The ergogenic effect of acute caffeine ingestion has been widely investigated; however, scientific information regarding tolerance to the performance benefits of caffeine, when ingested on a day-to-day basis, is scarce. The aim of this investigation was to determine the time course of tolerance to the ergogenic effects of a moderate dose of caffeine. Eleven healthy active participants took part in a cross-over, double-blind, placebo-controlled experiment. In one treatment, they ingested 3 mg/kg/day of caffeine for 20 consecutive days while in another they ingested a placebo for 20 days. Each substance was administered daily in an opaque unidentifiable capsule, and the experimental trials started 45 min after capsule ingestion. Two days before, and three times per week during each 20-day treatment, aerobic peak power was measured with an incremental test to volitional fatigue (25 W/min) and aerobic peak power was measured with an adapted version of the Wingate test (15 s). In comparison to the placebo, the ingestion of caffeine increased peak cycling power in the incremental exercise test by ~4.0 ±1.3% for the first 15 days (P<0.05) but then this ergogenic effect lessened. Caffeine also increased peak cycling power during the Wingate test on days 1, 4, 15, and 18 of ingestion by ~4.9 ±0.9% (P<0.05). In both tests, the magnitude of the ergogenic effect of caffeine vs. placebo was higher on the first day of ingestion and then progressively decreased. These results show a continued ergogenic effect with the daily ingestion of caffeine for 15–18 days; however, the changes in the magnitude of this effect suggest progressive tolerance.

This study aimed to investigate the fluctuations of muscle performance in the Smith machine half-squat exercise during three different phases of the menstrual cycle. Thirteen resistance-trained and eumenorrheic women volunteered to participate in the study (58.6 ± 7.8 kg, 31.1 ± 5.5 years). In a pre-experimental test, the half-squat one-repetition maximum (1RM) was measured. Body mass, tympanic temperature and urine concentration of the luteinizing hormone were estimated daily for ~30 days to determine the early follicular phase (EFP), the late follicular phase (LFP), and the mid-luteal phase (MLP) of the menstrual cycle. On the second day of each phase, performance of the Smith machine half-squats was assessed using 20, 40, 60 and 80% of one repetition maximum (1RM). In each load, force, velocity, and power output were measured during the concentric phase of the exercise by means of a rotatory encoder. The data were analyzed using one-way repeated measures ANOVA coupled with magnitude-based inferences. Overall, force, velocity and power output were very similar in all menstrual cycle phases with unclear differences in most of the pairwise comparisons and effect sizes >0.2. The results of this investigation suggest that eumenorrheic females have similar muscle strength and power performance in the Smith machine half-squat exercise during the EFP, LFP, and MLP phases of the menstrual cycle.

Aim: (i) to compare the effects of two different low-volume resistance priming sessions, where the external load is modified on neuromuscular performance after 6 h of rest; and (ii) to identify the effects on psychological readiness in participants with resistance training experience. Methods: Eleven participants (Body mass: 77.0 ± 8.9 kg; Body height: 1.76 ± 0.08 m; Half squat repetition maximum: 139.8 ± 22.4 kg) performed the priming session under three experimental conditions in a randomized and cross-over design during the morning. The control (CON) condition: no resistance training, "optimal load" (OL) condition: two half-squat sets with a velocity loss of around 20% were performed with the "optimal load", and 80% of repetition maximum (80% RM) condition: 2 half-squat sets with a velocity loss of around 20% were performed with the 80% RM. Countermovement jump (CMJ), mean power with OL (MP OL) and 80% RM (MP 80RM), and mean velocity with OL (MV OL) and 80% RM (MV 80RM) were assessed six hours after the intervention. Subjective readiness was also recorded prior to resistance training and evaluation. Significance was set at p < 0.05. Results: CMJ was higher after the 80% RM intervention than CON (p < 0.001; Δ = 6.5% [3.4-9.5]). MP OL and MV OL seemed to be unaffected by both morning sessions. Higher MP 80RM (p = 0.044; Δ = 9.7% [4.0-15.6]; d = 0.24[0.10-0.37]) and MV 80RM (p = 0.004; Δ = 8.1% [3.2-13.3]; d = 0.32[0.13-0.52]) after 80% RM than after CON were observed. No effect was observed on psychological readiness. Conclusions: 80% RM priming session increased CMJ height and the capacity to generate power and velocity under a high-load condition without any effect on psychological readiness.

