cycling performance, changes in rectal temperature (T _re) and stress responses in hot, humid conditions. Ten trained male cyclists/triathletes completed two exercise trials (75 min cycling at ~60% peak power output + 50 min seated recovery + 75% peak power output × 30 min performance trial) on separate occasions in 34°C, 60% relative humidity. During the recovery phase before the performance trial, the athletes consumed either the ISB (mean ± SD −0.8 ± 0.1°C) or the CLB (18.4 ± 0.5°C). Performance time was not significantly different after consuming the ISB compared with the CLB (29.42 ± 2.07 min for ISB vs. 29.98 ± 3.07 min for CLB, P = 0.263). T _re (37.0 ± 0.3°C for ISB vs. 37.4 ± 0.2°C for CLB, P = 0.001) and physiological strain index (0.2 ± 0.6 for ISB vs. 1.1 ± 0.9 for CLB, P = 0.009) were lower at the end of recovery and before the performance trial after ingestion of the ISB compared with the CLB. Mean thermal sensation was lower (P < 0.001) during recovery with the ISB compared with the CLB. Changes in plasma volume and the concentrations of blood variables (i.e., glucose, lactate, electrolytes, cortisol and catecholamines) were similar between the two trials. In conclusion, ingestion of ISB did not significantly alter exercise performance even though it significantly reduced pre-exercise T _re compared with CLB. Irrespective of exercise performance outcomes, ingestion of ISB during recovery from exercise in hot humid environments is a practical and effective method for cooling athletes following exercise in hot environments.     

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.     

The effect of passive heating and face cooling on perceived exertion during exercise in the heat

Increased body temperature is thought to be an important component of the higher perception of exertion that is a feature of fatigue during exercise in the heat but a causal relationship has yet to be demonstrated. We have investigated the effect of passive heating on the perception of exertion during a standard bout of exercise and also assessed the effect of cooling the head on compensating for the increased body temperature on the feelings of exertion. Ten male subjects performed a 14-min cycling exercise [average power ~63% of maximum power output ( _max)] at an ambient temperature of 35°C at resting rectal temperature [mean (SD): 37.49 (0.27)°C; control (CON) trial] on one occasion, and after sitting in a sauna to raise rectal temperature [mean (SD): 38.95(0.13)°C; sauna (SAU) trial]. During the exercise, subjects reported their ratings of overall perceived exertion (RPE), perceived exertion of the legs (RPE_legs) and thermal comfort (TC). A blood sample was collected by the end of the exercise for determination of plasma glucose, lactate and prolactin and haematocrit. RPE values were significantly elevated after passive heating [mean (SE): 14.5 (0.7) units in CON and 17.2 (0.5) units in SAU, at the end of exercise; P<0.001] as were the RPE_legs (P<0.01), while ratings of TC were similar in CON and SAU trials. Passive heating increased blood glucose (P<0.05) but had no effect on lactate at the end of the exercise. Plasma prolactin was markedly elevated as a result of the sauna exposure [mean (SE): 1598 (152) versus 225 (31) mU l^–1 in SAU and CON trials, respectively; P<0.001]. Six of the subjects repeated the two trials but with the face cooled during exercise (trials CON_FAN and SAU_FAN) that was achieved by combining face fanning and spraying the face with a mist of cooled water. Face cooling decreased RPE values after sauna to a point that no differences between the two conditions existed. RPE_legs scores and heart rate, however, remained higher in SAU_FAN compared with CON_FAN (P<0.05). We conclude that hyperthermia is a causative element of the increased perception of exertion during submaximal exercise in the heat and that the effect of increased core temperature on the feelings of exertion is modulated by face cooling.     

