The effects of the general antioxidant N-acetylcysteine (NAC) on muscle function and metabolism were examined. Isolated paired mouse extensor digitorum longus muscles were studied in the absence or presence of 20 mM NAC. Muscles were electrically stimulated to perform 100 isometric tetanic contractions (300 ms duration) at frequencies resulting in ∼85% of maximal force (70-150 Hz at 25-40 °C). NAC did not significantly affect peak force in the unfatigued state at any temperature but significantly slowed tetanic force development in a temperature-dependent fashion (e.g., time to 50% of peak tension averaged 35 ± 2 ms [control] and 37 ± 1 ms [NAC] at 25 °C vs. 21 ± 1 ms [control] and 52 ± 6 ms [NAC, P < 0.01] at 40 °C). During repeated contractions, NAC maximally enhanced peak force by the fifth tetanus at all temperatures (by ∼30%). Thereafter, the effect of NAC disappeared rapidly at high temperatures (35-40 °C) and more slowly at the lower temperatures (25-30 °C). At all temperatures, the enhancing effect of NAC on peak force was associated with a slowing of relaxation. NAC did not significantly affect myosin light chain phosphorylation at rest or after five contractions (∼50% increase vs. rest). After five tetani, lactate and inorganic phosphate increased about 20-fold and 2-fold, respectively, both in control and NAC-treated muscles. Interestingly, after five tetani, the increase in glucose 6-P was ∼2-fold greater, whereas the increase in malate was inhibited by ∼75% with NAC vs. control, illustrating the metabolic effects of NAC. NAC slightly decreased the maximum shortening velocity in early fatigue (five to seven repeated tetani). These data demonstrate that the antioxidant NAC transiently enhances muscle force generation by a mechanism that is independent of changes in myosin light chain phosphorylation and inorganic phosphate. The slowing of relaxation suggests that NAC enhances isometric force by facilitating fusion (i.e., delaying force decline between pulses). The initial slowing of tension development and subsequent slowing of relaxation suggest that NAC would result in impaired performance during a high-intensity dynamic exercise.

The amount of haemoglobin during puberty is related to endurance performance in adulthood. During male puberty, testosterone stimulates erythropoiesis and could therefore be used as a marker for later endurance performance. This cross-sectional study aimed to determine the relationship between serum testosterone concentration and haemoglobin mass (Hbmass) in both male and female children and adolescents and to evaluate the possible influences of altitude and training. Three-hundred and thirteen differentially trained boys and girls aged from 9 to 18 years and living at altitudes of 1000 and 2600 m above sea level entered the study. The stage of sexual maturation was determined according to the classification of Tanner. Testosterone was measured by ELISA. Hbmass was determined by CO-rebreathing. Haemoglobin concentration did not change during maturation in girls and was 11% higher during puberty in boys, while Hbmass was elevated by 33% in Tanner stage V compared to stage II in girls (498 ± 77 vs. 373 ± 88 g) and by 95% in boys (832 ± 143 vs. 428 ± 95 g). This difference can most likely be attributed to indirect testosterone influences through an increase in lean body mass (LBM) and to direct testosterone effects on erythropoiesis, which increase the Hbmass by ∼65 g per 1 ng/ml. Altitude and training statuses were not associated with testosterone, but with an increase in Hbmass (altitude by 1.1 g/kg LBM, training by 0.8 g/kg LBM). Changes in Hbmass are closely related to testosterone levels during male puberty. Further studies will show whether testosterone and Hbmass during childhood and adolescence can be used as diagnostic tools for endurance talents.

Three focus groups were formed with an average attendance of 12 students from different undergraduate programs, between the ages of 18 and 25. The content of the accounts was analyzed and categorized according to the factors influencing the selection of food and eating habits. Results Students identified sensory and hygiene factors, the cost of food, the availability of food and available time to eat as the main factors influencing food selection. We also identified the influence of friends and family, among others, in their choices. Students who participated reported to prefer food from home, eating most of their meals at home and having eating schedules influenced by academic activities. Conclusion Although students have knowledge about what is good for them in terms of food, in university life, the organization of academic schedule, food availability and economic resources show significant influence on their habits and choices. Strategies to promote healthy habits in universities should then prioritize the control of such barriers.

<p class="p1"><strong>Antecedentes.</strong> La investigación sobre los efectos de la exposición a la altura sobre la eritropoyesis y el metabolismo de hierro ha permitido conocer el comportamiento y las adaptaciones que se presentan en poblaciones residentes o expuestas a diversas alturas sobre el nivel del mar.</p><p class="p1"><strong>Objetivo.</strong> El presente artículo de revisión tiene como objetivo analizar la información científica disponible y actualizar al lector respecto al efecto de la altura sobre los indicadores de la eritropoyesis y el metabolismo del hierro.</p><p class="p1"><strong>Materiales y métodos.</strong> Se realizó una búsqueda de artículos de diferentes bases de datos como PubMed, MEDLINE, Scielo, EBSCO y OVID, la cual se hizo con base en los títulos médicos MeSH (Medical Subjects Headings) y DeCS Bireme (descriptores de la salud).</p><p class="p1"><strong>Resultados.</strong> A nivel de la eritropoyesis se puede observar un incremento de la eritropoyetina y de los reticulocitos con el incremento en la altura. En el metabolismo del hierro se puede apreciar un descenso de las reservas del hierro (ferritina) y un incremento de la transferrina y del receptor soluble de transferrina con ascenso en la altitud. </p><p class="p1"><span class="s1"><strong>Conclusión.</strong> La magnitud de estos incrementos depende del tiempo de exposición a la hipoxia, el género y la población, ya que se han encontrado diferencias entre etnias que viven a la misma altura pero presentan diferencias en las adaptaciones. Las investigaciones existentes están referidas a grandes alturas, pero en alturas intermedias por debajo de los 2600 m s. n. m. todavía existen grandes interrogantes.</span></p>

Introduction: To a considerable extent, the magnitude of blood volume (BV) and hemoglobin mass (Hbmass) contribute to the maximum O2-uptake (VO2max), especially in endurance-trained athletes. However, the development of Hbmass and BV and their relationships with VO2max during childhood are unknown. The aim of the present cross-sectional study was to investigate Hbmass and BV and their relationships with VO2max in children and adolescents. In addition, the possible influence of endurance training and chronic hypoxia was evaluated.Methods: A total of 475 differently trained children and adolescents (girls n = 217, boys n = 258; untrained n = 171, endurance trained n = 304) living at two different altitudes (∼1,000 m, n = 204, ∼2,600 m, n = 271) and 9–18 years old participated in the study. The stage of puberty was determined according to Tanner; Hbmass and BV were determined by CO rebreathing; and VO2max was determined by cycle ergometry and for runners on the treadmill.Results: Before puberty, there was no association between training status and Hbmass or BV. During and after puberty, we found 7–10% higher values in the trained groups. Living at a moderate altitude had a uniformly positive effect of ∼7% on Hbmass in all groups and no effect on BV. The VO2max before, during and after puberty was strongly associated with training (pre/early puberty: boys +27%, girls +26%; mid puberty: +42% and +45%; late puberty: +43% and +47%) but not with altitude. The associated effects of training in the pre/early pubertal groups were independent of Hbmass and BV, while in the mid- and late pubertal groups, 25% of the training effect could be attributed to the elevated Hbmass.Conclusions: The associated effects of training on Hbmass and BV, resulting in increased VO2max, can only be observed after the onset of puberty.