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Caffeine during Exercise in the Heat: Thermoregulation and Fluid-Electrolyte Balance
Abstract
To investigate the effects of caffeine ingestion on thermoregulation and fluid-electrolyte losses during prolonged exercise in the heat.
Seven endurance-trained ( .VO2max = 61 +/- 8 mL.kg.min) heat-acclimated cyclists pedaled for 120 min at 63% .VO2max in a hot-dry environment (36 degrees C; 29% humidity) on six occasions: 1) without rehydration (NF); 2) rehydrating 97% of sweat losses with water (WAT); 3) rehydrating the same volume with a 6% carbohydrate-electrolytes solution (CES); or combining these treatments with the ingestion of 6 mg caffeine.kg (-1) body weight 45 min before exercise, that is, 4) C(AFF) + NF; 5) C(AFF) + WAT; and 6) C(AFF) + CES.
Without fluid replacement (NF and C(AFF) + NF), final rectal temperature (T(REC)) reached 39.4 +/- 0.1 degrees C, whereas it remained at 38.7 +/- 0.1 degrees C during WAT (CES and C(AFF)+ WAT; (P < 0.05). Caffeine did not alter heat production, forearm skin blood flow, or sweat rate. However, C(AFF) + CES tended to elevate T(REC) above CES alone (38.9 +/- 0.1 degrees C vs 38.6 +/- 0.1 degrees C; P = 0.07). Caffeine ingestion increased sweat losses of sodium, chloride, and potassium ( approximately 14%; P < 0.05) and enlarged urine flow (28%; P < 0.05).
Caffeine ingested alone or in combination with water or a sports drink was not thermogenic or impaired heat dissipation. However, C(AFF) + CES tended to have a higher T(REC) than CES alone. Caffeine increased urine flow and sweat electrolyte excretion, but these effects are not enough to affect dehydration or blood electrolyte levels when exercising for 120 min in a hot environment.
... Overall, results are equivocal, with some showing statistically significant improvements in EP [12,13,23,24], while EP was unaffected by caffeine intake in others [14,[25][26][27][28][29][30][31]. On the other hand, results of some studies suggest that caffeine supplementation may increase resting energy expenditure [32,33], diuresis [34,35], and oxygen consumption [36], decrease sweat rate [35] and ad libitum fluid intake [35], and impair cutaneous blood flow [37], all of which singularly or in combination may contribute to increase heat stress during exercise. Because of the potential role played by heat strain in performance deterioration [18], several investigations have therefore examined the impact of preexercise caffeine intake on C T regulation during exercise [12-14, 23-25, 27-29, 33-35, 38-42]. ...
... The studies were published between 1994 and 2021 in nine different peer-reviewed journals. Seven studies were conducted in the USA [23-27, 35, 38] and one in each of the following countries: Australia [42], Belgium [29], Japan [39], Malaysia [13], Spain [34], and the UK [12]. ...
... The characteristics of studies that evaluated the impact of caffeine on C T regulation protocols were: caffeine dose of 6 ± 2 mg/kg body mass, elapsed time between the placebo or caffeine intake and onset of exercise of 58 ± 14 min, caffeine restriction time leading to the experiments of 43 ± 35 h (n = 10), ambient temperature and relative humidity of 34 ± 4 °C and 46 ± 13%, respectively, exercise duration of 70 ± 24 min and exercise intensity of 55 ± 8% V O 2peak . Wind speed was reported in only three studies [23,34,42]; therefore, these values are not presented. Exercise protocols consisted of either a running time-trial [26,27], a fixed-intensity cycling or walking period [24,34,35,38,39,42], a pre-load cycling period followed by a time-trial [12,23,25,29], or a running test to exhaustion [13]. ...
Background
Heat is associated with physiological strain and endurance performance (EP) impairments. Studies have investigated the impact of caffeine intake upon EP and core temperature (CT) in the heat, but results are conflicting. There is a need to systematically determine the impact of pre-exercise caffeine intake in the heat.
Objective
To use a meta-analytical approach to determine the effect of pre-exercise caffeine intake on EP and CT in the heat.
Design
Systematic review with meta-analysis.
Data Sources
Four databases and cross-referencing.
Data Analysis
Weighted mean effect summaries using robust variance random-effects models for EP and CT, as well as robust variance meta-regressions to explore confounders.
Study Selection
Placebo-controlled, randomized studies in adults (≥ 18 years old) with caffeine intake at least 30 min before endurance exercise ≥ 30 min, performed in ambient conditions ≥ 27 °C.
Results
Respectively six and 12 studies examined caffeine’s impact on EP and CT, representing 52 and 205 endurance-trained individuals. On average, 6 mg/kg body mass of caffeine were taken 1 h before exercises of ~ 70 min conducted at 34 °C and 47% relative humidity. Caffeine supplementation non-significantly improved EP by 2.1 ± 0.8% (95% CI − 0.7 to 4.8) and significantly increased the rate of change in CT by 0.10 ± 0.03 °C/h (95% CI 0.02 to 0.19), compared with the ingestion of a placebo.
Conclusion
Caffeine ingestion of 6 mg/kg body mass ~ 1 h before exercise in the heat may provide a worthwhile improvement in EP, is unlikely to be deleterious to EP, and trivially increases the rate of change in CT.
... Overall, results are equivocal, with some showing statistically significant improvements in EP [12, 13, 23, 24] while others did not [14,[25][26][27][28][29][30][31]. On the other hand, results of some studies suggest that caffeine supplementation may increase resting energy expenditure [32,33], diuresis [34,35], oxygen consumption [36], decrease sweat rate [35] and ad libitum fluid intake [35] and impair cutaneous blood flow [37], all of which singularly or in combination may contribute to increase heat stress during exercise. Because of the potential role played by heat strain on performance deterioration [18], several investigations have therefore examined the impact of pre-exercise caffeine intake on core body temperature (CT) regulation during exercise [12-14, 23-25, 27-29, [33][34][35][38][39][40][41][42]. ...
... On the other hand, results of some studies suggest that caffeine supplementation may increase resting energy expenditure [32,33], diuresis [34,35], oxygen consumption [36], decrease sweat rate [35] and ad libitum fluid intake [35] and impair cutaneous blood flow [37], all of which singularly or in combination may contribute to increase heat stress during exercise. Because of the potential role played by heat strain on performance deterioration [18], several investigations have therefore examined the impact of pre-exercise caffeine intake on core body temperature (CT) regulation during exercise [12-14, 23-25, 27-29, [33][34][35][38][39][40][41][42]. ...
... Mean power output in the caffeine condition (W) -mean power output in the placebo condition 34,35,38] regions; these areas provide slightly different figures of CT during exercise. However, this is irrelevant in the context of the current meta-analysis where we were focused on changes in CT within each of the included studies. ...
Background: Heat is associated with physiological strain and endurance performance (EP) impairments. Studies have investigated the impact of caffeine intake upon EP and core temperature (CT) in the heat, but results are conflicting. There is a need to systematically determine the impact of pre-exercise caffeine intake in the heat.
Objective: Use a meta-analytical approach to determine the effect of pre-exercise caffeine intake on EP and CT in the heat.
Design: Systematic review with meta-analysis.
Data sources: Four databases and cross-referencing.
Data analysis: Weighted mean effect summaries using random-effects models for EP and CT, as well as meta regressions with robust standard errors to explore confounders.
Study selection: Placebo-controlled, randomized studies in adults (≥ 18 yrs old) with caffeine intake at least 30 min before endurance exercise ≥ 30 min, performed in ambient conditions ≥ 27°C.
Results: Respectively 6 and 12 studies examined caffeine's impact on EP and CT, representing 52 and 205 endurance-trained individuals. On average, 6 mg/kg body mass of caffeine were taken 1 h before exercises of 70 min conducted at 34°C and 47% relative humidity. Caffeine supplementation improved EP by 2.0 +/- 0.7% (95% CI: 0.6 to 3.5%) and increased the rate of change in CT by 0.10 +/- 0.04°C/h (95% CI: 0.03 to 0.16°C/h), compared with the ingestion of a placebo.
Conclusion: Caffeine ingestion of 6 mg/kg body mass 1 h before an exercise in the heat provides a worthwhile improvement in EP of 2%, while trivially increasing the rate of change in CT by 0.10°C/h.
... Furthermore, the mean skin temperature and HR did not show significant differences between the conditions. These results were similar to previous results, which revealed that caffeine had no effect on the thermoregulatory responses, such as an increase in the core temperature, forearm skin blood flow, and mean skin temperature, compared with the placebo condition, during exercise in hot conditions (Del Coso et al., 2009;Hanson et al., 2019;Pitchford et al., 2014). A previous study suggested that caffeine ingestion significantly induced an increase in whole-body sweat loss by passive heating (Kim and Lee, 2013) and thermoneutral condition (Kim et al., 2011), but another study suggested that the sweating response during exercise in a hot environment was not affected by caffeine intake (Del Coso et al., 2009). ...
... These results were similar to previous results, which revealed that caffeine had no effect on the thermoregulatory responses, such as an increase in the core temperature, forearm skin blood flow, and mean skin temperature, compared with the placebo condition, during exercise in hot conditions (Del Coso et al., 2009;Hanson et al., 2019;Pitchford et al., 2014). A previous study suggested that caffeine ingestion significantly induced an increase in whole-body sweat loss by passive heating (Kim and Lee, 2013) and thermoneutral condition (Kim et al., 2011), but another study suggested that the sweating response during exercise in a hot environment was not affected by caffeine intake (Del Coso et al., 2009). Indeed, we found no significant difference in the sweat volume between conditions (caffeine, 2.9 ± 0.6 L; placebo, 2.8 ± 0.7 L; d = 0.13). ...
... experimental protocol, such as the passive or active heat stress, resting levels, or exercise type. Thus, our results were in line with the corresponding of Del Coso et al. (2009), who showed that the ingestion of caffeine did not affect the sweat loss amount, suggesting that a low caffeine dose (3 mg ⋅ kg − 1 ) had no effect on the thermoregulatory response during prolonged intermittent exercise in hot and humid environments. Considering these results, the reasons for the improvement of intermittent sprint performance in our study could be explained by the fact that a low caffeine dose ingestion did not affect the thermoregulatory responses compared to the placebo condition and, thus, did not attenuate its ergogenic effect on exercise in hot and humid environments. ...
While the effects of caffeine have been evaluated in relation to endurance exercise, few studies have assessed the ergogenic effects of low caffeine doses on intermittent exercise performance in hot and humid environments. Thus, we aimed to determine the effects of low-dose caffeine supplementation on intermittent exercise performance under these conditions. Eight male soccer players (age, 19.9 ± 0.3 years; height, 173.7 ± 6.3 cm; body mass, 65.1 ± 5.5 kg; VO2max, 50.0 ± 3.1 mL kg⁻¹ min⁻¹) participated in this double-blind, randomized, cross-over study. Caffeine was orally administered at 60 min before exercise (dosage, 3 mg kg⁻¹). The participants completed a 90-min intermittent sprint cycling protocol under two conditions (after receiving caffeine and placebo) at 32 °C and at 70% relative humidity. A significant improvement in the total amount of work was observed in the caffeine condition compared to the placebo condition (155.0 ± 15.8 vs 150.8 ± 14.5 kJ, respectively; p < 0.05, d = 0.28). In contrast, the rectal temperature measured at the end of exercise showed no significant difference between the conditions (38.9 ± 0.4 °C and 38.7 ± 0.5 °C in the caffeine and placebo conditions, respectively; p > 0.05, d = 0.57). Other thermal responses, such as the mean skin temperature, heart rate, or sweat volume, were not significantly different between these conditions. These results suggested that a low caffeine dose improved the intermittent sprint performance and the reasons could be explained by the fact that a low caffeine dose ingestion did not affect the thermoregulatory responses compared to the placebo condition and, thus, did not attenuate its ergogenic effect on exercise in hot and humid environments.
... Some investigations have reported an increase in core temperature following caffeine ingestion during exercise in the heat (Cheuvront et al., 2009;Ely et al., 2011;Kim et al., 2011;Millard-Stafford et al., 2007), but often these increases are observed at rest and the change in heat storage during exercise is similar to placebo conditions (Cheuvront et al., 2009;Ely et al., 2011;Kim et al., 2011). In contrast, several studies have shown that caffeine, in doses ranging from 3 to 9 mg kg −1 (∼250-700 mg), has no effect on the core temperature response during prolonged exercise in normal (∼20 • C) (Dunagan et al., 1998;Ganio et al., 2011a), warm (∼25-30 • C) (Falk et al., 1990;Wells et al., 1985) or hot environments (>30 • C) (Del Coso et al., 2009;Ganio et al., 2011a;Roti et al., 2006;Wemple et al., 1997). In addition, caffeine does not influence forearm blood flow (Del Coso et al., 2009), sweat rate or fluid-electrolyte balance (Del Coso et al., 2009;Ganio et al., 2011a;Millard-Stafford et al., 2007;Roti et al., 2006;Wemple et al., 1997), urine production (Ganio et al., 2011a;Millard-Stafford et al., 2007;Wemple et al., 1997) or heat storage during exercise in the heat. ...
... In contrast, several studies have shown that caffeine, in doses ranging from 3 to 9 mg kg −1 (∼250-700 mg), has no effect on the core temperature response during prolonged exercise in normal (∼20 • C) (Dunagan et al., 1998;Ganio et al., 2011a), warm (∼25-30 • C) (Falk et al., 1990;Wells et al., 1985) or hot environments (>30 • C) (Del Coso et al., 2009;Ganio et al., 2011a;Roti et al., 2006;Wemple et al., 1997). In addition, caffeine does not influence forearm blood flow (Del Coso et al., 2009), sweat rate or fluid-electrolyte balance (Del Coso et al., 2009;Ganio et al., 2011a;Millard-Stafford et al., 2007;Roti et al., 2006;Wemple et al., 1997), urine production (Ganio et al., 2011a;Millard-Stafford et al., 2007;Wemple et al., 1997) or heat storage during exercise in the heat. Further, there is no evidence to support the contention that chronic consumption of caffeine alters fluid-electrolyte balance or hydration status (Armstrong, 2002;Maughan and Griffin, 2003;Roti et al., 2006). ...
... In contrast, several studies have shown that caffeine, in doses ranging from 3 to 9 mg kg −1 (∼250-700 mg), has no effect on the core temperature response during prolonged exercise in normal (∼20 • C) (Dunagan et al., 1998;Ganio et al., 2011a), warm (∼25-30 • C) (Falk et al., 1990;Wells et al., 1985) or hot environments (>30 • C) (Del Coso et al., 2009;Ganio et al., 2011a;Roti et al., 2006;Wemple et al., 1997). In addition, caffeine does not influence forearm blood flow (Del Coso et al., 2009), sweat rate or fluid-electrolyte balance (Del Coso et al., 2009;Ganio et al., 2011a;Millard-Stafford et al., 2007;Roti et al., 2006;Wemple et al., 1997), urine production (Ganio et al., 2011a;Millard-Stafford et al., 2007;Wemple et al., 1997) or heat storage during exercise in the heat. Further, there is no evidence to support the contention that chronic consumption of caffeine alters fluid-electrolyte balance or hydration status (Armstrong, 2002;Maughan and Griffin, 2003;Roti et al., 2006). ...