Short-term exercise provides left ventricular myocardial protection against intermittent hypoxia-induced apoptosis in rats

We investigated whether exercise provides beneficial effects to attenuate intermittent hypoxia (IH)-induced myocardial apoptosis. Male Sprague-Dawley rats were randomly assigned to four groups: control (CON), IH, exercise (EXE) or IH interspersed with EXE (IHEXE). IH rats were exposed to repetitive hypoxia–reoxygenation cycles (30 s of 5% O₂; 45 s of 21% O₂, 6 h day⁻¹) during the light phase (1000–1600 h) for 12 consecutive days. EXE rats were habituated to treadmill running for 5 days, permitted 2 days of rest, followed by 5 exercise bouts (30 m min⁻¹ for 60 min on a 2% grade) on consecutive days during the dark phase (2000–2200 h). IHEXE rats were exposed to IH during the light phase interspersed with exercise programs during the dark phase on the same day. Apoptosis levels, cytochrome c (Cyt-c), cleaved caspase-3, oxidative stress and antioxidant capacity were determined in the left ventricular (LV) myocardium. IH rats showed higher myocardial levels of the apoptotic index, mitochondria-released Cyt-c, cleaved caspase-3 and oxidative stress and lower catalase activity levels than CON rats (p < 0.05, for all). These changes were not observed in EXE rats (p > 0.05, for all) except that catalase activity increased (p < 0.05). IHEXE rats showed lower myocardial levels of apoptotic index, mitochondria-released Cyt-c, cleaved caspase-3 and oxidative stress and higher catalase activity levels (p < 0.05, for all) than IH rats. We conclude that short-term exercise provides potent cardioprotective effects by attenuating IH-induced myocardial apoptosis.     

Do greater rates of body heat storage precede the accelerated reduction of self-paced exercise intensity in the heat?

Aim

To reevaluate the previous hypothesis that greater reductions in self-paced exercise intensity in the heat are mediated by early differences in the rate of body heat storage (S).

Methods

Eight trained volunteers cycled in 19 °C/1.8 kPa (COOL), 25 °C/1.2 kPa (NORM), and 34 °C/1.6 kPa (HOT), while maintaining an RPE of 16. Potential differences in S following the onset of exercise were assessed by comparing rates of esophageal temperature change (ΔT _es/Δt); and estimated S values using a traditional two-compartment thermometric model (S _therm) of changes in rectal (T _re) and skin (T _sk) temperature, and partitional calorimetry (S _cal).

Results

After 15 min of exercise, workload decreased more in HOT vs. COOL (P = 0.03), resulting in a shorter time (HOT: 40.7 ± 14.9 min; COOL: 53.5 ± 18.7 min; P = 0.04) to 70 % of initial workload. However, there were no preceding differences in ΔT _es/Δt between conditions (P = 0.18). S _therm values were different between HOT and COOL during the first 5 min of exercise (P < 0.05), primarily due to negative S _therm values (?32 ± 15 kJ min^?1) in COOL, which according to partitional calorimetric measurements, required improbably high (~56 kJ min^?1) rates of evaporation when no sweating on the back and thigh was observed until after 7.6 ± 1.5 min and 4.8 ± 1.7 min of exercise, respectively. S _cal values in the first 5 min of exercise confirmed S was actually positive in COOL (+21 ± 8 kJ min^?1) and not negative. Different S _therm values following the onset of exercise at different environmental temperatures are simply due to transient differences in the rate of change in T _sk.

Conclusion

Reductions in self-paced exercise intensity in the heat are not mediated by early differences in S following the onset of exercise.     

