Juan Del Coso

Caffeine effects on short-term performance during prolonged exercise in the heat.

PURPOSE To determine the effect of water, carbohydrate, and caffeine ingestion on fatigue during prolonged exercise in the heat. METHODS 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. RESULTS 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. CONCLUSION 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).

Dose response effects of a caffeine-containing energy drink on muscle performance: a repeated measures design.

BackgroundEnergy drinks have become the most used caffeine-containing beverages in the sport setting. The aim of this study was to determine the effects of two doses of a caffeine-containing energy drink on muscle performance during upper- and lower-body power-load tests.MethodsIn a randomized order, twelve active participants ingested 1 and 3 mg of caffeine per kg of body weight using a commercially available energy drink (Fure®, ProEnergetics) or the same drink without caffeine (placebo; 0 mg/kg). After sixty minutes, resting metabolic rate, heart rate and blood pressure were determined. Then, half-squat and bench-press power production with loads from 10 to 100% of 1 repetition maximum was determined using a rotator encoder.ResultsIn comparison to the placebo, the ingestion of the caffeinated drink increased mean arterial pressure (82 ± 7 < 88 ± 8 ≈ 90 ± 6 mmHg for 0 mg/kg, 1 mg/kg, 3 mg/kg of caffeine, respectively; P < 0.05) and heart rate (57 ± 7 < 59 ± 8 < 62 ± 8 beats/min, respectively; P < 0.05) at rest in a dose response manner, though it did not affect resting metabolic rate. While the ingestion of 1 mg/kg of caffeine did not affect maximal power during the power-load tests with respect to the placebo, 3 mg/kg increased maximal power in the half-squat (2554 ± 167 ≈ 2549 ± 161 < 2726 ± 167 W, respectively; P < 0.05) and bench-press actions (349 ± 34 ≈ 358 ± 35 < 375 ± 33 W, respectively; P < 0.05).ConclusionsA caffeine dose of at least 3 mg/kg in the form of an energy drink is necessary to significantly improve half-squat and bench-press maximal muscle power.

Caffeine during Exercise in the Heat: Thermoregulation and Fluid-Electrolyte Balance

PURPOSE To investigate the effects of caffeine ingestion on thermoregulation and fluid-electrolyte losses during prolonged exercise in the heat. METHODS 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. RESULTS 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). CONCLUSION 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.

Muscle Damage and Its Relationship with Muscle Fatigue During a Half-Iron Triathlon

Background To investigate the cause/s of muscle fatigue experienced during a half-iron distance triathlon. Methodology/Principal Findings We recruited 25 trained triathletes (36±7 yr; 75.1±9.8 kg) for the study. Before and just after the race, jump height and leg muscle power output were measured during a countermovement jump on a force platform to determine leg muscle fatigue. Body weight, handgrip maximal force and blood and urine samples were also obtained before and after the race. Blood myoglobin and creatine kinase concentrations were determined as markers of muscle damage. Results Jump height (from 30.3±5.0 to 23.4±6.4 cm; P<0.05) and leg power output (from 25.6±2.9 to 20.7±4.6 W · kg−1; P<0.05) were significantly reduced after the race. However, handgrip maximal force was unaffected by the race (430±59 to 430±62 N). Mean dehydration after the race was 2.3±1.2% with high inter-individual variability in the responses. Blood myoglobin and creatine kinase concentration increased to 516±248 µg · L−1 and 442±204 U · L−1, respectively (P<0.05) after the race. Pre- to post-race jump change did not correlate with dehydration (r = 0.16; P>0.05) but significantly correlated with myoglobin concentration (r = 0.65; P<0.001) and creatine kinase concentration (r = 0.54; P<0.001). Conclusions/significance During a half-iron distance triathlon, the capacity of leg muscles to produce force was notably diminished while arm muscle force output remained unaffected. Leg muscle fatigue was correlated with blood markers of muscle damage suggesting that muscle breakdown is one of the most relevant sources of muscle fatigue during a triathlon.

Running Pace Decrease during a Marathon Is Positively Related to Blood Markers of Muscle Damage

Background Completing a marathon is one of the most challenging sports activities, yet the source of running fatigue during this event is not completely understood. The aim of this investigation was to determine the cause(s) of running fatigue during a marathon in warm weather. Methodology/Principal Findings We recruited 40 amateur runners (34 men and 6 women) for the study. Before the race, body core temperature, body mass, leg muscle power output during a countermovement jump, and blood samples were obtained. During the marathon (27 °C; 27% relative humidity) running fatigue was measured as the pace reduction from the first 5-km to the end of the race. Within 3 min after the marathon, the same pre-exercise variables were obtained. Results Marathoners reduced their running pace from 3.5 ± 0.4 m/s after 5-km to 2.9 ± 0.6 m/s at the end of the race (P<0.05), although the running fatigue experienced by the marathoners was uneven. Marathoners with greater running fatigue (> 15% pace reduction) had elevated post-race myoglobin (1318 ± 1411 v 623 ± 391 µg L−1; P<0.05), lactate dehydrogenase (687 ± 151 v 583 ± 117 U L−1; P<0.05), and creatine kinase (564 ± 469 v 363 ± 158 U L−1; P = 0.07) in comparison with marathoners that preserved their running pace reasonably well throughout the race. However, they did not differ in their body mass change (−3.1 ± 1.0 v −3.0 ± 1.0%; P = 0.60) or post-race body temperature (38.7 ± 0.7 v 38.9 ± 0.9 °C; P = 0.35). Conclusions/Significance Running pace decline during a marathon was positively related with muscle breakdown blood markers. To elucidate if muscle damage during a marathon is related to mechanistic or metabolic factors requires further investigation.

