Biomedical subjects

J R Lacour

Publications and source records attributed to J R Lacour.

At least 37 records · Page 2Linked to original sources

PubMed2000

Influence of fatigue on EMG/force ratio and cocontraction in cycling.

PURPOSE: The purpose of the present study was to observe force and power losses and electromyographic manifestations of fatigue during repeated sprints performed on a friction-loaded cycle ergometer. METHODS: Ten subjects performed 15 maximal 5-s sprints with 25-s rests between them. Power, velocity, and torque were measured during sprints 1 and 13 and during two submaximal constant-velocity (50 rpm) periods of cycling performed before and after the sprints. The EMG signals of five leg muscles were stored to determine the EMG/force ratio of power producer muscles and the coactivation of antagonist muscles. The power producer muscles were activated to the same level during sprints 1 and 13, despite a loss of force, whereas the vastus lateralis muscle was recruited more during the submaximal cycling period under fatigue conditions. RESULTS: This led to an increased EMG/force ratio for the power producer muscles, indicating the peripheral fatigue status of these muscles. Antagonist muscles were less activated during the sprints after fatigue; whereas they stayed unchanged during the last submaximal cycling period. CONCLUSIONS: This suggests that there is a decrease in coactivation as agonist force is lost. This decrease in coactivation under fatigue conditions has not been previously reported and is probably due to the training status of the subjects. Subjects may have learned to better use their antagonist muscles to efficiently transfer force and power to the rotating pedal. This coordination can be adapted to cope with fatigue of the power producer muscles.

Adult↗

PubMed2000

Relation between heart rate variability and training load in middle-distance runners.

PURPOSE: Monitoring physical performance is of major importance in competitive sports. Indices commonly used, like resting heart rate, VO2max, and hormones, cannot be easily used because of difficulties in routine use, of variations too small to be reliable, or of technical challenges in acquiring the data. METHODS: We chose to assess autonomic nervous system activity using heart rate variability in seven middle-distance runners, aged 24.6 +/- 4.8 yr, during their usual training cycle composed of 3 wk of heavy training periods, followed by a relative resting week. The electrocardiogram was recorded overnight twice a week and temporal and frequency indices of heart rate variability, using Fourier and Wavelet transforms, were calculated. Daily training loads and fatigue sensations were estimated with a questionnaire. Similar recordings were performed in a sedentary control group. RESULTS: The results demonstrated a significant and progressive decrease in parasympathetic indices of up to -41% (P < 0.05) during the 3 wk of heavy training, followed by a significant increase during the relative resting week of up to +46% (P < 0.05). The indices of sympathetic activity followed the opposite trend, first up to +31% and then -24% (P < 0.05), respectively. The percentage increasing mean nocturnal heart rate variation remained below 12% (P < 0.05). There was no significant variation in the control group. CONCLUSION: This study confirmed that heavy training shifted the cardiac autonomic balance toward a predominance of the sympathetic over the parasympathetic drive. When recorded during the night, heart rate variability appeared to be a better tool than resting heart rate to evaluate cumulated physical fatigue, as it magnified the induced changes in autonomic nervous system activity. These results could be of interest for optimizing individual training profiles.

Adult↗

PubMed1999

Screening of obstructive sleep apnea syndrome by heart rate variability analysis.