Aims In male athletes, caffeine is considered an ergogenic aid to increase anaerobic performance during the Wingate anaerobic test (WANT). However, information about the effect of caffeine on WANT performance in female athletes is contradictory. Furthermore, it is unknown whether the ergogenicity of caffeine is present during all the phases of the menstrual cycle. The aim of this study was to investigate the effects of caffeine intake on WANT performance during 3 phases of the menstrual cycle. Methods Thirteen well‐trained eumenorrhoeic triathletes participated in a double‐blind, placebo‐controlled, cross‐over experimental trial. On 2 different days in each phase, and in randomized order, participants ingested caffeine (3 mg kg−1) or a placebo (cellulose). The menstrual cycle phases were individually characterized as follows: (i) early follicular; (ii) preovulatory; and (iii) midluteal. In each trial, participants performed a 15‐s adapted version of the WANT. Results In comparison to the placebo, caffeine increased peak power during the WANT in the early follicular (8.6 ± 0.8 vs 8.9 ± 0.9 W/kg, P = .04; effect size [d] = 0.45), preovulatory (8.6 ± 0.9 vs 8.9 ± 0.9 W/kg, P = .04; d = 0.23) and mid‐luteal phases (8.6 ± 0.8 vs 8.9 ± 0.9 W/kg, P < .01; d = 0.52). Conclusion The ergogenic effect of caffeine on WANT peak cycling power was of a similar magnitude in the follicular, preovulatory, and mid‐luteal phases. These results suggest that caffeine increases performance in the 15‐s Wingate test in women athletes and it might be considered an ergogenic aid to increase anaerobic performance in eumenorrhoeic women during their menstrual cycle.

Purpose: p-Synephrine, the principal alkaloid of bitter orange (Citrus aurantium), is widely used in dietary supplements for weight loss due to its purported effect of increasing fat oxidation. However, there is a paucity of scientific information about its effectiveness in enhancing fat oxidation during exercise. The aim of this investigation was to determine the effect of an acute dose of p-synephrine on substrate oxidation during prolonged and constant intensity exercise. Methods: In a double-blind and randomized experiment, 14 healthy subjects performed two acute experimental trials after ingesting either p-synephrine (3 mg•kg-1) or a placebo (cellulose). Energy expenditure and fat oxidation rates were continuously measured by indirect calorimetry during 1 h of continuous cycling at Fatmax, the intensity that induces maximal fat oxidation rate. Results: In comparison to the placebo, energy expenditure during 1 h of cycling remained unchanged with p-synephrine (698±129 vs. 686±123 kcal, P=0.08). However, p-synephrine increased whole-body fat oxidation (33.6±10.4 vs. 37.3±9.8 g, P<0.01) while also reducing carbohydrate oxidation (99.5±30.4 vs. 85.0±28.4 g, P<0.01). However, the magnitude of the shift on substrate oxidation induced by p-synephrine was small. Conclusion: Acute ingestion of p-synephrine augments fat oxidation during prolonged and constant-intensity exercise.

