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Dive into the research topics where J. R. Lacour is active.

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Featured researches published by J. R. Lacour.


European Journal of Applied Physiology | 2012

Mechanical determinants of 100-m sprint running performance

Jean-Benoı̂t Morin; Muriel Bourdin; Pascal Edouard; Nicolas Peyrot; Pierre Samozino; J. R. Lacour

Sprint mechanics and field 100-m performances were tested in 13 subjects including 9 non-specialists, 3 French national-level sprinters and a world-class sprinter, to further study the mechanical factors associated with sprint performance. 6-s sprints performed on an instrumented treadmill allowed continuous recording of step kinematics, ground reaction forces (GRF), and belt velocity and computation of mechanical power output and linear force–velocity relationships. An index of the force application technique was computed as the slope of the linear relationship between the decrease in the ratio of horizontal-to-resultant GRF and the increase in velocity. Mechanical power output was positively correlated to mean 100-m speed (Pxa0<xa00.01), as was the theoretical maximal velocity production capability (Pxa0<xa00.011), whereas the theoretical maximal force production capability was not. The ability to apply the resultant force backward during acceleration was positively correlated to 100-m performance (rsxa0>xa00.683; Pxa0<xa00.018), but the magnitude of resultant force was not (Pxa0=xa00.16). Step frequency, contact and swing time were significantly correlated to acceleration and 100-m performance (positively for the former, negatively for the two latter, all Pxa0<xa00.05), whereas aerial time and step length were not (all Pxa0>xa00.21). Last, anthropometric data of body mass index and lower-limb-to-height ratio showed no significant correlation with 100-m performance. We concluded that the main mechanical determinants of 100-m performance were (1) a “velocity-oriented” force–velocity profile, likely explained by (2) a higher ability to apply the resultant GRF vector with a forward orientation over the acceleration, and (3) a higher step frequency resulting from a shorter contact time.


European Journal of Applied Physiology | 1993

Ergometric and metabolic adaptation to a 5-s sprint training programme

M.-T. Linossier; Christian Denis; D. Dormois; André Geyssant; J. R. Lacour

SummaryThe effects of 7 weeks of sprint training (repeated 5-s all-out sprints) on maximal power output (Wν, max) determined during a force-velocity test and a 30-s Wingate test (Wpeak) were studied in ten students [22 (SD 2) years] exercising on a cycle ergometer. Before and after training, muscle biopsies were taken from vastus lateralis muscle at rest for the ten subjects and immediately after a training session for five of them. Sprint training induced an improvement both in peak performances by 25% (Wν, max and Wpeak) and in the 30-s total work by 16%. Before sprint training, the velocity reached with no load (ν0) was related to the resting muscle phosphocreatine (PCr) stores (r=0.87, P < 0.001). The training-induced changes in ν0 were observed only when these PCr stores were lowest. This pointed to a possible limiting role of low PCr concentrations in the ability to reach a high velocity. The improvement in performances was linked to an increase in the energy production from anaerobic glycolysis. This result was suggested in muscle by the increase in lactate production measured after a training session associated with the 20% higher activity of both phosphofructokinase and lactate dehydrogenase. The sprint training also increased the proportion of slow twitch fibres closely related to the decrease in fast twitch b fibres. This result would appear to demonstrate an appropriate adaptive reaction following high-intensity intermittent training for the slow twitch fibres which exhibit a greater oxidative capacity.


European Journal of Applied Physiology | 1996

Optimal velocity for maximal power production in non-isokinetic cycling is related to muscle fibre type composition

Christophe Hautier; M. T. Linossier; A. Belli; J. R. Lacour; Laurent M. Arsac

To determine whether power-velocity relationships obtained on a nonisokinetic cycle ergometer could be related to muscle fibre type composition, ten healthy specifically trained subjects (eight men and two women) performed brief periods of maximal cycling on a friction loaded cycle ergometer. Frictional force and flywheel velocity were recorded at a sampling frequency of 200 Hz. Power output was computed as the product of velocity and inertial plus frictional forces. Force, velocity and power were averaged over each down stroke. Muscle fibre content was determined by biopsy of the vastus lateralis muscle. Maximal down stroke power [14.36 (SD 2.37)W·kg−1] and velocity at maximal power [120 (SD 8) rpm] were in accordance with previous results obtained on an isokinetic cycle ergometer. The proportion of fast twitch fibres expressed in terms of cross sectional area was related to optimal velocity (r = 0.88, P < 0.001), to squat jump performance (r = 0.78, P < 0.01) and tended to be related to maximal power expressed per kilogram of body mass (r = 0.60, P = 0.06). Squat jump performance was also related to cycling maximal power expressed per kilogram of body mass (r = 0.87, P < 0.01) and to optimal velocity (r = 0.86, P < 0.01). All these data suggest that the nonisokinetic cycle ergometer is a good tool with which to evaluate the relative contribution of type II fibres to maximal power output. Furthermore, the strong correlation obtained demonstrated that optimal velocity, when related to training status, would appear to be the most accurate parameter to explore the fibre composition of the knee extensor muscle.