Aerobic power and peak power of elite America’s Cup sailors

Big-boat yacht racing is one of the only able bodied sporting activities where standing arm-cranking (‘grinding’) is the primary physical activity. However, the physiological capabilities of elite sailors for standing arm-cranking have been largely unreported. The purpose of the study was to assess aerobic parameters, VO_2peak and onset of blood lactate (OBLA), and anaerobic performance, torque–crank velocity and power–crank velocity relationships and therefore peak power (P _max) and optimum crank-velocity (ω_opt), of America’s Cup sailors during standing arm-cranking. Thirty-three elite professional sailors performed a step test to exhaustion, and a subset of ten grinders performed maximal 7 s isokinetic sprints at different crank velocities, using a standing arm-crank ergometer. VO_2peak was 4.7 ± 0.5 L/min (range 3.6–5.5 L/min) at a power output of 332 ± 44 W (range 235–425 W). OBLA occurred at a power output of 202 ± 31 W (61% of W_max) and VO₂ of 3.3 ± 0.4 L/min (71% of VO_2peak). The torque–crank velocity relationship was linear for all participants (r = 0.9 ± 0.1). P _max was 1,420 ± 37 W (range 1,192–1,617 W), and ω_opt was 125 ± 6 rpm. These data are among the highest upper-body anaerobic and aerobic power values reported. The unique nature of these athletes, with their high fat-free mass and specific selection and training for standing arm cranking, likely accounts for the high values. The influence of crank velocity on peak power implies that power production during on-board ‘grinding’ may be optimised through the use of appropriate gear-ratios and the development of efficient gear change mechanisms.     

Effects of ammonium chloride ingestion on phosphocreatine metabolism during moderate- and heavy-intensity plantar-flexion exercise

This study examined the effects of NH₄Cl ingestion on phosphocreatine (PCr) metabolism during 9 min of moderate- (MOD) and heavy- (HVY) intensity constant-load isotonic plantar-flexion exercise. Healthy young adult male subjects (n = 8) completed both a control (CON) and NH₄Cl ingestion (ACID) trial. Phosphorus-31 magnetic resonance spectroscopy was used to monitor changes in intracellular pH (pHi), [Pi], [PCr], and [ATP]. During the Middle (3–6 min) and Late (6–9 min) stages of HVY, ACID was associated with a higher (P < 0.05) intracellular hydrogen-ion concentration ([H⁺]i) [Middle: 246 (SD 36) vs. 202 (SD 36) mmol/l]; [Late: 236 (SD 35) vs. 200 (SD 39) mmol/l]. In addition, ACID was associated with a lower (P < 0.05) [PCr] relative to CON during the Early (0–3 min) [18.1 (SD 5.1) vs. 20.4 (SD 5.4) mmol/l] and Middle stages [14.1 (SD 5.4) vs. 16.7 (SD 6.0) mmol/l] of HVY. The amplitude of the primary component of PCr breakdown during the transition to HVY was greater in ACID than CON [14.5 (SD 5.8 vs. 11.3 (SD 4.8) mmol/l], however, the PCr slow component (continued slow decline in [PCr]) showed no difference (P > 0.05). The time constant for PCr breakdown (τPCr) was greater in HVY than MOD for both conditions [58 (SD 22) vs. 28 (SD 15) s ACID; 51 (SD 20) vs. 29 (SD 14) s CON] (P < 0.05). In summary, ACID increased PCr breakdown during the transition from MOD to HVY, but did not increase the magnitude of the PCr slow component.     

The influence of menthol on thermoregulation and perception during exercise in warm, humid conditions

Menthol has recently been added to various cooling products that claim to enhance athletic performance. This study assessed the effect of two such solutions during exercise in warm, humid conditions. Twelve participants (22 ± 2.9 years; [(V)\dot]\textO_2\textpeak \dot{V}{\text{O}}_{{2{\text{peak}}}} 47.4 ± 6.2 mL kg⁻¹ min⁻¹) completed a peak power (PO_peak) test and three separate exercise bouts in 30°C and 70% relative humidity after being sprayed with 100 mL of water containing either 0.05 or 0.2% l-menthol, or a control spray. During each trial, participants underwent 15 min of rest, spraying, 15 min of rest and 45 min of exercise at 45% of PO_peak. The following variables were measured: rectal temperature (T _re), sweat rate (SR), skin blood flow (SBF), heart rate (HR), thermal comfort (TC) and sensation (TS) votes, irritation (IRR) and rating of perceived exertion (RPE). Mean skin (MST) and body temperatures ( [`(T)]<sub>\textbody</sub> \bar{T}_{\text{body}} ) were calculated. There was no significant difference in MST, [`(T)]_\textbody \bar{T}_{\text{body}} SR, SBF, HR, TC or RPE between conditions. Spraying with 0.2% menthol significantly (P < 0.05) elevated T _re by 0.2°C compared to the other conditions. Both menthol sprays caused participants to feel significantly cooler than control spraying (P = 0.001), but 0.2% spraying induced significantly cooler sensations (P = 0.01) than 0.05% spraying. Both menthol sprays induced greater irritation (P < 0.001) than control spraying. These findings suggest that 0.05% menthol spraying induced cooler upper body sensations without measurable thermoregulatory impairment. T _re was significantly elevated with 0.2% spraying. Irritation persisted with both menthol sprays while TC remained unchanged, suggesting a causal relationship. The use in sport of a spray similar to those tested here remains equivocal.     