Caffeine is consumed by over 80% of U.S. adults. This review examines the effects caffeine has on cognitive and physical function, since most real-world activities require complex decision making, motor processing and movement. Caffeine exerts its effects by blocking adenosine receptors. Following low (∼40mg or ∼0.5 mg·kg(-1)) to moderate (∼300mg or 4 mg·kg(-1)) caffeine doses, alertness, vigilance, attention, reaction time and attention improve, but less consistent effects are observed on memory and higher-order executive function, such as judgement and decision making. Effects on physical performance on a vast array of physical performance metrics such as time-to-exhaustion, time-trial, muscle strength and endurance, and high-intensity sprints typical of team sports are evident following doses that exceed about 200mg (∼3mg·kg(-1)). Many occupations, including military, first responders, transport workers and factory shift workers, require optimal physical and cognitive function to ensure success, workplace safety and productivity. In these circumstances, that may include restricted sleep, repeated administration of caffeine is an effective strategy to maintain physical and cognitive capabilities.
... However, its diuretic effect is hardly appreciable in sportsmen and other people who take 2-3 servings of coffee (200-300 mg caffeine) per day. In recent studies 28 carried out in heat-acclimated cyclists pedaling for two hours at 63% VO2max in a hot-dry environment, the ingestion of 6 mg caffeine/kg weight as a supplement 45 min before the exercise increased the diuretic effect (28%) and the loss of the electrolytes sodium (Na), chlorine (Cl), and potassium (K) (14%) was also augmented. But these effects decreased if the caffeine was ingested as an ingredient of an isotonic drink, during two hours of exercise in a 36ºC atmosphere. ...
... But these effects decreased if the caffeine was ingested as an ingredient of an isotonic drink, during two hours of exercise in a 36ºC atmosphere. Despite its diuretic effect in repose, its diuretic effect during physical activity is unclear and further studies are needed to verify this effect in athletes, especially in those participating in very long distance races and those not acclimated to heat 28 . ...
... Concerning other ingredients found in energy drinks widely used for sport, caffeine at high doses (more than 300-500 mg), as well as other diuretic products (tea or tea extracts), can increase fluid and electrolytes excretion 28 . Taurine supplementation significantly decreased the enzyme activity of CYP and so probably interacts with some drugs, as has been observed for caffeine 44 . ...
Before, during and after physical activity, hydration is a limiting factor in athletic performance. Therefore, adequate hydration provides benefits for health and performance of athletes. Besides, hydration is associated to the intake of carbohydrates, protein, sodium, caffeine and other substances by different dietary aids, during the training and/or competition by athletes. These requirements have led to the development of different products by the food industry, to cover the nutritional needs of athletes. Currently in the European context, the legal framework for the development of products, substances and health claims concerning to sport products is incomplete and scarce. Under these conditions, there are many products with different ingredients out of European Food Safety Authority (EFSA) control where claims are wrong due to no robust scientific evidence and it can be dangerous for the health. Further scientific evidence should be constructed by new clinical trials in order to assist to the Experts Commitees at EFSA for obtaining robust scientific opinions concerning to the functional foods and the individual ingredients for sport population.
Copyright AULA MEDICA EDICIONES 2014. Published by AULA MEDICA. All rights reserved.
... Although exercise reduces urine formation, if fluid ingestion during prolonged exercise in the heat is enough to prevent dehydration, urine flow during exercise could reach the same levels as when at rest. 39 Some investigators have wondered whether the inclusion of caffeine in a rehydration drink could negatively affect fluid balance and,hence,thermoregulation during exercise.During prolonged exercise in a controlled hot environment (i.e., 33°C), male cyclists were invited to replace fluid losses (3.6 L) by consuming one of the following drinks: 1) water, 2) water + caffeine, 3) sports drink, 4) or sports drink + caffeine ( Figure 1). 39 Trials were compared to no fluid replacement (NF) with or without caffeine pills. ...
... 39 Some investigators have wondered whether the inclusion of caffeine in a rehydration drink could negatively affect fluid balance and,hence,thermoregulation during exercise.During prolonged exercise in a controlled hot environment (i.e., 33°C), male cyclists were invited to replace fluid losses (3.6 L) by consuming one of the following drinks: 1) water, 2) water + caffeine, 3) sports drink, 4) or sports drink + caffeine ( Figure 1). 39 Trials were compared to no fluid replacement (NF) with or without caffeine pills. When dehydration was not prevented (NF trials), urine production was found to be very low and adding caffeine had no diuretic effect.When subjects drank the sports drink,urine production increased, but caffeine added to the sports drink had no diuretic effect either.It is possible that the salt included in the sports drink counteracted the diuretic effects of the caffeine. ...
... However, when caffeine was added to water, urine production increased by 37% (Figure 1). 39 This increase in fluid losses via urine did not affect whole-body fluid balance, since urination represented a small percentage of total fluid loss (mostly sweat). Nevertheless, caffeine tended to increase core temperature when it was combined with the sports drink. ...
Energy drinks are increasingly popular among athletes and others. Advertising for these products typically features images conjuring great muscle power and endurance; however, the scientific literature provides sparse evidence for an ergogenic role of energy drinks. Although the composition of energy drinks varies, most contain caffeine; carbohydrates, amino acids, herbs, and vitamins are other typical ingredients. This report analyzes the effects of energy drink ingredients on prolonged submaximal (endurance) exercise as well as on short-term strength and power (neuromuscular performance). It also analyzes the effects of energy drink ingredients on the fluid and electrolyte deficit during prolonged exercise. In several studies, energy drinks have been found to improve endurance performance, although the effects could be attributable to the caffeine and/or carbohydrate content. In contrast, fewer studies find an ergogenic effect of energy drinks on muscle strength and power. The existing data suggest that the caffeine dose given in studies of energy drinks is insufficient to enhance neuromuscular performance. Finally, it is unclear if energy drinks are the optimal vehicle to deliver caffeine when high doses are needed to improve neuromuscular performance.
... There is evidence to suggest that caffeine supplementation is associated with increased core temperature, heart rate and sweat rate when compared to a placebo at a set work rate. 5,14,15 Thus plausible reasons for any lack of benefit from high dose caffeine under hot conditions may be due to some of the metabolic effects associated with caffeine such as increased core temperature 8 due to increased work output, or by affecting diuresis or sweat rate. 15,16 Caffeine supplementation has, in some cases, been shown to cause a greater rise in core temperature during steady-state endurance exercise in a hot environment compared with a placebo, 8 studies show only very subtle perturbations in body temperature and heat storage resulting from caffeine ingestion prior to exercise in the heat. ...
... 5,14,15 Thus plausible reasons for any lack of benefit from high dose caffeine under hot conditions may be due to some of the metabolic effects associated with caffeine such as increased core temperature 8 due to increased work output, or by affecting diuresis or sweat rate. 15,16 Caffeine supplementation has, in some cases, been shown to cause a greater rise in core temperature during steady-state endurance exercise in a hot environment compared with a placebo, 8 studies show only very subtle perturbations in body temperature and heat storage resulting from caffeine ingestion prior to exercise in the heat. 7,17 Nevertheless, it is possible that when exercise is performed in a hot environment, the ergogenic effects of caffeine are negated due to elevations in physiological variables such as body temperature, heart rate and sweat rate. ...
... This is inconsistent with earlier literature which has shown that caffeine does not influence fluid loss and sweat rates during exercise in both standard laboratory conditions 18 or hot environments. 15 Cyclists in the present study ingested the same amount of fluid and had the same body weight losses between trials, suggesting that caffeine did not increase sweat rate. Indeed, dehydration in the range reported in the current study (<2%) is unlikely to impair endurance performance. ...
The purpose of this investigation was to determine whether a moderate dose of caffeine would improve a laboratory simulated cycling time-trial in the heat.
Nine well-trained male subjects (VO2max 64.4±6.8mLmin(-1)kg(-1), peak power output 378±40W) completed one familiarisation and two experimental laboratory simulated cycling time-trials in environmental conditions of 35°C and 25% RH 90min after consuming either caffeine (3mgkg(-1) BW) or placebo, in a double blind, cross-over study.
Time-trial performance was faster in the caffeine trial compared with the placebo trial (mean±SD, 3806±359s versus 4079±333s, p=0.06, 90%CI 42-500s, 86% likelihood of benefit, d=-0.79). Caffeine ingestion was associated with small to moderate increases in average heart rate (p=0.178, d=0.39), VO2 (p=0.154, d=0.45), respiratory exchange ratio (p=0.292, d=0.35) and core temperature (p=0.616, d=0.22) when compared to placebo, however, these were not statistically significant. Average RPE during the caffeine supplemented time-trial was not significantly different from placebo (p=0.41, d=-0.13).
Caffeine supplementation at 3mgkg(-1) BW resulted in a worthwhile improvement in cycling time-trial performance in the heat.
... Among these ergogenic aids, Caffeine ingestion is highly prevalent among combat athletes [2,3] and this phenomenon has not been studied in judo either of Olympic combats considering real training situations. A full literature review did not demonstrate any research addressing caffeine ingestion and judo performance during the competitive season [4][5][6][7]. To obtain information for conditioning and strength training it is important to highlight that open task and intermittent sports training involve complex specific and cognitive skills over a prolonged period of time (120min), with high-intensity efforts (e.g. ...
... In agreement with these results, Armstrong et al. [21] state that caffeine does not result in excessive dehydration, hyperthermia, or impaired performance for exercise in hot conditions. Our results also corroborate the findings of Del Coso et al. [4], who observed that caffeine does not increase dehydration or diuresis, even when exercise is performed in hot environments, as the release of the antidiuretic hormone during exercise is possibly more potent than the diuretic action of caffeine [46]. Nevertheless, we emphasize that there is no scientific data to support the safety and effectiveness of chronic caffeine supplementation [26]. ...
Background
Nutritional ergogenic aids are foods or nutrients that can improve physical performance. Among these foods with ergogenic properties, caffeine has shown that it can increase the fat catabolism, strength, and improve the cognition and time reaction of an athlete, therefore, it is hoped that it can improve the performance of judokas. This study through a double-blind crossover (supplement X placebo) protocol, investigated the effects caffeine supplementation (single capsule containing 5 mg/kg body mass intake 60 min before the session) on biochemical, anthropometrical, physical, subjective and hemodynamic variables measured before, during and after two typical judo trainingcxs sessions (120-min: 40-min of gymnastics; 40-min of specific technics and; 40-min of judo combat).
Methods
8 high-level athletes (21.4 ± 2.0 years; 83.6 ± 15.2 kg; 1.8 ± 0.1 m; 17.9 ± 7.0 Fat%) were evaluated before and after each training for body mass, hydration, upper and lower limb power, performance in the special judo fitness test (SJFT), free fatty acids (FFA) in plasma, uric acid, glucose, lactate, heart rate, and pain. In addition, heart rate, FFA in plasma, uric acid, glucose, lactate, rating of perceived exertion and pain were assessed during the training.
Results
At 120 min, supplementation resulted in a higher concentration of plasma FFA (1.5 ± 0.5 vs. 1.0 ± 0.3 mmol/L; p = 0.047) and lactate (4.9 ± 1.8 vs. 3.0 ± 1.2 mmol/L; p = 0.047), and a lower concentration of uric acid (5.4 ± 0.9 vs. 7.0 ± 1.5 mg/dL; p = 0.04). Supplementation also resulted in performance maintenance (fatigue index) in the SJFT (Δ0.3 ± 2.0 vs Δ1.7 ± 2.5, for caffeine and placebo respectively, p = 0.046). No adverse effects were observed.
Conclusion
Based on the applied dose, intake time, and sample of this study, we can conclude that caffeine produces an ergogenic biochemical effect, and improves performance in judo athletes.
... In our study, SR increased during the thermoneutral condition when caffeine was ingested, which is comparable to what Kim et al. (2011) reported, but was lower after consumption of caffeine during the heat exposure condition. Our finding is in line with Del Coso et al. (Del Coso et al., 2009) but the combined evidence demonstrates uncertainty or lack of overall consistency. Our findings were likely driven by heat and caffeine's effects on water intake and urine volume: within both ambient conditions, caffeine increased urine volume acutely, but our caffeine dose was greater than what Seal et al. (7.5 mg/kg vs. 6 mg/kg) used (Seal et al., 2017). ...
... Although caffeine's effects on BP and SR/hydration varied across the two ambient conditions, caffeine's effect on T msk was null under both conditions. This is in agreement with previous studies examining skin temperature in cyclists (Del Coso et al., 2009;Ganio et al., 2011). ...
This study tested the interactive effects of heat and caffeine on exercise-induced physiological strain by using a 2x2 within-subjects factorial design. Thirty-five physically fit Caucasians underwent a bout of exercise under four conditions wherein ambient conditions (heat vs no heat) and caffeine (placebo vs caffeine; double-blinded) were manipulated. Exercise consisted of a 60-min walk and 5-min step/squat test while wearing weighted backpack. Primary outcomes include measures of physiologic strain (Core temperature [Tr] and heart rate [HR]). Secondary measures included blood pressure, markers of sweat loss, and creatine kinase (CK). Repeated measures models were created to evaluate the individual and combined effects of heat and caffeine. Key results indicated that heat and caffeine significantly increased Tr and HR after walking and stair-stepping. No significant heat by caffeine interactions were detected, and caffeine's main effects were relatively low (≤0.17 °C for Tr and ≤6.6 bpm for HR). Of note, heat and caffeine exhibited opposite effects on blood pressure: caffeine increased both systolic and diastolic blood pressure (by 6–7 mm Hg) and heat decreased them (by 4–6 mm Hg; ps < 0.05). In summary, heat and caffeine affected physiologic strain during exercise but exhibited no synergistic effects. In contrast, neither factor affected muscle damage. Clinical implications for heat illness risk in the military are discussed.
... 4 It can induce an increase in tympanic and body temperature through thermogenesis, activating the skin's propensity to sweat. 5 Del Coso et al. 6 observed that caffeine intake (6 mg/kg) during a bike test at 60% VO 2 max for two hours had no effect on sweat rate, and this result was independent of rehydration routines. Moreover, in men undergoing cycleergometer exercise, the consumption of a high concentration (10 mg/kg) of caffeine did not modify sweating rate or rectal temperature. ...
... Similarly, Roti et al. 24 observed no difference with caffeine supplementation of 3 and 6 mg/kg in subjects walking on a treadmill (see also Del Coso et al. 6 referenced previously). However, future studies might investigate the long-term effects of rehydration associated with caffeine supplementation 25 in order to evaluate the impact of prior liquid and caffeine intake on the rate of sweating in ballet dancers. ...
This study sought to investigate the effect of oral caffeine supplementation on sweat rate and blood pressure in ballet dancers. A double-blind study with placebo control was conducted with nine professional ballet dancers (average age: 28.5 ± 8.8 years). Oral caffeine supplementation (400 mg per dancer, 6.3 mg/kg, range: 4.9 to 8.6 mg/kg) was ingested one hour before a ballet session that was 5 hours in length. After 3 days a second 5-hour session was performed prior to which a placebo was given to the participants. Body weight, sweat rate, and blood pressure were measured before and after each session. Student's t-tests and ANOVAs were used to assess statistical differences. Results were considered significant at p < 0.05. It was found that acute caffeine supplementation did not change any of the variables when compared to placebo.
