A 5-month weight-reduction programme has a positive effect on body composition, aerobic fitness, and habitual physical activity of severely obese girls: a pilot evaluation study.

In this pilot study, we wished to determine whether a 5-month multidisciplinary programme of a combined dietary-nutritional education-exercise intervention would have favourable effects on the health status of 18 obese adolescent girls. Before and after the clinical intervention, body composition and habitual physical activity were assessed by bioelectrical impedance and accelerometry, respectively. Aerobic fitness and substrate utilization were determined by gas exchange using an incremental field test that mimics habitual conditions. Despite a significantly (P < 0.001) greater loss of fat mass (-8.7 +/- 4.1 kg) compared with fat-free mass (-2.8 +/- 2.2 kg), energy expenditure at rest decreased by 9% following the intervention. Maximal oxygen consumption [Vdot]O2max related to fat-free mass increased by 7% (P < 0.05), whereas substrate utilization during exercise did not change following the intervention. Moderate and intense physical activity increased by 15% (+20 min . day(-1); P < 0.05) and 45% (+25 min . day(-1); P < 0.01), respectively. A significant relationship was observed between change in habitual physical activity and change in .[Vdot]O2max fat-free mass (r = 0.56, P = 0.01). The present multidisciplinary programme enhanced the loss of fat mass relative to fat-free mass but not sufficiently so to prevent a decline in metabolic rate during rest. Our results suggest a coupling in the improvement of aerobic fitness and habitual physical activity in obese adolescent girls, and hence an improvement in behaviour in relation to physical activity.

Morning-to-evening differences in oxygen uptake kinetics in short-duration cycling exercise.

This study analyzed diurnal variations in oxygen (O(2)) uptake kinetics and efficiency during a moderate cycle ergometer exercise. Fourteen physically active diurnally active male subjects (age 23+/-5 yrs) not specifically trained at cycling first completed a test to determine their ventilatory threshold (T(vent)) and maximal oxygen consumption (VO(2max)); one week later, they completed four bouts of testing in the morning and evening in a random order, each separated by at least 24 h. For each period of the day (07:00-08:30 h and 19:00-20:30 h), subjects performed two bouts. Each bout was composed of a 5 min cycling exercise at 45 W, followed after 5 min rest by a 10 min cycling exercise at 80% of the power output associated with T(vent). Gas exchanges were analyzed breath-by-breath and fitted using a mono-exponential function. During moderate exercise, the time constant and amplitude of VO(2) kinetics were significantly higher in the morning compared to the evening. The net efficiency increased from the morning to evening (17.3+/-4 vs. 20.5+/-2%; p<0.05), and the variability of cycling cadence was greater during the morning than evening (+34%; p<0.05). These findings suggest that VO(2) responses are affected by the time of day and could be related to variability in muscle activity pattern.

Effects of short-term normobaric hypoxia on haematology, muscle phenotypes and physical performance in highly trained athletes.

This study aimed to determine the impact of short-term normobaric hypoxia on physiology and performance in highly trained athletes. Twelve (7 male and 5 female) athletes were randomly assigned into two groups and spent 8 h per night for two consecutive nights a week over 3 weeks under either short-term normobaric hypoxia (simulating 3636 m altitude, inspired O2=13%) or in normobaric normoxia in a single-blind study. Following a 3 week washout period, athletes were then exposed to the other condition. Athletes were tested for maximal oxygen consumption and time to exhaustion on an electromagnetically braked cycle ergometer before and after each treatment in addition to being tested for anaerobic performance (Wingate test) on a modified Monark cycle ergometer. Blood samples were taken throughout the experiment and vastus lateralis muscle biopsies were taken before and after each treatment. Increases in red blood cell count, haematocrit, haemoglobin, platelet number and erythropoietin concentration were observed following short-term normobaric hypoxia. Except for a modest decrease in phosphofructokinase activity following short-term normobaric hypoxia, no changes were observed in muscle enzyme activities, buffer capacity, capillary density or morphology. No performance measures were changed following short-term normobaric hypoxia or normobaric normoxia. Although short-term normobaric hypoxia exposure increased levels of a number of haematological parameters, this was not associated with improved aerobic or anaerobic performance in highly trained athletes.

Muscle coordination changes during intermittent cycling sprints.

Maximal muscle power is reported to decrease during explosive cyclical exercises owing to metabolic disturbances, muscle damage, and adjustments in the efferent neural command. The aim of the present study was to analyze the influence of inter-muscle coordination in fatigue occurrence during 10 intermittent 6-s cycling sprints, with 30-s recovery through electromyographic activity (EMG). Results showed a decrease in peak power output with sprint repetitions (sprint 1 versus sprint 10: -11%, P<0.01) without any significant modifications in the integrated EMG. The timing between the knee extensor and the flexor EMG activation onsets was reduced in sprint 10 (sprint 1 versus sprint 10: -90.2 ms, P<0.05), owing to an earlier antagonist activation with fatigue occurrence. In conclusion, the maximal power output, developed during intermittent cycling sprints of short duration, decreased possibly due to the inability of muscles to maintain maximal force. This reduction in maximal power output occurred in parallel to changes in the muscle coordination pattern after fatigue.

[Habitual physical activity during growth]. / L'activité physique habituelle au cours du développement.

