Physiological Demands of Elite Cross-Country Skiing During a Real Competition.

The aim of this study was to assess different physiological variables before and after a 5-km (women) and 10-km (men) cross-country skiing competition to determine potential mechanisms of fatigue. Fourteen elite-level skiers competed in an official cross-country skiing competition using the classical style (9 men and 5 women). Instantaneous skiing velocity was measured during the race by means of 15-Hz global positioning system devices. Before and after the race, a sample of venous blood was obtained to assess changes in blood lactate and serum electrolyte and myoglobin concentrations. Prerace to postrace changes in blood oxygen saturation, forced vital capacity during a spirometry test, jump height during a countermovement jump, and handgrip force were also measured. Mean race speed was 15.8 ± 2.5 and 15.4 ± 1.5 km·h, whereas mean heart rate was 171 ± 6 and 177 ± 3 b·min for men and women, respectively. There were no significant prerace to postrace changes in jump height, handgrip force, and forced vital capacity in men and women. Blood oxygen saturation was reduced from prerace to postrace in men (95.9 ± 2.1% to 93.1 ± 2.3%, p = 0.02) and women (97.8 ± 1.1% to 92.4 ± 2.1%, p < 0.01), whereas blood lactate concentration increased at the end of the race in men (1.4 ± 0.5 to 4.9 ± 2.1 mmol·L, p < 0.01) and women (1.9 ± 0.1 to 6.9 ± 3.2 mmol·L, p < 0.01). After the race, blood markers of muscle damage were at low concentrations, whereas serum electrolytes remained unchanged. Fatigue in 5- and 10-km cross-country skiing competitions was related to a reduced blood oxygen carrying capacity and presumably increased muscle and blood acidosis, whereas the influence of exercise-induced muscle damage on fatigue was minor.

Acute consumption of a caffeinated energy drink enhances aspects of performance in sprint swimmers.

This study investigated the effect of a caffeinated energy drink on various aspects of performance in sprint swimmers. In a randomised and counterbalanced order, fourteen male sprint swimmers performed two acute experimental trials after the ingestion of a caffeinated energy drink (3 mg/kg) or after the ingestion of the same energy drink without caffeine (0 mg/kg; placebo). After 60 min of ingestion of the beverages, the swimmers performed a countermovement jump, a maximal handgrip test, a 50 m simulated competition and a 45 s swim at maximal intensity in a swim ergometer. A blood sample was withdrawn 1 min after the completion of the ergometer test. In comparison with the placebo drink, the intake of the caffeinated energy drink increased the height in the countermovement jump (49.4 (SD 5.3) v. 50.9 (SD 5.2) cm, respectively; P<0.05) and maximal force during the handgrip test with the right hand (481 (SD 49) v. 498 (SD 43) N; P<0.05). Furthermore, the caffeinated energy drink reduced the time needed to complete the 50 m simulated swimming competition (27.8 (SD 3.4) v. 27.5 (SD 3.2) s; P<0.05), and it increased peak power (273 (SD 55) v. 303 (SD 49) W; P <0.05) and blood lactate concentration (11.0 (SD 2.0) v. 11.7 (SD 2.1) mM; P<0.05) during the ergometer test. The caffeinated energy drink did not modify the prevalence of insomnia (7 v. 7%), muscle pain (36 v. 36%) or headache (0 v. 7%) during the hours following its ingestion (P>0.05). A caffeinated energy drink increased some aspects of swimming performance in competitive sprinters, whereas the side effects derived from the intake of this beverage were marginal at this dosage.

A caffeinated energy drink improves jump performance in adolescent basketball players.