European Journal of Applied Physiology | 1996

Muscle function during brief maximal exercise: accurate measurements on a friction-loaded cycle ergometer

Laurent M. Arsac; A. Belli; J. R. Lacour

A friction loaded cycle ergometer was instrumented with a strain gauge and an incremental encoder to obtain accurate measurement of human mechanical work output during the acceleration phase of a cycling sprint. This device was used to characterise muscle function in a group of 15 well-trained male subjects, asked to perform six short maximal sprints on the cycle against a constant friction load. Friction loads were successively set at 0.25, 0.35, 0.45, 0.55, 0.65 and 0.75 N·kg−1 body mass. Since the sprints were performed from a standing start, and since the acceleration was not restricted, the greatest attention was paid to the measurement of the acceleration balancing load due to flywheel inertia. Instantaneous pedalling velocity (v) and power output (P) were calculated each 5 ms and then averaged over each downstroke period so that each pedal downstroke provided a combination of v, force and P. Since an 8-s acceleration phase was composed of about 21 to 34 pedal downstrokes, this many v-P combinations were obtained amounting to 137–180 v-P combinations for all six friction loads in one individual, over the widest functional range of pedalling velocities (17–214 rpm). Thus, the individuals muscle function was characterised by the v-P relationships obtained during the six acceleration phases of the six sprints. An important finding of the present study was a strong linear relationship between individual optimal velocity (vopt) and individual maximal power output (Pmax) (n = 15, r = 0.95, P < 0.001) which has never been observed before. Since vopt has been demonstrated to be related to human fibre type composition both vopt, Pmax and their inter-relationship could represent a major feature in characterising muscle function in maximal unrestricted exercise. It is suggested that the present method is well suited to such analyses.


Pacing and Clinical Electrophysiology | 2002

Frequent and prolonged asymptomatic episodes of paroxysmal atrial fibrillation revealed by automatic long-term event recorders in patients with a negative 24-hour holter

Frédéric Roche; Jean-Michel Gaspoz; Antoine Da Costa; Karl Isaaz; David Duverney; Vincent Pichot; Frédéric Costes; J. R. Lacour; Jean-Claude Barthélémy

ROCHE, F., et al.: Frequent and Prolonged Asymptomatic Episodes of Paroxysmal Atrial Fibrillation Revealed by Automatic Long‐Term Event Recorders in Patients with a Negative 24‐Hour Holter. The presence, frequency, and duration of episodes of paroxysmal atrial fibrillation (PAF) is difficult to establish. This is caused by the limited duration of standard Holter recordings and to the unsatisfactory yield of patient‐triggered event recorders, because of asymptomatic events and of an inconsistent use of the patient dependent triggering function. A prospective cohort of 65 consecutive patients with recurrent palpitations and a negative 24‐hour ECG Holter was investigated by means of a cardiac event recorder bearing continuous automatic arrhythmia analysis and storage. Over a mean duration of 77 ± 36 hours, episodes of PAF were diagnosed in 20 (31%) patients, who had a total of 37 episodes; mean duration of PAF episodes was 7 hours 50 minutes ± 8/hours 45 minutes (minimum 45 minutes, maximum 28 hours). Eleven (55%) of these 20 patients were asymptomatic and would have remained undiagnosed without the automatic mode of the event recorder. Asymptomatic PAF episodes were longer than symptomatic ones (10 hours 30 minutes ± 6 hours 30 minutes vs 4 hours 50 minutes ± 4 hours, P < 0.05). In addition, episodes of sustained paroxysmal supraventricular tachycardia (PSVT) were diagnosed in 39 (57%) patients, of whom 34 (87%) were symptomatic. In this prospective cohort, a second standard 24‐hour monitoring would have missed 44% of the patients with PAF or PSVT and a classical patient‐triggered event recorder 13%. In patients still complaining of palpitations after one negative 24‐hour Holter, numerous, prolonged, and often asymptomatic episodes of PAF can be revealed by long‐term automatic event recorders. These devices should help clarify the clinical consequences of such episodes.