BACKGROUND: Enhanced nocturnal heart rate variability (HRV) has been evoked in sleep-related breathing disorders. However, its capacity to detect obstructive sleep apnea syndrome (OSAS) has not been systematically determined. Thus, we evaluated the discriminant power of HRV parameters in a first group of patients (G1) and validated their discriminant capacity in a second group (G2). METHODS AND RESULTS: In G1, 39 of 91 patients (42.8%) were identified as diseased by polysomnography, as were 24 of 52 patients (46%) in G2. Time-domain HRV variables (SD of NN intervals [SDNN], mean of the standard deviations of all NN intervals for all consecutive 5-minute segments of the recording [SDNN index], square root of the mean of the sum of the squares of differences between adjacent normal RR intervals [r-MSSD], and SD of the averages of NN intervals in all 5-minute segments of the recording [SDANN]) were calculated for daytime and nighttime periods, as well as the differences between daytime and nighttime values (Delta[D/N]). Correlations between HRV variables and OSAS status were analyzed in G1 by use of receiver-operating characteristic (ROC) curves and logistic regression analysis. By ROC curve analysis, 7 variables were significantly associated with OSAS. After adjustment for other variables through multiple logistic regression analysis, Delta[D/N]SDNN index and Delta[D/N] r-MSSD remained significant independent predictors of OSAS, with ORs of 8.22 (95% CI, 3.16 to 21.4) and 2.86 (95% CI, 1.21 to 6.75), respectively. The classification and regression tree methodology demonstrated a sensitivity reaching 89.7% (95% CI, 73.7 to 97.7) with Delta[D/N] SDNN index and a specificity of 98.1% (95% CI, 86.4 to 100) with Delta[D/N] SDNN using appropriate thresholds. These thresholds, applied to G2, yielded a sensitivity of 83% using Delta[D/N] SDNN index and a specificity of 96.5% using Delta[D/N] SDNN. CONCLUSIONS: Time-domain HRV analysis may represent an accurate and inexpensive screening tool in clinically suspected OSAS patients and may help focus resources on those at the highest risk.

Adult↗

PubMed1999

Influence of acute and chronic exercise on insulin-like growth factor-I in healthy active elderly men and women.

We examined the influence of physical activity (PA) and acute resistance exercise on insulin-like growth factor I (IGF-I) in 39 healthy, independent, community-dwelling elderly volunteers (14 men and 25 women) aged from 66 to 84. In a longitudinal non-interventional study, we compared the fluctuations in IGF-I levels and changes in habitual PA over a 6-month period. PA was evaluated by a questionnaire QAPSE (Questionnaire d'Activité Physique Saint-Etienne), and expressed by two activity indices: mean habitual daily energy expenditure (MHDEE), and daily energy expenditure corresponding to leisure time sports activities (sports activity index). In an experimental design we compared IGF-I levels before, at 1 and 15 minutes after short quadriceps muscle exertion (10 consecutive repetitions) carried out with optimal muscle power development. Changes in IGF-I levels over a 6-month period were positively related to changes in MHDEE (r = 0.41; p<0.01), and sports activity (r = 0.40; p<0.02). When analyzed by gender, these correlations were still statistically significant in women (r = 0.39; p = 0.05 and r = 0.41; p<0.05), but not in men (r = 0.36; p = 0.21 and r = 0.20; p = 0.50). No changes (p = 0.17) were observed in serum IGF-I concentrations after the acute exercise protocol. These findings indicate that IGF-I levels are positively related to fluctuations in habitual PA, at least in women. Further research is needed to establish the best intensity and duration of exercise training to induce these changes.

Aged↗

PubMed1999

Reduced cardiac sympathetic autonomic tone after long-term nasal continuous positive airway pressure in obstructive sleep apnoea syndrome.

The increased sympathetic activation that occurs in obstructive sleep apnoea (OSA) may play an important role in associated morbidity. We investigated the effect of long-term (3 month) nasal continuous positive airway pressure (CPAP) on the autonomic nervous system assessed by heart rate variability (HRV). Fourteen patients (12 men), mean age 61.4 +/- 8.1 years, with OSA underwent continuous synchronized electrocardiographic and polysomnographic monitoring. The apnoea/hypopnoea index (AHI) decreased from 50.6 +/- 13.7 to 2.2 +/- 2.5 events h-1 after CPAP. HRV analysis showed significant decreases in low frequency (LF; from 7.12 +/- 1.06 to 6.22 +/- 1.18 ln ms2 Hz-1; P < 0.001), high frequency (HF; from 5.91 +/- 0.87 to 5.62 +/- 0.92 ln ms2 Hz-1; P < 0.05) and LF/HF (from 1.21 +/- 0.12 to 1.11 +/- 0.15 ln ms2 Hz-1; P < 0.001) when the patients were asleep. The decrease in LF/HF was prolonged into the daytime (from 1.33 +/- 0.22 to 1.24 +/- 0.21 ln ms2 Hz-1; P < 0.001). Treatment of OSA by CPAP significantly reduced the parameters of cardiac sympathetic tone, a favourable effect.

