The aim of the current study was to investigate the effects of acute caffeine supplementation on anaerobic capacity determined by the alternative maximal accumulated oxygen deficit (MAODALT) in running effort. Eighteen recreational male runners [29 ± 7years; total body mass 72.1 ± 5.8 kg; height 176.0 ± 5.4cm; maximal oxygen uptake (VO2max) 55.8 ± 4.2 ml·kg-1 ·min-1] underwent a graded exercise test. Caffeine (6 mg·kg-1) or a placebo were administered 1 hr before the supramaximal effort at 115% of the intensity associated with VO2max in a double-blind, randomized cross-over study, for MAODALT assessment. The time to exhaustion under caffeine condition (130.2 ± 24.5s) was 11.3% higher (p = .01) than placebo condition (118.8 ± 24.9 s) and the qualitative inference for substantial changes showed a very likely positive effect (93%). The net participation of the oxidative phosphorylation pathway was significantly higher in the caffeine condition (p = .02) and showed a likely positive effect (90%) of 15.3% with caffeine supplementation. The time constant of abrupt decay of excess postexercise oxygen consumption (τ1) was significantly different between caffeine and placebo conditions (p = .03) and showed a likely negative effect (90%), decreasing -8.0% with caffeine supplementation. The oxygen equivalents estimated from the glycolytic and phosphagen metabolic pathways showed a possibly positive effect (68%) and possibly negative effect (78%) in the qualitative inference with caffeine ingestion, respectively. However, the MAODALT did not differ under the caffeine or placebo conditions (p = .68). Therefore, we can conclude that acute caffeine ingestion does not modify the MAODALT, reinforcing the robustness of this method. However, caffeine ingestion can alter the glycolytic and phosphagen metabolic pathway contributions to MAODALT.
Rodrigo De Araujo Bonetti De Poli, Willian Eiji Miyagi, Fabio Yuzo Nakamura and Alessandro Moura Zagatto
Javier Raya-González, Fabio Yuzo Nakamura, Daniel Castillo, Javier Yanci and Maurizio Fanchini
Purpose: To examine the association and predictive ability of internal load markers with regard to noncontact injuries in young elite soccer players. Methods: Twenty-two soccer players (18.6 [0.6] y) who competed in the Spanish U19 League participated in the study. During a full season, noncontact injuries were recorded and, using session rating of perceived exertion, internal weekly load (sum of load of all training sessions and matches for each week) and acute:chronic workload ratio (typically, acute = current week and chronic = rolling 4-wk average) were calculated. A generalized estimating equation analysis was used to examine the association of weekly and acute:chronic load-ratio markers with a noncontact injury in the subsequent week. Load variables were also analyzed for predictive ability with receiver operating characteristic curve and area under the curve. Results: No association was found for weekly load (odds ratio = 1.00; 90% confidence interval, 0.99–1.00) and acute:chronic load ratio (odds ratio = 0.16; 90% confidence interval, 0.01–1.84) with respect to injury occurrence. In addition, the analyzed load markers showed poor ability to predict injury occurrence (area under the curve < .50). Conclusions: The results of this study suggest that internal load markers are not associated with noncontact injuries in young soccer players and present poor predictive capacity with regard to the latter.
Carla Cristiane Silva, Maurizio Bertollo, Felipe Fossati Reichert, Daniel Alexandre Boullosa and Fábio Yuzo Nakamura
To examine which body position and indices present better reliability of heart rate variability (HRV) measures in children and to compare the HRV analyzed in different body positions between sexes.
Twenty eutrophic prepubertal children of each sex participated in the study. The RR intervals were recorded using a portable heart rate monitor twice a day for 7 min in the supine, sitting, and standing positions. The reproducibility was analyzed using the intraclass correlation coefficient (ICC; two way mixed) and within-subject coefficient of variation (CV).Two-way ANOVA with repeated measures was used to compare the sexes.
High levels of reproducibility were indicated by higher ICC in the root-mean-square difference of successive normal RR intervals (RMSSD: 0.93 and 0.94) and Poincaré plot of the short-term RR interval variability (SD1: 0.92 and 0.94) parameters for boys and girls, respectively, in the supine position. The ICCs were lower in the sitting and standing positions for all HRV indices. In addition, the girls presented significantly higher values than the boys for SDNN and absolute high frequency (HF; p < .05) in the supine position.
The supine position is the most reproducible for the HRV indices in both sexes, especially the vagal related indices.
Carla Cristiane da Silva, Ligia Maxwell Pereira, Jefferson Rosa Cardoso, Jonathan Patrick Moore and Fábio Yuzo Nakamura
The positive effects of physical training on heart rate variability (HRV) in healthy adults are widely recognized; however, the responsiveness to training in healthy children has not yet been established. The aim of this study was to determine the influence of physical training on HRV in prepubertal healthy children. Systematic computerized searches were performed from 1950 to 2012 in the following databases: Medline, Embase, Cinahl, Lilacs, Scielo, SportDiscus, ProQuest; Web of Science; PEDro; Academic Search Premier and the Cochrane Library. The key words used were: heart rate variability, autonomic nervous system, exercise training, physical activity, continuous exercise, intermittent exercise, children, prepubescent, adolescents, and healthy. Although the database search initially identified 6,164 studies, after removing duplicates and excluding by title the number was 148, however, only 2 studies were included in this systematic review. The meta-analysis compared the experimental group (n = 29) with the control group (n = 28) for the HRV parameters: RR intervals, SDNN, RMSSD, pNN50, LF (log), HF (log), LF/HF and Total Power (log). The meta-analysis demonstrated similar HRV indices between both the experimental and control groups. In conclusion, the available results from randomized controlled trials do not support the hypothesis that physical training improves HRV in healthy children[AUQ2].
Fabio Giuliano Caetano, Murilo José de Oliveira, Ana Lorena Marche, Fábio Yuzo Nakamura, Sergio Augusto Cunha and Felipe Arruda Moura
The purposes of this study were to investigate sprints and to characterize repeated-sprint sequences (RS) performed by athletes during professional futsal matches. We analyzed 97 players during 5 official matches using the DVideo automatic tracking system. The sprints were analyzed during the first and second halves according to playing position, and RS were categorized according to the number of sprints and the time between them. The results showed an increase (F[1, 2520] = 3.96; P = .046) in the sprint duration from the first (mean = 3.1 ± 1.3) to the second half (mean = 3.2 ± 1.2). However, no differences were found for other variables (distance covered, peak velocity, initial velocity, recovery time between sprints, and sprints performed per minute) or among playing positions. In addition, when considering RS, the results showed that RS comprising two sprints interspersed with a maximum of 15 seconds of recovery were significantly more frequent than other RS. The findings of this study characterizing the sprinting features of futsal players can help coaches to plan physical training and assessments according to the requirements of the sport.