Jason K. W. Lee

Cold Drink Ingestion Improves Exercise Endurance Capacity in the Heat

PURPOSE To investigate the effect of drink temperature on cycling capacity in the heat. METHODS On two separate trials, eight males cycled at 66 +/- 2% VO2peak (mean +/- SD) to exhaustion in hot (35.0 +/- 0.2 degrees C) and humid (60 +/- 1%) environments. Participants ingested three 300-mL aliquots of either a cold (4 degrees C) or a warm (37 degrees C) drink during 30 min of seated rest before exercise and 100 mL of the same drink every 10 min during exercise. Rectal and skin temperatures, heart rate, and sweat rate were recorded. Ratings of thermal sensation and perceived exertion were assessed. RESULTS Exercise time was longer (P < 0.001) with the cold drink (63.8 +/- 4.3 min) than with the warm drink (52.0 +/- 4.1 min). Rectal temperature fell by 0.5 +/- 0.1 degrees C (P < 0.001) at the end of the resting period after ingestion of the cold drinks. There was no effect of drink temperature on mean skin temperature at rest (P = 0.870), but mean skin temperature was lower from 20 min during exercise with ingestion of the cold drink than with the warm drink (P < 0.05). Heart rate was lower before exercise and for the first 35 min of exercise with ingestion of the cold drink than with the warm drink (P < 0.05). Drink temperature influenced sweat rate (1.22 +/- 0.34 and 1.40 +/- 0.41 L x h(-1) for the cold and the warm drink, respectively; P < 0.05). Ratings of thermal sensation and perceived exertion (P < 0.01) during exercise were lower when the cold drink was ingested. CONCLUSION Compared with a drink at 37 degrees C, the ingestion of a cold drink before and during exercise in the heat reduced physiological strain (reduced heat accumulation) during exercise, leading to an improved endurance capacity (23 +/- 6%).

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

Abstract 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 ([Vdot]O2peak) for 90 min (dry bulb temperature: 25.3°C, s = 0.5; relative humidity: 60%, s = 5). Four 400-ml aliquots of flavoured water at 10°C (cold), 37°C (warm) or 50°C (hot) were ingested after 30, 45, 60, and 75 min of exercise. Immediately after the 90 min of exercise, participants cycled at 95%[Vdot]O2peak 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°C, s = 0.30; warm: 38.10°C, s = 0.33; hot: 38.21°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°C, s = 0.64; warm: 34.53°C, s = 0.69; hot: 34.71°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.

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

Abstract Nine males cycled at 53% (s = 2) of their peak oxygen uptake ([Vdot]O2peak) for 90 min (dry bulb temperature: 25.4°C, s = 0.2; relative humidity: 61%, s = 3). One litre of flavoured water at 10 (cold), 37 (warm) or 50°C (hot) was ingested 30 – 40 min into exercise. Immediately after the 90 min of exercise, participants cycled at 95%[Vdot]O2peak 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°C, s = 0.5; warm trial: 34.4°C, s = 0.5; hot trial: 34.7°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.

Ice Slurry on Outdoor Running Performance in Heat

The efficacy of ingestion of ice slurry on actual outdoor endurance performance is unknown. This study aimed to investigate ice slurry ingestion as a cooling intervention before a 10 km outdoor running time-trial. Twelve participants ingested 8 g · kg (- 1) of either ice slurry ( - 1.4°C; ICE) or ambient temperature drink (30.9°C; CON) and performed a 15-min warm-up prior to a 10 km outdoor running time-trial (Wet Bulb Globe Temperature: 28.2 ± 0.8°C). Mean performance time was faster with ICE (2 715 ± 396 s) than CON (2 730 ± 385 s; P=0.023). Gastrointestinal temperature (Tgi) reduced by 0.5 ± 0.2°C after ICE ingestion compared with 0.1 ± 0.1°C (P<0.001) with CON. During the run, the rate of rise in Tgi was greater (P=0.01) with ICE than with CON for the first 15 min. At the end of time-trial, Tgi was higher with ICE (40.2 ± 0.6°C) than CON (39.8 ± 0.4°C, P=0.005). Ratings of thermal sensation were lower during the cooling phase and for the first kilometre of the run ( - 1.2 ± 0.8; P<0.001). Although ingestion of ice slurry resulted in a transient increase in heat strain following a warm up routine, it is a practical and effective pre-competition cooling manoeuvre to improve performance in warm and humid environments.