Critical power in adolescents: physiological bases and assessment using all-out exercise

This study examined whether critical power (CP) in adolescents: (1) provides a landmark for maximal steady-state exercise; and (2) can be determined using ‘all-out’ exercise. Nine active 14–15 year olds (6 females, 3 males) performed five cycling tests: (1) a ramp test to determine [(V)\dot]\textO_2 \textpeak \dot{V}{\text{O}}_{{2\,{\text{peak}}}} ; (2) up to four constant power output tests to determine CP; (3–4) constant power output exercise 10% above and 10% below CP; and (5) a 3 min all-out cycle test to establish the end power (EP) at 90 and 180 s of exercise. All participants completed 30 min of exercise below CP and were characterized by steady-state blood lactate and [(V)\dot]\textO₂ {\dot{V}\text{O}}_{2} profiles. In contrast, time to exhaustion during exercise above CP was 15.0 ± 7.0 min and characterized by an inexorable rise in blood lactate and a rise, stabilization (~91% [(V)\dot]\textO_2 \textpeak {\dot{V}\text{O}}_{{2\,{\text{peak}}}} ) and fall in [(V)\dot]\textO₂ {\dot{V}\text{O}}_{2} (~82% [(V)\dot]\textO_2 \textpeak {\dot{V}\text{O}}_{{2\,{\text{peak}}}} ) prior to exhaustion. Eight out of nine participants completed the 3 min test and their EPs at 90 s (148 ± 29 W) and 180 s (146 ± 30 W) were not different from CP (146 ± 27 W) (P = 0.98). The typical error of estimates for establishing CP using EP at 90 s or 180 s of the 3 min test were 25 W (19.7% CV) and 25 W (19.6% CV), respectively. CP in active adolescence provides a valid landmark for maximal steady-state exercise, although its estimation on an individual level using the 3 min all-out test may be of limited value.     

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.     

The effect of selective beta1-blockade on EMG signal characteristics during progressive endurance exercise

This study analysed the effect of selective β₁-blockade on neuromuscular recruitment characteristics during progressive endurance exercise. Ten healthy subjects ingested a selective β₁-blocker, acebutolol (200 mg b.d.), for 7 days (for one of two cycling trials), with a 10-day wash-out period between trials. On the last day of acebutolol ingestion subjects performed three successive 15-min rides at 30%, 50% and 70% of their peak power output and then cycled at increasing (15 W min^–1) work rates to exhaustion. Force output, heart rate, submaximal V˙O₂, rate of perceived exertion (RPE), electromyographic (EMG) data and blood lactate were captured during the cycling activity. Peak work rate [270 (111) W vs 197 (75) W, CON vs BETA, P <0.01], time to exhaustion [49.7 (23.2) min vs 40.3 (23.7) min, CON vs BETA, P <0.05] and heart rate [mean, for the full ride 135.5 (38.3) beats min^–1 vs 111.5 (30.0) beats min^–1 CON vs BETA, P <0.05] were significantly lower for the group who ingested β₁-blockade (BETA) compared to the control group (CON). Although not significant, submaximal V˙O₂ was reduced in BETA during the ride, while RPE was significantly higher during the ride for BETA (P <0.01). Mean integrated electromyography was higher in the BETA group although these differences were not significant. Mean power frequency values of the BETA group showed a significant (P <0.05) shift to the upper end of the spectrum in comparison to the control group. Lactate values [11.7 (3.5) mmol.l^–1 vs 7.1 (4.1) mmol.l^–1 CON vs BETA] were significantly lower (P <0.05) at exhaustion in BETA. Significant reductions in cycling performance were found when subjects ingested β₁-blockers. This study has shown significant shifts to the upper end of the EMG frequency spectrum after β₁-blocker ingestion, which could be caused by a change in neuromuscular recruitment strategy to compensate for the impaired submaximal exercise performance. Electronic Publication     

