F.-X. Gamelin

Intense exercise increases circulating endocannabinoid and BDNF levels in humans—Possible implications for reward and depression

The endocannabinoid system is known to have positive effects on depression partly through its actions on neurotrophins, such as Brain-Derived Neurotrophic Factor (BDNF). As BDNF is also considered the major candidate molecule for exercise-induced brain plasticity, we hypothesized that the endocannabinoid system represents a crucial signaling system mediating the beneficial antidepressant effects of exercise. Here we investigated, in 11 healthy trained male cyclists, the effects of an intense exercise (60 min at 55% followed by 30 min at 75% W(max)) on plasma levels of endocannabinoids (anandamide, AEA and 2-arachidonoylglycerol, 2-AG) and their possible link with serum BDNF. AEA levels increased during exercise and the 15 min recovery (P<0.001), whereas 2-AG concentrations remained stable. BDNF levels increased significantly during exercise and then decreased during the 15 min of recovery (P<0.01). Noteworthy, AEA and BDNF concentrations were positively correlated at the end of exercise and after the 15 min recovery (r>0.66, P<0.05), suggesting that AEA increment during exercise might be one of the factors involved in exercise-induced increase in peripheral BDNF levels and that AEA high levels during recovery might delay the return of BDNF to basal levels. AEA production during exercise might be triggered by cortisol since we found positive correlations between these two compounds and because corticosteroids are known to stimulate endocannabinoid biosynthesis. These findings provide evidence in humans that acute exercise represents a physiological stressor able to increase peripheral levels of AEA and that BDNF might be a mechanism by which AEA influences the neuroplastic and antidepressant effects of exercise.

Continuous vs. Interval Aerobic Training in 8- to 11-Year-Old Children

Baquet, G, Gamelin, F-X, Mucci, P, Thévenet, D, Van Praagh, E, and Berthoin, S. Continuous vs. interval aerobic training in 8- to 11-year-old children. J Strength Cond Res 24(5): 1381-1388, 2010-The aim of the present study was to show if the use of continuous-running training vs. intermittent-running training has comparable or distinct impact on aerobic fitness in children. At first, children were matched according to their chronological age, their biological age (secondary sexual stages), and their physical activity or training status. Then, after randomization 3 groups were composed. Sixty-three children (X 9.6 ± 1.0 years) were divided into an intermittent-running training group (ITG, 11 girls and 11 boys), a continuous-running training group (CTG, 10 girls and 12 boys), and a control group (CG, 10 girls and 9 boys). Over 7 weeks, ITG and CTG participated in 3 running sessions per week. Before and after the training period, they underwent a maximal graded test to determine peak oxygen uptake (peak &OV0312;o2) and maximal aerobic velocity (MAV). Intermittent training consisted of short intermittent runs with repeated exercise and recovery sequences lasting from 5/15 to 30/30 seconds. With respect to continuous training sessions, repeated exercise sequences lasted from 6′ to 20′. Training-effect threshold for statistical significance was set at p < 0.05. After training, peak &OV0312;o2 was significantly improved in CTG (+7%, p < 0.001) and ITG (+4.8%, p < 0.001), whereas no difference occurred for the CG (−1.5%). Similarly, MAV increased significantly (p < 0.001) in both CTG (+8.7%) and ITG (+6.4%) with no significant change for CG. Our results demonstrated that both continuous and intermittent-running sessions induced significant increase in peak &OV0312;o2 and MAV. Therefore, when adequate combinations of intensity/duration exercises are offered to prepubertal children, many modalities of exercises can successfully be used to increase their aerobic fitness. Aerobic running training is often made up of regular and long-distance running exercises at moderate velocity, which causes sometimes boredom in young children. During the developmental years, it seems therefore worthwhile to use various training modalities, to make this activity more attractive and thus create conditions for progress and enhanced motivation.