Adult↗

PubMed1999

Relationship of physical activity and fitness to lipid and lipoprotein (a) in elderly subjects.

PURPOSE: To determine, both by a cross-sectional and longitudinal study design, the relationship of maximal oxygen consumption (VO2max) and physical activity (PA) to blood lipids and lipoprotein(a) [Lp(a)] in a population of healthy and weight-stable elderly volunteers aged 66-84 yr. METHODS: In a cross-sectional study in 52 subjects (23 men and 29 women), all independent variables (age, anthropometric, VO2max, and PA indices) were used in a multiple stepwise regression analysis to select variables influencing lipid and lipoprotein parameters. In a prospective nonintervention study, 38 subjects (17 men and 21 women) were reexamined after 6 months. RESULTS: In a cross-sectional study, sports activity index contributed significantly to total cholesterol (TC), low density lipoprotein (LDL) cholesterol (LDL-C), TC/high density lipoprotein (HDL) cholesterol (HDL-C) ratio, and LDL-C/HDL-C ratio variance in men, whereas VO2max accounted for 23% variance of apolipoprotein A-I in women. In a prospective study, there was no indication that any measured variable was correlated with absolute or relative changes in PA indices in the total group or when analyzed by gender. CONCLUSIONS: These data confirm that favorable relationship between PA/fitness and blood lipid profile is visible in elderly people but spontaneous changes in habitual PA are not a sufficient stimulus to alter serum lipid and lipoprotein levels in this population. Furthermore, there is no direct association between Lp(a) levels and PA, fitness, or body composition in the elderly men and women.

Aged↗

PubMed1999

Wavelet transform to quantify heart rate variability and to assess its instantaneous changes.

Heart rate variability is a recognized parameter for assessing autonomous nervous system activity. Fourier transform, the most commonly used method to analyze variability, does not offer an easy assessment of its dynamics because of limitations inherent in its stationary hypothesis. Conversely, wavelet transform allows analysis of nonstationary signals. We compared the respective yields of Fourier and wavelet transforms in analyzing heart rate variability during dynamic changes in autonomous nervous system balance induced by atropine and propranolol. Fourier and wavelet transforms were applied to sequences of heart rate intervals in six subjects receiving increasing doses of atropine and propranolol. At the lowest doses of atropine administered, heart rate variability increased, followed by a progressive decrease with higher doses. With the first dose of propranolol, there was a significant increase in heart rate variability, which progressively disappeared after the last dose. Wavelet transform gave significantly better quantitative analysis of heart rate variability than did Fourier transform during autonomous nervous system adaptations induced by both agents and provided novel temporally localized information.

Adrenergic beta-Antagonists↗

PubMed1999

Anaemia and iron deficiency in athletes. Practical recommendations for treatment.

Trained athletes frequently experience low levels of blood haemoglobin (13 to 14 g/100ml in men and 12 g/100ml in women) plus low haematocrit and low ferritin levels. These parameters define the concept of 'sports anaemia'. Low iron levels may be due to mechanical haemolysis, intestinal bleeding, haematuria, sweating, low iron intake or poor intestinal absorption. The resulting decrease in blood gas transport and muscle enzyme activity impairs performance. The concept of sports anaemia can be criticised. Simply measuring the blood levels does not take into account the haemodilution that occurs in athletes because of training. The lack of these measurements makes it difficult to diagnose anaemia or evaluate any treatment. Anaemia is treated by preventing decreased iron stores through a balanced food intake or iron supplements. Self-medications must be discouraged because of intolerance, risk of overdose and many other drug interactions.

Altitude↗

PubMed1998

Effects of indomethacin and polyunsaturated fatty acid diet on exercise-induced hypoxaemia in master athletes.

