Hot Ambient Conditions Research Articles

Changes of Hematological Markers during a Multi-stage Ultra-marathon Competition in the Heat.

This study examined the changes in resting hematological variables in ultra-endurance runners throughout a multi-stage ultra-marathon competition, and compared athletes that completed all stages with those that failed to complete at least one stage within the cut-off time of competition. 19 ultra-endurance runners competing in a 230 km multi-stage ultra-marathon, conducted over 5 consecutive days in hot ambient conditions (32-40°C T(max)), volunteered to participate in the study. Each day, whole blood samples were collected prior to stage commencement and analyzed for full cell counts by Coulter counter. Linear increases were observed for leukocytes, monocytes and lymphocytes; with increases until Stage 3 and a decrease thereafter. Granulocytes showed a cubic growth exponent, indicating decrements to baseline after the significant increments until Stage 3. Hemoglobin and hematocrit showed linear decrements throughout the multi-stage ultra-marathon. No changes in erythrocytes and platelets were observed throughout the multi-stage ultra-marathon. Granulocytes, erythrocytes, hemoglobin and hematocrit changes along the multi-stage ultra-marathon differed in runners that completed all stages compared to those who failed to complete at least one stage within the cut-off time. Multi-stage ultra-marathon in the heat has a large impact on hematological responses of ultra-endurance runners associated with altered performance.

High-Dose Probiotic Supplementation Containing Lactobacillus casei for 7 Days Does Not Enhance Salivary Antimicrobial Protein Responses to Exertional Heat Stress Compared With Placebo.

The study aimed to determine whether high-dose probiotic supplementation containing Lactobacillus casei (L. casei) for 7 consecutive days enhances salivary antimicrobial protein (S-AMP) responses to exertional-heat stress (EHS). Eight endurance-trained male volunteers (age 26 ± 6 years, nude body mass 70.2 ± 8.8 kg, height 1.75 ± 0.05 m, VO2max 59 ± 5 ml·kg-1·min-1 [M ± SD]) completed a blinded randomized and counterbalanced crossover design. Oral supplementation of the probiotic beverage (PRO; L. casei . 1011 colony-forming units·day-1) or placebo (PLA) was consumed for 7 consecutive days before 2 hr running exercise at 60% VO2max in hot ambient conditions (34.0° C and 32% RH). Body mass and unstimulated saliva and venous blood samples were collected at baseline (7 days before EHS), pre-EHS, post-EHS (1 hr, 2 hr, and 4 hr), and at 24 hr. Saliva samples were analyzed for salivary (S) IgA, α-amylase, lysozyme, and cortisol. Plasma samples were analyzed for plasma osmolality. Body mass and plasma osmolality did not differ between trials. Saliva flow rate remained relatively constant throughout the experimental design in PRO (overall M ± SD = 601 ± 284 μl/min) and PLA (557 ± 296 μl/min). PRO did not induce significant changes in resting S-AMP responses compared with PLA (p > .05). Increases in S-IgA, S-α-amylase, and S-cortisol responses, but not S-lysozyme responses, were observed after EHS (p < .05). No main effects of trial or Time x Trial interaction were observed for S-AMP and S-cortisol responses. Supplementation of a probiotic beverage containing L. casei for 7 days before EHS does not provide any further oral-respiratory mucosal immune protection, with respect to S-AMP, over PLA.

Consensus recommendations on training and competing in the heat

Exercising in the heat induces thermoregulatory and other physiological strain that can lead to impairments in endurance exercise capacity. The purpose of this consensus statement is to provide up-to-date recommendations...

Consensus Recommendations on Training and Competing in the Heat.

Exercising in the heat induces thermoregulatory and other physiological strain that can lead to impairments in endurance exercise capacity. The purpose of this consensus statement is to provide up-to-date recommendations to optimize performance during sporting activities undertaken in hot ambient conditions. The most important intervention one can adopt to reduce physiological strain and optimize performance is to heat acclimatize. Heat acclimatization should comprise repeated exercise–heat exposures over 1–2 weeks. In addition, athletes should initiate competition and training in an euhydrated state and minimize dehydration during exercise. Following the development of commercial cooling systems (e.g., cooling vests), athletes can implement cooling strategies to facilitate heat loss or increase heat storage capacity before training or competing in the heat. Moreover, event organizers should plan for large shaded areas, along with cooling and rehydration facilities, and schedule events in accordance with minimizing the health risks of athletes, especially in mass participation events and during the first hot days of the year. Following the recent examples of the 2008 Olympics and the 2014 FIFA World Cup, sport governing bodies should consider allowing additional (or longer) recovery periods between and during events for hydration and body cooling opportunities when competitions are held in the heat.