The role of the endocannabinoid system in skeletal muscle and metabolic adaptations to exercise: potential implications for the treatment of obesity

The results of recent studies add the endocannabinoid system, and more specifically CB1 receptor signalling, to the complex mechanisms that negatively modulate insulin sensitivity and substrate oxidation in skeletal muscle. CB1 receptors might become overactive in the skeletal muscle during obesity due to increased levels of endocannabinoids. However, quite surprisingly, one of the most studied endocannabinoids, anandamide, when administered in a sufficient dose, was shown to improve muscle glucose uptake and activate some key molecules of insulin signalling and mitochondrial biogenesis. This is probably because anandamide is only a partial agonist at CB1 receptors and interacts with other receptors (PPARγ, TRPV1), which may trigger positive metabolic effects. This putative beneficial role of anandamide is worth considering because increased plasma anandamide levels were recently reported after intense exercise. Whether the endocannabinoid system is involved in the positive exercise effects on mitochondrial biogenesis and glucose fatty acid oxidation remains to be confirmed. Noteworthy, when exercise becomes chronic, a decrease in CB1 receptor expression in obese metabolically deregulated tissues occurs. It is then tempting to hypothesize that physical activity would represent a complementary alternative approach for the clinical management of endocannabinoid system deregulation in obesity, without the side effects occurring with CB1 receptor antagonists.

Two months of endurance training does not alter diastolic function evaluated by TDI in 9–11-year-old boys and girls

Objective: Superior global cardiac performance (ie stroke volume) is classically reported after training in children. Current knowledge of the impact of exercise training on myocardial relaxation, a major component of left ventricular (LV) filling and subsequently stroke volume, is, however, limited in the paediatric population. This study aimed to investigate the effect of aerobic training on LV wall motion velocities by tissue Doppler imaging (TDI) in healthy children. Methods: 25 children (11 girls, 14 boys) were enrolled in a 2 month high-intensity aerobic training programme and 25 (12 girls and 13 boys) served as controls. The children (9–11 years old) performed a graded maximal exercise test on a treadmill to evaluate maximal oxygen uptake. Standard Doppler echocardiography and TDI measurements were performed at baseline and end of the study. Tissue Doppler systolic, early and late myocardial velocities were obtained at the mitral annulus in the septal, lateral, inferior and posterior walls. Results: Maximal oxygen uptake increased by 6.5% (before: 51.6 (SD 4.2), after: 55.0 (4.5) ml/min/kg p<0.001) after training. A modest but significant increase in left ventricular end-diastolic diameter was also noticed (before: 46.1 (3.4), after: 48.3 (4.3) mm.BSA-1/2, p<0.001), whereas left ventricular wall thickness and mass were unchanged. Neither transmitral inflow velocities nor early and late wall motion (Em: before = 18.4 (2.7), after = 18.0 (2.3) cm/s, Am: before = 6.8 (1.2), after = 6.7 (1.3) cm/s) were affected by training. Shortening fraction and regional systolic function (Sm: before = 10.1 (1.6), after = 10.2 (1.4) cm/s) by TDI were also unchanged. Conclusion: High-intensity aerobic sessions repeated over a 2 month period failed to improve regional diastolic function assessed by TDI in healthy young children.

Swimmers can train in hypoxia at sea level through voluntary hypoventilation.

This study used an innovative technique of pulse oximetry to investigate whether swimmers can train under hypoxic conditions through voluntary hypoventilation (VH). Ten trained subjects performed a front crawl swimming series with normal breathing (NB), VH at high (VHhigh) and low pulmonary volume (VHlow). Arterial oxygen saturation was continuously measured via pulse oximetry (SpO2) with a waterproofed forehead sensor. Gas exchanges were recorded continuously and lactate concentration ([La]) was assessed at the end of each test. In VHlow, SpO2 fell down to 87% at the end of the series whereas it remained above 94% in VHhigh during most part of the series. Ventilation, oxygen uptake and end-tidal O2 pressure were lower in both VHhigh and VHlow than in NB. Compared to NB, [La] significantly increased in VHlow and decreased in VHhigh. This study demonstrated that swimmers can train under hypoxic conditions at sea level and can accentuate the glycolytic stimulus of their training if they perform VH at low but not high pulmonary volume.