This study aimed at investigating the effects of a commercially available energy drink on shooting precision, jump performance and endurance capacity in young basketball players. Sixteen young basketball players (first division of a junior national league; 14.9 ± 0.8 years; 73.4 ± 12.4 kg; 182.3 ± 6.5 cm) volunteered to participate in the research. They ingested either (a) an energy drink that contained 3 mg of caffeine per kg of body weight or (b) a placebo energy drink with the same appearance and taste. After 60 min for caffeine absorption, they performed free throw shooting and three-point shooting tests. After that, participants performed a maximal countermovement jump (CMJ), a repeated maximal jumps test for 15 s (RJ-15), and the Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1). Urine samples were obtained before and 30 min after testing. In comparison to the placebo, the ingestion of the caffeinated energy drink did not affect precision during the free throws (Caffeine = 70.7 ± 11.8 % vs placebo = 70.3 ± 11.0 %; P = 0.45), the three-point shooting test (39.9 ± 11.8 vs 38.1 ± 12.8 %; P = 0.33) or the distance covered in the Yo-Yo IR1 (2,000 ± 706 vs 1,925 ± 702 m; P = 0.19). However, the energy drink significantly increased jump height during the CMJ (38.3 ± 4.4 vs 37.5 ± 4.4 cm; P < 0.05) mean jump height during the RJ-15 (30.2 ± 3.6 vs 28.8 ± 3.4 cm; P < 0.05) and the excretion of urinary caffeine (1.2 ± 0.7 vs 0.1 ± 0.1 µg/mL; P < 0.05). The intake of a caffeine-containing energy drink (3 mg/kg body weight) increased jump performance although it did not affect basketball shooting precision.

A 7-day oral supplementation with branched-chain amino acids was ineffective to prevent muscle damage during a marathon.

The aim of this study was to determine the effectiveness of a 7-day oral supplementation with branched-chain amino acids (BCAA) to prevent muscle damage during a marathon. Forty-six experienced runners were randomly divided into two groups, one with BCAA supplementation (n = 25, supplemented with 5 g day(-1) of powdered 1:0.5:0.5 leucine:isoleucine:valine, during the 7 days prior to the competition) and the other as a control group (n = 21, supplemented with an isocaloric placebo). Before the marathon race and within 3 min of finishing, leg muscle power was measured with a maximal countermovement jump and a urine sample was obtained. During the race, running pace was measured by means of a time-chip. Myoglobin concentration was determined in the urine samples as an indirect marker of muscle damage. A visual analog scale (0-10 points) was used to assess leg muscle pain during the race. In the BCAA group, the mean running pace during the marathon was similar to the control group (3.3 ± 0.4 vs. 3.3 ± 0.5 m s(-1), respectively, 0.98). The pre- to post-race reduction in muscle power was similar in both BCAA and control groups (-23.0 ± 16.1 vs. -17.3 ± 13.8 %, P = 0.13). Post-race urine myoglobin concentration was similar in both BCAA and control groups (5.4 ± 7.5 vs. 4.5 ± 8.6 µg mL(-1), P = 0.70). Finally, there were no differences between groups in the perceived muscle pain during the race (6 ± 1 vs. 5 ± 1 points, P = 0.80). A 7-day supplementation of BCAA (5 g day(-1)) did not increase the running performance during a marathon. Furthermore, BCAA supplementation was ineffective to prevent muscle power loss, muscle damage or perceived muscle pain during a marathon race.

Caffeine-containing energy drink improves physical performance in female soccer players.

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.

The use of energy drinks in sport: perceived ergogenicity and side effects in male and female athletes.

The use of caffeine containing energy drinks has dramatically increased in the last few years, especially in the sport context because of its reported ergogenic effect. The ingestion of low to moderate doses of caffeinated energy drinks has been associated with adverse side effects such as insomnia or increased nervousness. The aim of the present study was to assess psycho-physiological changes and the prevalence of side effects resulting from the ingestion of 3 mg caffeine/kg body mass in the form of an energy drink. In a double-blind and placebo controlled experimental design, ninety experienced and low-caffeine-consuming athletes (fifty-three male and thirty-seven female) in two different sessions were provided with an energy drink that contained 3 mg/kg of caffeine or the same decaffeinated energy drink (placebo; 0 mg/kg). At 60 min after the ingestion of the energy drink, participants completed a training session. The effects of ingestion of these beverages on psycho-physiological variables during exercise and the rate of adverse side effects were measured using questionnaires. The caffeinated energy drink increased self-perceived muscle power during exercise compared with the placebo beverage (6·41 (sd 1·7) v. 5·66 (sd 1·51); P= 0·001). Moreover, the energy drink produced a higher prevalence of side effects such as insomnia (31·2 v. 10·4 %; P< 0·001), nervousness (13·2 v. 0 %; P= 0·002) and activeness (16·9 v. 3·9 %; P= 0·007) than the placebo energy drink. There were no sex differences in the incidence of side effects (P>0·05). The ingestion of an energy drink with 3 mg/kg of caffeine increased the prevalence of side effects. The presence of these side effects was similar between male and female participants.