Conductive and evaporative precooling lowers mean skin temperature and improves time trial performance in the heat.

Self-paced endurance performance is compromised by moderate-to-high ambient temperatures that are evident in many competitive settings. It has become common place to implement precooling prior to competition in an attempt to alleviate perceived thermal load and performance decline. The present study aimed to investigate precooling incorporating different cooling avenues via either evaporative cooling alone or in combination with conductive cooling on cycling time trial performance. Ten trained male cyclists completed a time trial on three occasions in hot (35 °C) ambient conditions with the cooling garment prepared by (a) immersion in water (COOL, evaporative); (b) immersion in water and frozen (COLD, evaporative and conductive); or (c) no precooling (CONT). COLD improved time trial performance by 5.8% and 2.6% vs CONT and COOL, respectively (both P < 0.05). Power output was 4.5% higher for COLD vs CONT (P < 0.05). Mean skin temperature was lower at the onset of the time trial following COLD compared with COOL and CONT (both P < 0.05) and lasted for the first 20% of the time trial. Thermal sensation was perceived cooler following COOL and COLD. The combination of evaporative and conductive cooling (COLD) had the greatest benefit to performance, which is suggested to be driven by reduced skin temperature following cooling.

Sprint performance under heat stress: A review.

Training and competition in major track-and-field events, and for many team or racquet sports, often require the completion of maximal sprints in hot (>30 °C) ambient conditions. Enhanced short-term (<30 s) power output or single-sprint performance, resulting from transient heat exposure (muscle temperature rise), can be attributed to improved muscle contractility. Under heat stress, elevations in skin/core temperatures are associated with increased cardiovascular and metabolic loads in addition to decreasing voluntary muscle activation; there is also compelling evidence to suggest that large performance decrements occur when repeated-sprint exercise (consisting of brief recovery periods between sprints, usually <60 s) is performed in hot compared with cool conditions. Conversely, poorer intermittent-sprint performance (recovery periods long enough to allow near complete recovery, usually 60-300 s) in hotter conditions is solely observed when exercise induces marked hyperthermia (core temperature >39 °C). Here we also discuss strategies (heat acclimatization, precooling, hydration strategies) employed by "sprint" athletes to mitigate the negative influence of higher environmental temperatures.

Effect of heat and heat acclimatization on cycling time trial performance and pacing.

ABSTRACTPurposeThis study aimed to determine the effects of heat acclimatization on performance and pacing during outdoor cycling time trials (TT, 43.4 km) in the heat.MethodsNine cyclists performed three TT in hot ambient conditions (TTH, approximately 37°C) on the first (TTH-1), sixth (TTH-2), and 14th (TTH-3) days of training in the heat. Data were compared with the average of two TT in cool condition (approximately 8°C) performed before and after heat acclimatization (TTC).ResultsTTH-1 (77 ± 6 min) was slower (P = 0.001) than TTH-2 (69 ± 5 min), and both were slower (P < 0.01) than TTC and TTH-3 (66 ± 3 and 66 ± 4 min, respectively), without differences between TTC and TTH-3 (P > 0.05). The cyclists initiated the first 20% of all TT at a similar power output, irrespective of climate and acclimatization status; however, during TTH-1, they subsequently had a marked decrease in power output, which was partly attenuated after 6 d of acclimatization and was further reduced after 14 d. HR was higher during the first 20% of TTH-1 than that in the other TT (P < 0.05), but there were no differences between conditions from 30% onward. Final rectal temperature was similar in all TTH (40.2°C ± 0.4°C, P = 1.000) and higher than that in TTC (38.5°C ± 0.6°C, P < 0.001).ConclusionsAfter 2 wk of acclimatization, trained cyclists are capable of completing a prolonged TT in a similar time in the heat compared with cool conditions, whereas in the unacclimatized state, they experienced a marked decrease in power output during the TTH.