PREDICTION OF ONE-HOUR RUNNING PERFORMANCE USING CONSTANT DURATION TESTS

Critical velocity (CV) represents, theoretically, the highest velocity that can be sustained without fatigue. The aim of this study was to compare CV computed from 5 mathematical models in order to determine which CV estimate is better correlated with 1-hour performance and which model provides the most accurate prediction of performance. Twelve trained middle- and long-distance male runners (29 ± 5 years) performed 3 randomly ordered constant duration tests (6, 9, and 12 minutes), a maximal running velocity test for the estimation of CV, and a 1-hour track test (actual performance). Two linear, 2 nonlinear, and 1 exponential mathematical models were used to estimate CV and to predict the highest velocity that could be sustained during 1 hour (predicted performance). Although all CV estimates were correlated with performance (0.80 < r < 0.93, p < 0.01), it appeared that CV estimated from the exponential model was more closely associated with performance than all other models (r = 0.93; p < 0.01). Analysis of the bias ± 95% interval of confidence between actual and predicted performance revealed that none of the models provided an accurate prediction of the 1-hour performance velocity. In conclusion, the estimation of CV allows us to rank middle- and long-distance runners with regard to their ability to perform well in long-distance running. However, no models provide an accurate prediction of performance that could be used as a reference for coaches or athletes.

Longitudinal Follow-Up of Physical Activity During School Recess: Impact of Playground Markings

To promote physical activity (PA) among children, few studies have reported long-term effects of playground marking during school recess. The aim of this study was to investigate the impact of a playground design on childrens recess PA across 12 months and to evaluate the influence of covariates on the intervention effects with accelerometry data. Two hundred and eighty-three children (aged 6–11 years) were selected from 3 elementary schools. Two experimental schools received a recess-based intervention; the third one served as a control group. The design of playgrounds was based on a multicolored zonal design. Childrens PA was measured with a uniaxial accelerometer twice a day (morning and afternoon recess) during a 4-day school week. Times spent below and above different PA levels, varying from sedentary (SED, <1.5 METs), light PA (LPA, <4 METs), and from moderate to very high (MVPA, ≥ 4 METs) were calculated before and after 6 and 12 months intervention. A three level (time, pupil, school) multilevel analysis was used to control the intervention effect across time on SED, LPA, and MVPA. The playground intervention was effective after 6 months for LPA (+2.5%, CI 0.65/4.29, P < 0.01) and after 12 months for MVPA (+3.1%, CI 0.62/5.54, P < 0.01). Moreover, negative non-significant intervention effects were found for SED and LPA. Baseline PA and sex were significant covariates to the contrary of body mass index and age. Playground markings intervention can modify positively long-term school recess total PA.

Cardiorespiratory Responses to Continuous and Intermittent Exercises in Children

The aim of the study was to characterize aerobic responses to high intensity intermittent (HIIE) and continuous (CE) exercises in prepubertal children. 26 children aged 8 to 11-year-old took part in a preliminary session to determine peakVO2 and Maximal Aerobic Velocity (MAV). In 5 subsequent experimental visits, the participants completed 2 CE and 3 HIIE sessions in a randomized order. HIIE consisted of short intermittent 10-s and 20-s running bouts at 100 to 130% MAV, interspersed with recovery periods of equal duration (S-HIIE1 and S-HIIE2 respectively) and 5-s of sprinting and jumping at maximal intensity with 15-s recovery periods (S-HIIE3). CE consisted of 2 10-min running periods at 80% and 85% MAV with a 5-min recovery period. CE protocols elicited higher average VO2 and exercise time spent above 95% of peakVO2 compared to the HIIE protocols. S-HIIE 1 and S-HIIE 2 elicited similar average VO2 response, higher than S-HIIE 3. Our study shows that CE activated the aerobic system to a greater extent than S-HIIE in prepubertal children, as reflected by the time above 95% of peakVO2 during exercise. However, isotime S-HIIE protocols comprising 10-s or 20-s exercise bouts at an intensity above MAV result in similar times above 95% of peakVO2 during exercise.