We have previously reported a reduction in exercise-induced hypoxaemia following polyunsaturated fatty acid supplementation (PUFA). Although this might have been explained by increases in membrane fluidity, a clear explanation could not be provided due to potentially confounding influences of series-2 prosta- glandin mediated effects resulting from PUFA. In this investigation, ten master athletes [mean age 48.1 (SEM 6) years, maximal oxygen uptake (VO2max) 3.39 (SEM 0.21) l x min(-1)] completed a maximal cycling test (Ctrl) which was repeated after the administration of 150 mg of indomethacin to inhibit prostaglandin synthesis, both before and after 6 weeks of 3.66-g PUFA x day(-1). Cardiorespiratory parameters were obtained simultaneously with brachial arterial blood sampling for partial pressure of oxygen in arterial blood (PaO2), partial pressure of carbon dioxide in arterial blood (PaCO2), pH, oxygen saturation in arterial blood and lactate concentration determinations. A significant decrease in PaO2 (mmHg) from rest [93 (SEM 1.5)] was observed for exercise intensities of more than 40% VO2max in Ctrl reaching 75.9 (SEM 2.1) at VO2max. PUFA resulted in a 5.0 (SEM 0.68) mmHg upward shift (P < 0.05) in the PaO2-oxygen uptake relationship, reducing the difference in partial pressure of oxygen between alveolar air and arterial blood (P(A-a)O2) at VO2max [Ctrl 36 (SEM 1.6) vs PUFA 33 (SEM 2.2) mmHg] while PaCO2, remained unchanged. Indomethacin had no effect on either PaO2, ideal partial pressure of oxygen in alveolar gas or P(A-a)O2 in either Ctrl or after PUFA. In contrast, the fall in pH was significantly reduced after indomethacin while VCO2, PaCO2 and lactacidaemia remained unchanged. These observations confirm an effect of PUFA on exercise PaO2 behaviour which does not appear to be mediated by the influence of a series-2 prostaglandin.

Adult↗

PubMed1998

Peak anaerobic power in elderly men.

The relationship of maximal anaerobic power (Pmax) of the quadriceps muscle and corresponding optimal shortening velocity (vopt) with age, habitual physical activity (PA) and maximal oxygen consumption (VO2max) were assessed in 37 healthy older [71.1 (SD 3.8) years] men and compared to those of 16 young [22.7 (SD 3.4) years] men. The PA was evaluated using a questionnaire. The Pmax and vopt were measured on a friction loaded non-isokinetic cycle ergometer. The Pmax was expressed relative to body mass - Pmax x kg(-1), and relative to the mass of the two quadriceps muscles - Pmax x kgquad(-1). The decline of Pmax x kg(-1) from youth to advanced age (8.3% per decade) was greater than the decrease in quadriceps muscle mass (3.8% per decade), in Pmax x kgquad(-1) (5.9% per decade) and in vopt (4.3% per decade). In the older men, a negative relationship of Pmax x kg(-1) (r = -0.33) and Pmax x kgquad(-1) (r = -0.44) with age was found. Ergometer measurements were not correlated with PA activity indices or VO2max, while VO2max was positively associated with PA. In a multiple stepwise regression analysis age was the only variable that contributed significantly to Pmax x kg(-1) and Pmax x kgquad(-1) variances. Our findings indicated that in these healthy elderly men, unlike the fall in VO2max, habitual PA did not attenuate the decline in Pmax of the quadriceps muscle with age. This finding was different from a previously described relationship in older women and would suggest sex differences in determining Pmax in healthy older subjects.

Adult↗

PubMed1998

The spring-mass model and the energy cost of treadmill running.

During running, the behaviour of the support leg was studied by modelling the runner using an oscillating system composed of a spring (the leg) and of a mass (the body mass). This model was applied to eight middle-distance runners running on a level treadmill at a velocity corresponding to 90% of their maximal aerobic velocity [mean 5.10 (SD 0.33) m x s(-1)]. Their energy cost of running (Cr). was determined from the measurement of O2 consumption. The work, the stiffness and the resonant frequency of both legs were computed from measurements performed with a kinematic arm. The Cr was significantly related to the stiffness (P < 0.05, r=-0.80) and the absolute difference between the resonant frequency and the step frequency (P < 0.05, r=0.79) computed for the leg producing the highest positive work. Neither of these significant relationships were obtained when analysing data from the other leg probably because of the work asymmetry observed between legs. It was concluded that the spring-mass model is a good approach further to understand mechanisms underlying the interindividual differences in Cr.