Energy Modeling and Chillers Sizing of HVAC System for a Hotel Building

With energy shortage issue rises, value of energy conservation grows. The energy consumption of HVAC system reaches about 50% of the building especially for the hot and humid ambient condition in Taiwan. Energy modeling code eQUEST was applied to evaluate the energy consumption of a hotel building. Through the validation of simulation data and field measurement data, the energy-efficient chiller sizing approach can be obtained. The results revealed that the energy saving of 10.5% can be achieved by optimizing the chiller capacity sizing. The approach by energy modelling in this study will identify the best practice under limited budget as well as to reduce the trial-and-error effort while chiller sizing decision for energy saving have to be carried out.

Human cardiovascular responses to passive heat stress.

Heat stress increases human morbidity and mortality compared to normothermic conditions. Many occupations, disease states, as well as stages of life are especially vulnerable to the stress imposed on the cardiovascular system during exposure to hot ambient conditions. This review focuses on the cardiovascular responses to heat stress that are necessary for heat dissipation. To accomplish this regulatory feat requires complex autonomic nervous system control of the heart and various vascular beds. For example, during heat stress cardiac output increases up to twofold, by increases in heart rate and an active maintenance of stroke volume via increases in inotropy in the presence of decreases in cardiac preload. Baroreflexes retain the ability to regulate blood pressure in many, but not all, heat stress conditions. Central hypovolemia is another cardiovascular challenge brought about by heat stress, which if added to a subsequent central volumetric stress, such as hemorrhage, can be problematic and potentially dangerous, as syncope and cardiovascular collapse may ensue. These combined stresses can compromise blood flow and oxygenation to important tissues such as the brain. It is notable that this compromised condition can occur at cardiac outputs that are adequate during normothermic conditions but are inadequate in heat because of the increased systemic vascular conductance associated with cutaneous vasodilation. Understanding the mechanisms within this complex regulatory system will allow for the development of treatment recommendations and countermeasures to reduce risks during the ever-increasing frequency of severe heat events that are predicted to occur.

Feeling the heat in sport

Feeling the heat in sport

The Reliability and Adaptive Responses of Gross Efficiency in Hot Ambient Conditions

This study evaluated the reliability and adaptive responses of cycling gross efficiency (GE) performed at different intensities, across 3 trials in simulated hot (~30°C) temperatures. Twelve cyclists performed 3 hot (30±0.7ºC and RH of 50±2.9%) GE sessions, comprising 3 sub-maximal work rates of 150 W, 200 W and 250 W (5-min each), separated by 24-h. Paired t-tests revealed no changes (P>0.05) in GE between trials. 95% limits of agreement demonstrated random error in GE ranging from 1.71% (250 W; trials 1-2) to 2.32% (200 W; trials 1-2), leading to a total error of -2.45%. The coefficient of variation (CV%) ranged from 3.1±0.4% (250 W; trials 1-2) to 4.0±0.5% (200 W; trials 1-2). Among non-acclimated, well-trained cyclists, GE did not change between consecutive submaximal cycling bouts performed in the heat. The reliability of GE when cycling in the heat (CV=3.1-4.0%) is similar to that reported among cyclists in thermoneutral environments. Whilst the interpretation of GE reliability was dependent on the adopted statistical technique, it can be small enough to detect typical changes owing to heat exposure.

Physiological and Performance Responses to a Training Camp in the Heat in Professional Australian Football Players

To examine the physiological and performance responses to a heat-acclimatization camp in highly trained professional team-sport athletes. Eighteen male Australian Rules Football players trained for 2 wk in hot ambient conditions (31-33°C, humidity 34-50%). Players performed a laboratory-based heat-response test (24-min walk + 24 min seated; 44°C), a YoYo Intermittent Recovery Level 2 Test (YoYoIR2; indoor, temperate environment, 23°C) and standardized training drills (STD; outdoor, hot environment, 32°C) at the beginning and end of the camp. The heat-response test showed partial heat acclimatization (eg, a decrease in skin temperature, heart rate, and sweat sodium concentration, P < .05). In addition, plasma volume (PV, CO rebreathing, +2.68 [0.83; 4.53] mL/kg) and distance covered during both the YoYoIR2 (+311 [260; 361] m) and the STD (+45.6 [13.9; 77.4] m) increased postcamp (P < .01). None of the performance changes showed clear correlations with PV changes (r < .24), but the improvements in running STD distance in hot environment were correlated with changes in hematocrit during the heat-response test (r = -.52, 90%CI [-.77; -.12]). There was no clear correlation between the performance improvements in temperate and hot ambient conditions (r < .26). Running performance in both hot and temperate environments was improved after a football training camp in hot ambient conditions that stimulated heat acclimatization. However, physiological and performance responses were highly individual, and the absence of correlations between physical-performance improvements in hot and temperate environments suggests that their physiological basis might differ.

