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Introduction: Nitric oxide (NO) precursor supplementation has been shown to increase NO bioavailability and can potentially improve vascular function and exercise performance. It remains unclear whether the combination of NO precursor supplementation and exercise training has synergic effects on exercise performance. This study aims to assess the effect of chronic nitrate and citrulline intake on exercise training adaptations in healthy young individuals., Methods: In this randomized, double-bind trial, 24 healthy young (12 females) subjects performed vascular function assessment (blood pressure, pulse wave velocity, postischemia vasodilation, and cerebrovascular reactivity) and both local (submaximal isometric unilateral knee extension) and whole-body (incremental cycling) exercise tests to exhaustion before and after a 2-month exercise training program and daily intake of a placebo or a nitrate-rich salad and citrulline (N + C, 520 mg nitrate and 6 g citrulline) drink. Prefrontal cortex and quadriceps oxygenation was monitored continuously during exercise by near-infrared spectroscopy., Results: N + C supplementation had no effect on vascular function and muscle and cerebral oxygenation during both local and whole-body exercise. N + C supplementation induced a significantly larger increase in maximal knee extensor strength (+5.1 ± 3.5 vs +0.2 ± 5.5 kg, P = 0.008) as well as a trend toward a larger increase in knee extensor endurance (+35.2 ± 26.1 vs +24.0 ± 10.4 contractions, P = 0.092) than placebo, but no effect on exercise training-induced maximal aerobic performance improvement., Conclusion: These results suggest that chronic nitrate and citrulline supplementation enhances the effect of exercise training on quadriceps muscle function in healthy active young individuals, but this does not translate into improved maximal aerobic performances.

Training induces volume- and time-dependent morphological and functional changes in the heart. Heart rhythm disorders, such as atrial arrhythmia (including atrial fibrillation and atrial flutter), are a well-established consequence of such long-term endurance practice. Although resting bradycardia and first-degree atrioventricular persist in veteran athletes, a higher conduction system impairment has never been reported neither at rest nor during exercise. We report here two cases of Type II second-degree atrioventricular block occurring during exercise in middle-age well-trained athletes. Because animal and human studies suggest that a progressive myocardial fibrosis could explain such phenomenon, long-term training could also have consequences on the conduction pathways.

Purpose: Despite identical oxygen uptake (VO2), enhanced heart rate (HR) and cardiac output (Q) responses have been reported in eccentric (ECC) versus concentric (CON) cycle exercise. The aim of this study was to describe the specific circulatory adjustments (HR and stroke volume (SV)) to incremental ECC cycle exercise in order to: 1) determine the HR values leading to identical VO2 in ECC and CON cycling; and 2) estimate the interindividual variability of this HR correspondence between the two exercise modes, with emphasis upon rehabilitation and training purposes., Methods: Eight healthy male subjects (age, 28 +/- 2 yr) participated in this study. They performed CON and ECC cycle incremental exercises (power output increases of 50 W every 3 min). Breath-by-breath gas exchange analysis and beat-by-beat thoracic impedancemetry were used to determine VO2 and Q, respectively., Results: At the same metabolic power (VO2 of 1.08 +/- 0.05 L x min(-1) in CON vs 1.04 +/- 0.06 L x min in ECC), SV was not different, but HR was 17% higher in ECC (P < 0.01), leading to a 27% enhanced Q (P < 0.01). Q and HR net adjustments (exercise minus resting values) in ECC versus CON muscle involvement demonstrated important interindividual variability with coefficients of variation amounting to 32% and 30%, respectively., Conclusion: In practice, if a given level of VO2 is to be reached, ECC HR has to be set above the CON one. Taking into account the interindividual variability of the circulatory adjustments in ECC versus CON muscle involvement, a precise HR correspondence can be established individually from the VO2/HR relationship obtained using ECC incremental testing, allowing prescription of accurate target HR for rehabilitation or training purposes.