European Journal of Applied Physiology | 1996

Water balance during and after marathon running.

J. Pastene; M. Germain; Anne-Marie Allevard; Claude Gharib; J. R. Lacour

To describe the time course of plasma volume alterations and the changes in the plasma concentrations of hormones regulating water balance in relation to a marathon race, six experienced marathon runners (five men, one women) aged 28 (SD 6) years were studied during and for the 3 days following a treadmill marathon run at 68 (SD 5)% of maximal oxygen consumption. Haematocrit, haemoglobin, plasma protein (Prot) and electrolyte (Na+, K+) concentration, osmolality (osm), plasma concentrations of renin (Ren), aldosterone (Ald) and atrial natriuretic peptide (ANP) were determined at rest in a sitting position (T−30), and then after 30 min in an upright posture (R0), while running a marathon at 10 km (R10), 30 km (R30) and 42.2 km (Rend), and after the marathon at 30 min (T30), 60 min (T60), 120 min (T120) and 24 h (TD+1), 48 h (TD+2) and 72 h (TD+3). The changes in plasma volume (PV), Prot, osm and Na+ observed during the race were nonsignificant. Significant increases in plasma concentration of K+ [4.8 (SD 0.6) vs 5.5 (SD 0.6) mmol·l−1; P < 0.01], Ren [38 (SD 57) vs 197 (SD 145) pmol·l−1; P < 0.02] and Ald [175 (SD 142) vs 1632 (SD 490) pmol·−1; P < 0.01] were observed at Rend. A significant increase of ANP (P < 0.05) was only found after R10. Body mass significantly decreased by 2.0 kg (P < 0.01) during the race in spite of the ingestion of 1.46 (SD 0.34) 1 of a 5% glucose solution. Urinary volume and Na+ excretion dropped significantly after the completion of the marathon in comparison with the day before [2600 vs 1452 ml·day−1 (P < 0.02) and 161.3 vs 97.1 mmol·l−1 (P < 0.05)]. At TD+1 and TD+2 a significant increase in PV was noted, compared to T−30. The lack of a decrease in PV during the marathon may have been due to the production of 402 g of metabolic water and by the release of 1280 g of water stored in glycogen complexes in muscle and liver. Thus, the hormone response during the marathon may have been due to the effects of the exercise itself and not to the effects of dehydration. The postmarathon PV expansion may be explained by a protein shift to the intravascular space and by renal sodium retention.


European Journal of Applied Physiology | 1996

Optic fibre as a transducer of tendomuscular forces

Paavo V. Komi; Alain Belli; V. Huttunen; R. Bonnefoy; André Geyssant; J. R. Lacour

Direct in vivo tendon force measurements open up new possibilities for understanding of muscletendon loads during natural locomotion. The present report presents a new optic fibre method for such applications. The method is based on light intensity modulation by mechanical modification of the geometric properties of the optic fibre. A special optic fibre with a plastic covering buffer and with a total diameter of either 265 μm or 500 μm was carefully prepared at both ends for receiving and transmitting light. The fibre was inserted through the rabbit common calcaneal tendon with a 20 gauge needle. By removing the needle the optic fibre remained in situ. Static loading demonstrated that the voltage output of the optic fibre transducer showed a good linear fit of r =.999 with added loads. In dynamic loading conditions the optic fibre followed well the response of a strain gauge transducer, which was also attached to the tendon. The optic fibre method seems suitable for many applications for tensile and possibly ligament force measurements.


European Journal of Applied Physiology | 1995

Mechanical step variability during treadmill running

Alain Belli; J. R. Lacour; Paavo V. Komi; R. Candau; Christian Denis

The present study was designed to study intra-individual step variability measured both on vertical displacement of the body (ΔZ) and on step time (Δt) parameters by means of a kinematic arm and during treadmill running. A group of 17 subjects ran successively at 60%, 80%, 100% and 140% of their maximal aerobic velocity (vamax). The total number of steps analysed was 6116. The absolute ΔZ step variability (σΔZ) ranged between 5 mm and 21 mm while the absolute Δt variability (σΔt) ranged between 6 ms and 40 ms. Step variabilities were due to step asymmetry (from 38.5% to 48.5% of the step variability) and to stride variability. For submaximal velocities (60%, 80%, and 100%vamax) both σΔt and σΔZ were independent of velocity or body dimensions whereas differences between subjects were significant (P < 0.01) for σΔZ. On the other hand, variabilities were significantly increased when velocity was changed from submaximal to the 140%vamax level. Furthermore, at submaximal levels σΔZ was linked to the subjects energy cost of running (P < 0.05). Therefore, the intra-individual step variability should not be neglected in future studies on mechanical efficiency of running and it is suggested that, to obtain a good accuracy (better than 1%,P < 0.05) on mean value and variability of the mechanical parameters, measurements should be performed on at least 32–64 consecutive steps, which corresponds to about 15 to 20 s of running.