Effects of strenuous exercise on stallion sperm quality

Some stallions are expected to perform athletically and breed contemporarily. Athletic activity has the potential, especially during the summer months, to induce thermal stress to the testes, resulting in reduced reproductive capability due to decreased sperm quality and libido. Thus, the objective of this study was to determine the effect of strenuous exercise on stallion sperm quality in hot, humid conditions (thermal heat index 38.08±3.77 to 42.88±3.33). Miniature Horse stallions (n=7) were assigned to treatment group based on age and semen quality. Treatment stallions (n=3) were exercised 4 d/wk for 90 min for 12 wk, whereas control stallions (n=4) were tied in the shade. Semen was collected from stallions for 5 consecutive days every 4 wk to evaluate sperm quality. Scrotal and neck temperatures were recorded using implanted subdermal thermosensory devices. In addition, rectal temperature and heart rate were recorded. Exercised stallions had higher mean rectal (39.27 vs. 37.07 °C; P<0.0001), neck (39.77 vs. 37.44 °C; P<0.0001), and scrotal (34.90 vs. 33.40 °C, P<0.0001) temperatures than control stallions during the 90-min exercise and 30-min recovery period. No differences were detected in sperm quality characteristics between treatment groups (P>0.05). Results suggest that previous reports of reduced sperm quality in stallions in training may have causes other than transiently elevated scrotal and body temperature. Strenuously exercising stallions for up to 90 min under hot and humid ambient conditions may not be harmful to spermatogenesis.

Impact of air distribution system on quality of ventilation in small aircraft cabin

A ventilation system of sufficient performance is the basic condition for comfort and health risk free environment in enclosed aircraft cabin spaces. The airflow pattern and spreading of fresh air into the cabin space mainly depend on the type of the air distribution system and location of heat sources/sinks. The present study deals with the investigation of the dependency between the type of the air distribution system and indoor air quality in a cabin of a small transport aircraft. The mock-up interior geometry of a small aircraft cabin for nine passengers was adopted for the investigation. Three types of the air distribution system were investigated: a typical mixing ventilation system, a modified mixing ventilation system and an under-aisle displacement ventilation system. The quality of ventilation was assessed based on the local mean age of air using CFD software Star-CCM+. At first, the CFD model of a typical mixing ventilation was validated against the experimental data of airflow in the mock-up of the small aircraft cabin. The validated model was then used for the evaluation of the three distribution systems under cold, mild and hot ambient environment conditions from the point of their performance for several typical aircraft operational conditions. Results of the study show a strong dependence of the air distribution systems performance on the ambient conditions. The most stable air distribution was reached with the modified mixing air distribution system. Other types of ventilation systems failed to provide sufficient ventilation and cooling under hot ambient conditions.

Hot ambient conditions shift the Force / EMG relationship

PurposeThis manuscript reports the data from two interventions on human subjects aiming to determine the effect of elevated core (HOT-core, study 1, 14 participants) and skin (HOT-skin, study 2, 11 participants) temperature on the force / EMG relationship.MethodsIn both studies, participant underwent an experimental trial and a control (CON) trial, in which maximal voluntary contractions (MVC) of the plantar flexors, surface EMG recordings of both the soleus and gastrocnemius medialis (GM), and electrical stimulation of the tibial nerve were performed to determine the percentage of voluntary activation (VA). During the HOT-core trial, rectal temperature was passively increased and then clamped at 39°C by adjusting the room temperature in the range of 46-50°C. During the HOT-skin trial, tests were performed in a temperate environment (~20°C) and skin temperature was locally affected by applying a cool or a hot pack during 1 min.ResultsHOT-core resulted in a decrease in MVC torque (−19%) and VA (−5%) (p < 0.05). HOT-skin did not induce any changes in MVC torque (−1%) or VA (+0%). However, the EMG activity (RMS) was decreased both in HOT-core (soleus −40%, GM −33%) and HOT-skin (soleus −10%, GM −13%), compared with CON (p < 0.05).ConclusionThe effect of skin temperature on EMG recordings may be attributed to both methodological and physiological factors. Hot ambient conditions shift the Torque / EMG relationship to the left, with the decrement in torque induced with passive hyperthermia lower than the decrement in EMG.