The American Football Uniform: Uncompensable Heat Stress and Hyperthermic Exhaustion

Context:

In hot environments, the American football uniform predisposes athletes to exertional heat exhaustion or exercise-induced hyperthermia at the threshold for heat stroke (rectal temperature [T_re] > 39°C).

Objective:

To evaluate the differential effects of 2 American football uniform configurations on exercise, thermal, cardiovascular, hematologic, and perceptual responses in a hot, humid environment.

Design:

Randomized controlled trial.

Setting:

Human Performance Laboratory.

Patients or Other Participants:

Ten men with more than 3 years of competitive experience as football linemen (age  =  23.8 ± 4.3 years, height  =  183.9 ± 6.3 cm, mass  =  117.41 ± 12.59 kg, body fat  =  30.1% ± 5.5%).

Intervention(s):

Participants completed 3 controlled exercise protocols consisting of repetitive box lifting (lifting, carrying, and depositing a 20.4-kg box at a rate of 10 lifts per minute for 10 minutes), seated recovery (10 minutes), and up to 60 minutes of treadmill walking. They wore one of the following: a partial uniform (PART) that included the National Football League (NFL) uniform without a helmet and shoulder pads; a full uniform (FULL) that included the full NFL uniform; or control clothing (CON) that included socks, sneakers, and shorts. Exercise, meals, and hydration status were controlled.

Main Outcome Measure(s):

We assessed sweat rate, T_re, heart rate, blood pressure, treadmill exercise time, perceptual measurements, plasma volume, plasma lactate, plasma glucose, plasma osmolality, body mass, and fat mass.

Results:

During 19 of 30 experiments, participants halted exercise as a result of volitional exhaustion. Mean sweat rate, T_re, heart rate, and treadmill exercise time during the CON condition were different from those measures during the PART (P range, .04–.001; d range, 0.42–0.92) and FULL (P range, .04–.003; d range, 1.04–1.17) conditions; no differences were detected for perceptual measurements, plasma volume, plasma lactate, plasma glucose, or plasma osmolality. Exhaustion occurred during the FULL and PART conditions at the same T_re (39.2°C). Systolic and diastolic blood pressures (n  =  9) indicated that hypotension developed throughout exercise (all treatments). Compared with the PART condition, the FULL condition resulted in a faster rate of T_re increase (P < .001, d  =  0.79), decreased treadmill exercise time (P  =  .005, d  =  0.48), and fewer completed exercise bouts. Interestingly, T_re increase was correlated with lean body mass during the FULL condition (R²  =  0.71, P  =  .005), and treadmill exercise time was correlated with total fat mass during the CON (R²  =  0.90, P < .001) and PART (R²  =  0.69, P  =  .005) conditions.

Conclusions:

The FULL and PART conditions resulted in greater physiologic strain than the CON condition. These findings indicated that critical internal temperature and hypotension were concurrent with exhaustion during uncompensable (FULL) or nearly uncompensable (PART) heat stress and that anthropomorphic characteristics influenced heat storage and exercise time to exhaustion.