Compression stockings do not improve muscular performance during a half-ironman triathlon race.

PURPOSE: This study aimed at investigating the effectiveness of compression stockings to prevent muscular damage and preserve muscular performance during a half-ironman triathlon. METHODS: Thirty-six experienced triathletes volunteered for this study. Participants were matched for age, anthropometric data and training status and placed into the experimental group (N = 19; using ankle-to-knee graduated compression stockings) or control group (N = 17; using regular socks). Participants competed in a half-ironman triathlon celebrated at 29 ± 3 °C and 73 ± 8% of relative humidity. Race time was measured by means of chip timing. Pre- and post-race, maximal height and leg muscle power were measured during a countermovement jump. At the same time, blood myoglobin and creatine kinase concentrations were determined and the triathletes were asked for perceived exertion and muscle soreness using validated scales. RESULTS: Total race time was not different between groups (315 ± 45 for the control group and 310 ± 32 min for the experimental group; P = 0.46). After the race, jump height (-8.5 ± 3.0 versus -9.2 ± 5.3%; P = 0.47) and leg muscle power reductions (-13 ± 10 versus -15 ± 10 %; P = 0.72) were similar between groups. Post-race myoglobin (718 ± 119 versus 591 ± 100 µg/mL; P = 0.42) and creatine kinase concentrations (604 ± 137 versus 525 ± 69 U/L; P = 0.60) were not different between groups. Perceived muscle soreness (5.3 ± 2.1 versus 6.0 ± 2.0 arbitrary units; P = 0.42) and the rating of perceived effort (17 ± 2 versus 17 ± 2 arbitrary units; P = 0.58) were not different between groups after the race. CONCLUSION: Wearing compression stockings did not represent any advantage for maintaining muscle function or reducing blood markers of muscle damage during a triathlon event.

Influence of dorsiflexion shoes on jump performance.

The goal of dorsiflexion sports shoes is to increase jumping capacity by means of a lower position of the heel in relation to the forefoot which results in additional stretching of the ankle plantar flexors. The aim of this study was to compare a dorsiflexion sports shoe model with two conventional sports shoe models in a countermovement jump test. The sample consisted of 35 participants who performed a countermovement jump test on a force platform wearing the three models of shoes. There were significant differences in the way force was manifested (P<0.05) in the countermovement jump test, with a decrease in the velocity of the center of gravity and an increase in force at peak power and mean force in the concentric phase. Moreover, peak power was reached earlier with the dorsiflexion sports shoe model. The drop of the center of gravity was increased in CS1 in contrast to the dorsiflexion sports shoe model (P<.05). However, the dorsiflexion sports shoes were not effective for improving either peak power or jump height (P>.05). Although force manifestation and jump kinetics differ between dorsiflexion shoes and conventional sports shoes, jump performance was similar.

Caffeine-containing energy drink improves sprint performance during an international rugby sevens competition.

The aim of this study was to determine the effects of a caffeine-containing energy drink on physical performance during a rugby sevens competition. A second purpose was to investigate the post-competition urinary caffeine concentration derived from the energy drink intake. On two non-consecutive days of a friendly tournament, 16 women from the Spanish National rugby sevens Team (mean age and body mass = 23 ± 2 years and 66 ± 7 kg) ingested 3 mg of caffeine per kg of body mass in the form of an energy drink (Fure(®), ProEnergetics) or the same drink without caffeine (placebo). After 60 min for caffeine absorption, participants performed a 15-s maximal jump test, a 6 × 30 m sprint test, and then played three rugby sevens games against another national team. Individual running pace and instantaneous speed during the games were assessed using global positioning satellite (GPS) devices. Urine samples were obtained pre and post-competition. In comparison to the placebo, the ingestion of the energy drink increased muscle power output during the jump series (23.5 ± 10.1 vs. 25.6 ± 11.8 kW, P = 0.05), running pace during the games (87.5 ± 8.3 vs. 95.4 ± 12.7 m/min, P < 0.05), and pace at sprint velocity (4.6 ± 3.3 vs. 6.1 ± 3.4 m/min, P < 0.05). However, the energy drink did not affect maximal running speed during the repeated sprint test (25.0 ± 1.5 vs. 25.0 ± 1.7 km/h). The ingestion of the energy drink resulted in a higher post-competition urine caffeine concentration than the placebo (3.3 ± 0.7 vs. 0.2 ± 0.1 µg/mL; P < 0.05). In summary, 3 mg/kg of caffeine in the form of a commercially available energy drink considerably enhanced physical performance during a women's rugby sevens competition.