Salivary antimicrobial protein responses during multistage ultramarathon competition conducted in hot environmental conditions

Prolonged strenuous exercise is commonly reported to depress oral-respiratory immune status and increase the incidence of upper respiratory symptoms. This novel investigation aimed to determine the salivary antimicrobial responses and hydration status of ultraendurance runners (n = 23) during a 230-km multistage ultramarathon conducted in hot ambient conditions (32-40 °C). Body mass was measured and unstimulated saliva and venous blood samples were taken before and after each stage of the ultramarathon. Ad libitum fluid intake was permitted throughout each race day. Upper respiratory symptoms were monitored during and until 4 weeks after race completion. Samples were analyzed for salivary immunoglobulin A (IgA), lysozyme, α-amylase, and cortisol, as well as for plasma and saliva osmolality. Mean exercise-induced body mass loss over the 5 stages ranged from 1.3% to 2.4%. Overall mean pre- and post-stage plasma osmolality measurements in the ultraendurance runners were 279 ± 14 mOsmol·kg(-1) and 293 ± 15 mOsmol·kg(-1), respectively. Decreases in saliva flow rate (overall change 22%) and post-stage increases in saliva osmolality (36%) were observed in the ultraendurance runners during the ultramarathon. Reduced salivary IgA (32%) (p < 0.001 vs. pre-stage salivary IgA), enhanced salivary α-amylase (187%) (p < 0.001 vs. pre-stage salivary α-amylase), and no change in salivary lysozyme secretion rates were observed in the ultraendurance runners throughout the ultramarathon. Only 1 ultraendurance runner reported upper respiratory symptoms during and 1 month after competition. Observed depressions in salivary IgA secretion rates were offset by favourable increases in salivary α-amylase and unchanged lysozyme responses in the majority of runners during the competition. Ensuring euhydration throughout a multistage ultramarathon competition in the heat may play a role in protecting the upper respiratory tract.

Water and sodium intake habits and status of ultra-endurance runners during a multi-stage ultra-marathon conducted in a hot ambient environment: an observational field based study

BackgroundAnecdotal evidence suggests ultra-runners may not be consuming sufficient water through foods and fluids to maintenance euhydration, and present sub-optimal sodium intakes, throughout multi-stage ultra-marathon (MSUM) competitions in the heat. Subsequently, the aims were primarily to assess water and sodium intake habits of recreational ultra-runners during a five stage 225 km semi self-sufficient MSUM conducted in a hot ambient environment (Tmax range: 32°C to 40°C); simultaneously to monitor serum sodium concentration, and hydration status using multiple hydration assessment techniques.MethodsTotal daily, pre-stage, during running, and post-stage water and sodium ingestion of ultra-endurance runners (UER, n = 74) and control (CON, n = 12) through foods and fluids were recorded on Stages 1 to 4 by trained dietetic researchers using dietary recall interview technique, and analysed through dietary analysis software. Body mass (BM), hydration status, and serum sodium concentration were determined pre- and post-Stages 1 to 5.ResultsWater (overall mean (SD): total daily 7.7 (1.5) L/day, during running 732 (183) ml/h) and sodium (total daily 3.9 (1.3) g/day, during running 270 (151) mg/L) ingestion did not differ between stages in UER (p < 0.001 vs. CON). Exercise-induced BM loss was 2.4 (1.2)% (p < 0.001). Pre- to post-stage BM gains were observed in 26% of UER along competition. Pre- and post-stage plasma osmolality remained within normal clinical reference range (280 to 303 mOsmol/kg) in the majority of UER (p > 0.05 vs. CON pre-stage). Asymptomatic hyponatraemia (<135 mmol/L) was evident pre- and post-stage in n = 8 UER, corresponding to 42% of sampled participants. Pre- and post-stage urine colour, urine osmolality and urine/plasma osmolality ratio increased (p < 0.001) as competition progressed in UER, with no change in CON. Plasma volume and extra-cellular water increased (p < 0.001) 22.8% and 9.2%, respectively, from pre-Stage 1 to 5 in UER, with no change in CON.ConclusionWater intake habits of ultra-runners during MSUM conducted in hot ambient conditions appear to be sufficient to maintain baseline euhydration levels. However, fluid over-consumption behaviours were evident along competition, irrespective of running speed and gender. Normonatraemia was observed in the majority of ultra-runners throughout MSUM, despite sodium ingestion under benchmark recommendations.