The three objectives of the present review of the literature were to: characterize the evolution of habitual physical activity (HPA) during growth; evaluate the tracking of HPA from childhood to adulthood; and analyse the level of HPA in children and adolescents according to public health recommendations. Data indicates that HPA decreases from childhood to adulthood about 7% per year, with a great reduction during puberty and adolescence concurrent to changes in the type of physical activity. It appears that HPA is not quite steady (0.09 < r < 0.66) during growth, which means that behavioural changes occur. Being very active during childhood or adolescence does not necessarily translate into a high level of HPA in adulthood. The mean values of HPA of children and adolescents vary from 15 to 90 min.day(-1) between studies, and for most of them HPA has been higher or close to public health recommendations. However, these results mask a great number of children and adolescents who are inactive or becoming inactive (40 to 45% of the population).

[Effects of recovery duration and time of day on sprint performance]. / Durée de la récupération et puissance maximale anaérobie au cours de la journée.

Effects of recovery duration (2-3 s, 15 s, 30 s, 1 min, and 2 min) and time of day (9 a.m., 2 p.m., and 6 p.m.) on sprint performance were studied in 9 subjects using a cycle ergometer. The peak power (Ppeak) and the total work performed (W) were determined from changes in instantaneous power, taking into account the inertia of the flywheel. A decrease in Ppeak and W was observed after 15 s and 2-3 s recovery (p < 0.001). A logarithmic relationship (y = 3.92 ln x + 81.5; r = 0.82; n = 9) was found between Ppeak (%Ppeak of the first sprint) and the duration of the recovery (half-time = 14.3 s; SD = 7.6). Data indicated that there was no significant effect of time of day on Ppeak and W, regardless of the duration of recovery. The recovery processes occurred in a very short time and did not seem to be affected by biological rhythms.

Maximal intermittent cycling exercise: effects of recovery duration and gender.

This study aimed to evaluate potential gender differences in recovery of power output during repeated all-out cycling exercise. Twenty men and thirteen women performed four series of two sprints (Sp1 and Sp2) of 8 s, separated by 15-, 30-, 60-, and 120-s recovery. Peak power (Ppeak), power at the 8th s, total mechanical work, and time to Ppeak were calculated for each sprint. Ppeak and mechanical work decreased significantly between Sp1 and Sp2 after 15-s recovery in both men (-6.4 and -9.4%, respectively) and women (-7.4 and -6.8%, respectively). Time to Ppeak did not change between recovery durations, but women reached their peak power more slowly than men (on average 5.15 +/- 1.2 and 3.8 +/- 1.2 s, respectively; P < 0.01). During Sp1 and Sp2, linear regressions from Ppeak to power at the 8th s showed a greater power decrease (%Ppeak) in women compared with men (P < 0.05). In conclusion, patterns of power output recovery between two consecutive short bouts were similar in men and women, despite lower overall performance and greater fatigability during sprints in women.

Habitual physical activity in children and adolescents during school and free days.

PURPOSE: The purpose of this study was to analyze habitual physical activity (HPA) of boys and girls from primary school to high school. METHODS: One hundred eighty-two schoolchildren and teenagers (6-20 yr) were studied at primary school (PS, N= 64), junior high school (JHS, N= 67), and senior high school (SHS, N= 51). HR was continuously monitored during the whole week to assess HPA during school days and free days. Total physical activity (TPA), low physical activity (LPA), moderate physical activity (MPA), and vigorous physical activity (VPA) were evaluated from the time spent each day above 50%HR reserve (HRR), below 50%HRR, between 50% and 70%HRR, and above 70%HRR, respectively. RESULTS: During school days, TPA decreased by 69% in male subjects (P< 0.05) and by 36% in female subjects (N= 0.058) from PS to SHS. In contrast, TPA did not vary significantly during free days (male subjects, PS: 62 +/- 37 min x d, SHS: 63 +/- 67 min x d; female subjects, PS: 75 +/- 59 min x d, SHS: 62 +/- 44 min x d ). Gender differences were only observed during school days at PS for TPA (male subjects: 121 +/- 37 min x d vs female subjects: 92 +/- 44 min x d, P< 0.05) and VPA (male subjects: 38 +/- 21 min x d vs female subjects: 18 +/- 12 min x d, P< 0.05). Male and female subjects were more inactive during free days than during school days at PS (P< 0.05). No effect of the type of day and gender was observed for all indices of HPA at high schools. CONCLUSIONS: Our results highlight the importance of taking into account the type of day (school day vs free day) in the analysis of children and adolescents' HPA.

Estudio comparativo de la funcion respiratoria en Niños bolivianos de la altura y el tropico; influencia del estado nutricional y antropometrico / Comparative study of respiratory function of Bolivian children and the influence of the nutritional and anthropometric status

Nuestro proposito tiene una doble finalidad, en primer lugar hacer un analisis de los factores que contribuyen en la funcion respiratoria de niños expuestos a diferentes ambientes ecologicos, altura y tropico y de diferente estado nutricional; en segundo lugar un estudio comparativo que permite ratificar los valores de referencia establecidos con el fin de efectuar una evaluacion funcional en patologia respiratoria infantil. Se comparan los volumenes pulmonares de cuatro grupos de niños en edad prepuberal habitantes de altura (LA PAz 3700 m sobre el nivel del mar, presion barometrica: 495 mmHg y de tierras bajas (Santa Cruz, 420 msnm, presion barometrica: 760 mmHg). El grupo de la altura GA (N=67) fue estudiado en el Instituto Boliviano de Altura (I.B.B.A), y dividido en dos subgrupos GA1 que corresponde a niños de nivel socioeconomico de nivel alto (N=23) y GA2 de nivel socioeconomico bajo (N=44). El grupo de tierras bajas GB (N=71) fue estudiado en CENETROP, y dividido en dos subgrupos GB1 formados por niños de nivel socioeconomicos altos (N=43) y GB2 de nivel socioeconomico bajo (N=28).