Differences in the Contractile Properties of the Biceps Femoris and Semitendinosus Muscles Throughout a Season in Professional Soccer Players.

The aim of this study was to monitor seasonal changes in the mechanical and neuromuscular characteristics of the knee flexor muscles with tensiomyography, the biceps femoris (BF) and semitendinosus (ST) muscles, of 27 soccer players. All male professional soccer players (age 25 ± 4 years) were measured at the beginning of the preseason (second week) and in the competitive season (10 weeks later). The variables contraction time (Tc) and muscle displacement (Dm) showed significant differences in some muscles, and in others they indicated a tendency to change. In general, the BF improved (more explosive and better muscle tone) and the ST worsened (slower and worse muscle tone) its values during the season. The findings of this study suggest that usual daily soccer training and weekly competition might produce antagonistic changes between the knee flexor muscles.

Effects of 3 mg/kg Body Mass of Caffeine on the Performance of Jiu-Jitsu Elite Athletes.

The effects of caffeine were investigated in judo, boxing, taekwondo and Brazilian jiu-jitsu. However, this substance was never investigated regarding traditional jiu-jitsu. Therefore, the aim of this research was to analyze the effects of caffeine in the Special Judo Fitness Test (SJFT) and technical variables during combat in traditional jiu-jitsu elite athletes. Methods: Twenty-two young professionals of traditional jiu-jitsu, 11 men and 11 women (age = 22 ± 4 (18−33) years, body mass = 66.6 ± 10.8 (46.2−86.1) kg, height = 1.70 ± 0.9 (1.55−1.85) m) with 15 ± 7 years of experience in traditional jiu-jitsu, participated in a double-blind, counterbalanced, crossover study. In two different conditions, the traditional jiu-jitsu athletes ingested 3 mg/kg body mass of caffeine or a placebo. After 60 min, they performed the SJFT test to measure throwing performance, and subsequently, combat to analyze offensive and defensive hitting techniques. Results: Caffeine had a main effect on the number of throws during the SJFT test (P < 0.01). In addition, it was effective in sets 2 (13 ± 2 vs. 14 ± 2; p = 0.01) and 3 (12 ± 2 vs. 13 ± 1; p = 0.03). There was also a main effect during the test on heart rate when caffeine was ingested (F = 12.48, p < 0.01). The effects of caffeine were similar compared to the placebo condition regarding performance during combat both in offensive and defensive fighting variables Conclusions: the pre-exercise ingestion of 3 mg/kg body mass of caffeine increased performance in the SJFT test, decreased fatigue perception, and increased power and endurance perception in professionally traditional jiu-jitsu athletes. However, it did not seem to improve offensive and defensive technical actions during combat.

Caffeine Doses of 3 mg/kg Increase Unilateral and Bilateral Vertical Jump Outcomes in Elite Traditional Jiu-Jitsu Athletes.

Caffeine increases vertical jump, although its effects on kinetics and kinematics during different phases of bilateral and unilateral jumps remain unclear. The aim of this study was to identify the effects of 3 mg/kg on kinetic, kinematic and temporal variables in the concentric and eccentric phases of bilateral and unilateral countermovement jumps. A total of 16 Spanish national team traditional Jiu-Jitsu athletes took part in two experimental trials (3 mg/kg caffeine or placebo) in a randomized, double-blind crossover study. Sixty minutes after ingestion, bilateral and unilateral jumps were performed on a force platform. Compared to the placebo, caffeine increased bilateral jump height (p = 0.008; Δ% = 4.40), flight time (p = 0.008; Δ% = 2.20), flight time:contraction time (p = 0.029; Δ% = 8.90), concentric impulse (p = 0.018; Δ% = 1.80), peak power (p = 0.049; Δ% = 2.50), RSI-modified (p = 0.011; Δ% = 11.50) and eccentric mean braking force (p = 0.045; Δ% = 4.00). Additionally, caffeine increased unilateral RSI-mod in both legs (Left: p = 0.034; Δ% = 7.65; Right: p = 0.004; Δ% = 11.83), left leg flight time (p = 0.044; Δ% = 1.91), left leg jump height (p = 0.039; Δ% = 3.75) and right leg FT:CT (p = 0.040; Δ% = 9.72). Caffeine in a dose of 3 mg/kg BM in elite Jiu-Jitsu athletes is a recommended ergogenic aid as it increased performance of bilateral and unilateral vertical jumps. These increases were also accompanied by modified jump execution during the different phases of the countermovement prior to take-off.