An attempt to estimate service terms of tableware made of amino resins

This study presents a first attempt to estimate the service terms of food contact articles made of melamine/formaldehyde and urea/formaldehyde plastics. This was achieved by following the continuous release of formaldehyde into food simulants throughout the use phase until the levels of formaldehyde migration exceeded the specific migration limit (SML), or samples were damaged and not suitable for further tests. Two test conditions were established to follow customary practices as much as possible: scenario 1, successive washing; and scenario 2, alternate courses of exposure and washing. Real melamine tableware showed conformity to the SML of formaldehyde over the course of 1500 successive washings; the estimated service term was 750 days, or about 2 years. Moreover, this service term agreed well with that found in real practice. When washing urea/formaldehyde tableware with sponges, the levels of formaldehyde migration remained below the SML, but samples eventually fractured. In the case of scrubbing pads, the levels of formaldehyde migration constantly increased and ultimately exceeded the SML. Scenario 2 resulted in accelerated migration of formaldehyde, and the SML was exceeded more rapidly than in scenario 1. Because surface roughening occurred during customary use and also during washing with scrubbing pads, it was necessary to adopt reduction factors to take into account the effects of handling when calculating service terms of articles. The results showed reduction factors ranging from 1 to 3, depending on test conditions (scenario 1 or 2) and anticipated use conditions (hot fill or use at ambient temperature). Thus, the estimated service terms of urea formaldehyde products were 117 and 175 days under hot fill and ambient conditions, respectively. These results corresponded with service terms observed in real practice, which were reported to be in the ranges of 3–4 and 6–7 months, respectively. Taking into account the time and expenses consumed during experiments, scenario 1 (successive washing with scrubbing pads) would be recommended as an appropriate method for following the migration of formaldehyde over repeated use phases and for estimating the service terms of amino-resin-based articles for food contact use.

Individual responses to short-term heat acclimatisation as predictors of football performance in a hot, dry environment

ObjectivesTo identify the relationship between field performance in a hot environment and individual heat acclimatisation responses in football players.MethodsNineteen semiprofessional football players completed a match in 21°C followed by 6...

Hot conditions improve power output during repeated cycling sprints without modifying neuromuscular fatigue characteristics

This study investigated the effect of hot conditions on repeated sprint cycling performance and post-exercise alterations in isometric knee extension function. Twelve physically active participants performed 10×6-s "all-out" sprints on a cycle ergometer (recovery=30s), followed 6min later by 5×6-s sprints (recovery=30s) in either a neutral (24°C/30%rH) or a hot (35°C/40%rH) environment. Neuromuscular tests including voluntary and electrically evoked isometric contractions of the knee extensors were performed before and after exercise. Average core temperature during exercise was higher (38.0±0.1 vs. 37.7±0.1°C, respectively; P<0.05) in hot versus neutral environments. Peak power output decreased (-17.9% from sprint 1 to sprint 10 and -17.0% from sprint 11 to sprint 15; P<0.001) across repetitions. Average peak power output during the first ten sprints was higher (+3.1%; P<0.01) in the hot ambient temperature condition. Maximal strength (-12%) and rate of force development (-15 to -26%, 30-200ms from the onset of contraction) decreased (P<0.001) during brief contractions after exercise, irrespectively of the ambient temperature. During brief maximal contractions, changes in voluntary activation (~80%) were not affected by exercise or temperature. Voluntary activation declined (P<0.01) during the sustained contraction, with these reductions being more pronounced (P<0.05) after exercise but not affected by the ambient temperature. Resting twitch amplitude declined (P<0.001) by ~42%, independently of the ambient temperature. In conclusion, heat exposure has no effect on the pattern and the extent of isometric knee extensor fatigue following repeated cycling sprints in the absence of hyperthermia.