Background: Homozygosity for the X-allele in the ACTN3 R577X (rs1815739) polymorphism results in the complete absence of α-actinin-3 in sarcomeres of fast-type muscle fibers. In elite athletes, the ACTN3 XX genotype has been related to inferior performance in speed and power-oriented sports; however, its influence on exercise phenotypes in recreational athletes has received less attention. We sought to determine the influence of ACTN3 genotypes on common exercise phenotypes in recreational marathon runners. Methods: A total of 136 marathoners (116 men and 20 women) were subjected to laboratory testing that included measurements of body composition, isometric muscle force, muscle flexibility, ankle dorsiflexion, and the energy cost of running. ACTN3 genotyping was performed using TaqMan probes. Results: 37 runners (27.2%) had the RR genotype, 67 (49.3%) were RX and 32 (23.5%) were XX. There was a difference in body fat percentage between RR and XX genotype groups (15.7 ± 5.8 vs. 18.8 ± 5.5%; effect size, ES, = 0.5 ± 0.4, p = 0.024), whereas the distance obtained in the sit-and-reach-test was likely lower in the RX than in the XX group (15.3 ± 7.8 vs. 18.4 ± 9.9 cm; ES = 0.4 ± 0.4, p = 0.046). Maximal dorsiflexion during the weight-bearing lunge test was different in the RR and XX groups (54.8 ± 5.8 vs. 57.7 ± 5.1 degree; ES = 0.5 ± 0.5, p = 0.044). Maximal isometric force was higher in the RR than in the XX group (16.7 ± 4.7 vs. 14.7 ± 4.0 N/kg; ES = −0.5 ± 0.3, p = 0.038). There was no difference in the energy cost of running between genotypes (~4.8 J/kg/min for all three groups, ES ~0.2 ± 0.4). Conclusions: The ACTN3 genotype might influence several exercise phenotypes in recreational marathoners. Deficiency in α-actinin-3 might be accompanied by higher body fatness, lower muscle strength and higher muscle flexibility and range of motion. Although there is not yet a scientific rationale for the use of commercial genetic tests to predict sports performance, recreational marathon runners who have performed such types of testing and have the ACTN3 XX genotype might perhaps benefit from personalized strength training to improve their performance more than their counterparts with other ACTN3 genotypes.

Aims:The main mechanism behind caffeine's ergogenicity lies in its tendency to bind to adenosine receptors, although other mechanisms might be involved. The aim of this investigation was to analyse the effects of caffeine on muscle oxygen saturation during exercise of increasing intensity. Methods:Thirteen healthy and active individuals volunteered to participate in a randomized, double blind, placebo-controlled crossover trial. During 2 different trials, participants either ingested a placebo (cellulose) or 3 mg/kg of caffeine. After waiting for 60 min to absorb the substances, participants underwent a maximal ramp cycle ergometer test (25 W/min). Near infrared spectrometers were positioned on each leg's vastus lateralis to monitor tissue O 2 saturation. Blood lactate concentration was measured 1 min after the end of the exercise test. Results:In comparison to the placebo, the ingestion of caffeine improved the maximal wattage (258 ± 50 vs 271 ± 54 W, respectively, P < .001, effect size [ES] = 0.27; 95% confidence interval [CI] 0.14-0.35) and blood lactate concentration (11.9 ± 3.8 vs 13.7 ± 3.5 mmol/L, P = .029, ES = 0.38; 95% CI 0.14-0.75) at the end of the test.Caffeine increased muscle oxygen saturation at several exercise workloads with a main effect found in respect to the placebo (F = 6.28, P = .029; ES = 0.30 to 0.54; 95% CI 0.01-0.78). Peak pulmonary ventilation (124 ± 29 vs 129 ± 23 L/min, P = 0.035, ES = 0.25; 95% CI 0.07-0.40) and peak oxygen uptake (3.18 ± 0.70 vs 3.33 ± 0.88 L/min, P = 0.032, ES = 0.26; 95% CI 0.08-0.51) were also increased with caffeine.Conclusion: Acute ingestion of 3 mg/kg of caffeine improved peak aerobic performance and increased peak pulmonary ventilation. In addition, caffeine induced changes in muscle oxygen saturation during submaximal workloads, suggesting that this mechanism might also contribute to caffeine's ergogenic effect. K E Y W O R D Scycling, high intensity exercise, muscle oxygenation, near infrared spectroscopy, VO 2 max The authors confirm that the Principal Investigator for this paper is Juan del Coso and he had direct clinical responsibility for patients.

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