Interindividual variability in sweat electrolyte concentration in marathoners

Background: Sodium (Na+) intake during exercise aims to replace the Na+ lost by sweat to avoid electrolyteimbalances, especially in endurance disciplines. However, Na+ needs can be very different among individuals because of the great inter-individual variability in sweat electrolyte concentration. The aim of this investigation was to determine sweat electrolyte concentration in a large group of marathoners. Methods: A total of 157 experienced runners (141 men and 16 women) completed a marathon race (24.4 ± 3.6 °C and 27.7 ± 4.8 % of humidity). During the race, sweat samples were collected by using sweat patches placed on the runners’ forearms. Sweat electrolyte concentration was measured by using photoelectric flame photometry. Results: As a group, sweat Na+ concentration was 42.9 ± 18.7 mmol·L−1 (minimal-maximal value = 7.0–95.5 mmol·L−1), sweat Cl− concentration was 32.2 ± 15.6 mmol·L−1 (7.3–90.6 mmol·L−1) and sweat K+ concentration was 6.0 ± 0.9 mmol·L−1 (3.1–8.0 mmol·L−1). Women presented lower sweat Na+ (33.9 ± 12.1 vs 44.0 ± 19.1 mmol·L−1; P = 0.04) andsweat Cl− concentrations (22.9 ± 10.5 vs 33.2 ± 15.8 mmol·L−1; P = 0.01) than men. A 20 % of individuals presented asweat Na+ concentration higher than 60 mmol·L−1 while this threshold was not surpassed by any female marathoner. Sweat electrolyte concentration did not correlate to sweat rate, age, body characteristics, experience or training. Although there was a significant correlation between sweat Na+ concentration and running pace (r = 0.18; P = 0.03), this association was weak to interpret that sweat Na+ concentration increased with running pace. Conclusions: The inter-individual variability in sweat electrolyte concentration was not explained by any individual characteristics except for individual running pace and sex. An important portion (20 %) of marathoners might need special sodium intake recommendations due to their high sweat salt losses

Myosin Light Chain Kinase (MLCK) Gene Influences Exercise Induced Muscle Damage during a Competitive Marathon

Myosin light chain kinase (MLCK) phosphorylates the regulatory light chain (RLC) of myosin producing increases in force development during skeletal muscle contraction. It has been suggested that MLCK gene polymorphisms might alter RLC phosphorylation thereby decreasing the ability to produce force and to resist strain during voluntary muscle contractions. Thus, the genetic variations in the MLCK gene might predispose some individuals to higher values of muscle damage during exercise, especially during endurance competitions. The aim of this investigation was to determine the influence of MLCK genetic variants on exercise-induced muscle damage produced during a marathon. Sixty-seven experienced runners competed in a marathon race. The MLCK genotype (C37885A) of these marathoners was determined. Before and after the race, a sample of venous blood was obtained to assess changes in serum myoglobin concentrations and leg muscle power changes were measured during a countermovement jump. Self-reported leg muscle pain and fatigue were determined by questionnaires. A total of 59 marathoners (88.1%) were CC homozygotes and 8 marathoners (11.9%) were CA heterozygotes. The two groups of participants completed the race with a similar time (228 ± 33 vs 234 ± 39 min; P = 0.30) and similar self-reported values for fatigue (15 ± 2 vs 16 ± 2 A.U.; P = 0.21) and lower-limb muscle pain (6.2 ± 1.7 vs 6.6 ± 1.8 cm; P = 0.29). However, CC marathoners presented higher serum myoglobin concentrations (739 ± 792 vs 348 ± 144 μg·mL-1; P = 0.03) and greater pre-to-post- race leg muscle power reduction (-32.7 ± 15.7 vs -21.2 ± 21.6%; P = 0.05) than CA marathoners. CA heterozygotes for MLCK C37885A might present higher exercise-induced muscle damage after a marathon competition than CC counterparts

The Role of Stress in Understanding Differences in Sedentary Behavior in Hispanic/Latino Adults: Results from the Hispanic Community Health Study/Study of Latinos Sociocultural Ancillary Study

Chronic stress and/or lifetime traumatic stress can create a self-reinforcing cycle of unhealthy behaviors, such as overeating and sedentary behavior, that can lead to further increases in stress. This study examined the relationship between stress and sedentary behavior in a sample of Hispanic/Latino adults (N = 4244) from the Hispanic Community Health Study/Study of Latinos Sociocultural Ancillary Study

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 %; P0·05). 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

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; P0·05). 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 dosag

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 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

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