Thermoregulatory responses to constant versus variable-intensity exercise in the heat.

PURPOSE To compare the thermoregulatory responses between constant (CON) and variable-intensity exercise (VAR) in a dry-hot environment (36 degrees C, 29% relative humidity, and 2.5 m x s(-1) airflow). METHODS In a random order, seven endurance-trained, heat-acclimated subjects cycled either at 60% VO2max (CON) or alternating 1.5 min at 90% VO2max with 4.5 min at 50% VO2max (VAR). Total work output (915 +/- 100 kJ) and exercise duration (90 min) were identical in both trials. RESULTS Net metabolic heat production was not different between trials (394 +/- 12 vs 408+/- 11 W x m(-2) for VAR vs CON). However, heat storage (60 +/- 3 vs 48 +/- 4 W x m(-2)), the increase in rectal temperature (1.6 +/- 0.1 vs 1.3 +/- 0.1 degrees C), and final heart rate (HR; 147 +/- 5 vs 141 +/- 4 beats x min(-1)) were all higher for VAR than for CON (P < 0.05). During VAR, averaged forearm skin blood flow (S(K)BF) was lower, whereas whole-body sweat rate (1.23 +/- 0.1 vs 1.11 +/- 0.1 L x h(-1)) and dehydration (2.8 +/- 0.1% vs 2.5 +/- 0.2%) were higher than during CON (P < 0.05). Final blood lactate during VAR was higher than during CON (3.5+/- 0.4 vs 2.1 +/- 0.3 mmol x L(-1); P < 0.05). CONCLUSION Ninety minutes of variable-intensity exercise in a hot environment increases heat storage and fluid deficit in comparison to the same amount of work performed in a constant-load mode. VAR increases not only thermal (i.e., heat storage) but also cardiovascular (i.e., heart rate) and metabolic (i.e., blood lactate) stresses, which makes it less advisable than CON when the goal is to minimize physiological stress.

Anaerobic performance when rehydrating with water or commercially available sports drinks during prolonged exercise in the heat

The effects that rehydrating drinks ingested during exercise may have on anaerobic exercise performance are unclear. This study aimed to determine which of four commercial rehydrating drinks better maintains leg power and force during prolonged cycling in the heat. Seven endurance-trained and heat-acclimatized cyclists pedaled for 120 min at 63% maximum oxygen consumption in a hot, dry environment (36 degrees C; 29% humidity, 1.9 m.s-1 airflow). In five randomized trials, during exercise, subjects drank 2.4 +/- 0.1 L of (i) mineral water (WAT; San Benedetto), (ii) 6% carbohydrate-electrolyte solution (Gatorade lemon), (iii) 8% carbohydrate-electrolyte solution (Powerade Citrus Charge), (iv) 8% carbohydrate-electrolyte solution with lower sodium concentration than other sports drinks (Aquarius orange), or (v) did not ingest any fluid (DEH). Fluid balance, rectal temperature (Trec), maximal cycling power (Pmax), and leg maximal voluntary isometric contraction (MVC) were measured. During DEH, subjects lost 3.7 +/- 0.2% of initial body mass, whereas subjects lost only 0.8% +/- 0.1% in the other trials (p < 0.05). Final Trec was higher in DEH than in the rest of the trials (39.4 +/- 0.1 degrees C vs. 38.7 +/- 0.1 degrees C; p < 0.05). Pmax was similar among all trials. Gatorade and Powerade preserved MVC better than DEH (-3.1% +/- 2% and -3.8% +/- 2% vs. -11% +/- 2%, p < 0.05), respectively, whereas WAT and Aquarius did not (-6% +/- 2%). Compared with DEH, rehydration with commercially available sports drinks during prolonged exercise in the heat preserves leg force, whereas rehydrating with water does not. However, low sodium concentration in a sports drink seems to preclude its ergogenic effects on force.

Enhancing physical performance in male volleyball players with a caffeine-containing energy drink.