Biomechanical Phenomena↗

PubMed1998

A method for assessing muscle fatigue during sprint exercise in humans using a friction-loaded cycle ergometer.

This study investigated the mechanical changes induced by muscle fatigue caused by repeated sprints and determined whether a friction-loaded cycle ergometer has any advantages for assessing muscle fatigue. Nine subjects performed 15 sprints, each of 5 s with a 25-s rest, on a friction-loaded cycle ergometer. The averaged force, power and velocity of each push-off were calculated. Maximal power decreased by 17.9%, with a concomitant slowing of muscle contraction, but without any change in the maximal force. These results demonstrated that repeated sprints slow down muscle contraction, leading to a fall in maximal power without any loss of force. This would suggest that fast twitch fibres are selectively fatigued by repeated sprints. However, the ergometer used in the present study made it difficult to evaluate the relative influences of contraction velocity and sprinting time. This was certainly the most important limitation. On the other hand, it showed the advantage of measuring instantaneous power and total work dissipated in the environment simultaneously. It also permitted a force-velocity relationship to be obtained from a single sprint and this relationship is known to be closely related to the muscle fibre composition.

Adult↗

PubMed1998

Physical activity, fitness and integrated antioxidant system in healthy active elderly women.

We have related the oxidative stress and antioxidant defence system to maximal oxygen consumption (VO2max) and physical activity in elderly women. Twenty-nine community dwelling, healthy, active women aged 66-82 years participated in this study. Physical activity was measured by a questionnaire and expressed using two physical activity indices: mean habitual daily energy expenditure (MHDEE) and daily energy expenditure corresponding to leisure time sports activities (Sports activity index). Malondialdehyde (MDA), plasma total antioxidant status (TAS), the red blood cell (RBC) superoxide dismutase (SOD) and glutathione peroxidase (GPX) as well as serum GPX activities were determined under resting conditions. MDA was correlated positively with VO2max (r = 0.42), while RBC GPX was significantly negatively associated with VO2max (r =-0.39), MHDEE (r=-0.38) and sports activity index (rho=-0.36). Our data suggest that in healthy active older women the relationship between physical activity/fitness and antioxidant defence system may be complex, and that for some parameters an unfavourable influence of strenuous exercise may exist. The findings of this cross-sectional design need to be supported in further prospective studies before the associations are accepted as real.

Aged↗

PubMed1998

Physical activity and dehydroepiandrosterone sulphate, insulin-like growth factor I and testosterone in healthy active elderly people.

OBJECTIVE: to examine the association of physical activity and cardio-respiratory fitness with dehydroepiandrosterone sulphate (DHEAS), insulin-like growth factor I (IGF-I) and testosterone in healthy elderly people. DESIGN: cross-sectional study. SETTING: university research department and department of geriatric medicine. PARTICIPANTS: 60 independent, community-dwelling elderly subjects (26 men and 34 women) aged 66-84 who volunteered to participate. MEASUREMENTS: physical activity was evaluated by the Questionnaire d'Activité Physique Saint-Etienne and expressed by three indices: mean habitual daily energy expenditure (MHDEE), daily energy expenditure (DEE) [comprising activities with intensities corresponding to at least three metabolic equivalents (MET; 3.5 ml.kg1 x min1 of oxygen consumption)] and sport activity. Cardio-respiratory fitness was expressed by maximal oxygen consumption (VO2max). RESULTS: In women, DHEAS correlated with VO2max (partial correlation: r=0.33; P=0.05), MHDEE (r=0.50; P=0.002), DEE > 3 METs (r=0.49; P=0.003) and sport activity (r=0.35; P=0.04) whereas IGF-I correlated with MHDEE (r=0.48; P=0.004). DHEAS was correlated with IGF-I (r=0.43; P < 0.02) and with testosterone (r=0.41; P < 0.02). No such correlation was found in men. CONCLUSION: lower habitual physical activity is related to lower levels of circulating DHEAS and IGF-I independently of age and anthropometric measures. Lower maximal aerobic capacity is associated with lower DHEAS concentrations, in healthy elderly women.