Predicting race time in male amateur marathon runners.

BACKGROUND: The aim of the study was to analyze the relationship between anthropometry, training characteristics, muscular strength and effort-related cardiovascular response and marathon race time in male amateur runners. METHODS: A total of 84 male amateur marathon runners aged between 23 and 70 years took part in this study (41.0±9.5 years). All of them competed in the 2013 edition of the Madrid Marathon with a finish time between 169.8 and 316 minutes (226.0±28.5 minutes). Age, running experience, number of marathon races finished, mean kilometers run weekly in the last three months, and previous personal best time in the 10 km, half marathon and marathon were recorded. Moreover, anthropometric characteristics, and the results from the Ruffier Test and a whole-body isometric force test were measured. After the marathon, the race time was registered. RESULTS: Training volume (r=-0.479; P=0.001), previous running milestones (marathon r=0.756; half-marathon r=0.812; 10-km r=0.732; P<0.001), cardiovascular fitness (r=0.371; P=0.001) and anthropometric variables (body mass, Body Mass Index, body fat percentage, skinfolds and lower leg volume) were correlated to marathon performance (P<0.05). Two regression models appeared from the data with r2>0.50. The best, including body fat percentage, heart rate change during the recovery after the Ruffier Test and the half-marathon race time, was strongly correlated with real marathon performance (r=0.77; P<0.001). A second regression model was proposed replacing the half-marathon performance with the 10-km race time, reducing the correlation to 0.73 (P<0.001). CONCLUSIONS: Marathon performance could be partially predicted by two different equations, including body fat percentage, recovery heart rate in the Ruffier Test and a half-marathon or 10-km performance.

Respiratory function is associated to marathon race time.

BACKGROUND: The purpose of this study was to analyze the relationship between marathon race time and expiratory pulmonary parameters in a heterogeneous group of amateur marathoners. METHODS: A total of 110 marathon runners (age=41.9±9.4 yr, body mass=74.0±9.1 kg, height=175.0±8.0 cm) volunteered to participate in this study. First, they completed a questionnaire about running experience and best performance time in the 10-km, half-marathon and marathon competitions. Then, they performed a maximal spirometry test following guidelines for standardized spirometry. Measurement included peak expiratory flow (PEF), forced expiratory volume in the first second (FEV1) and forced vital capacity (FVC). All these expiratory variables were normalized for the participant's body mass. Within 3 days of the spirometry test, participants competed in an official marathon and race time was measured by a chip-timing. After this, participants were grouped by their marathon race time as follows: <210 min, N.=33; between 210 and 240 min, N.=31; and >240 min, N.=46). RESULTS: Marathon race time correlated to the FVC·kg-1 (r=-0.41; P<0.001), to FEV1·kg-1 (r=-0.40; P<0.001), and PEF·kg-1 (r=-0.50; P=0.005). However, self-reported running experience did not show significant correlations to FVC·kg-1 and PEF·kg-1 (P>0.05). The group of faster marathoners (e.g., <210 min) had greater FEV1·kg-1 (<210 min group: 0.064±0.009; 210-240 min group: 0.058±0.008; >240 min group: 0.057±0.009; P<0.001) and higher FVC·kg-1 (<210 min group: 0.081±0.011; 210-240 min group: 0.075±0.012; >240 min group: 0.072±0.010; P<0.001) than the other two groups of slower runners. CONCLUSIONS: These results suggest a significant relationship between individual pulmonary function and marathon race time. Thus, a higher lung capacity per kg of body mass might be a key variable for marathon performance in amateur runners.

Changes in Serum Free Amino Acids and Muscle Fatigue Experienced during a Half-Ironman Triathlon.