... The extension of time-to-task failure in this open-ended single-leg knee extensor task after caffeine ingestion was correlated with MEP amplitude at the start of exercise, clearly implicating an increased corticospinal excitability as an important mechanism of caffeine's action. Caffeine has also consistently been shown to increase central drive, measured as knee extensor voluntary activation (VA), in both fresh (14,15) and fatigued (15) muscle, and a meta-analysis (1) indicates a moderate-to largeeffect size of caffeine on VA (0.67 effect size). ...
... The extension of time-to-task failure in this open-ended single-leg knee extensor task after caffeine ingestion was correlated with MEP amplitude at the start of exercise, clearly implicating an increased corticospinal excitability as an important mechanism of caffeine's action. Caffeine has also consistently been shown to increase central drive, measured as knee extensor voluntary activation (VA), in both fresh (14,15) and fatigued (15) muscle, and a meta-analysis (1) indicates a moderate-to largeeffect size of caffeine on VA (0.67 effect size). ...
Background
Caffeine has been shown to enhance exercise performance and capacity. The mechanisms remain unclear but are suggested to relate to adenosine receptor antagonism, resulting in increased central motor drive, reduced perception of effort, and altered peripheral processes such as enhanced calcium handling and extracellular potassium regulation. Our aims were to investigate how caffeine (i) affects knee extensor PCr kinetics and pH during repeated sets of single-leg knee extensor exercise to task failure and (ii) modulates the interplay between central and peripheral neural processes. We hypothesized that the caffeine-induced extension of exercise capacity during repeated sets of exercise would occur despite greater disturbance of the muscle milieu due to enhanced peripheral and corticospinal excitatory output, central motor drive, and muscle contractility.Methods
Nine healthy active young men performed five sets of intense single-leg knee extensor exercise to task failure on four separate occasions: for two visits (6 mg·kg−1 caffeine vs placebo), quadriceps 31P-magnetic resonance spectroscopy scans were performed to quantify phosphocreatine kinetics and pH, and for the remaining two visits (6 mg·kg−1 caffeine vs placebo), femoral nerve electrical and transcranial magnetic stimulation of the quadriceps cortical motor area were applied pre- and post exercise.ResultsThe total exercise time was 17.9 ± 6.0% longer in the caffeine (1,225 ± 86 s) than in the placebo trial (1,049 ± 73 s, p = 0.016), and muscle phosphocreatine concentration and pH (p < 0.05) were significantly lower in the latter sets of exercise after caffeine ingestion. Voluntary activation (VA) (peripheral, p = 0.007; but not supraspinal, p = 0.074), motor-evoked potential (MEP) amplitude (p = 0.007), and contractility (contraction time, p = 0.009; and relaxation rate, p = 0.003) were significantly higher after caffeine consumption, but at task failure MEP amplitude and VA were not different from placebo. Caffeine prevented the reduction in M-wave amplitude that occurred at task failure (p = 0.039).Conclusion
Caffeine supplementation improved high-intensity exercise tolerance despite greater-end exercise knee extensor phosphocreatine depletion and H+ accumulation. Caffeine-induced increases in central motor drive and corticospinal excitability were attenuated at task failure. This may have been induced by the afferent feedback of the greater disturbance of the muscle milieu, resulting in a stronger inhibitory input to the spinal and supraspinal motor neurons. However, causality needs to be established through further experiments.
... Given the established benefits of caffeine on aerobic-endurance based activities [1,2,3], the latter seems highly unlikely. In contrast, the idea of an increase in energy turnover forms part of the rationale for those studies that have investigated potential debilitative effects of caffeine on exercise tolerance in hot environments [38][39][40][41][42]. Despite a couple of exceptions [38,39], and a recurring theme of poor sample sizes and issues with experimental design [40]; there is little evidence of any caffeine-induced increases in metabolic rate or core temperature under those conditions [40][41][42]. ...
... In contrast, the idea of an increase in energy turnover forms part of the rationale for those studies that have investigated potential debilitative effects of caffeine on exercise tolerance in hot environments [38][39][40][41][42]. Despite a couple of exceptions [38,39], and a recurring theme of poor sample sizes and issues with experimental design [40]; there is little evidence of any caffeine-induced increases in metabolic rate or core temperature under those conditions [40][41][42]. Then again, and in contrast to the general consensus, those same studies have also mostly reported no effect of caffeine on sustained high-intensity aerobic exercise [38][39][40]. ...
Objectives:
The aim of this study was to evaluate the effects of caffeine on physiological responses to submaximal exercise, with a focus on blood lactate concentration ([BLa]).
Methods:
Using a randomised, single-blind, crossover design; 16 endurance-trained, male cyclists (age: 38 ± 8 years; height: 1.80 ± 0.05 m; body mass: 76.6 ± 7.8 kg; [Formula: see text]: 4.3 ± 0.6 L∙min-1) completed four trials on an electromagnetically-braked cycle ergometer. Each trial consisted of a six-stage incremental test (3 minute stages) followed by 30 minutes of passive recovery. One hour before trials 2-4, participants ingested a capsule containing 5 mg∙kg-1 of either caffeine or placebo (maltodextrin). Trials 2 and 3 were designed to evaluate the effects of caffeine on various physiological responses during exercise and recovery. In contrast, Trial 4 was designed to evaluate the effects of caffeine on [BLa] during passive recovery from an end-exercise concentration of 4 mmol∙L-1.
Results:
Relative to placebo, caffeine increased [BLa] during exercise, independent of exercise intensity (mean difference: 0.33 ± 0.41 mmol∙L-1; 95% likely range: 0.11 to 0.55 mmol∙L-1), but did not affect the time-course of [BLa] during recovery (p = 0.604). Caffeine reduced ratings of perceived exertion (mean difference: 0.5 ± 0.7; 95% likely range: 0.1 to 0.9) and heart rate (mean difference: 3.6 ± 4.2 b∙min-1; 95% likely range: 1.3 to 5.8 b∙min-1) during exercise, with the effect on the latter dissipating as exercise intensity increased. Supplement × exercise intensity interactions were observed for respiratory exchange ratio (p = 0.004) and minute ventilation (p = 0.034).
Conclusions:
The results of the present study illustrate the clear, though often subtle, effects of caffeine on physiological responses to submaximal exercise. Researchers should be aware of these responses, particularly when evaluating the physiological effects of various experimental interventions.
... Ten studies recruited male participants exclusively, with the remaining recruiting either female participants exclusively (n = 2) or mixed groups (n = 4). Except for one study, 18 most studies recruited young participants with a median age of 27 yr (min-max: [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. Most studies (n = 13) employed crossover designs. ...
... Half of the studies monitored treatment effect over 12 h, and the remaining half explored acute treatment effect (mode = 3 h). Participants were either in free living, 12,25-27 free living plus exercise, 28 exercise, 29,30 or rest 6,13,18,31-36 conditions for the duration of the main data collection period. ...
Objectives
Although ergogenic, acute caffeine ingestion may increase urine volume, prompting concerns about fluid balance during exercise and sport events. This meta-analysis evaluated caffeine induced diuresis in adults during rest and exercise.
Design
Meta-analysis.
Methods
A search of three databases was completed on November 1, 2013. Only studies that involved healthy adults and provided sufficient information concerning the effect size (ES) of caffeine ingestion on urine volume were included. Sixteen studies met the inclusion criteria, providing a total of 28 ESs for the meta-analysis. Heterogeneity was assessed using a random-effects model.
Results
The median caffeine dosage was 300 mg. The overall ES of 0.29 (95% confidence interval (CI) = 0.11-0.48, p = 0.001) corresponds to an increase in urine volume of 109 ± 195 mL or 16.0 ± 19.2% for caffeine ingestion vs. non-caffeine conditions. Subgroup meta-analysis confirmed exercise as a strong moderator: active ES = 0.10, 95% CI = -0.07-0.27, p = 0.248 vs. resting ES = 0.54, 95% CI = 0.22-0.85, p = 0.001 (Cochran's Q, p = 0.019). Females (ES = 0.75, 95% CI = 0.38-1.13, p < 0.001) were more susceptible to diuretic effects than males (ES = 0.13, 95% CI = -0.05-0.31, p = 0.158) (Cochran's Q, p = 0.003).
Conclusions
Caffeine exerted a minor diuretic effect which was negated by exercise. Concerns regarding unwanted fluid loss associated with caffeine consumption are unwarranted particularly when ingestion precedes exercise.
... Caffeinated beverages are routinely consumed for their beneficial effects on mood, alertness, cognition, and physical performance. Also, contrary to popular belief, several studies have shown that caffeinated fluids contribute to hydration in a similar manner to noncaffeinated fluids (26,133,202). To determine the effects of caffeinated beverages on hydration status, Grandjean et al. (202) had 19 to 39 year old free-living men (participating in light exercise only) consume various combinations of caffeinated and noncaffeinated beverages, including water only; water and caffeinated cola; water, caffeinated cola, and instant coffee; or water and noncaffeinated citrus soft drink; in a counterbalanced, crossover manner for one 24-h period. ...
... Because caffeine is a sympathetic nervous system stimulant and is a mild diuretic, athletes are sometimes advised to abstain from caffeine. However, research has shown that moderate caffeine intake (<∼450 mg) does not result in chronic water/electrolyte imbalances, reduced exercise-heat tolerance, or an increased risk of heat illnesses (22,26,133). ...
The objective of this article is to provide a review of the fundamental aspects of body fluid balance and the physiological consequences of water imbalances, as well as discuss considerations for the optimal composition of a fluid replacement beverage across a broad range of applications. Early pioneering research involving fluid replacement in persons suffering from diarrheal disease and in military, occupational, and athlete populations incurring exercise- and/or heat-induced sweat losses has provided much of the insight regarding basic principles on beverage palatability, voluntary fluid intake, fluid absorption, and fluid retention. We review this work and also discuss more recent advances in the understanding of fluid replacement as it applies to various populations (military, athletes, occupational, men, women, children, and older adults) and situations (pathophysiological factors, spaceflight, bed rest, long plane flights, heat stress, altitude/cold exposure, and recreational exercise). We discuss how beverage carbohydrate and electrolytes impact fluid replacement. We also discuss nutrients and compounds that are often included in fluid-replacement beverages to augment physiological functions unrelated to hydration, such as the provision of energy. The optimal composition of a fluid-replacement beverage depends upon the source of the fluid loss, whether from sweat, urine, respiration, or diarrhea/vomiting. It is also apparent that the optimal fluid-replacement beverage is one that is customized according to specific physiological needs, environmental conditions, desired benefits, and individual characteristics and taste preferences. © 2014 American Physiological Society. Compr Physiol 4:575-620, 2014.
... Shaded areas represent the doses for which are anticipated positive effects and negligible ergogenic, which may be the result of the effect of negative cognitive and mood at higher doses. Numerous studies dealing with the opportunities offered by the various doses and combinations of caffeine, carbohydrates and electrolytes balance the hydrological balance of the organism of athletes (Fiala, Casa & Roti 2004;Millard-Stafford 2007;Del Coso, Estevez & Mora-Rodriguez 2009). In conclusion, the use of caffeine in rehydration is related to the dose of caffeine managed within the range shown (3-6 mg/kg BW -1 ) and which does not affect the rates of perspiration, loss of urine or indices of the state of hydration during physical effort (Jenna 2009). ...
... Ten healthy male college students participated in the experiment (age: 21.8 ± 0.8 years, height: 173.7 ± 7.2 cm, mass: 64.2 ± 4.8 kg, body mass index: 21.3 ± 1.6). The participants were advised to refrain from eating food for 2 h before the experiment, from consuming alcohol for 24 h before the experiment, and from consuming caffeine on the day of the experiment [12]. Each participant followed the experimental procedures for one sample per day, taking 2 days in total to complete the experiment. ...
We measured the psychophysiological responses of participants wearing two kinds of undershirts made from hydrophobic fibers to investigate the sensation of clothing comfort. In the experiment, participants perspired following exercise. The perspiration increased the humidity within the clothing, decreased the skin surface temperature, and worsened the comfort sensation. Multiple regression analysis revealed a stuffy sensation and a skin contact sensation as factors of the comfort sensation. Measurements of physiological responses revealed that the low-frequency/high-frequency ratio obtained from an electrocardiogram had high negative correlation with comfort sensation in the exercise/rest process. A difference in the moisture transport properties of the samples revealed that participants discerned a stuffy sensation and cool sensation, and there is the possibility that the difference in the stuffy sensation of the samples can be evaluated by the CVRR, which is an index of parasympathetic nerve activity.
... Caffeine is an alkaloid of the methylated xanthine family and an adenosine receptor antagonist, which can be foun main effect on performance is its effects on central nervous system stimulation by adenosine antagonism and, although it also serves to increase motor unit recruitment 46 , and improving thermoregulation 47 . ...
Introduction:Tennis is characterized by a large number of competitions and little recovery time between them. Thus, tennis players and coaching staff have become interested in the role that nutrition can play in maximizing sports performance. The scientific literature does not have recent narrative and/or systematic reviews about to nutrition in tennis. The aim of this study is to map, describe and discuss the state of the science of nutrition and dietetic practices for tennis players from a theoretical and contextual point of view, to enable focused future systematic reviews.
Material and methods: A narrative review through the Dialnet, Elsevier, Medline, Pubmed and Web of Science databases, through a search strategy based on keywords separated by Boolean connectors. A series of inclusion / exclusion criteria were applied to select those investigations that responded to the aim of the work.
Results: Nutritional recommendations on carbohydrate intake depend on the training load, 5-7 g/kg/day g/kg/day for normal training and 7-10 g/kg/day for competitive periods or high training load. The recommended protein intake is 1.8 g/kg/day and 1 g/kg/day of lipids. The supplements that can optimize tennis performance are caffeine, sodium bicarbonate, creatine and -alanine. Beetroot juice can be a possible aid to consider in dietetic-nutritional planning in tennis players.
Conclusions: Performance and health of tennis player can be optimized, as well as adequate periodization of nutrients and supplements, meeting to the physiological demands of tennis.
... Também tem sido sugerido que a cafeína reduz o fluxo sanguíneo cutâneo, aumen- tando a temperatura interna durante o exercício que pode potencialmente levar a exaustão pelo calor (Armstrong et al., 2007).Bebidas energéticas (BE) contêm na sua composição cafeína e tornou-se popular entre atletas (Petroczi et al., 2008), devido à suposta ação ergogênica favorecendo o desem- penho (Lara et al., 2015;Prins et al., 2016). Assim, é interessante investigar o efeito do consumo prévio de BE no balanço hidroeletrolítico durante o exercício, já que a maioria dos estudos avalia o efeito diurético da cafeína quando consumida em dose isolada (Del Coso,Estevez, & Mora-Rodriguez, 2009; Wemple, Lamb, & McKeever, 1997) Todavia, nos últimos anos, a ingestão de BE sem carboidratos (sugar free) aumentou en- tre os esportistas e praticantes de atividade física, possivelmente porque muitos indivíduos ativos optam por ser uma bebida cafeinada, sem açúcar e com baixo teor calórico(Candow, Kleisinger, Grenier, & Dorsch, 2009). Assim, o objetivo do presente estudo foi verificar o efeito da ingestão prévia de BE com e sem carboidratos sobre o equilíbrio hidroeletrolítico no exercício contínuo em cicloergômetro. ...