There are no scientific data about the effects of caffeine intake on volleyball performance. The aim of this study was to investigate the effect of a caffeine-containing energy drink to enhance physical performance in male volleyball players. A double-blind, placebo-controlled, randomized experimental design was used. In 2 different sessions separated by 1 wk, 15 college volleyball players ingested 3 mg of caffeine per kg of body mass in the form of an energy drink or the same drink without caffeine (placebo). After 60 min, participants performed volleyball-specific tests: standing spike test, maximal squat jump (SJ), maximal countermovement jump (CMJ), 15-s rebound jump test (15RJ), and agility T-test. Later, a simulated volleyball match was played and recorded. In comparison with the placebo drink, the ingestion of the caffeinated energy drink increased ball velocity in the spike test (73 ± 9 vs 75 ± 10 km/h, P < .05) and the mean jump height in SJ (31.1 ± 4.3 vs 32.7 ± 4.2 cm, P < .05), CMJ (35.9 ± 4.6 vs 37.7 ± 4.4 cm, P < .05), and 15RJ (29.0 ± 4.0 vs 30.5 ± 4.6 cm, P < .05). The time to complete the agility test was significantly reduced with the caffeinated energy drink (10.8 ± 0.7 vs 10.3 ± 0.4 s, P < .05). In addition, players performed successful volleyball actions more frequently (24.6% ± 14.3% vs 34.3% ± 16.5%, P < .05) with the ingestion of the caffeinated energy drink than with the placebo drink during the simulated game. A caffeine-containing energy drink, with a dose equivalent to 3 mg of caffeine per kg body mass, might be an effective ergogenic aid to improve physical performance and accuracy in male volleyball players.

Injuries Among Spanish Male Amateur Soccer Players A Retrospective Population Study

Background: Soccer is the most popular sport worldwide, with about 265 million players, both professionals and amateurs. Most research investigating soccer injuries has focused on professional players because they have greater exposure time, but most soccer players are at the recreational level. Purpose: To undertake a retrospective epidemiological study of the injuries sustained in Spanish amateur soccer during the 2010-2011 season. Study Design: Descriptive epidemiological study. Methods: Any injuries incurred by the 134,570 recreational soccer players (aged 18-55 years) registered with the Spanish Football Federation were reported to the federation’s medical staff. A standardized medical questionnaire, based on the Fédération International de Football Association (FIFA) Medical and Research Centre (F-MARC) consensus for collection procedures in studies of soccer injuries, was used to classify the injury according to type, severity, location, and treatment. Results: A total of 15,243 injuries were reported, with an average of 0.11 injuries per player and per year. From the total number of injuries, 67.2% were classified as injuries that resulted in time loss, while the remaining 32.7% were injuries that required medical attention. Most injuries led to a minimum of 1 competitive match being missed (87%), and only 2.5% were recurrent injuries. The rate of injuries per 1000 hours of play was double during games (1.15/1000 hours) compared with during training (0.49/1000 hours). From the total number of injuries reported, 7.7% corresponded to goalkeepers, 24.2% to forwards, 33.8% to defenders, and 34.3% to midfielders. The knee (29.9%) and ankle joints (12.4%) were the most common body locations injured, while ligament sprains and ruptures accounted for 32.1% of the total injuries attended. Older amateur players (age ≥30 years) had a greater number of injuries per year and per 1000 hours of play than their younger counterparts. Conclusion: The risk of injury in amateur soccer is lower than that previously reported in professional players. The most common complaints in amateur players are knee ligament injuries. Further research is needed to investigate ways of reducing the incidence of injuries in amateur soccer.

Analysis of dehydration and strength in elite badminton players.

Background The negative effects of dehydration on aerobic activities are well established. However, it is unknown how dehydration affects intermittent sports performance. The purpose of this study was to identify the level of dehydration in elite badminton players and its relation to muscle strength and power production. Methodology Seventy matches from the National Spanish badminton championship were analyzed (46 men’s singles and 24 women’s singles). Before and after each match, jump height and power production were determined during a countermovement jump on a force platform. Participants’ body weight and a urine sample were also obtained before and after each match. The amount of liquid that the players drank during the match was also calculated by weighing their individual drinking bottles. Results and Discussion Sweat rate during the game was 1.14±0.46 l/h in men and 1.02±0.64 l/h in women. The players rehydrated at a rate of 1.10±0.55 l/h and 1.01±0.44 l/h in the male and female groups respectively. Thus, the dehydration attained during the game was only 0.37±0.50% in men and 0.32±0.83% in women. No differences were found in any of the parameters analyzed during the vertical jump (men: from 31.82±5.29 to 32.90±4.49 W/kg; p>0.05, women: from 26.36±4.73 to 27.25±4.44 W/kg; p>0.05). Post-exercise urine samples revealed proteinuria (60.9% of cases in men and 66.7% in women), leukocyturia (men = 43.5% and women = 50.0%) and erythrocyturia (men = 50.0% and women = 21.7%). Conclusions Despite a moderate sweat rate, badminton players adequately hydrated during a game and thus the dehydration attained was low. The badminton match did not cause muscle fatigue but it significantly increased the prevalence of proteinuria, leukocyturia and erythrocyturia.