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 a euhydrated state and minimize dehydration during exercise. Following the development of commercial cooling systems (e.g., cooling vest), 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.

Self-paced exercise performance in the heat after pre-exercise cold-fluid ingestion.

CONTEXT Precooling is the pre-exercise reduction of body temperature and is an effective method of improving physiologic function and exercise performance in environmental heat. A practical and effective method of precooling suitable for application at athletic venues has not been demonstrated. OBJECTIVE To confirm the effectiveness of pre-exercise ingestion of cold fluid without fluid ingestion during exercise on pre-exercise core temperature and to determine whether pre-exercise ingestion of cold fluid alone without continued provision of cold fluid during exercise can improve exercise performance in the heat. DESIGN Randomized controlled clinical trial. SETTING Environmental chamber at an exercise physiology laboratory that was maintained at 32°C, 60% relative humidity, and 3.2 m/s facing air velocity. PATIENTS OR OTHER PARTICIPANTS Seven male recreational cyclists (age = 21 ± 1.5 years, height = 1.81 ± 0.07 m, mass = 78.4 ± 9.2 kg) participated. INTERVENTION(S) Participants ingested 900 mL of cold (2°C) or control (37°C) flavored water in 3 300-mL aliquots over 35 minutes of pre-exercise rest. MAIN OUTCOME MEASURE(S) Rectal temperature and thermal comfort before exercise and distance cycled, power output, pacing, rectal temperature, mean skin temperature, heart rate, blood lactate, thermal comfort, perceived exertion, and sweat loss during exercise. RESULTS During rest, a greater decrease in rectal temperature was observed with ingestion of the cold fluid (0.41 ± 0.16°C) than the control fluid (0.17 ± 0.17°C) over 35 to 5 minutes before exercise (t(6) = -3.47, P = .01). During exercise, rectal temperature was lower after ingestion of the cold fluid at 5 to 25 minutes (t(6) range, 2.53-3.38, P ≤ .05). Distance cycled was greater after ingestion of the cold fluid (19.26 ± 2.91 km) than after ingestion of the control fluid (18.72 ± 2.59 km; t(6) = -2.80, P = .03). Mean power output also was greater after ingestion of the cold fluid (275 ± 27 W) than the control fluid (261 ± 22 W; t(6) = -2.13, P = .05). No differences were observed for pacing, mean skin temperature, heart rate, blood lactate, thermal comfort, perceived exertion, and sweat loss (P > .05). CONCLUSIONS We demonstrated that pre-exercise ingestion of cold fluid is a simple, effective precooling method suitable for field-based application.

Effects of milk ingestion on prolonged exercise capacity in young, healthy men

OBJECTIVE The effects of fluid intake during prolonged exercise have been extensively studied but at present there exists little information on the effects of milk-based drinks on the response to prolonged exercise. Thus, the purpose of this study was to investigate the effects of milk-based drinks on exercise capacity. METHODS Eight healthy males (age 24 +/- 4 y, height 1.76 +/- 0.04 m, mass 68.9 +/- 9.5 kg, body fat 12.5 +/- 2.4%, peak oxygen consumption 4.3 +/- 0.6 L/min) exercised to volitional exhaustion at 70% peak oxygen consumption on four occasions. Subjects ingested 1.5 mL/kg body mass of plain water, a carbohydrate-electrolyte solution, low-fat (0.1%) milk, or low-fat (0.1%) milk with added glucose before and every 10 min during exercise. The effect of the drink on exercise capacity and the cardiovascular, metabolic, and thermoregulatory responses to prolonged exercise were examined. RESULTS Exercise time to exhaustion was not significantly influenced by the drink ingested (P = 0.19), but there was a tendency for subjects to exercise longer when the carbohydrate-electrolyte (110.6, range 82.0-222.7 min), milk (103.3, range 85.7-228.5 min), or milk plus glucose (102.8, range 74.3-167.1 min) was ingested compared with water (93.3, range 82.4-192.3 min). The solution ingested did not influence the cardiovascular, metabolic, or thermoregulatory response to exercise. CONCLUSION The results of this study suggest that although the low-fat milk-based fluids did not enhance exercise capacity over that seen with the ingestion of plain water, the effect was comparable to that observed with a carbohydrate-electrolyte beverage.