... Roti et al., concluded that acute caffeine ingestion, in chronically consuming subjects (3 and 6 mg/kg per day), did not alter fluid-electrolyte, exercise endurance or thermoregulatory responses during 90 minutes of walking in the heat (100ºF) when compared with no caffeine [46]. In addition, Del Coso and colleagues reported that caffeine ingestion at 6 mg/kg body mass was not thermogenic and did not impair heat dissipation when men exercised in the heat (97ºF) for two hours [47]. ...
... Subjects were advised to refrain from eating spicy food and consuming alcohol 24 h before testing and also to refrain from drinking coffee on the testing day (Del Coso, Estevez, & Mora-Rodriguez, 2009). They were also requested not to participate in exhaustive sport activity 48 h before testing. ...
This study aimed to identify sex-related differences in clothing-microclimate and subjective perceptions while wearing two outdoor jackets in a setting that is representative for outdoor sports at a leisure level. Ten male and 10 female subjects were testing a thin one-layer jacket and a wind- and waterproof three-layer membrane jacket in a climatic chamber (12 °C, 40% relative humidity) during rest, exercise and recovery. Relative humidity, temperature and sweat residues in the clothing system, perceptions of comfort and physiological parameters were measured. For females, relative humidity, sweat residues and loss of body mass were significantly lower without significantly influencing perceptions of comfort. It can be concluded that sex has a strong effect on clothing-microclimate in outdoor jackets with drier microclimate for females. Furthermore, our findings suggest that females are more sensitive to humidity within the clothing system and that they cool easier, especially in periods of rest.
... Bebidas energéticas (BE) contêm na sua composição cafeína e tornou-se popular entre atletas (Petroczi et al., 2008), devido à suposta ação ergogênica favorecendo o desempenho (Lara et al., 2015;Prins et al., 2016). Assim, é interessante investigar o efeito do consumo prévio de BE no balanço hidroeletrolítico durante o exercício, já que a maioria dos estudos avalia o efeito diurético da cafeína quando consumida em dose isolada (Del Coso, Estevez, & Mora-Rodriguez, 2009;Wemple, Lamb, & McKeever, 1997) Todavia, nos últimos anos, a ingestão de BE sem carboidratos (sugar free) aumentou entre os esportistas e praticantes de atividade física, possivelmente porque muitos indivíduos ativos optam por ser uma bebida cafeinada, sem açúcar e com baixo teor calórico (Candow, Kleisinger, Grenier, & Dorsch, 2009 (Chisholm, Collis, Kulak, Davenport, & Gruber, 1975) e pela Tabela de Risco Coronariano proposta pela Michigan Heart Association (Mcardle, Katch, & Katch, 2008 (Horswill, 1998). (Wemple et al., 1997). ...
... 23 Subjects were advised to refrain from eating spicy food and consuming alcohol 24 hours before testing and also to refrain from drinking coffee on the testing day. 24 They were also requested not to participate in exhaustive sports activities 48 hours before testing. To ensure consistent hydration status, participants were asked to drink 500 ml of water one hour before and to empty their bladder immediately before testing. ...
The goal of this study was to investigate the effect of differences in water vapor permeability (WVP) of outdoor jackets on moisture management, subjective perceptions and physiological parameters under conditions typically encountered in outdoor sports.
Four outdoor jackets differing only in their WVP were compared in a repeated measures study. A total of 19 subjects (nine females) were tested in a climatic chamber at 10℃ and 40% relative humidity. The protocol consisted of 15 min of rest, 50 min of treadmill running at 60% of the individual maximal running velocity, and 15 min of passive recovery.
We found that jackets featuring greater WVP helped to reduce relative humidity underneath the jacket, resulting in less sweat residue in the clothing system and drier skin during exercise and rest. Subjects were also able to perceive the differences in the microclimate and reported feeling more comfortable and drier in the more permeable jackets. However, WVP did not have a significant effect on oxygen consumption, heart rate, tympanic temperature, overall loss of subjects’ body mass or on perceived exertion.
It can be concluded that outdoor jackets with higher WVP benefit moisture management during submaximal exercise in cool temperatures by reducing relative humidity in the clothing system mostly during rest periods. This effect leads to a drier skin which favors perceived comfort and might reduce the after-chill effect. However, WVP of outdoor jackets neither significantly affects physiological responses nor perceived exertion during submaximal exercise in a cool environment.
... Effects of stimulant drinks [20][21][22] are related primarily to the presence of caffeine in the composition. In the literature, the effect of drinks composed by CTG on exercise performance has been compared against placebo [23][24][25][26][27][28] . In humans, improved athletic performance after taking 3-6 mg of caffeine per kg of body weight, has been described in different types of exercise, especially in endurance activities [29][30][31] . ...
Introduction: Caffeinated drinks are used for improve performance. Animal models represent investigational strategy that circumvents most of the drawbacks of research in humans, including motivational factors and the placebo effect. No animal model that could test whether different forms of administering caffeine affect exercise propensity was found in the literature.
Methods: An animal model of grouped voluntary exercise was tested. Two-month-old male C57/bl mice were housed in a cage fitted with one running wheel and a monitoring system. Six animals per cage were introduced individually. To assess the sensitivity of the model, the effect of different caffeinated drinks was observed in mice exercising ad libitum. During 2 days, the mice received: 1) pure anhydrous caffeine 0.125 mg/mL (PC), 2) cola drink (CC), and 3) caffeine-taurine-glucuronolactone drink (CTG), intercalating wash-out periods of 2 days, receiving pure water.
Results: The distance run during the periods of water ingestion was significantly lower than during the periods of stimulant drinks ingestion: PC (5.6±1.3 km; p = 0.02), of CC ingestion (7.6±0.6 km; p = 0.001), and of CTG ingestion (8.3±1.6 km; p = 0.009). The performances when ingesting the three caffeinated drinks do not follow a dose-response curve.
Conclusions: The model described here was able to measure the effect of caffeine intake on voluntary exercise of mice. The sensitivity of the model to the effect of caffeine needs to be further validated. The action of each component of the drinks on exercise performance needs to be clarified in future research. The present model is adequate for such investigation.
Key words: Exercise; caffeine; energy drinks; running
... It is worth noting that Wemple et al. [15] did not observe caffeine induced diuresis when their subjects exercised during the final 3 h of their protocol. These results and those of others suggest that the diuretic effect of caffeine is absent [23], or substantially reduced [24], during exercise. ...
When utilized separately, pre-exercise hyperhydration or consumption of caffeine have both been shown to be ergogenic. Acute caffeine consumption has also been shown to promote diuresis in some situations, but this effect has not been studied when caffeine is used in conjunction with sodium-aided hyperhydration. We measured urine production during hyperhydration strategies performed with and without caffeine. Fifteen euhydrated subjects performed five strategies by consuming 20 mL water/kg bm alone (NT), or with a placebo (PL), 5 mg/kg bm caffeine (Caf), 110 mg/kg bm NaCl (Na), or 5 mg caffeine +110 mg NaCl/kg bm (CafNa). Total urine excretion was measured for 2 h following treatment consumption and expressed as a percentage of the total water consumed. Total twohour urine excretion values were 103 16% (NT), 102 15% (PL), 116 18% (Caf), 68 14% (Na) and 85 14% (CafNa) of water consumed. No significant difference in urine excretion was detected between NT and PL. Caf resulted in significantly more, and Na in significantly less, urine excretion compared to all other strategies. CafNa resulted in significantly less urine excretion than NT, PL, and Caf, but significantly more excretion than Na. The results suggest that hyperhydration can be achieved when an acute caffeine dose is consumed in conjunction with sodium-aided hyperhydration; however, the level of hyperhydration is significantly less than attained when an equal dose of water and sodium are consumed without caffeine
... 4 However, during exercise under the same environmental conditions, the same caffeine dose co-administered with carbohydrates elicited a higher core temperature than isolated carbohydrate intake. 12 laboratory-based studies have examined the influence of 6 mg kg −1 caffeine on endurance cycle performance in the heat without additional carbohydrates. 5,3 Roelands et al. 5 reported no ergogenic effect of caffeine but an increase in core temperature during prolonged exercise at a fixed work-rate, while Ganio et al. 3 observed an improvement in endurance cycle performance but no thermogenic effects. ...
Objectives:
This study investigated the influence of a moderate caffeine dose on endurance cycle performance and thermoregulation during prolonged exercise in high ambient temperature.
Design:
Double-blind cross-over study.
Methods:
Eight healthy, recreationally active males (mean±SD; age: 22±1 years; body mass: 71.1±8.5kg; VO2peak: 55.9±5.8mLkg(-1)min(-1); Wmax: 318±37W) completed one VO2peak test, one familiarisation trial and two experimental trials. After an overnight fast, participants ingested a placebo or a 6mgkg(-1) caffeine dose 60min before exercise. The exercise protocol consisted of 60min of cycle exercise at 55% Wmax, followed by a 30min performance task (total kJ produced) in 30°C and 50% RH.
Results:
Performance was enhanced (Cohen's d effect size=0.22) in the caffeine trial (363.8±47.6kJ) compared with placebo (353.0±49.0kJ; p=0.004). Caffeine did not influence core (p=0.188) or skin temperature (p=0.577) during exercise. Circulating prolactin (p=0.572), cortisol (p=0.842) and the estimated rates of fat (p=0.722) and carbohydrate oxidation (p=0.454) were also similar between trial conditions. Caffeine attenuated perceived exertion during the initial 60min of exercise (p=0.033), with no difference in thermal stress across trials (p=0.911).
Conclusions:
Supplementation with 6mgkg(-1) caffeine improved endurance cycle performance in a warm environment, without differentially influencing thermoregulation during prolonged exercise at a fixed work-rate versus placebo. Therefore, moderate caffeine doses which typically enhance performance in temperate environmental conditions also appear to benefit endurance performance in the heat.
... However, runners can rest assured that research refutes any purported measurable effects on thermoregulation, fluidelectrolyte balance, and exercise-heat tolerance. 17,20 That is, caffeine intake does not appear to be appreciably thermogenic or interfere with heat dissipation during running or other exercise in the heat. Therefore, even with large doses, caffeine consumption prior to going out on a training run or beginning a race will not likely increase physiological strain to augment exertional heat illness risk or impede or lessen on-course performance. ...
Synopsis:
Running well and safely in the heat is challenging for all runners, from recreational to elite. As environmental heat stress (heat stress modulated or augmented by air temperature, humidity, wind speed, and solar radiation) and the intensity and duration of a training run or race increase, so are metabolic heat production, the parallel need for heat transfer from the body to maintain thermal equilibrium, the consequent increase in blood flow to the skin, and the concomitant sweating response progressively and proportionally amplified. An accumulating total body-water deficit from extensive sweating and escalating level of cardiovascular and thermal strain will, in due course, considerably challenge a runner's physiology, perception of effort, and on-course well-being and performance. However, with the appropriate preparation and modifications to planned running intensity and distance, runners can safely tolerate and effectively train and compete in a wide range of challenging environmental conditions. Clinicians play a key role in this regard as an effective resource for providing the most effective guidelines and making the best overall individual recommendations regarding training and competing in the heat.
... The outcomes of caffeine ingestion on physical performance have been mainly tested using pure anhydrous caffeine supplied to experimental subjects in pills (Burke 2008;Coso et al. 2008Coso et al. , 2009Doherty and Smith 2004). However, the current use of caffeine in sports mainly comes from the ingestion of commercially available energy drinks (Hoffman 2010). ...
There is little information about the effects of caffeine intake on female team-sport performance. The aim of this study was to investigate the effectiveness of a caffeine-containing energy drink to improve physical performance in female soccer players during a simulated game. A double-blind, placebo controlled and randomized experimental design was used in this investigation. In two different sessions, 18 women soccer players ingested 3 mg of caffeine/kg in the form of an energy drink or an identical drink with no caffeine content (placebo). After 60 min, they performed a countermovement jump (CMJ) and a 7 × 30 m sprint test followed by a simulated soccer match (2 × 40 min). Individual running distance and speed were measured using GPS devices. In comparison to the placebo drink, the ingestion of the caffeinated energy drink increased the CMJ height (26.6 ± 4.0 vs 27.4 ± 3.8 cm; P < 0.05) and the average peak running speed during the sprint test (24.2 ± 1.6 vs 24.5 ± 1.7 km/h; P < 0.05). During the simulated match, the energy drink increased the total running distance (6,631 ± 1,618 vs 7,087 ± 1,501 m; P < 0.05), the number of sprints bouts (16 ± 9 vs 21 ± 13; P < 0.05) and the running distance covered at >18 km/h (161 ± 99 vs 216 ± 103 m; P < 0.05). The ingestion of the energy drink did not affect the prevalence of negative side effects after the game. An energy drink with a dose equivalent to 3 mg of caffeine/kg might be an effective ergogenic aid to improve physical performance in female soccer players.
... No obstante, según Maughan et al. 31 , el efecto diurético de la cafeína puede ser considerable en deportistas no habituados. Según Del Coso et al. 32 en ciclistas aclimatados al calor al 63% VO 2 max 2 h y con 6 mg cafeína/kg, se observó que aumentaba la diuresis (28%) y la pérdida de electrolitos (14%). Pero estos efectos disminuían si se tomaba con bebida isotónica, no afectando en un ejercicio de 2 h a 36º C, con lo cual sus efectos sólo podrían observarse en carreras de muy larga distancia y no aclimatados al calor. ...
The needs of water and electrolytes are quite variants, depending on age, physiological or environmental conditions. In most long-term sports, usual weight loss of 3-6%, affect in athletic performance. The effects of a 6% dehydration could be improved with individualized diet-specific nutritional strategies and allow only a 2-3% dehydration, which affect metabolic efficiency but will not risk the health. On the contrary, hyperhydration can be dangerous and is associated with hyponatremia that can cause cerebral edema or respiratory failure. Sports drinks should moisturize, providing minerals and carbohydrates and increase the absorption of water by an ideal combination of salts and sugars. Therefore, it is important to provide correct hydration -protocols before, during and after physical activity, as well as know possible limitations of the sport.
... Caffeine has been thought to promote thermogenesis and increase short-term metabolism, total daily energy expenditure, and body temperature. 10,17 However, these added thermogenic effects were not observed in studies that involved exercise [11][12][13]29 or cold exposure. 14,15 It has also been reported that the thermal state of the body significantly influences CIVD, such that hyperthermia increases T f Á min and T f Á max and hypothermia decreases these finger temperature parameters. ...
The purpose of the study was to investigate the effect of caffeine intake on finger cold-induced vasodilation (CIVD).
Ten healthy men underwent 6 experimental trials characterized by control (NCAFF) or caffeine intake (CAFF) via chewing gum (300 mg of caffeine) while resting on a chair or performing submaximal (70% maximal oxygen consumption) or maximal (100% maximal oxygen consumption) treadmill exercise (Bruce protocol) followed by immersion of the middle finger in a water bath (5°C) for 20 minutes. Finger temperature (Tf ) and time parameters of the first CIVD cycle and post-test norepinephrine were measured.
