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Purpose: Caffeine is widely considered an ergogenic aid to increase anaerobic performance although most of this evidence is supported by investigations with only male samples. To date, it is unknown if the ergogenic effect of caffeine on anaerobic performance is of similar magnitude in men and women athletes. The aim of this study was to determine the magnitude of the ergogenic effect of caffeine on the Wingate test in men and women. Methods: In a double-blind, placebo-controlled, cross-over experimental trial, ten women athletes and ten men athletes performed a 15-s adapted version of the Wingate test after ingesting 3 mg of caffeine per kg of body mass or a placebo (cellulose). Results: In comparison to the performance obtained in the 15-s Wingate test with a placebo, caffeine increased peak power in men (9.9 ± 0.8 vs. 10.1 ± 0.8 W/kg, p < 0.01, d = 0.26) and in women (8.8 ± 0.9 vs. 9.1 ± 0.8 W/kg, p = 0.04, d = 0.30). Caffeine was also effective to increase the mean power in men (8.9 ± 0.7 vs. 9.0 ± 0.7 W/kg, p = 0.01, d = 0.21) and women (8.1 ± 0.7 vs. 8.3 ± 0.7 W/kg, p = 0.01, d = 0.27). The ergogenic effect of caffeine on the 15-s Wingate peak power (2.3 ± 3.2% in men and 3.2 ± 2.8% in women; p = 0.46) and mean power (2.0 ± 1.7% and 2.4 ± 2.3%, respectively; p = 0.93) was of similar magnitude in both sexes. Conclusion: Acute ingestion of 3 mg kg−1 of caffeine enhanced peak and mean cycling power during a 15-s adapted version of the Wingate test in men and women and the ergogenic effect was of similar magnitude in both sexes. This information suggests that both men and women athletes might obtain similar benefits from caffeine supplementation during anaerobic exercise. [ABSTRACT FROM AUTHOR]

Summary: This investigation presents a comparison of calcaneus bone stiffness of endurance runners of different ages and age-matched controls. We found that there was an age-associated decline in calcaneus bone stiffness in the control group while endurance runners prevented this decline, with a higher effect as the participants increased their age. Purpose: Previous investigations have found that endurance runners have higher bone mineral density and other bone quality variables in mechanically loaded bones. However, it is unknown if endurance running might counteract the decline in bone stiffness that occurs with age. The purpose of this study was to compare calcaneus bone stiffness of endurance runners of different ages to age-matched controls. Methods: In a descriptive cross-sectional study, 182 endurance-trained male runners and 116 healthy untrained male controls underwent an ultrasonographic assessment of the calcaneus bone in the right and left heels. Calcaneal bone stiffness was calculated from assessments of the broadband ultrasound attenuation and the speed of sound. Results: The line of best fit for the association between age and calcaneus stiffness was different between marathoners and controls (Z = − 2.1, P = 0.02). A two-way ANCOVA (condition × age) with body mass, and body mass index as covariates, revealed that there were main effects of condition (F = 26.8, P < 0.01) and age (F = 4.2, P < 0.01) for calcaneus stiffness, with a significant interaction between these two factors (F = 2.8, P = 0.03). The post hoc analysis revealed that calcaneus stiffness was significantly higher in marathoners of 40–44 years (121.5 ± 18.2 vs 101.1 ± 21.3 arbitrary units [A.U.], P = 0.01), 45–49 years (121.5 ± 19.7 vs 104.3 ± 13.4 A.U., P = 0.04), and > 50 years (111.2 ± 17.9 vs 92.4 ± 16.0 A.U., P < 0.01) than their untrained counterparts of the same age with no statistically significant differences in the remaining age groups. Conclusion: Endurance runners of > 40 years had higher values of calcaneus stiffness than controls, providing evidence to support the potential effect of endurance running to reduce the age-related decline on calcaneus bone stiffness. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to identify and describe the time course of tolerance to the most common caffeine-induced side effects. Methods: Eleven participants took part in a crossover, double-blind placebo-controlled experimental design. In one phase, participants ingested 3 mg/kg/day of caffeine for 20 days, while in another phase, they ingested a placebo. Resting heart rate and blood pressure were measured three times per week during each 20-day phase and a quantitative survey was used to categorise the magnitude of side effects. Results: In the pairwise comparison with the placebo, the ingestion of caffeine increased systolic (+ 7.8 ± 10.1%, P < 0.05) and diastolic blood pressure (+ 6.4 ± 12.9% P < 0.05) for the first 8 days of ingestion, but then this effect became attenuated for both outcomes (on day 20, − 1.1 ± 4.3% and + 0.9 ± 9.6%, respectively). The ingestion of caffeine did not affect heart rate at any time point. Caffeine increased the feelings of nervousness and vigour and the rating of gastrointestinal complaints, insomnia and diuresis at several time points in the treatment (P < 0.05) and they did not disappear after 20 days of ingestion. Conclusions: The daily intake of 3 mg/kg of caffeine induced a meaningful elevation in arterial blood pressure that disappeared after 8 days. However, other caffeine-induced effects such as increased nervousness and vigour, irritability, insomnia and diuresis remained after 20 days of consecutive caffeine ingestion. Although there was clear tolerance to the effect of caffeine on blood pressure, the persistence of other side effects suggests the inconvenience of maintaining a chronic caffeine intake, at least at the dose of 3 mg/kg/day. [ABSTRACT FROM AUTHOR]