The aim of this study was to investigate the relationship between changes in serum free amino acids, muscle fatigue and exercise-induced muscle damage during a half-ironman triathlon. Twenty-six experienced triathletes (age = 37.0 ± 6.8 yr; experience = 7.4 ± 3.0 yr) competed in a real half-ironman triathlon in which sector times and total race time were measured by means of chip timing. Before and after the race, a countermovement jump and a maximal isometric force test were performed, and blood samples were withdrawn to measure serum free amino acids concentrations, and serum creatine kinase levels as a blood marker of muscle damage. Total race time was 320 ± 37 min and jump height (-16.3 ± 15.2%, P < 0.001) and isometric force (-14.9 ± 9.8%; P = 0.007) were significantly reduced after the race in all participants. After the race, the serum concentration of creatine kinase increased by 368 ± 187% (P < 0.001). In contrast, the serum concentrations of essential (-27.1 ± 13.0%; P < 0.001) and non-essential amino acids (-24.4 ± 13.1%; P < 0.001) were significantly reduced after the race. The tryptophan/BCAA ratio increased by 42.7 ± 12.7% after the race. Pre-to-post changes in serum free amino acids did not correlate with muscle performance variables or post-race creatine kinase concentration. In summary, during a half-ironman triathlon, serum amino acids concentrations were reduced by > 20%. However, neither the changes in serum free amino acids nor the tryptophan/BCAA ratio were related muscle fatigue or muscle damage during the race.

The use of compression stockings during a marathon competition to reduce exercise-induced muscle damage: are they really useful?

STUDY DESIGN: Case-control study; ecological study. OBJECTIVES: To examine the efficacy of wearing compression stockings to prevent muscle damage and to maintain running performance during a marathon competition. BACKGROUND: Exercise-induced muscle damage has been identified as one of the main causes of the progressive decrease in running and muscular performance found during marathon races. METHODS: Thirty-four experienced runners were pair-matched for age, anthropometric data, and best race time in the marathon, and randomly assigned to a control group (n = 17) of runners who wore conventional socks or to a group of runners who wore foot-to-knee graduated compression stockings (n = 17). Before and after the race, a sample of venous blood was obtained, and jump height and leg muscle power were measured during a countermovement jump. Serum myoglobin and creatine kinase concentrations were determined as blood markers of muscle fiber damage. RESULTS: Total race time was not different between the control group and the compression stockings group (210 ± 23 and 214 ± 22 minutes, respectively; P = .58). Between the control group and the compression stockings group, postrace reductions in leg muscle power (-19.8% ± 17.7% versus -24.8% ± 18.4%, respectively; P = .37) and jump height (-25.3% ± 14.1% versus -32.5% . 20.4%, respectively; P = .27) were similar. At the end of the race, there were no differences between the control group and the compression stockings group in serum myoglobin (568 ± 347 ng·mL(-1) versus 573 ± 270 ng·mL(-1), respectively; P = .97) and creatine kinase concentration (390 ± 166 U·L(-1) versus 487 ± 227 U·L(-1), respectively; P = .16). CONCLUSION: The use of compression stockings did not improve running pace and did not prevent exercise-induced muscle damage during the marathon. Wearing compression stockings during long-distance running events is an ineffective strategy to avoid the deleterious effects of muscle damage on running performance. LEVEL OF EVIDENCE: Therapy, level 2b.

Enhancing physical performance in elite junior tennis players with a caffeinated energy drink.

The aim of this study was to investigate the effectiveness of a caffeinated energy drink to enhance physical performance in elite junior tennis players. In 2 different sessions separated by 1 wk, 14 young (16 ± 1 y) elite-level tennis players ingested 3 mg caffeine per kg body mass in the form of an energy drink or the same drink without caffeine (placebo). After 60 min, participants performed a handgrip-strength test, a maximal-velocity serving test, and an 8 × 15-m sprint test and then played a simulated singles match (best of 3 sets). Instantaneous running speed during the matches was assessed using global positioning (GPS) devices. Furthermore, the matches were videotaped and notated afterward. In comparison with the placebo drink, the ingestion of the caffeinated energy drink increased handgrip force by ~4.2% ± 7.2% (P = .03) in both hands, the running pace at high intensity (46.7 ± 28.5 vs 63.3 ± 27.7 m/h, P = .02), and the number of sprints (12.1 ± 1.7 vs 13.2 ± 1.7, P = .05) during the simulated match. There was a tendency for increased maximal running velocity during the sprint test (22.3 ± 2.0 vs 22.9 ± 2.1 km/h, P = .07) and higher percentage of points won on service with the caffeinated energy drink (49.7% ± 9.8% vs 56.4% ± 10.0%, P = .07) in comparison with the placebo drink. The energy drink did not improve ball velocity during the serving test (42.6 ± 4.8 vs 42.7 ± 5.0 m/s, P = .49). The preexercise ingestion of caffeinated energy drinks was effective to enhance some aspects of physical performance of elite junior tennis players.