Exercise duration for submaximal and maximal exercise was 8.9 ± 0.9 and 12.4 ± 0.8 minutes, respectively. CAFF had no effect on Tf, but exercise increased minimal Tf in NCAFF (9.08 ± 1.27°C, 13.02 ± 2.13°C, and 13.25 ± 1.63°C in rest, submaximal, and maximal exercise, respectively) and CAFF (8.76 ± 1.39°C, 12.50 ± 1.91°C, and 12.79 ± 1.20°C). Maximal Tf was significantly higher in NCAFF (15.98 ± 1.04°C, 16.18 ± 1.56°C, and 15.14 ± 1.52°C) than in CAFF (13.56 ± 1.19°C, 15.52 ± 1.31°C, and 14.39 ± 1.43°C), resulting in a significant difference between minimal and maximal Tf in rest (NCAFF, 6.89 ± 1.56°C and CAFF, 4.79 ± 1.23°C), but not in exercise conditions. CAFF had no effect on CIVD time responses, but exercise significantly shortened CIVD onset and peak time compared with rest in both NCAFF and CAFF. Norepinephrine concentration was significantly greater in CAFF (290.6 ± 113.0 pg/mL, 278.1 ± 91.4 pg/mL, and 399.8 ± 125.5 pg/mL) than NCAFF (105.6 ± 29.5 pg/mL, 199.6 ± 89.6 pg/mL, and 361.5 ± 171.3 pg/mL).
Caffeine intake before finger immersion in cold water does not result in a thermogenic effect and adversely affects CIVD responses, whereas exercise modifies CIVD temperature and time responses.
... A concern that energy drinks can increase the risk for dehydration was raised based on evidence that caffeine can induce diuresis and natriuresis (43). However, in several well-designed studies, caffeine consumption has not been shown to impair hydration, exacerbate dehydration, or impair thermoregulation (11,22). In a recent review of the literature, Armstrong et al. (4) have surmised that caffeine does not reduce exercise-heat tolerance or increase the risk for hyperthermia. ...
RECENT RESEARCH HAS INDICATED THAT ENERGY DRINKS ARE THE MOST POPULAR SUPPLEMENT BESIDES MULTIVITAMINS IN THE AMERICAN ADOLESCENT AND YOUNG ADULT POPULATION. MORE THAN 30% OF ALL AMERICAN MALE AND FEMALE ADOLESCENTS USE THESE SUPPLEMENTS ON A REGULAR BASIS. ENERGY DRINKS ARE ALSO REPORTED TO BE THE MOST POPULAR SUPPLEMENT (41.7% OF THE 403 ATHLETES SURVEYED) AMONG YOUNG (17.7 ± 2.0 YEARS) ELITE BRITISH ATHLETES. THIS BRIEF REVIEW WILL EXAMINE THE EFFICACY OF THESE ENERGY DRINKS REGARDING PERFORMANCE IMPROVEMENTS AND METABOLIC ENHANCEMENT. IN ADDITION, ISSUES RELATING TO THE SAFETY OF ENERGY DRINK CONSUMPTION WILL ALSO BE DISCUSSED.
... Due to their low cost, accessibility, and the relatively low frequency of deleterious side-effects derived from their consumption, caffeine-containing energy drinks have become the most popular supplement in the sports population, with a prevalence of 73% in American college athletes [3], 75% in Canadian Varsity athletes [4] and 42% in British elite athletes [5]. Whereas the outcomes of caffeine ingestion (from natural sources and pills) are well known [6,7,8,9] , the effects of caffeinecontaining energy drinks on sports performance have been the object of fewer studies. The first report concerning the effects of energy drinks on physical performance was carried out by Alford and co-workers in 2001 [10]. ...
To investigate the effects of a caffeine-containing energy drink on soccer performance during a simulated game. A second purpose was to assess the post-exercise urine caffeine concentration derived from the energy drink intake.
Nineteen semiprofessional soccer players ingested 630 ± 52 mL of a commercially available energy drink (sugar-free Red Bull®) to provide 3 mg of caffeine per kg of body mass, or a decaffeinated control drink (0 mg/kg). After sixty minutes they performed a 15-s maximal jump test, a repeated sprint test (7 × 30 m; 30 s of active recovery) and played a simulated soccer game. Individual running distance and speed during the game were measured using global positioning satellite (GPS) devices. In comparison to the control drink, the ingestion of the energy drink increased mean jump height in the jump test (34.7 ± 4.7 v 35.8 ± 5.5 cm; P<0.05), mean running speed during the sprint test (25.6 ± 2.1 v 26.3 ± 1.8 km · h(-1); P<0.05) and total distance covered at a speed higher than 13 km · h(-1) during the game (1205 ± 289 v 1436 ± 326 m; P<0.05). In addition, the energy drink increased the number of sprints during the whole game (30 ± 10 v 24 ± 8; P<0.05). Post-exercise urine caffeine concentration was higher after the energy drink than after the control drink (4.1 ± 1.0 v 0.1 ± 0.1 µg · mL(-1); P<0.05).
A caffeine-containing energy drink in a dose equivalent to 3 mg/kg increased the ability to repeatedly sprint and the distance covered at high intensity during a simulated soccer game. In addition, the caffeinated energy drink increased jump height which may represent a meaningful improvement for headers or when players are competing for a ball.
... Studies investigating the effects of caffeine on hydration and thermal regulation have tended to focus on its acute effects and included well-conditioned persons wearing sports clothing as subjects. Nevertheless, the data has not shown a link to heat illness and increased risk of dehydration [12,13]. However, caffeine has diuretic as well as stimulant properties [14]. ...
Recently published case reports, coupled with a large observational study of 1017 deployed servicemen to Iraq (January 2009), has highlighted the issue and potential concerns regarding the unregulated use of dietary and exercise supplements within the British military. Consequently, an exploratory pilot study was undertaken to assess whether the findings of the previous Iraq study were applicable to current deployed British servicemen in Afghanistan.
This was a voluntary questionnaire-based study targeted at individuals attending a health promotion fair in Camp Bastion, Afghanistan in June 2010.
From 150 questionnaires handed out there were 87 completed questionnaires (58% return). The mean age was 28.0 (SD 7.1; range of 18-50 years) with 89.7% being male. From the total of 87 persons 46.0% were self-declared current smokers with 37.9% admitting to drinking >6 caffeinated drinks per day. Forty nine persons (56.3%) admitted to a history of supplement use with 35 (40.2% compared with 32.0% in 2009 in Iraq) declaring current use. The average duration of supplement use among current users was 3.0 (2.0-9.0) months. The main sources of supplement supply were via local NAAFI purchase (57.1%), internet purchase (40.0%) and via their local chemist (2.9%). The main types of supplement used were proteins/amino acids (85.7%), creatine (34.3%), chromium (31.4%), stimulants (17.1%), hydroxycut (5.7%), and testosterone boosters (1.2%) with no persons admitting to the use of ephedra or anabolic steroids.
A significant proportion of the British servicemen employed on operations in Afghanistan who were sampled, admitted to current dietary and exercise supplement use whilst on deployment. The results of this small study suggest that their use on operations may be increasing. Smoking rates and caffeine consumption, on deployment, remain high in the British military. A larger detailed study with greater representation among soldiers deployed to forward operating bases would be helpful to fully appreciate the scale of supplement use.
... The use of caffeine (1,3,7-trimethylxanthine) is one of the most controversial behaviors to be evaluated by sports organizations and anti-doping authorities. On the one hand, there is abundant scientific evidence regarding the ergogenic effects of caffeine in a wide variety of sports specialties (Doherty and Smith 2004; Burke 2008; Davis and Green 2009; Ganio et al. 2009 ), while health-related problems derived from caffeine ingestion are negligible in adults (Roti et al. 2006; Del Coso et al. 2009). On the other hand, caffeine is a naturally occurring compound in many foods and drinks (e.g., chocolate , coffee, tea), or it may be added to many beverages, dietary supplements, and over-the-counter medications. ...
The aim of this investigation was to determine the use of caffeine by athletes after its removal from the World Anti-Doping Agency list. For this purpose, we measured the caffeine concentration in 20 686 urine samples obtained for doping control from 2004 to 2008. We utilized only urine samples obtained after official national and international competitions. Urine caffeine concentration was determined using alkaline extraction followed by gas chromatography-mass spectrometry. The limit of detection (LOD) was set at 0.1 µg·mL(-1). The percentage of urine samples below the LOD was 26.2%; the remaining 73.8% of the urine samples contained caffeine. Most urine samples (67.3%) had urinary caffeine concentrations below 5 µg·mL(-1). Only 0.6% of urine samples exceeded the former threshold for caffeine doping (12 µg·mL(-1)). Triathlon (3.3 ± 2.2 µg·mL(-1)), cycling (2.6 ± 2.0 µg·mL(-1)), and rowing (1.9 ± 1.4 µg·mL(-1)) were the sports with the highest levels of urine caffeine concentration; gymnastics was the sport with the lowest urine caffeine concentration (0.5 ± 0.4 µg·mL(-1)). Older competitors (>30 y) had higher levels of caffeine in their urine than younger competitors (<20 y; p < 0.05); there were no differences between males and females. In conclusion, 3 out of 4 athletes had consumed caffeine before or during sports competition. Nevertheless, only a small proportion of these competitors (0.6%) had a urine caffeine concentration higher than 12 µg·mL(-1). Endurance sports were the disciplines showing the highest urine caffeine excretion after competition.
The clothing comfort sensation is a combination of complex components, including psychological and physiological responses. General linear analysis is not always sufficient for the evaluation of the clothing comfort sensation. The current study sought to predict the clothing comfort sensation of wearing an undershirt using an artificial neural network (ANN). We constructed ANN models with psychological sensation data and physiological response data as inputs, including electrocardiogram and thermo-physiological indicators, and the clothing comfort sensation as the output. For the input layer of the model, three conditions were used: the psychological response data only, the physiological response data only, and both the psychological and physiological data. The number of hidden layers in the models ranged from one to three, and the number of units in each hidden layer was changed when fixed values of 30, 60, and 90 were used, or according to the number of data points in the input conditions. The results revealed that, among the three conditions, the accuracy rate was higher when both psychological and physiological response data were used as input. The prediction results exhibited an accuracy rate of up to 85% for unknown test data. The results suggest that the method of evaluating the state of clothing comfort sensation when wearing an undershirt using psychophysiological response measurement was effective and that neural networks are useful for predicting the clothing comfort sensation.
Background and aims:
Caffeine mouth rinsing has emerged as an alternative to oral caffeine consumption for improving performance without provoking lower gastrointestinal distress. However, it remains unclear if hydration status and sweat rate are negatively affected by caffeine mouth rinsing. This study is aimed at evaluating the effects of 10 seconds of caffeine mouth rinsing (1.2% anhydrous caffeine solution) on hydration status and sweat rate following a 10 km run trial.
Methods:
Ten recreationally trained runners (30.1 ± 6.4 y) volunteered to participate in this double-blind, placebo-controlled, and crossover research study. Participants completed two 10 km run trials separated by approximately one week. Immediately prior to running, participants completed a 10-second mouth rinse protocol with either 300 mg of caffeine or microcrystalline cellulose (placebo) diluted in 25 mL of water. The effects of caffeine mouth rinsing on hydration status and sweat rate were assessed following a 10 km run trial.
Results:
Sweat rate (placebo: 15.34 ± 9.71 vs. caffeine: 11.91 ± 6.98 mL · min-1; p = 0.39), dehydration (placebo: 1.20 ± 0.57 vs. caffeine: 1.49 ± 0.29%; p = 0.15), and hydration (placebo: 15.32 ± 9.71 vs. caffeine: 11.89 ± 6.99 mL · min-1; p = 0.37) measures were not significantly different between trials.
Conclusion:
Caffeine mouth rinse does not appear to alter the hydration status or sweat rate following a 10 km run.
The book is designed to provide a flowing description of the physiology of heat stress, the illnesses associated with heat exposure, recommendations on optimising health and performance, and an examination of Olympic sports played in potentially hot environmental conditions. In the first section the book examines how heat stress effects performance by outlining the basics of thermoregulation and how these responses impact on cardiovascular, central nervous system, and skeletal muscle function. It also outlines the pathophysiology and treatment of exertional heat illness, as well as the role of hydration status during exercise in the heat. Thereafter, countermeasures (e.g. cooling and heat acclimation) are covered and an explanation as to how they may aid in decreasing the incidence of heat illness and minimise the impairment in performance is provided. A novel and particular feature of the book is its inclusion of sport-specific chapters in which the influence of heat stress on performance and health is described, as well as strategies and policies adopted by the governing bodies in trying to offset the deleterious role of thermal strain. Given the breadth and scope of the sections, the book will be a reference guide for clinicians, practitioners, coaches, athletes, researchers, and students.
The heat is a formidable opponent for tennis players at all levels of competition. Extensive on-court sweat loss and thermal strain during tennis in the heat can recognizably impact performance and exacerbate related clinical risk. This is notably evident during extreme hot-weather tournaments, or when multiple singles matches are played in the heat on the same day and the scheduled rest and recovery periods between contests are inappropriately brief. Numerous practical offsetting measures, including appropriate hydration management, can be proactively implemented by players, coaches, and administrators to effectively reduce heat-related clinical risk and optimize on-court performance. However, heat safety guidelines from the tennis governing bodies need to be more tennis-specific and informed by more extensive data from real-world competition scenarios for all age groups and levels of play. Knowledgeably integrating relevant data across multiple domains and modeling using advanced technology and analytics will play a key role in this solution.
The purpose of this study was to test the hypothesis that consuming a soft drink (i.e., a high fructose, caffeinated beverage) during and following exercise in the heat elevates biomarkers of acute kidney injury (AKI) in humans. Twelve healthy adults drank 2 L of an assigned beverage during 4 h of exercise in the heat (35.1 ± 0.1°C, 61 ± 5% relative humidity) in counterbalanced soft drink (Soft Drink) and water (Water) trials, and ≥1 L of the same beverage after leaving the laboratory. Stage 1 AKI (i.e., increased serum creatinine ≥0.3 mg/dL) was detected at post-exercise in 75% of participants in the Soft Drink trial compared to 8% in Water (P=0.02). Furthermore, urinary neutrophil gelatinase-associated lipocalin (NGAL), a biomarker of AKI, was higher during an overnight collection period after the Soft Drink trial compared to Water in both absolute concentration (6 ± 4 ng/dL vs. 5 ± 4 ng/dL, P<0.04) and after correcting for urine flow rate (6 ± 7 [ng×dL-1]/[mL×min-1] vs. 4 ± 4 [ng×dL-1]/[mL×min-1], P=0.03). Changes in serum uric acid from pre-exercise were greater in the Soft Drink trial than Water at post-exercise (P<0.01) and 24 h (P=0.05). There were greater increases from pre-exercise in serum copeptin, a stable marker of vasopressin, at post-exercise in the Soft Drink trial (P<0.02) than Water. These findings indicate that consuming a soft drink during and following exercise in the heat induces AKI, likely via vasopressin mediated mechanisms.
The heightened concern with aesthetics can lead to indiscriminate use of
Anabolic Androgenic Steroids (AAS), leading to serious health problems. Objectives: To
determine the prevalence of AAS among bodybuilders in the city of Teresina, Piauí.