First reported cases of exercise-associated hyponatremia in Asia.

There are no reported cases of exercise-associated hyponatremia (EAH) in tropical Asia. This study aimed to investigate the incidence of EAH at the on-site medical tent and fluid balance in long distance foot races in a warm and humid environment. Body mass was taken before and after the races (42-km marathon; 84-km ultra-marathon). Blood sodium concentration was measured for symptomatic runners admitted to the medical tent. Mean (SD) dry bulb temperature was 29.0 (0.6)°C, relative humidity 89 (2)% and wind speed 0.3 (0.5) m/s. Three out of the 8 symptomatic runners admitted to the medical tent were diagnosed with hyponatremia, with blood sodium concentrations of 134 mmol/L in a 42-km runner, and 131 and 117 mmol/L in two 84-km runners. In the 42-km race, mean % ΔBM was -1.6 (1.2)%, ranging from -5.7 to 1.4%, and 22 runners (7%) gained weight. In the 84-km race, mean % ΔBM was -2.3 (1.7)%, ranging from -8.0 to 1.4%, and 9 runners (8%) gained weight. In addition to the 3 cases of symptomatic hyponatremia observed, 8% of the 84-km runners and 7% of the 42-km runners gained weight during the race. This indicates the need to disseminate advice for the prevention and treatment of EAH for races held in the tropics.

Cold drink attenuates heat strain during work-rest cycles.

There is limited information on the ingestion of cold drinks after exercise. We investigated the thermoregulatory effects of ingesting drinks at 4°C (COLD) or 28°C (WARM) during work-rest cycles in the heat. On 2 separate occasions, 8 healthy males walked on the treadmill for 2 cycles (45 min work; 15 min rest) at 5.5 km/h with 7.5% gradient. Two aliquots of 400 mL of plain water at either 4°C or 28°C were consumed during each rest period. Rectal temperature (T re ), skin temperature (T sk ), heart rate and subjective ratings were measured. Mean decrease in T re at the end of the final work-rest cycle was greater after the ingestion of COLD drinks (0.5±0.2°C) than WARM drinks (0.3±0.2°C; P<0.05). Rate of decrease in T sk was greater after ingestion of COLD drinks during the first rest period (P<0.01). Mean heart rate was lower after ingesting COLD drinks (P<0.05). Ratings of thermal sensation were lower during the second rest phase after ingestion of COLD drinks (P<0.05). The ingestion of COLD drinks after exercise resulted in a lesser than expected reduction of T re . Nevertheless, the reduction in T re implies a potential for improved work tolerance during military and occupational settings in the heat.

The role of fluid temperature and form on endurance performance in the heat.

Exercising in the heat often results in an excessive increase in body core temperature, which can be detrimental to health and endurance performance. Research in recent years has shifted toward the optimum temperature at which drinks should be ingested. The ingestion of cold drinks can reduce body core temperature before exercise but less so during exercise. Temperature of drinks does not seem to have an effect on the rate of gastric emptying and intestinal absorption. Manipulating the specific heat capacity of a solution can further induce a greater heat sink. Ingestion of ice slurry exploits the additional energy required to convert the solution from ice to water (enthalpy of fusion). Body core temperature is occasionally observed to be higher at the point of exhaustion with the ingestion of ice slurry. There is growing evidence to suggest that ingesting ice slurry is an effective and practical strategy to prevent excessive rise of body core temperature and improve endurance performance. This information is especially important when only a fixed amount of fluid is allowed to be carried, often seen in some ultra‐endurance events and military operations. Future studies should evaluate the efficacy of ice slurry in various exercise and environmental conditions.