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.

Metabolic dysfunction in late-puberty adolescent girls with type 1 diabetes: relationship to physical activity and dietary intakes.

AIMS: At puberty, type 1 diabetes (T1D) among young girls can lead to excess body weight, insulin resistance, deterioration of glycaemic control and dyslipidaemia. Although biological factors contribute largely to such metabolic dysfunction, little is known of the role of behavioural factors such as physical activity and diet. METHODS: This study investigated the association between metabolic dysfunction measured after a 12-h overnight fast and behavioural factors, including diet (4-day diary) and physical activity (validated questionnaire), in 19 postmenarchal adolescent girls with T1D compared with 19 healthy girls. RESULTS: T1D girls displayed higher levels of fat mass, insulin resistance (higher plasma glucose, serum leptin and waist-to-hip ratios) and dyslipidaemia (higher LDL-C and apolipoprotein B levels, lower HDL-C and apolipoprotein A-1 levels). Also, contrary to what is usually observed in T1D adults, serum adiponectin, an important vessel protector, was not raised in T1D adolescent girls compared with healthy controls. Quantity and quality of dietary macronutrient intakes as well as physical activity levels were comparable in both groups, although the T1D girls with the poorest metabolic profiles reported having the healthiest diets (fewer total calories, more protein and less carbohydrates). However, in T1D girls, less physical activity and more time spent watching television were associated with poorer metabolic profiles (higher waist-to-hip ratios, fat mass and leptin levels, and lower adiponectin, HDL-C and apolipoprotein A-1 levels). CONCLUSION: Collectively, these data suggest that physical inactivity is linked to metabolic dysfunction to a greater extent than unhealthy dietary habits in postmenarchal T1D adolescent girls.

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.

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.

Validity of the polar S810 to measure R-R intervals in children.

Intervals between two consecutive cardiac beats (R-R intervals) and the subsequent analysis of heart rate variability (HRV) obtained simultaneously from the Polar S810 heart rate monitor (HRM) and an electrocardiogram (ECG) in a supine position were compared in twelve children (age 9.6 +/- 0.9 years) before and after protocol correction. R-R intervals were significantly different between the ECG and the HRM uncorrected and corrected signal (p < 0.001, effect size [ES] = 0.005, and 0.005, respectively). However, the bias (95 % confidence interval) was 0.80 (- 124.76 - 123.16) ms and 0.80 (- 12.76 - 11.16) ms, respectively. HRV parameters derived from both signals were not different (p > 0.05) and well correlated (r > 0.99, p < 0.05), except SD2 (p < 0.05, ES = 0.000; r = 0.99). These data support the validity of the Polar S810 HRM to measure R-R intervals and make the subsequent HRV analysis in a supine position in children.

Reliability of postexercise heart rate recovery.

Passive postexercise heart rate (HR) recovery is currently used in the assessment of endurance athletes to determine changes in performance or in the clinical setting as a predictor of all-cause mortality. The purpose of this investigation was to assess the reliability of HR recovery. Thirty healthy subjects performed two maximal and two submaximal treadmill exercises, followed by 5 minutes of passive recovery. HR signal was used to compute raw and Delta (exercise - recovery) HR after 1, 2, 3, and 5 minutes of exercise cessation. A mono-exponential function was fitted to the data using the least squares procedure. We found no significant bias between repeated measures. Relative reliability was lower for Delta HR when compared with raw HR (0.43 < ICC < 0.71 vs. 0.68 < ICC < 0.83, respectively). Absolute reliability was relatively constant over time for raw HR (SEM = approximately 8 %), while it decreased exponentially from the 1st (SEM = approximately 20 %) to the 5th minute of recovery (SEM = approximately 8 %) for Delta HR. The reliability of parameter estimates from exponential curve fitting was less consistent, since both ICC (0.43 to 0.88) and SEM (5.7 to 21.4 %) differed from one parameter to the other according to the intensity of exercise. We conclude that passive postexercise HR recovery reliability is heterogeneous. Raw HR is the desired method to describe it.

Effect of training and detraining on heart rate variability in healthy young men.

The purpose of this study was to investigate the effect of twelve weeks of aerobic training and eight weeks of training cessation on Heart Rate Variability (HRV). Ten healthy young men (Age: 21.7 +/- 2.2 years; Height: 179.2 +/- 6.9 cm; Mass 72.7 +/- 11.1 kg) completed an incremental test and a 60 degrees tilt test during which R-R intervals were recorded before (T0) and after (T12) 12 weeks of intensive training, and after 2, 4 and 8 weeks of training cessation (D2, D4 and D8, respectively). HRV was computed in time and frequency domains. Training resulted in a significant increase in estimated VO2max after T12 (p < 0.01), followed by a significant decrease during D2 and D8 (p < 0.05). Total power (LF + HF) and low frequency power (LF) increased significantly in the supine position after the training period (p < 0.05) and decreased moderately after D2 (p > 0.05) to stabilize afterwards. LF + HF and LF were not different from T0 at D8 (p > 0.05). It was concluded that eight weeks of training cessation allow to reverse the cardiovascular autonomic adaptations induced by 12 weeks of intensive training in healthy young men.

Heart rate variability before and after knee surgery in amateur soccer players.

OBJECTIVE: To analyze the consequences on heart rate variability (HRV) of a hospitalization period due to surgery of the knee in sportsmen. PATIENTS: Ten soccer players who had undergone knee surgery took part in this study. DESIGN: HRV was measured before and after hospitalization within a 7-day interval. RESULTS: After the hospitalization phase, heart rate at rest increased significantly (3 beats/minute). A significant decrease of 7% in the cardiac inter beat interval (R-R interval), P < 0.05 and a 66% decrease in total power spectral density: -66%, P < 0.05 were observed. The disturbance of the autonomic nervous system could be due to a variation in cardiac vagal activity resulting in a 64% decrease in the high frequencies (P < 0.05). This variation was not associated with a modification in normalized markers (LFn.u., HFn.u.) and LF/HF ratio (P > 0.05). CONCLUSION: In sportsmen, a hospitalization period led to an increase in resting heart rate and was associated with a disturbance of the autonomic nervous system.