Purpose: Aging is associated with decreased heart rate variability (HRV). As aerobic training is known to increase HRV, the purpose of this study was to evaluate the influence of long-term lifestyle on HRV in very old adults with regard to their usual physical activity., Methods: Twenty-four older adults (mean 75.7 +/- 0.2 yr) were divided into two groups according to their sport activities assessed by the Modified Baecke Questionnaire for Older Adults. Sedentary subjects (SED) were compared to elderly regularly involved in sport activities (SP). The subjects were supine for 20 min and the last 5 min were used to determine HR and HRV indexes as the standard deviation of normal intervals (SDNN), the root-mean-square differences of successive normal R-R intervals (RMSSD), and the high-frequency (HF) and low-frequency (LF) power. Physical activity was evaluated during 1 wk by triaxial accelerometry and analyzed in terms of intensity and duration., Results: Daily physical activity energy expenditure given by the accelerometer was significantly higher in SP than in SED (P < 0.05). SP spent more time per week in activity of intensity higher than 3 resting metabolic equivalents (METs), but total activity time was significantly higher for SED than for SP (P < 0.05). SP showed significantly (P < 0.05) lower resting heart rate than SED, higher global HRV (SDNN), and higher parasympathetic-related HRV indexes (RMSSD, HF, and HF/(LF+HF)) (P < 0.05)., Conclusions: Our results indicate that in very old subjects a long-term sportive lifestyle, which increases total daily energy expenditure and physical activity intensity, is associated with higher global HRV and vagal-related indexes and thus may counteract the age-related decline in cardiac autonomic control better than a sedentary lifestyle.

Purpose: It has been suggested that an intermittent work exercise test (IWET) is as efficient but better tolerated than continuous exercise for rehabilitation. Although systemic and pulmonary cardiovascular adjustments have been investigated for continuous exercise, it has not been done for IWET with exercise bouts near maximal work rate., Methods: In seven healthy subjects, the pulmonary hemodynamics have been studied by the aid of heart catheterization during a strenuous 30-min bicycle IWET where a 4-min work set at the first ventilatory threshold (VT1) alternated with a 1-min work set at the second ventilatory threshold (VT2)., Results: During the IWET, cardiac output increased then remained stable with decreasing stroke volume and increasing heart rate, which became near maximal at the end of the test. Mean pulmonary arterial pressure increased from rest to the fifth minute of exercise and decreased significantly thereafter (P<0.01). An identical evolution was observed for mean systemic arterial pressure (SAP)., Conclusion: Pulmonary hemodynamics adapt well in healthy subjects during a strenuous IWET despite the performance of exercise bouts of near maximal intensity.

Purpose: We evaluated the associations between accelerometer-estimated physical activity (PA) intensity and heart rate variability (HRV) and examined mediation of these associations by glycemic control indices and other cardiovascular disease risk factors., Methods: Data were from 1668 participants (X[Combining Overline]age = 45.9 ± 3.5 yr, 58.0% female, 39.9% black) who participated in year 20 (2005-2006) of the Coronary Artery Risk Development in Young Adults Fitness Study. The ActiGraph 7164 estimated participants' mean minutes per day of vigorous-intensity PA (VPA), moderate-intensity PA (MPA), and light-intensity PA (LPA) over 7 d. Three sequential 10-s 12-lead ECG strips were used to derive standard deviation of all normal RR intervals (SDNN) and root mean square of all successive RR intervals (rMSSD) HRV. Mediators representing glycemic control indices included fasting glucose, fasting insulin, and 2-h oral glucose tolerance, with other mediators being traditional cardiovascular disease risk factors. Multiple linear regression assessed independent associations of PA intensity with HRV per 1-SD. Mediation analyses computed the proportion of the PA-HRV association attributable to physiological mediators., Results: Participants averaged 2.7 ± 6.2 min·d, 33.0 ± 22.0 min·d, and 360.2 ± 83.8 min·d of VPA, MPA, and LPA, respectively, with mean values for SDNN (32.6 ± 22.4 ms) and rMSSD (34.0 ± 24.8 ms) similar. After adjustment for demographic and lifestyle behaviors, VPA was associated with both HRV metrics (SDNN: std beta = 0.06 [0.03, 0.10]; rMSSD: std beta = 0.08 [0.05, 0.12]) and LPA with rMSSD only (std beta = 0.05 [0.01, 0.08]). Fasting insulin and glucose mediated 11.6% to 20.7% of the association of VPA and LPA with HRV, with triglycerides also potentially mediating these associations (range, 9.6%-13.4%)., Conclusions: Accelerometer-estimated VPA was associated with higher (i.e., improved) HRV. Light-intensity PA also demonstrated a positive association. Mediation analyses suggested these associations may be most attributable to glucose-insulin dynamics.