Pacing and Clinical Electrophysiology | 2002

Cardiac Interbeat Interval Increment for the Identification of Obstructive Sleep Apnea

Frédéric Roche; David Duverney; Isabelle Court-Fortune; Vincent Pichot; Frédéric Costes; J. R. Lacour; Anestis Antoniadis; Jean-Michel Gaspoz; Jean-Claude Barthélémy

ROCHE, F., et al.: Cardiac Interbeat Interval Increment for the Identification of Obstructive Sleep Apnea. The prevalence of obstructive sleep apnea syndrome (OSAS) is high in developed countries but its diagnosis is costly. Based on physiological evidence, the frequency component of heart rate variability (HRV) was evaluated as a simple and inexpensive diagnostic tool in OSAS. The predictive accuracy of frequency‐domain HRV variables obtained from 24‐hour ECG Holter monitoring (the power spectral density of the interbeat interval increment of very low frequencies, “VLFIpsd,” and its percentage over the total power spectral density, “%VLFI”), and of established time‐domain HRV variables were analyzed by comparison with respiratory disturbances indexes assessed by complete polysomnography in 124 consecutive patients (98 men aged 53.8 ± 11.2 years) with clinically suspected OSAS. OSAS was present in 54 (43.5%) patients according to standard criteria. Using receiver operating characteristic curve analysis, two of the three most powerful predictors were frequency‐domain variables: %VLFI (W = 0.80, P < 0.0001), and VLFIpsd (W = 0.79, P < 0.0001). Using a multiple logistic regression analysis, %VLFI was the most strongly associated with diseased status (adjusted OR: 8.4; 95% CI: 3.4–19.5). Using an appropriate threshold, %VLFI demonstrated a diagnostic sensitivity of 87%. A 3‐month continuous positive airway pressure treatment significantly improved the same parameter. Frequency‐domain analysis of the interbeat interval increment appears as a powerful tool for OSAS diagnosis and follow‐up. The simplicity of its analysis and of its use makes of it a well‐suited variable for mass screening of OSAS patients.


European Journal of Applied Physiology | 1997

Accuracy of pulse oximetry during intense exercise under severe hypoxic conditions

Henri Benoit; Frédéric Costes; Léonard Féasson; J. R. Lacour; Frédéric Roche; Christian Denis; André Geyssant; Jean Claude Barthélémy

Abstract There is a growing need to measure arterial oxygen saturation with a non-invasive method during heavy exercise under severe hypoxic conditions. Although the accuracy of pulse oximetry has been challenged by several authors, it has not been done under extreme conditions. The purpose of this study was to evaluate the accuracy of a pulse oximeter (Satlite, Datex, Finland) during exercise under hypoxic conditions where arterial oxygen saturation was below 75%, simulating exercise at extreme altitude. Ten healthy non-smoking men performed two exercise studies of 30u2009min under normoxia and under hypoxia on two consecutive days. The exercise intensity was 80% of maximal O2 consumption of O2max. Arterial oxygen saturation measured by pulse oximetry was corrected (SpO2[corr]) according to previously published equations and was compared to arterial oxygen saturation (SaO2) in blood samples taken simultaneously from the radial artery. Reference arterial saturation values ranged from 57.2 to 97.6% for the whole data set. This data set was split according to low (SaO2u2009≤u200975%) and high (SaO2u2009>u200975%) SaO2 values. The error of pulse oximetry (SpO2[corr]− SaO2) was 2.05 (0.87)% [mean (SD)] and 1.80 (1.81)% for high and low SaO2 values, respectively. SpO2[corr] and SaO2 were highly correlated (ru2009=u20090.93, SEEu2009=u20091.8) for low values. During high-intensity constant workload under severe hypoxic conditions, once corrected, pulse oximetry provides an estimate of SaO2 with a mean error of 2%. Thus, the correction previously described for SpO2 values above 75% saturation applies also to SpO2 values in the range of 57–75% during exercise under hypoxic conditions.

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Alain Belli

University of Lausanne

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Fabrice Viale

University of La Réunion

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