Purpose: Exercise-induced muscle damage has been identified as one of the main causes of the progressive decrease in running and muscular performance in marathoners. The aim of this investigation was to determine the influence of the ACTN3 genotype on exercise-induced muscle damage produced during a marathon.Methods: Seventy-one experienced runners competed in a marathon race. Before and after the race, a sample of venous blood was obtained and maximal voluntary leg muscle power was measured during a countermovement jump. In the blood samples, the ACTN3 genotype (R577X) and the changes in serum creatine kinase and myoglobin concentrations were measured. Data from RX heterozygotes and XX mutant homozygotes were grouped as X allele carriers and compared to RR homozygotes.Results: At the end of the race, X allele carriers presented higher serum myoglobin (774 ± 852 vs 487 ± 367 U L-1; P = 0.02) and creatine kinase concentrations (508 ± 346 vs 359 ± 170 ng mL-1; P = 0.04) than RR homozygotes. Pre-to-post-race maximal voluntary leg muscle power reduction was more pronounced in X allele carriers than RR homozygotes (-34.4 ± 16.1 vs -27.3 ± 15.4%; P = 0.05). X allele carriers self-reported higher levels of lower limb muscle pain (7 ± 2 vs 6 ± 2 cm; P = 0.02) than RR homozygotes at the end of the race.Conclusions: In comparison to RR homozygotes, X allele carriers for the R577X polymorphism of the ACTN3 gene presented higher values for typical markers of exercise-induced muscle damage during a competitive marathon. Thus, the absence of a functional α-actinin-3 produced by the X allele might induce higher levels of muscle breakdown during prolonged running events. [ABSTRACT FROM AUTHOR]

Purpose: Alpha-actinin-3, encoded by the ACTN3 gene, is an actin-binding protein with an important role in myofibril contraction and muscle force output. In humans, there is a relatively common deficiency of the α-actinin-3 due to homozygosity in a polymorphism of the ACTN3 gene (R577X, rs1815739), that has been related to decreased resistance to strain during voluntary muscle contractions. The purpose of this study was to investigate the influence of the ACTN3 genotype on the level of exercise-induced muscle damage attained by 23 experienced triathletes during an official half-ironman competition.Methods: Before and after the race, a sample of venous blood was obtained and jump height was measured during a countermovement jump. The changes in serum creatine kinase (CK-MM isoform) were measured in the blood samples and muscle pain was measured with a visual analogue scale (0-10 cm). Data from RX heterozygotes and XX mutant homozygotes were grouped as X-allele carriers (n = 13) and compared to RR homozygotes (n = 10).Results: Race time was very similar between groups (313 ± 31 vs. 313 ± 25 min; P = 0.45); however, pre-to-post-competition reduction in jump height was greater in X-allele carriers than RR homozygotes (-18.4 ± 11.4 vs. -8.2 ± 6.9%; P = 0.04). At the end of the race, X-allele carriers presented higher serum CK-MM concentrations (682 ± 144 vs. 472 ± 269 U/L; P = 0.03), and there was also a tendency for higher self-reported values of lower limb muscle pain (7.7 ± 1.1 vs. 6.3 ± 2.3 cm; P = 0.06).Conclusions: X-allele triathletes in the ACTN3 R577X polymorphism presented greater signs of exercise-induced muscle damage during a half-ironman race than RR homozygotes. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this investigation was to determine the influence of endurance running on calcaneus bone stiffness in male and female runners.Methods: A total of 122 marathoners (longer distance runners, men = 101; women = 21) and 81 half-marathon and 10-km runners (shorter distance runners; men = 48; women = 33), competing in an international running event, underwent an ultrasonographic assessment of the right and left calcaneus. Calcaneus bone stiffness was estimated using the measurements of the speed of sound (SOS) and broadband ultrasound attenuation (BUA). Seventy-five age-matched sedentary people served as the control group.Results: Male and female longer distance runners and shorter distance runners presented higher values than sedentary counterparts in SOS (P < 0.05), and calcaneus stiffness (P < 0.05). Although there were no significant differences between longer distance and shorter distance runners in the ultrasonographic variables, longer distance runners presented greater effects size in SOS (1.00 vs. 0.93 males; 1.10 vs. 0.77 females), BUA (0.62 vs. 0.25 males; 0.89 vs. 0.20 females) and calcaneus stiffness (0.88 vs. 0.66 males; 1.20 vs. 0.60 females) than shorter distance endurance runners.Conclusion: Calcaneus bone stiffness was higher in all endurance runners compared to a sedentary control population. The volume of ground reaction forces which occur during endurance running might induce the adaptation of the calcaneus bone. [ABSTRACT FROM AUTHOR]