Methods: It is a cross-sectional, quantitative exploratory and retrospective study. After
identification of the gyms registered on the Regional Council of Physical Education (CREF 5
- CE/MA/PI), it was applied a questionnaire as a research tool, containing objective questions
on socioeconomic variables, training and on the use of AAS. Data were analyzed using
frequency and Chi-square test (P <0.05). Results: The study consisted of 400 subjects (24.7 ±
6.34 years), 69.5% (n = 278) were male. Use prevalence was 7.75% (n = 31). The users were
male, young (18-25 years). The most used substances were Nandrolone (28.4%),
Testosterone propionate (20.9%) and Testosterone Cypionate (14.9%), with the
recommendation of use made by a colleague or friend (67.7%). The main side effects cited in
the survey were acne, mood variations, irritability, headaches and anxiety. Conclusions:
Therefore, the results of this study identify and contribute for the comprehension of an old
problem, still emerging, which requires relevant policies to act against its use.
Purpose
This study examined the rehydration achieved by drinking different beverages during a short-term recovery period (REC) after exercise-induced dehydration.
Methods
Thirteen well-trained men (age 22.1 ± 3.3 yr, body mass 61.2 ± 9.1 kg, VO 2max 64.9 ± 4.0 ml · kg ⁻¹ · min ⁻¹ , maximum heart rate 198 ± 7 beats/min) ran for 60 min on 3 occasions on a level treadmill at 70% VO 2max . All trials were performed in thermoneutral conditions (21 °C, 71% relative humidity) and were separated by at least 7 d. During 4 hr REC, the subjects consumed either a volume of a carbohydrate-electrolyte beverage (CE), lemon tea (LT), or distilled water (DW) equal to 150% of the body weight (BW) lost during the previous run. The fluid was consumed in 6 equal volumes at 30, 60, 90, 120, 150, and 180 min of REC.
Results
After the completion of the 60-min run, the subjects lost ~2.0% of their preexercise BW in all trials, and no differences were observed in these BW changes between trials. At the end of REC, the greatest fraction of the retained drink occurred when the CE drink was consumed (CE vs. LT vs. DW: 52% ± 18% vs. 36% ± 15% vs. 30% ± 14%, p < .05). The CE drink also caused the least diuretic effect (CE vs. LT vs. DW: 638 ± 259 vs. 921 ± 323 vs. 915 ± 210 ml, p < .05) and produced the optimal restoration of plasma volume (CE vs. LT vs. DW: 11.2% ± 2.0% vs. –3.1% ± 1.8% vs. 0.2% ± 2.1%, p < .05).
Conclusion
The results of this study suggest that CE drinks are more effective than DW or LT in restoring fluid balance during short-term REC after exercise-induced dehydration.
Ahtletes and physically active people consume many ingredients with purported ergogenic effects, a few of which have already been well documented, while most others have not. Some of these components may interact negatively with the major, conventional ingredients in sports drinks. In this chapter on the need of other elements in rehydration, only those ingredients that have been studied in association with the rehydration properties of beverages will be discussed in this chapter. Because the main ingredients in rehydration beverages are discussed in other chapters of the book, and some others have already been reviewed extensively, emphasis will be placed on some recent work on other elements as they relate to post-exercise rehydration. And since potential ingredients will be presented from the perspective of the renal paradox—the fact that fluid intake by dehydrated humans results in a significant urine output and a compromised rehydration—the chapter begins with a presentation of this concept.
Energy drinks such as Sting, Red bull, Full Throttle, Rockstar, Monster are thronging the local market, excessively advertised and readily incorporated into a routine, as a part of healthy life style. Some of these energy drinks have already been banned by Denmark, Germany and Australia. Since these drinks claim to boost instant energy, with prolonged physical endurance; their consumption is increasing day by day. These drinks are combination of herbs, stimulants, sugars, vitamins and other food additives and have a claim that their synergistic effects could improve energy, boost stamina and performance. Their increased consumption without awareness of the side effects might pose a threat to the well-being of a person and could precipitate adverse effects, in terms of toxicities. This concern has evoked us to focus our research based on animals, male albino wistar rats exposed to energy drink (9ml / day) for 14 days, compared to their water administered counterparts and its subsequent withdrawal (14 days). Behavioral activities were monitored on the 13 th day. Home cage and open field activity were increased upon administration, while withdrawal tended to show a decline in the locomotor effects. Animals in elevated plus maze (EPM) and light/dark (anxiety measurement paradigms) exhibited anxiolysis upon administration, but not on withdrawal. Sting administered animals exhibited significant antidepressant effect in forced swim test (FST) these effects were not observed after withdrawal. Administration impaired long term memory in Morris water maze (MWM) but memory was improved upon withdrawal. These results are discussed in terms of the mechanism induced by synergistic components of Sting, associated with the behavioral toxicities observed. These results suggest that although Sting has shown very promising results in most of behavioral experimental paradigms but Sting induced impairment of memory during consumption could be related to its toxic side effects. Moreover long term studies could help us to strengthen this notion in exploring other Sting induced toxicities with larger n (number of animals). Toxicity surveillance of ED is essential because most of ingredients are under studied and not regulated. This might be a preliminary preclinical approach to establish awareness in Pakistani population with reference to energy boosting beverages.
Competitive tennis in the heat can prompt substantial sweat losses and extensive consequent body water and electrolyte deficits, as well as a level of thermal strain that considerably challenges a player's physiology, perception of effort, and on-court well-being and performance. Adequate hydration and optimal performance can be notably difficult to maintain when multiple same-day matches are played on successive days in hot weather. Despite the recognised effects of the heat, much more research needs to be carried out to better appreciate the broader scope and full extent of the physiological demands and hydration and thermal strain challenges facing junior and adult players in various environments, venues and competition scenarios. However, certain recommendations of best practices should be emphasised to minimise exertional heat illness risk and improve player safety, well-being and on-court performance.
The purpose of this study was to investigate the effectiveness of a caffeine-containing energy drink in enhancing rugby players' physical performance during a simulated match. A second purpose was to determine the urinary caffeine excretion derived from the energy drink intake. In a randomized and counterbalanced order, 26 elite rugby players (mean ± SD for age and body mass, 25 ± 2 y and 93 ± 15 kg) played 2 simulated rugby games (2 × 30 min) 60 min after ingesting (i) 3 mg of caffeine per kilogram of body mass in the form of an energy drink (Fure, ProEnergetics) or (ii) the same drink without caffeine (placebo). During the matches, the individual running distance and the instantaneous speed were measured, and the number of running actions above 20 km·h(-1) (i.e., sprints) were determined, using global positioning system devices. The number of impacts above 5 g during the matches was determined by accelerometry. The ingestion of the energy drink, compared with the placebo, increased the total distance covered during the match (4749 ± 589 vs 5139 ± 475 m, p < 0.05), the running distance covered at more than 20 km·h(-1) (184 ± 38 vs 208 ± 38 m, p < 0.05), and the number of sprints (10 ± 7 vs 12 ± 7, p < 0.05). The ingestion of the energy drink also resulted in a greater overall number of impacts (481 ± 352 vs 641 ± 366, p < 0.05) and a higher postexercise urine caffeine concentration (0.1 ± 0.1 vs 2.4 ± 0.9 μg·mL(-1), p < 0.05). The use of an energy drink with a caffeine dose equivalent to 3 mg·kg(-1) considerably enhanced the movement patterns of rugby players during a simulated match.
This study examined the rehydration achieved by drinking different beverages during a short-term recovery period (REC) after exercise-induced dehydration.
Thirteen well-trained men (age 22.1 ± 3.3 yr, body mass 61.2 ± 9.1 kg, VO(2max) 64.9 ± 4.0 ml · kg-1 · min-1, maximum heart rate 198 ± 7 beats/min) ran for 60 min on 3 occasions on a level treadmill at 70% VO(2max). All trials were performed in thermoneutral conditions (21 °C, 71% relative humidity) and were separated by at least 7 d. During 4 hr REC, the subjects consumed either a volume of a carbohydrate-electrolyte beverage (CE), lemon tea (LT), or distilled water (DW) equal to 150% of the body weight (BW) lost during the previous run. The fluid was consumed in 6 equal volumes at 30, 60, 90, 120, 150, and 180 min of REC.
After the completion of the 60-min run, the subjects lost ~2.0% of their preexercise BW in all trials, and no differences were observed in these BW changes between trials. At the end of REC, the greatest fraction of the retained drink occurred when the CE drink was consumed (CE vs. LT vs. DW: 52% ± 18% vs. 36% ± 15% vs. 30% ± 14%, p < .05). The CE drink also caused the least diuretic effect (CE vs. LT vs. DW: 638 ± 259 vs. 921 ± 323 vs. 915 ± 210 ml, p < .05) and produced the optimal restoration of plasma volume (CE vs. LT vs. DW: 11.2% ± 2.0% vs. -3.1% ± 1.8% vs. 0.2% ± 2.1%, p < .05).
The results of this study suggest that CE drinks are more effective than DW or LT in restoring fluid balance during short-term REC after exercise-induced dehydration.
There is a belief that caffeinated drinks, such as tea, may adversely affect hydration. This was investigated in a randomised controlled trial. Healthy resting males (n 21) were recruited from the general population. Following 24 h of abstention from caffeine, alcohol and vigorous physical activity, including a 10 h overnight fast, all men underwent four separate test days in a counter-balanced order with a 5 d washout in between. The test beverages, provided at regular intervals, were 4 × 240 ml black (i.e. regular) tea and 6 × 240 ml black tea, providing 168 or 252 mg of caffeine. The controls were identical amounts of boiled water. The tea was prepared in a standardised way from tea bags and included 20 ml of semi-skimmed milk. All food taken during the 12 h intervention period was controlled, and subjects remained at rest. No other beverages were offered. Blood was sampled at 0, 1, 2, 4, 8 and 12 h, and a 24 h urine sample was collected. Outcome variables were whole blood cell count, Na, K, bicarbonate, total protein, urea, creatinine and osmolality for blood; and total volume, colour, Na, K, creatinine and osmolality for urine. Although data for all twenty-one participants were included in the analysis (mean age 36 years and mean BMI 25·8 kg/m(2)), nineteen men completed all conditions. Statistical analysis, using a factorial ANOVA approach within PROC MIXED, revealed no significant differences between tea and water for any of the mean blood or urine measurements. It was concluded that black tea, in the amounts studied, offered similar hydrating properties to water.
Caffeine is a common substance in the diets of most athletes and it is now appearing in many new products, including energy drinks, sport gels, alcoholic beverages and diet aids. It can be a powerful ergogenic aid at levels that are considerably lower than the acceptable limit of the International Olympic Committee and could be beneficial in training and in competition. Caffeine does not improve maximal oxygen capacity directly, but could permit the athlete to train at a greater power output and/or to train longer. It has also ben shown to increase speed and/or power output in simulated race conditions. These effects have been found in activities that last as little as 60 seconds or as long as 2 hours. There is less information about the effects of caffeine on strength; however, recent work suggests no effect on maximal ability, but enhanced endurance or resistance to fatigue. There is no evidence that caffeine ingestion before exercise leads to dehydration, ion imbalance, or any other adverse effects. The ingestion of caffeine as coffee appears to be ineffective compared to doping with pure caffeine. Related compounds such as theophylline are also potent ergogenic aids. Caffeine may act synergistically with other drugs including ephedrine and anti-inflammatory agents. It appears that male and female athletes have similar caffeine pharmacokinetics, i.e., for a given dose of caffeine, the time course and absolute plasma concentrations of caffeine and its metabolites are the same. In addition, exercise or dehydration does not affect caffeine pharmacokinetics. The limited information available suggests that caffeine non-users and users respond similarly and that withdrawal from caffeine may not be important. The mechanism(s) by which caffeine elicits its ergogenic effects are unknown, but the popular theory that it enhances fat oxidation and spares muscle glycogen has very little support and is an incomplete explanation at best. Caffeine may work, in part, by creating a more favourable intracellular ionic environment in active muscle. This could facilitate force production by each motor unit.
Eight well-trained cyclists were dehydrated (median [P25-P75 percentiles]) 3.21 [2.97-3.56]% of body mass by cycling in the heat (28 C). During the first 2 h of recovery, the subjects randomly ingested ad libitum either a caffeinated soft drink (CC), a low Na+ mineral water (MW), or an isotonic carbohydrate-electrolyte solution (CES). Fluid intake and urine loss amounted respectively to 2.77 [2.34-2.85] kg, 1.00 [0.82-1.20] kg for CC, 2.15 [1.86-2.79] kg, 0.96 [0.40-1.49] kg for MW, and 2.86 [2.15-3.58] kg, 1.10 [0.86- 1.50] kg for CES. Electrolyte retention was calculated from electrolyte intake with the drink and loss with the urine. Consumption of CC and MW which were low in electrolytes resulted in marked loss of Na+, K+, Cl-, Mg2+ and Ca2+. Consumption of CES resulted in Na+, Mg2+ and Ca2+ retention while K+ and Cl- loss were not influenced. The significantly lower Na+, Mg2+ and Ca2+ loss with CES compared to both CC and MW may be explained by its higher electrolyte content in CES, compared to CC and MW, which only had minor amounts of these electrolytes. Furthermore, it was shown that CC potentiated urinary Mg2+ and Ca2+ excretion. It is concluded that: 1) Post-exercise MW or CC ingestion results in a negative electrolyte balance, 2) Caffeine containing beverages potentiate Mg2+ and Ca2+ excretion; 3) Consumption of CES containing moderate amounts of Na+, Mg2+ and Ca2+ results in sufficient replacement to compensate for urinary losses.
This study investigated the effects of caffeine supplementation on thermoregulation and body fluid balance during prolonged exercise in a thermoneutral environment (25 degrees C, 50% RH). Seven trained male subjects exercised on a treadmill at an intensity of 70-75% of maximal oxygen consumption to self-determined exhaustion. Subjects exercised once after caffeine and once after placebo ingestion, given in a double-blind crossover design. Five milligrams per kilogram body weight of caffeine followed by 2.5 mg.kg-1 of caffeine were given 2 and 0.5 h before exercise, respectively. Rectal temperature was recorded and venous blood samples were withdrawn every 15 min. Water loss and sweat rate were calculated from the difference between pre- and post-exercise body weight, corrected for liquid intake. Following caffeine ingestion, when compared with placebo, no significant difference in final temperature or in percent change in plasma volume were found. No significant differences were observed in total water loss (1376 +/- 154 vs. 1141 +/- 158 mL, respectively), sweat rate (12.4 +/- 1.1 vs. 10.9 +/- 0.7 g.m-2.min-1, respectively), rise in rectal temperature (2.1 +/- 0.3 vs. 1.5 +/- 0.4 degrees C, respectively), nor in the calculated rate of heat storage during exercise (134.4 +/- 17.7 vs. 93.5 +/- 22.5 W, respectively). Thus, in spite of the expected rise in oxygen uptake, caffeine ingestion under the conditions of this study does not seem to disturb body fluid balance or affect thermoregulation during exercise performance.