Activities of Daily Living↗

PubMed1998

Rearfoot-forefoot orientation and traumatic risk for runners.

Factors making runners more susceptible to injuries were identified with a comparative study between a healthy control group (216) and runners (66) suffering from overuse pathology. On static and dynamic footprint, the angles alpha0 (static) and alpha1 (dynamic) between heel and forefoot have been measured. Analysis showed that the injured subjects have a more pronated foot than control group subjects. These results suggest that the pronating foot configuration would be an injury risk factor.

Adult↗

PubMed1998

Leg stiffness and foot orientations during running.

This study was done to determine whether leg stiffness (Kleg) during running was related to rearfoot-to-forefoot angle in standing (RFAst) and running (RFArun). Footprints obtained from 32 subjects were used to calculate RFAst and RFArun, defined as positive when forefoot axis was abducted from rearfoot axis. A spring-mass model was used to calculate Kleg in running from ground reaction forces, measured by a force platform. The Kleg of runners (13.0 +/- 2.7 kN x m(-1)) was negatively correlated with RFAst (-8.4 degrees +/- 6.4 degrees) and RFArun (-0.4 degrees +/- 7.2 degrees). When runners were divided into opened foot (RFArun > 0; N = 19) and closed foot (RFArun < 0; N = 12) groups, the Kleg of opened foot runners was less than that of the closed runners. We suggest that foot structure is a factor responsible for the differences in leg stiffness observed in runners.

Adult↗

PubMed1997

Accuracy of an automatic and patient-triggered long-term solid memory ambulatory cardiac event recorder.

This study evaluated the R-Test Evolution, a new type of cardiac event recorder bearing both patient-triggered and automatic capabilities. Its 7-day automatic arrhythmia analysis showed promising clinical advantages, especially when investigating patients with unexplained rare events such as syncope, feeling of weakness or faintness, palpitations, stroke, or in patients inconsistent in their use of patient-triggered recordings.

Arrhythmias, Cardiac↗

PubMed1997

Habitual physical activity and peak anaerobic power in elderly women.

The aim of this study was to investigate the relationship between maximal anaerobic power (Pmax) and corresponding optimal velocity (Vopt) and habitual physical activity (PA) on the one hand and with maximal oxygen consumption (VO2max) on the other hand, in elderly women. Twenty-nine community dwelling, healthy women aged 66-82 years participated in the study. PA was evaluated using the Questionnaire d'Activite Physique Saint-Etienne (QAPSE) and expressed using two QAPSE activity indices: mean habitual daily energy expenditure (MHDEE) and daily energy expenditure corresponding to leisure time sports activities (sports activity). The subjects' Pmax and Vopt were measured while they cycled on a friction-loaded non-isokinetic cycle ergometer. Pmax was expressed relative to body mass [Pmax/kg(W.kg-1)], and relative to the mass of two quadriceps muscles [Pmax/Quadr(W.kg-1Quadr)]. A negative relationship between Pmax/kg (Spearman's r = -0.56; P < 0.01), Pmax/Quadr (r = -0.53; P < 0.01) and Vopt (r = -0.45; P < 0.05) and age was found. Pmax/kg was positively associated with MHDEE (r = 0.51; P < 0.01) and sports activity (r = 0.58; P < 0.01), as were Pmax/Quadr and Vopt (r = 0.55; P < 0.01 and r = 0.54; P < 0.01, respectively). Pmax/kg, Pmax/Quadr and Vopt correlated positively with VO2max. The positive relationship between ergometer measurements and PA indices was similar to that between VO2max and PA. Pmax/kg was, moreover, closely related to Vopt (r = 0.77; P < 0.001). When a multiple stepwise regression analysis was used to select the variables influencing ergometer measurements, MHDEE contributed significantly to Pmax/kg variance, whereas sports activity contributed to Pmax/Quadr and Vopt variances. In conclusion, the data from this cross-sectional study suggest that in healthy elderly women habitual PA, and especially leisure time PA, alleviates the decline of the Pmax of the quadriceps muscles.

Aged↗