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To test the hypothesis that cycling exercise modulates heart rate variability (HRV), we applied a short-time Fourier transform on the electrocardiogram of subjects performing a maximal graded cycling test. A pedaling frequency component (PFC) in HRV was continuously observed over the time course of the exercise test and extracted from R-R interval series obtained from 15 healthy subjects with a heterogeneous physical fitness, exercising at three different pedaling frequency ( n = 5): 70, 80, and 90 rpm. From 30 to 50% of the maximal power output (Pmax), in the 90 rpm group, spectral aliasing caused PFC to overlap with the respiratory sinus arrhythmia (RSA) band, significantly overestimating the PFC amplitude ( APFC). In the meantime, APFC did not increase significantly from its minimal values in the 70 rpm (∼1.26 ms) and 80 rpm (∼1.20 ms) groups. Then, from 60 to 100% maximal power output (Pmax), workload increase caused a significant ∼2.8-, ∼3.3-, and ∼3.4-fold increase in APFC in the 70, 80, and 90 rpm groups, respectively, with no significant difference between groups. At peak exercise, APFC accounted for ∼43, ∼39, and ∼49% of the total HRV in the 70, 80, and 90 rpm groups, respectively. Our findings indicate that cycling continuously modulates the cardiac chronotropic response to exercise, inducing a new component in HRV, and that workload increase during intense exercise further accentuates this cardiolocomotor coupling. Moreover, because PFC and RSA overlapped at low workloads, methodological care should be taken in future studies aiming to quantify RSA as an index of parasympathetic activity.

This study was conducted to investigate the effects of giving short-term doses of creatine by mouth to healthy older male subjects, taking into account their training status. A group of 42 volunteers was divided into three: a sedentary group composed of elderly sedentary men [n = 14, mean age 70.1 (SEM 1.2) years], a trained group composed of elderly trained cyclists [n = 14, mean age 66.4 (SEM 1.4) years] and a young group composed of young sedentary men [n = 14, mean age 26.0 (SEM 1.2) years]. In each group, double-blind randomization was carried out: one half was given creatine (3x5 g x day(-1)), and the other was given an iso-nitrogenated placebo (3x10 g x day(-1)). Before and after the 5 days during which the supplements were given, all subjects performed five all-out 10-s sprints separated by 60-s intervals of passive recovery, seated on a cycle ergometer. Power output, work done and heart rate data were recorded during each sprint. The elderly and the young sedentary subgroups given creatine showed significant (P < 0.05) improvements in maximal power (+3.7% and +2.0%, respectively) and work done (+4.1% and +5.1%, respectively) in the subsequent tests. In contrast, no significant change in pedalling performances was observed in the trained elderly subjects. The creatine did not change the exercise and recovery heart rate profiles, in any group. Our study suggested that creatine given by mouth increases the anaerobic power and work capacity of sedentary people of different ages during maximal pedalling tasks. However, the level of physical activity seems to be a determinant of the ergogenic effect of creatine in older subjects.

Twenty malnourished subjects (average age 67 years old) treated by cyclic enteral nutrition were assigned to an active or control group according to whether they took part or not in a 3-week aerobic training program. Subjects underwent the following tests on d(0)-d(1) and d(20)-d(21): calculation of a global nutritional deficiency index (GND), bioelectrical impedance analysis, evaluation of daily energy expenditures using a 24 h heart rate (HR) recorder and a pedometer, maximal voluntary isometric strength assessment (MVIS), and symptoms limited maximal oxygen uptake ((.)VO(2 max. SL) estimation. Although energy intakes were similar in both groups, active subjects showed greater improvements (P0.05) than control subjects regarding GND (-9.8 vs -4.8%), serum albumin and prealbumin. Active subjects also showed a greater increase (P0.05) in pedometer readings compared to control subjects. Reduction of resting HR was observed in active (-5 beat/mn, P0.05) whereas no significant changes in average HR were noted in either group, reflecting increased metabolic activity. Compared to control, active subjects showed significant (P0.05) improvements in MVIS (0.8 vs 0.1 N/kg) and (.)VO(2 max. SL) (5.5 vs 1.4 mL/min/kg). Short-term aerobic training has positive effects on nutritional recovery and functional capacities in elderly malnourished subjects and should be recommended whenever possible.

International audience; We present a novel analysis tool for time delay estimation in electrocardiographic signal processing. This tool enhances PR interval estimation (index of the atrioventricular conduction time) by limiting the distortion effect of the T wave overlapping the P wave at high heart rates. Our approach consists of modeling the T wave, cancelling its influence, and finally estimating the PR intervals during exercise and recovery with the proposed generalized Woody method. Different models of the T wave are presented and compared in a statistical summary that quantitatively justifies the improvements introduced by this study. Among the different models tested, we found that a piecewise linear function significantly reduces the T wave-induced bias in the estimation process. Combining this modeling with the proposed time delay estimation method leads to accurate PR interval estimation. Using this method on real ECGs recorded during exercise and its recovery, we found: 1) that the slopes of PR interval series in the early recovery phase are dependent on the subjects' training status (average of the slopes for sedentary men = 0.11 ms/s, and for athlete men = 0.28 ms/s), and 2) an hysteresis phenomenon exists in the relation PR/RR intervals when data from exercise and recovery are compared.

International audience; It has been shown that a pedaling frequency component can be extracted from the heart rate variability (HRV) signal using a time-varying filter. It is shown that this filter can be implemented directly in the time-frequency plane with different approaches. The need of resampling the data is also discussed with regard to the artifacts produced when the shanon condition is not fulfilled. In order to interpret the similar amplitude profiles of the pedaling component for untrained and trained subjects, an attempt for the model parameters setting is proposed. Consistent results on a large data set illustrate the feasibility of such processing.

International audience; During exercise, analysis of the spectral components of the heart rate variability (i.e. R-R interval series variability; HRV) points out a new high frequency component related to the pedalling frequency. This component is independent of the classical low and high frequency bands related to the autonomic nervous system modulation of the heart period. It is not related to ECG distortion or artifacts, and could be linked to the mechanical influence of the muscle pump on venous return. To assess this new component, we develop and propose a method based on a time-varying filter, designed in the time-frequency plane, as well as a new model to link the potential input of the modulation (the muscle pump) to the pedalling frequency component of HRV.

International audience; The analysis of heart period series is a difficult task especially under graded exercise conditions. From all the information present in these series, we are the most interested in the coupling between respiratory and cardiac systems, known as respiratory sinus arrythmia. In this paper, we show that precise patterns concerning the respiratory frequency can be extracted from the heart period series. An evolutive model is introduced in order to achieve tracking of the main respiratory-related frequencies and their time-varying amplitudes. Since respiration acts to modulate the sinus rhythm, we relate the frequencies and amplitudes to this modulation by analyzing in detail its nonlinear transformation giving the heart period signal. This analysis is performed assuming stationary conditions but also in the realistic case where the mean heart period, the amplitude, and the frequency of the respiration are time-varying. Since this paper is devoted to the theoretical and complete presentation of the method used in a physiological study published elsewhere, the capabilities of our method will be illustrated in a realistic simulated case.