This study investigated the effects of acute ingestion of caffeine (C), ephedrine (E) and their combination (C+E) on time to exhaustion during high-intensity exercise. Using a repeated-measures, double-blind design, eight male subjects exercised on a cycle ergometer at a power output that led to exhaustion after about 12.6 min during a placebo (P) control trial. They did this 1.5 h after ingesting either C (5 mg · kg−1), E (1 mg · kg−1), C+E, or P. Trials were separated by 1 week. Venous blood was sampled before and during exercise. The mean (SD) times to exhaustion were 12.6 (3.1) (P), 14.4 (4.1) (C), 15.0 (5.7) (E) and 17.5 (5.8) (C+E) min. Only the C+E treatment significantly increased time to exhaustion compared to P. Oxygen consumption (V˙O2), carbon dioxide production (V˙CO2), minute ventilation (V˙
E) and the respiratory exchange ratio (RER) were similar during exercise for all trials. Heart rate during exercise was significantly increased for the C+E and C trials compared to P. Subjective ratings of perceived exertion during exercise were significantly lower after C+E compared to P. All treatments significantly increased lactate levels. Free fatty acid (FFA) levels were significantly increased by C ingestion. Glycerol levels were increased by C+E and C ingestion. Glucose levels were also higher with the drug treatments compared to P. Increased monamine availability after C+E treatment was suggested by measurements of catecholamines and dopamine. In conclusion, the combination of C+E significantly prolonged exercise time to exhaustion compared to P, while neither C nor E treatments alone significantly changed time to exhaustion. The improved performance was attributed to increased central nervous system stimulation.
The effect of addition of different dosages of caffeine (Caf) to a carbohydrate-electrolyte solution (CES) on metabolism, Caf excretion, and performance was examined. Subjects (n = 15) ingested 8 ml/kg of water placebo (Pla-W), 7% CES (Pla-CES), or 7% CES with 150, 225, and 320 mg/l Caf (CES-150, CES-225, and CES-320, respectively) during a warm-up protocol (20 min) and 3 ml/kg at one-third and two-thirds of a 1-h time trial. Performance was improved with Caf supplementation: 62.5 +/- 1.3, 61.5 +/- 1.1, 60.4 +/- 1.0, 58.9 +/- 1.0, and 58.9 +/- 1.2 min for Pla-W, Pla-CES, CES-150, CES-225, and CES-320, respectively. The postexercise urinary Caf concentration (range 1.3-2.5 microg/ml) was dose dependent and always far below the doping level of the International Olympic Committee (12 microg/ml) in all subjects. Sweat Caf excretion during exercise exceeded postexercise early-void urinary Caf excretion. Caffeinated CES did not enhance free fatty acid availability, ruling out the fact that performance improvement resulted from enhanced fat oxidation. It is concluded that addition of relatively low amounts of Caf to CES improves performance and that postexercise urinary Caf concentration remained low.
Caffeine is a common substance in the diets of most athletes and it is now appearing in many new products, including energy drinks, sport gels, alcoholic beverages and diet aids. It can be a powerful ergogenic aid at levels that are considerably lower than the acceptable limit of the International Olympic Committee and could be beneficial in training and in competition. Caffeine does not improve maximal oxygen capacity directly, but could permit the athlete to train at a greater power output and/or to train longer. It has also been shown to increase speed and/or power output in simulated race conditions. These effects have been found in activities that last as little as 60 seconds or as long as 2 hours. There is less information about the effects of caffeine on strength; however, recent work suggests no effect on maximal ability, but enhanced endurance or resistance to fatigue. There is no evidence that caffeine ingestion before exercise leads to dehydration, ion imbalance, or any other adverse effects. The ingestion of caffeine as coffee appears to be ineffective compared to doping with pure caffeine. Related compounds such as theophylline are also potent ergogenic aids. Caffeine may act synergistically with other drugs including ephedrine and anti-inflammatory agents. It appears that male and female athletes have similar caffeine pharmacokinetics, i.e., for a given dose of caffeine, the time course and absolute plasma concentrations of caffeine and its metabolites are the same. In addition, exercise or dehydration does not affect caffeine pharmacokinetics. The limited information available suggests that caffeine non-users and users respond similarly and that withdrawal from caffeine may not be important. The mechanism(s) by which caffeine elicits its ergogenic effects are unknown, but the popular theory that it enhances fat oxidation and spares muscle glycogen has very little support and is an incomplete explanation at best. Caffeine may work, in part, by creating a more favourable intracellular ionic environment in active muscle. This could facilitate force production by each motor unit.
In order to assess the intrarenal mechanisms responsible for the natriuretic action of caffeine, the renal clearances of (51)Cr-EDTA [used as a measure of glomerular filtration rate (GFR)] and lithium (used as an index of end-proximal fluid delivery) were measured in eight healthy males before (control period) and immediately after (experimental period) a 400 mg oral dose of caffeine (given over 90 min) or placebo. In caffeine-treated subjects, the fractional excretion of sodium rose from 1.00+/-0.25% in the control period to 1.47+/-0.18% in the experimental period, while corresponding values on the placebo day were 1.04+/-0.16% and 0.70+/-0.07% respectively. GFR was unchanged following either caffeine or placebo. When compared with the placebo day, caffeine caused increases in lithium clearance (experimental period values: caffeine, 37+/-1 ml/min; placebo, 28+/-2 ml/min; P <0.001), the fractional excretion of lithium (caffeine, 34+/-1%; placebo, 26+/-2%; P <0.001) and the sodium/lithium clearance ratio (used as an index of the fraction of sodium delivered to the distal nephron that escapes reabsorption therein: caffeine, 4.4+/-0.3%; placebo, 2.8+/-0.2%; P <0.001). These results suggest that reduced fractional sodium reabsorption in both the proximal tubule and the distal nephron contributes to the acute natriuretic effect of caffeine. The data also confirm the importance of controlling caffeine intake when investigating renal function using lithium clearance.
Both carbohydrate (CHO) and caffeine have been used as ergogenic aids during exercise. It has been suggested that caffeine increases intestinal glucose absorption, but there are also suggestions that it may decrease muscle glucose uptake. The purpose of the study was to investigate the effect of caffeine on exogenous CHO oxidation. In a randomized crossover design, eight male cyclists (age 27 +/- 2 yr, body mass 71.2 +/- 2.3 kg, maximal oxygen uptake 65.7 +/- 2.2 ml x kg(-1) x min(-1)) exercised at 64 +/- 3% of maximal oxygen uptake for 120 min on three occasions. During exercise subjects ingested either a 5.8% glucose solution (Glu; 48 g/h), glucose with caffeine (Glu+Caf, 48 g/h + 5 mg x kg(-1) x h(-1)), or plain water (Wat). The glucose solution contained trace amounts of [U-13C]glucose so that exogenous CHO oxidation could be calculated. CHO and fat oxidation were measured by indirect calorimetry, and 13C appearance in the expired gases was measured by continuous-flow IRMS. Average exogenous CHO oxidation over the 90- to 120-min period was 26% higher (P < 0.05) in Glu+Caf (0.72 +/- 0.04 g/min) compared with Glu (0.57 +/- 0.04 g/min). Total CHO oxidation rates were higher (P < 0.05) in the CHO ingestion trials compared with Wat, but they were highest when Glu+Caf was ingested (1.21 +/- 0.37, 1.84 +/- 0.14, and 2.47 +/- 0.23 g/min for Wat, Glu, and Glu+Caf, respectively; P < 0.05). There was also a trend (P = 0.082) toward an increased endogenous CHO oxidation with Glu+Caf (1.81 +/- 0.22 g/min vs. 1.27 +/- 0.13 g/min for Glu and 1.12 +/- 0.37 g/min for Wat). In conclusion, compared with glucose alone, 5 mg x kg(-1) x h(-1) of caffeine coingested with glucose increases exogenous CHO oxidation, possibly as a result of an enhanced intestinal absorption.
The development of symptomatic hyponatraemia consequent on participation in marathon and ultraendurance races has led to questions about its aetiology and prevention.
To evaluate: (a) the assertion that sweat sodium losses cannot contribute to the development of hyponatraemia during endurance exercise; (b) the adequacy of fluid replacement recommendations issued by the International Marathon Medical Directors Association (IMMDA) for races of 42 km or longer; (c) the effectiveness of commercial sports drinks, compared with water, for attenuating plasma sodium reductions.
A mathematical model was used to predict the effects of different drinking behaviours on hydration status and plasma sodium concentration when body mass, body composition, running speed, weather conditions, and sweat sodium concentration were systematically varied.
Fluid intake at rates that exceed sweating rate is predicted to be the primary cause of hyponatraemia. However, the model predicts that runners secreting relatively salty sweat can finish ultraendurance exercise both dehydrated and hyponatraemic. Electrolyte-containing beverages are predicted to delay the development of hyponatraemia. The predictions suggest that the IMMDA fluid intake recommendations adequately sustain hydration over the 42 km distance if qualifiers-for example, running pace, body size-are followed.
Actions to prevent hyponatraemia should focus on minimising overdrinking relative to sweating rate and attenuating salt depletion in those who excrete salty sweat. This simulation demonstrates the complexity of defining fluid and electrolyte consumption rates during athletic competition.
This double-blind experiment examined the effects of a caffeinated sports drink during prolonged cycling in a warm environment. Sixteen highly trained cyclists completed 3 trials: placebo, carbohydrate-electrolyte sports drink (CES), and caffeinated sports drink (CES+CAF). Subjects cycled for 135 min, alternating between 60% and 75% VO2max every 15 min for the first 120 min, followed by a 15-min performance ride. Maximal voluntary (MVC) and electrically evoked contractile properties of the knee extensors were measured before and after cycling. Work completed during the performance ride was 15-23% greater for CES+CAF than for the other beverages. Ratings of perceived exertion were lower with CES+CAF than with placebo and CES. After cycling, the MVC strength loss was two-thirds less for CES+CAF than for the other beverages (5% vs. 15%). Data from the interpolated-twitch technique indicated that attenuated strength loss with CES+CAF was explained by reduced intrinsic muscle fatigue.
Caffeine is regarded as a diuretic despite evidence that hydration is not impaired with habitual ingestion. The purpose of this study was to determine whether a caffeinated sports drink impairs fluid delivery and hydration during exercise in warm, humid conditions (28.5 degrees C, 60% relative humidity). Sixteen cyclists completed 3 trials: placebo (P), carbohydrate-electrolyte (CE), and caffeinated (195 mg/L) sports drink (CAF+CE). Subjects cycled for 120 min at 60-75%VO2max followed by 15 min of maximal-effort cycling. Heart rate and rectal temperature were similar until the final 15 min, when these responses and exercise intensity were higher with CAF+CE than with CE and P. Sweat rate, urine output, plasma- volume losses, serum electrolytes, and blood deuterium-oxide accumulation were not different. Serum osmolality was higher with CAF+CE vs. P but not CE. The authors conclude that CAF+CE appears as rapidly in blood as CE and maintains hydration and sustains cardiovascular and thermoregulatory function as well as CE during exercise in a warm, humid environment.
The effect of caffeine on the resting metabolic rate (RMR) was investigated in endurance exercise-trained (N=14) and inactive (N=10) male individuals. Subjects were also classified into regular and non-regular consumers of caffeine. After an overnight fast, RMR was measured Using an indirect calorimeter open circuit system.Thereafter, Subjects orally an indirect consumed 300 mg of caffeine, after which RMR was measured for 90 min.Five of the exercise-trained subjects were also studied after the administration of a placebo.Plasma concentration of glycerol and free fatty acid andrespiratory exchange ratio (R) were measured at each 15-min interval. Before caffeine ingestion, no significant differences were observed in RMR, R, glycerol, free fatty acid and blood pressure levels between exercise-trained and inactive groups. Following caffeine consumption, a three-way analysis of variance revealed that inactive subjects exhibited a greater increase (P<0.05) in RMR than did exercise-trained subjects. No significant differences were observed in RMR response between regular or nonregular consumers of caffeine. Moreover, no differences were observed in glycerol, free fatty acid, heart rate, and blood pressure response between exercise-trained and inactive subjects and between regular and non-regular consumers of caffeine. These results suggest that endurance training results in a reduced thermogenic response to a caffeine challenge. (C)1985The American College of Sports Medicine
Using a double-blind, randomized, cross-over protocol, we studied the effect of a single dose of oral caffeine on plasma renin activity, catecholamines and cardiovascular control in nine healthy, young, non-coffee drinkers maintained in sodium balance throughout the study period. Caffeine (250 mg) or placebo was administered in a methylxanthine-free beverage to overnight-fasted supine subjects who had had no coffee, tea or cola in the previous three weeks. Caffeine increased plasma renin activity by 57 per cent, plasma norepinephrine by 75 per cent and plasma epinephrine by 207 per cent. Urinary normetanephrine and metanephrine were increased 52 per cent and 100 per cent respectively. Mean blood pressure rose 14/10 mm Hg one hour after caffeine ingestion. There was a slight fall and then a rise in heart rate. Plasma caffeine levels were usually maximal one hour after ingestion but there was considerable individual variation. A 20 per cent increase in respiratory rate correlated well with plasma caffeine levels. Under the conditions of study caffeine was a potent stimulator of plasma renin activity and adrenomedullary secretion. Whether habitual ingestion has similar effects remains to be determined.
The purpose of this experiment was to determine whether fluid ingestion attenuates the hyperthermia and cardiovascular drift that occurs during exercise dehydration due to increases in blood volume. In addition, forearm blood flow, which is indicative of skin blood flow, was measured to determine whether the attenuation of hyperthermia and cardiovascular drift during exercise with fluid ingestion is due to higher skin blood flow. On three different occasions, seven trained cyclists [mean age, body weight, and maximum oxygen uptake: 23 +/- 3 yr, 73.9 +/- 10.5 kg, and 4.75 +/- 0.34 (SD) l/min, respectively] cycled at a power output equal to 62-67% maximum oxygen uptake for 2 h in a warm environment (33 degrees C, 50% relative humidity, wind speed 2.5 m/s). During exercise, they randomly received no fluid (NF) or a volume of a carbohydrate-electrolyte fluid replacement solution (FR) sufficient to replace 80 +/- 2% of sweat loss or were intravenously infused with 5.3 ml/kg of a blood volume expander (BVX; 6% dextran in saline). The infusion of 398 +/- 23 ml of BVX maintained blood volume at levels similar to that when 2,404 +/- 103 ml of fluid were ingested during FR and greater than that when no fluid was ingested during the 2nd h of exercise (P less than 0.05). However, BVX and NF resulted in similar esophageal and rectal temperatures, forearm blood flow, and elevations in serum osmolality and sodium concentration during 2 h of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)
This study assessed the effectiveness of two common rehydration beverages (a caffeinated diet cola (DC) and a 6% carbohydrate-electrolyte (CE) solution) compared with water (W) for whole body rehydration, gastric emptying and blood volume (BV) restoration during a 2 h rehydration period following exercise-induced dehydration. Subjects (mean VO2max = 4.2 +/- 0.6 l.min-1.min-1; n = 19) exercised at 60-80% VO2max in the heat (32 degrees C; 40% rh) until approximately 2.5% (1.95 +/- 0.12 kg) of their body weight (BW) was lost. After exercise, the subjects sat for 2 h in a thermoneutral environment (21 degrees C; 60% rh) and drank a volume of DC, W and CE equal to the fluid lost. Fluids were consumed in two boluses averaging 1,046 +/- 198 and 912 +/- 186 ml at 0 and 45 min of the 2 h rehydration period, respectively. At the end of the rehydration period, no fluid remained in the stomach during any of the trials as indicated by epigastric impedance. However, in all the trials the subjects were somewhat hypohydrated (range 0.6-0.9 kg BW below euhydrated BW; p less than 0.05) after the 2 h rehydration period since additional water and BW were lost as a result of urine formation, respiration, sweat and metabolism. The percentage of body weight loss that was regained (used as an index of % rehydration) during DC (54 +/- 5%) was significantly lower than that of W and CE (64 +/- 5% and 69 +/- 5%, respectively; p less than 0.05; n = 10).(ABSTRACT TRUNCATED AT 250 WORDS)
Thirty-seven women, aged 31-78 years, on two separate mornings consumed a decaffeinated beverage to which 6 mg caffeine/kg lean body mass or no caffeine were added. Total urine output of water, calcium, magnesium, sodium, chloride, potassium and creatinine increased in the two hours following caffeine ingestion when compared to the control beverage. Increased urinary mineral (mg)/urinary creatinine (g) ratios were seen for calcium (120 to 200), magnesium (70 to 110), sodium (3,800 to 6,200) and chloride (9,200 to 14,800), following the caffeinated beverage. Creatinine clearance did not change significantly. The percent reabsorption of calcium (98.6% to 97.5%, p less than .001) and magnesium (97.0% to 94.2%, p less than .0001) decreased significantly during the post-caffeine period. The calcium and magnesium filtered loads did not differ significantly between the caffeine and no caffeine beverages. Therefore, caffeine-induced urinary loss of calcium and magnesium is largely attributable to a reduction in calcium and magnesium renal reabsorption, although the physiological mechanism and tubular segment affected remain to be established.
