Effets de l'entraînement et de l'hypoxie sur le contrôle neurovégétatif de la fonction cardiovasculaire évalué par la variabilité de la fréquence cardiaque

[Résumé en français] L'hypoxie aiguë et l'entraînement en endurance ont des effets opposés sur le système neurovégétatif et la fonction cardiovasculaire. Le modèle " living high-training low " (LHTL) pourrait limiter ces adaptations liées à l'entraînement en endurance seul. Un stage LHTL (16 h/j, 2500-3000m, 13 jours) limite la baisse de la fréquence cardiaque (FC) et de la modulation sympathique sur le cœur liée à l'entraînement alors que les résistances vasculaires et la pression artérielle sont augmentées (Etude 1). Ces adaptations semblent principalement dues à l'exposition à l'hypoxie (Etude 2). Des effets rémanents de l'hypoxie ont pu se prolonger jusqu'au début de la séance d'entraînement suivante et s'additionner avec la réponse à l'exercice. Il est peu probable que les effets de l'entraînement aérobie du stage LHTL se soient additionnés avec la réponse à l'hypoxie (Etude 3). L'analyse de la variabilité de la FC semble bien adaptée à l'évaluation du contrôle neurovégétatif lors d'études de terrain.PARIS13-BU Sciences (930792102) / SudocSudocFranceF

Autonomic adaptations in Andean trained participants to a 4220-m altitude marathon

Purpose: Both training and chronic hypoxia act on the autonomic nervous system. Because trained Andean high-altitude natives could perform a high-altitude marathon (4220 m above sea level) in 02:27:23 h, we hypothesized that living in chronic hypoxia does not limit the training-induced benefits on the autonomic modulation of the heart. Methods: Trained (N = 13) and sedentary (N = 11) Andean high-altitude natives performed an active orthostatic test. Eight of the trained subjects repeated the test 6-8 and 20-24 h after the end of a high-altitude marathon. Resting heart rate (HR) and the autonomic modulation of the heart were assessed by time domain and spectral analysis of HR variability (HRV): sympathetic (RR low frequency (LF)) and parasympathetic (RR high frequency (HF)) modulations, and sympathovagal balance (RR-LF:HF ratio). Results: Trained subjects exhibited a higher total power of HRV and a lower resting HR (+30%, P < 0.005) than sedentary subjects secondary to a higher and dominant parasympathetic modulation on sympathetic activity (RR-HF, RR-LF:HF ratio). At 6-8 h after the marathon, total power of HRV decreased (-69%), whereas resting HR increased from basal level (+22%), mainly because of a rise in sympathetic modulation (RR-LF, RR-LF:HF ratio). From 8 to 24 h of recovery, sympathetic modulation fell (RR-LF, RR-LF:HF ratio) and all HRV parameters were restored. Responses to the active standing position did not change between each recording session. Conclusion: Living in chronic hypoxia does not limit the training-induced benefits on the autonomic control of the cardiovascular system in Andean high-altitude ratives. The sympathetic predominance on the heart observed 6-8 h after the high-altitude marathon disappeared after 1 d of recovery. Therefore, living at high altitude does not impair the autonomic response to training

Absorption of creatine supplied as a drink, in meat or in solid form

Etude comparative du taux de créatine dans le sang, 6h après avoir ingéré 2g de créatine contenue soit dans de la viande ou soit dans une solution

Improvement of energy expenditure prediction from heart rate during running

We aimed to develop new equations that predict exercise-induced energy expenditure (EE) more accurately than previous ones during running by including new parameters as fitness level, body composition and/or running intensity in addition to heart rate (HR). Original equations predicting EE were created from data obtained during three running intensities (25%, 50% and 70% of HR reserve) performed by 50 subjects. Five equations were conserved according to their accuracy assessed from error rates, interchangeability and correlations analyses: one containing only basic parameters, two containing VO2max or speed at VO2max and two including running speed with or without HR. Equations accuracy was further tested in an independent sample during a 40 min validation test at 50% of HR reserve. It appeared that: (1) the new basic equation was more accurate than pre-existing equations (R2 0.809 versus. 0,737 respectively); (2) the prediction of EE was more accurate with the addition of VO2max (R2 = 0.879); and (3) the equations containing running speed were the most accurate and were considered to have good agreement with indirect calorimetry. In conclusion, EE estimation during running might be significantly improved by including running speed in the predictive models, a parameter readily available with treadmill or GPS

Eighteen days of 'living high, training low' stimulate erythropoiesis and enhance aerobic performance in elite middle-distance runners

International audienceThe efficiency of "living high, training low" (LHTL) remains controversial, despite its wide utilization. This study aimed to verify whether maximal and/or submaximal aerobic performance were modified by LHTL and whether these effects persist for 15 days after returning to normoxia. Last, we tried to elucidate whether the mechanisms involved were only related to changes in oxygen-carrying capacity. Eleven elite middle-distance runners were tested before (Pre), at the end (Post1), and 15 days after the end (Post2) of an 18-day LHTL session. Hypoxic group (LHTL, n = 5) spent 14 h/day in hypoxia (6 nights at 2,500 m and 12 nights at 3,000 m), whereas the control group (CON, n = 6) slept in normoxia (1,200 m). Both LHTL and CON trained at 1,200 m. Maximal oxygen uptake and maximal aerobic power were improved at Post1 and Post2 for LHTL only (+7.1 and +3.4% for maximal oxygen uptake, +8.4 and +4.7% for maximal aerobic power, respectively). Similarly oxygen uptake and ventilation at ventilatory threshold increased in LHTL only (+18.1 and +12.2% at Post1, +15.9 and +15.4% at Post2, respectively). Heart rate during a 10-min run at 19.5 km/h decreased for LHTL at Post2 (-4.4%). Despite the stimulation of erythropoiesis in LHTL shown by the 27.4% increase in serum transferrin receptor and the 10.1% increase in total hemoglobin mass, red cell volume was not significantly increased at Post1 (+9.2%, not significant). Therefore, both maximal and submaximal aerobic performance in elite runners were increased by LHTL mainly linked to an improvement in oxygen transport in early return to normoxia and probably to other process at Post2