Influence of successive badminton matches on muscle strength, power, and body-fluid balance in elite players.

The aim was to analyze the influence of competitive round on muscle strength, body-fluid balance, and renal function in elite badminton players during a real competition. Body mass, jump height during a countermovement jump, handgrip force, and urine samples were obtained from 13 elite badminton players (6 men and 7 women) before and after the 2nd-round and quarterfinal matches of the national Spanish badminton championship. Sweat rate was determined by using prematch-to-postmatch body-mass change and by weighing individually labeled fluid bottles. Sweat rates were 1.04 ± 0.62 and 0.98 ± 0.43 L/h, while rehydration rate was 0.69 ± 0.26 and 0.91 ± 0.52 L/h for the 2nd round and quarterfinals, respectively. Thus, dehydration was 0.47% ± 1.03% after the 2nd round and 0.23% ± 0.43% after the quarterfinals. There were no differences in prematch-to-postmatch jump height, but jump height was reduced from 37.51 ± 8.83 cm after the 2nd-round game to 34.82 ± 7.37 cm after the quarterfinals (P < .05). No significant differences were found in handgrip force when comparing prepost matches or rounds, although there were significant differences between dominant and nondominant hands (P < .05). The succession of rounds caused the appearance of proteinuria, hematuria, glycosuria, and higher nitrite and ketone concentrations in urine. Rehydration patterns during a real badminton competition were effective to prevent dehydration. A badminton match did not affect jump height or handgrip force, but jump height was progressively reduced by the competitive round. Badminton players' renal responses reflected diminished renal flux due to the high-intensity nature of this racket sport.

The influence of ankle dorsiflexion on jumping capacity and the modified agility t-test performance.

Dorsiflexion sport shoes aim to increase jumping capacity and speed by means of a lower position of the heel in comparison with the forefoot, favouring additional stretching of the ankle plantar flexors. In previous studies, contradictory results have been found on the benefits of using this type of shoe. With the aim of comparing a dorsiflexion sport shoe model (DF) with a conventional sport shoe (CS), 41 participants performed a countermovement jump (CMJ) test and an agility test (MAT) with both models of shoe. There were no significant differences in the jump test [CS=35.3 cm (6.4) and DF=35.6 cm (6.4), P>0.05]. In the agility test, the conventional shoe obtained better results than the model with dorsiflexion with regard to time taken to complete the circuit [CS=6236 ms (540) and DF=6377 ms (507), P<0.05)]. In spite of producing pre-stretching of the plantar muscles, the DF sport shoes were not effective for improving either jump power or agility in a specific test.

Influence of body mass loss and myoglobinuria on the development of muscle fatigue after a marathon in a warm environment.

The aim of this study was to determine the changes in body mass and myoglobinuria concentration in recreational runners during a marathon in a warm environment, and the relation of these changes to muscle fatigue. We recruited 138 amateur runners (114 men and 24 women) for the study. Before the race, leg muscle power output was measured during a countermovement jump on a force platform, body weight was measured, and a urine sample was obtained. Within 3 min of race completion (28 °C; 46% relative humidity), the runners repeated the countermovement jump, body weight was measured again, and a second urine sample was obtained. Myoglobin concentration was determined in the urine samples. After the race, mean body mass reduction was 2.2% ± 1.2%. Fifty-five runners (40% of the total) reduced their body mass by less than 2%, and 10 runners (7.2%) reduced their body mass by more than 4%. Only 3 runners increased their body mass after the marathon. Mean leg muscle power reduction was 16% ± 10%. Twenty-four runners reduced their muscle power by over 30%. No myoglobin was detected in the prerace urine specimens, whereas postrace urinary myoglobin concentration increased to 3.5 ± 9.5 µg·mL(-1) (p < 0.05). Muscle power change after the marathon significantly correlated with postrace urine myoglobin concentration (r = -0.55; p < 0.001), but not with body mass change (r = -0.08; p = 0.35). After a marathon in a warm environment, interindividual variability in body mass change was high, but only 7% of the runners reduced their body mass by more than 4%. The correlation between myoglobinuria and muscle power change suggests that muscle fatigue is associated with muscle breakdown.