The effect of caffeine on the resting metabolic rate (RMR) was investigated in endurance exercise-trained (N = 14) and inactive (N = 10) male individuals. Subjects were also classified into regular and non-regular consumers of caffeine. After an overnight fast, RMR was measured using an indirect calorimetry open circuit system. Thereafter, subjects orally consumed 300 mg of caffeine, after which RMR was measured for 90 min. Five of the exercise-trained subjects were also studied after the administration of a placebo. Plasma concentrations of glycerol and free fatty acid and respiratory exchange ratio (R) were measured at each 15-min interval. Before caffeine ingestion, no significant differences were observed in RMR, R, glycerol, free fatty acid and blood pressure levels between exercise-trained and inactive groups. Following caffeine consumption, a three-way analysis of variance revealed that inactive subjects exhibited a greater increase (P less than 0.05) in RMR than did exercise-trained subjects. No significant differences were observed in RMR response between regular or nonregular consumers of caffeine. Moreover, no differences were observed in glycerol, free fatty acid, heart rate, and blood pressure response between exercise-trained and inactive subjects and between regular and non-regular consumers of caffeine. These results suggest that endurance training results in a reduced thermogenic response to a caffeine challenge.
Observations on hematocrit (Hct) and hemoglobin (Hb) were made in 6 men before and after running long enough to cause a 4% decrease in body weight. Subscripts B and A were used to denote before dehydration and after dehydration, respectively. Relations were derived between BV(b), BV(a), HB(b), Hb(a), Hct(b), and Hct(a) with which the percentage decreases in BV, CV, and PV can be calculated, as well as the concentration of hemoglobin in red cells, g/100 ml-1 (MCHC). When subjects reach the same level of dehydration the water loss from the various body compartments may vary reflecting the difference in salt losses in sweat. Changes in PV calculated from the increase in plasma protein concentration averaged -7.5% compared with -12.2% calculated from changes in Hb and Hct. The difference could be accounted for by a loss of 6% plasma protein from the circulation.
Evaporative water loss from the respiratory tract was determined over a wide range of exercise. The absolute humidity of the expired air was the same at all levels of exercise and equal to that measured at rest. The rate of respiratory water loss during exercise was found to be 0.019 of the oxygen uptake times (44 minus water vapor pressure). The rate of weight loss during exercise due to CO2-O2 exchange was calculated. For exercise at oxygen consumption rates exceeding 1.5 L/min in a dry environment with a water vapor pressure of 10 mm Hg, the total rate of weight loss via the respiratory tract is on the order of 2-5 g/min.
1. We manipulated plasma catecholamines (combined adrenaline and noradrenaline concentrations) to three levels during prolonged exercise to determine their effect on cutaneous and forearm vascular conductance (CVC and FVC), oesophageal temperature (T(oes)) and cardiovascular responses. 2. On three occasions, seven endurance-trained men cycled at 65% VO2, max in the heat (33.1 +/- 0.7 degrees C) for 120-150 min. During the control trial (150 min duration), 0.45% saline was intravenously infused (SI) starting at 30 min, at a rate that replaced a third of the fluid losses. The infusion start time and rate were identical in all three trials. During SI, plasma catecholamine levels increased progressively and were 18.2 +/- 2.7 pmol ml-1 at 150 min. In another trial (120 min duration), adrenaline was infused (AI) at 0.1 microgram kg-1 min-1 and plasma catecholamine levels were elevated 6 pmol ml-1 above SI during the 60-120 min period. In a third trial (150 min duration), an 18% glucose solution was infused (GI) at a rate that maintained plasma glucose levels above 11 mM and plasma catecholamine levels were 5.0-5.5 pmol ml-1 lower (P < 0.05) than SI from 120-150 min. 3. Heat production and sweat rate were not different during the three trials and neither was the decline in stroke volume, cardiac output and mean arterial pressure. 4. Soon after beginning AI, CVC decreased 15%, T(oes) increased by 0.4 +/- 0.1 degree C and heart rate increased by 6 +/- 1 beats min-1; these significant (P < 0.05) differences from SI were maintained throughout the bout. As a result of GI, FVC was 15% higher than SI and T(oes) and heart rate were attenuated by 0.3 +/- 0.1 degree C and 7 +/- 1 beats min-1 at 150 min compared with SI (P < 0.05). 5. In conclusion, large increases in plasma catecholamine levels cause hyperthermia during exercise by vasoconstricting the skin. The mechanisms by which hyperglycaemia (i.e. 11 mM) attenuates hyperthermia are less clear and may be due to others factors besides attenuation of the plasma catecholamine response to exercise.
We compared the effects of caffeinated vs non-caffeinated carbohydrate electrolyte (CE) drinks on urine volume (UV), free water clearance (CH2O), fractional excretion of water (FEH2O), and osmolar excretion during 4 h of rest or 1 h rest followed by 3 h of cycling at 60% VO2max in six subjects. We also tested maximal performance at 85% VO2max following the 3-h exercise trials. Throughout the two resting trials and the two rest + exercise trials, subjects ingested CE (total volume = 35 ml/kg) without (PLAC) or with (CAFF) caffeine (25 mg/dl). Blood samples were collected, and body weight and UV were recorded every hour. Urine and blood were analyzed for osmolality and creatinine, and plasma catecholamine concentrations were determined. At rest, mean (+/-SE) UV between 60 min and 240 min was greater for CAFF (1843 +/- 166 ml) vs PLAC (1411 +/- 181 ml) (p < 0.01); during exercise the difference in UV between CAFF (398 +/- 32 ml) and PLAC (490 +/- 57 ml) was not significant. Cycling performance was unaffected by caffeine. Plasma catecholamine concentrations were not different between PLAC and CAFF but were greater during exercise than rest (p < 0.01) and may have counteracted the diuretic effect of caffeine observed at rest. Thus, CAFF consumed in CE during moderate endurance exercise apparently does not compromise bodily hydration status.
This study examined the acute effects of caffeine on the cardiovascular system during dynamic leg exercise. Ten trained, caffeine-naive cyclists (7 women and 3 men) were studied at rest and during bicycle ergometry before and after the ingestion of 6 mg/kg caffeine or 6 mg/kg fructose (placebo) with 250 ml of water. After consumption of caffeine or placebo, subjects either rested for 100 min (rest protocol) or rested for 45 min followed by 55 min of cycle ergometry at 65% of maximal oxygen consumption (exercise protocol). Measurement of mean arterial pressure (MAP), forearm blood flow (FBF), heart rate, skin temperature, and rectal temperature and calculation of forearm vascular conductance (FVC) were made at baseline and at 20-min intervals. Plasma ANG II was measured at baseline and at 60 min postingestion in the two exercise protocols. Before exercise, caffeine increased both systolic blood pressure (17%) and MAP (11%) without affecting FBF or FVC. During dynamic exercise, caffeine attenuated the increase in FBF (53%) and FVC (50%) and accentuated exercise-induced increases in ANG II (44%). Systolic blood pressure and MAP were also higher during exercise plus caffeine; however, these increases were secondary to the effects of caffeine on resting blood pressure. No significant differences were observed in heart rate, skin temperature, or rectal temperature. These findings indicate that caffeine can alter the cardiovascular response to dynamic exercise in a manner that may modify regional blood flow and conductance.
Caffeine can enhance mean arterial blood pressure (MAP) and attenuate forearm blood flow (FBF) and forearm vascular conductance (FVC) during exercise in thermal neutral conditions without altering body temperature. During exercise at higher ambient temperatures, where a greater transfer of heat from the body core to skin would be expected, caffeine-induced attenuation of FBF (i.e. cutaneous blood flow) could attenuate heat dissipation and increase body temperature (T(re)). We hypothesized that during exercise at an ambient temperature of 38 degrees C, caffeine increases MAP, and attenuates FBF and FVC such that T(re) is increased. Eleven caffeine-naive, active men, were studied at rest and during exercise after ingestion of a placebo or 6 mg kg(-1) of caffeine. MAP, heart rate (HR), FBF, FVC, T(re) skin temperature (T(sk)) and venous lactate concentrations (lactate) were assessed sequentially during rest at room temperature, after 45 min of exposure to an ambient temperature of 38 degrees C, and during 35 min of submaximal cycling. Heat exposure caused increases in MAP, FBF, FVC and T(sk) that were not altered by caffeine. HR, T(re), and lactate were unaffected. During exercise, only MAP (95 +/- 2 vs. 102 +/- 2 mmHg), HR (155 +/- 10 vs. 165 +/- 10 beats min(-1)), and lactate (2.0 +/- 0.4 vs. 2.3 +/- 0.4 mmol l(-1)) were increased by caffeine. These data indicate that increases in cutaneous blood flow during exercise in the heat are not reduced by caffeine. This may be because of activation of thermal reflexes that cause cutaneous vasodilation capable of offsetting caffeine-induced reductions in blood flow. Caffeine-induced increases in lactate, MAP and HR during exercise suggest that this drug and high ambient temperatures increase production of muscle metabolites that cause reflex cardiovascular responses.
Recreational enthusiasts and athletes often are advised to abstain from consuming caffeinated beverages (CB). The dual purposes of this review are to (a) critique controlled investigations regarding the effects of caffeine on dehydration and exercise performance, and (b) ascertain whether abstaining from CB is scientifically and physiologically justifiable. The literature indicates that caffeine consumption stimulates a mild diuresis similar to water, but there is no evidence of a fluid-electrolyte imbalance that is detrimental to exercise performance or health. Investigations comparing caffeine (100-680 mg) to water or placebo seldom found a statistical difference in urine volume. In the 10 studies reviewed, consumption of a CB resulted in 0-84% retention of the initial volume ingested, whereas consumption of water resulted in 0-81% retention. Further, tolerance to caffeine reduces the likelihood that a detrimental fluid-electrolyte imbalance will occur. The scientific literature suggests that athletes and recreational enthusiasts will not incur detrimental fluid-electrolyte imbalances if they consume CB in moderation and eat a typical U.S. diet. Sedentary members of the general public should be a less risk than athletes because their fluid losses via sweating are smaller.
On the basis of an analysis of the skin temperature data on three resting human subjects from 112 experiments, a simple weighting system for computing the mean skin temperature from observations on four areas of the body, namely, chest, arms, thighs, and legs, has been proposed. The proposed system of weighting yields mean skin temperature values identical with the elaborate Hardy-Dubois weighting formula. The value of the medial thigh temperature as an index of the mean skin temperature has also been investigated and discussed.
skin temperature measurement
Submitted on May 20, 1963
Dietitians, exercise physiologists, athletic trainers, and other sports medicine personnel commonly recommend that exercising adults and athletes refrain from caffeine use because it is a diuretic, and it may exacerbate dehydration and hyperthermia. This review, contrary to popular beliefs, proposes that caffeine consumption does not result in the following: (a) water-electrolyte imbalances or hyperthermia and (b) reduced exercise-heat tolerance.
To determine the effect of water, carbohydrate, and caffeine ingestion on fatigue during prolonged exercise in the heat.
Seven endurance-trained cyclists (V O2max = 61 +/- 8 mL.kg.min) pedaled for 120 min at 63% V O2max in a hot-dry environment (36 degrees C; 29% humidity), ingesting either no fluid (NF), water (WAT) to replace 97% fluid losses, the same volume of a 6% carbohydrate-electrolyte solution (CES), or each of these treatments along with ingestion of 6 mg of caffeine per kilogram of body weight (NF + CAFF, WAT + CAFF, and CES + CAFF). At regular intervals during exercise, maximal cycling power (PMAX) was measured. Before and after exercise, maximal voluntary contraction (MVC), voluntary activation (VA), and electrically evoked contractile properties of the quadriceps were determined.
Without fluid replacement (NF and NF + CAFF), subjects were dehydrated by 3.8 +/- 0.3%, and rectal temperature reached 39.4 +/- 0.3 degrees C, while it was maintained at 38.7 +/- 0.3 degrees C in trials with rehydration (P < 0.05). Trials with caffeine ingestion increased PMAX by 3% above trials without caffeine (P < 0.05). MVC reductions after exercise were larger with NF (-11 +/- 5%) than for the rest of the trials (P < 0.05). MVC was reduced in WAT compared with CES + CAFF (-6 +/- 4 vs 2 +/- 4%; P < 0.05). However, NF + CAFF maintained MVC at the level of the CES trial. VA showed the same treatment response pattern as MVC. There were no differences in electrically evoked contractile properties among trials.
During prolonged exercise in the heat, caffeine ingestion (6 mg.kg body weight) maintains MVC and increases PMAX despite dehydration and hyperthermia. When combined with water and carbohydrate, caffeine ingestion increases maximal leg force by increasing VA (i.e., reducing central fatigue).
This study investigated the effects of three different doses of caffeine on physiological responses to exercise in young children.
Forty healthy children (20 boys and 20 girls) volunteered for a random, double-blind, counterbalanced study where they received either placebo (PL), 1 mg.kg(-1) (CAF-1), 3 mg.kg(-1) (CAF-3), or 5 mg.kg(-1) (CAF-5) caffeine, 60 min prior to preexercise measures, followed by cycle ergometer exercise at 25 W and then 60% VO2peak. During this time, heart rate (HR), oxygen consumption (VO2), and respiratory exchange ratio (RER) were measured continuously, while blood pressure (BP) was measured every 2 min.
There were no significant gender x treatment interactions, and so the boys' and girls' data were combined. At preexercise, CAF-5 SBP and DBP were significantly (P < 0.05) higher than PL. Both CAF-1 and CAF-3 DBP were also significantly (P < 0.05) higher versus PL at preexercise. There were no treatment effects for exercise BP. At rest and during both exercise intensities, HR was significantly (P < 0.05) lower in CAF-3 (approximately 5 bpm) and CAF-5 (approximately 6 bpm) versus PL. There were no significant effects of CAF on metabolism (VO2 or RER) except for a lower RER in CAF-1 versus CAF-5 at 60% VO2peak.
Low, mild, and moderate (1, 3, and 5 mg.kg(-1)) doses of caffeine have no effect on substrate use as reflected by RER. Further, caffeine intake resulted in an increase in BP and decrease in HR at preexercise and a slight decrease in HR with CAF-3 and CAF-5 versus PL during exercise.