Biomedical subjects

V L Billat

Publications and source records attributed to V L Billat.

23 records · Page 2Linked to original sources

PubMed1999

Determination of the velocity associated with the longest time to exhaustion at maximal oxygen uptake.

The so-called velocity associated with VO2max, defined as the minimal velocity which elicits VO2max in an incremental exercise protocol (v(VO2max)), is currently used for training to improve VO2max. However, it is well known that it is not the sole velocity which elicits VO2max and it is possible to achieve VO2max at velocities lower and higher than v(VO2max). The goal of this study was to determine the velocity which allows exercise to be maintained the longest time at v(VO2max). Using the relationship between time to exhaustion at VO2max in the all-out runs at 90%, 100%, 120% and 140% of v(VO2max) and distance run at VO2max, the velocity which elicits the longest time to exhaustion at VO2max (CV') was determined. For the six subjects tested (physical education students), this velocity was not significantly different from v(VO2max) (16.96+/-0.92 km x h(-1) vs 17.22+/-1.12 km x h(-1), P = 0.2 for CV' and v(VO2max), respectively) and these two velocities were correlated (r = 0.88, P = 0.05).

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PubMed1999

The role of cadence on the VO2 slow component in cycling and running in triathletes.

The purpose of this study was to compare the effect of two different types of cyclic severe exercise (running and cycling) on the VO2 slow component. Moreover we examined the influence of cadence of exercise (freely chosen [FF] vs. low frequency [LF]) on the hypothesis that: 1) a stride frequency lower than optimal and 2) a pedalling frequency lower than FF one could induce a larger and/or lower VO2 slow component. Eight triathletes ran and cycled to exhaustion at a work-rate corresponding to the lactate threshold + 50% of the difference between the work-rate associated with VO2max and the lactate threshold (delta 50) at a freely chosen (FF) and low frequency (LF: - 10 % of FF). The time to exhaustion was not significantly different for both types of exercises and both cadences (13 min 39 s, 15 min 43 s, 13 min 32 s, 15 min 05 s for running at FF and LF and cycling at FF and LF, respectively). The amplitude of the VO2 slow component (i.e. difference between VO2 at the last and the 3rd min of the exercise) was significantly smaller during running compared with cycling, but there was no effect of cadence. Consequently, there was no relationship between the magnitude of the VO2 slow component and the time to fatigue for a severe exercise (r = 0.20, p = 0.27). However, time to fatigue was inversely correlated with the blood lactate concentration for both modes of exercise and both cadences (r = - 0.42, p = 0.01). In summary, these data demonstrate that: 1) in subjects well trained for both cycling and running, the amplitude of the VO2 slow component at fatigue was larger in cycling and that it was not significantly influenced by cadence; 2) the VO2 slow component was not correlated with the time to fatigue. If the nature of the linkage between the VO2 slow component and the fatigue process remains unclear, the type of contraction regimen depending on exercise biomechanic characteristics seems to be determinant in the VO2 slow component phenomenon for a same level of training.

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PubMed1999

Interval training at VO2max: effects on aerobic performance and overtraining markers.

PURPOSE: Between inefficient training and overtraining, an appropriate training stimulus (in terms of intensity and duration) has to be determined in accordance with individual capacities. Interval training at the minimal velocity associated with VO2max (vVO2max) allows an athlete to run for as long as possible at VO2max. Nevertheless, we don't know the influence of a defined increase in training volume at vVO2max on aerobic performance, noradrenaline, and heart rate. METHODS: Eight subjects performed 4 wk of normal training (NT) with one session per week at vVO2max, i.e., five repetitions run at 50% of the time limit at vVO2max, with recovery of the same duration at 60% vVO2max. They then performed 4 wk of overload training (OT) with three interval training sessions at vVO2max. RESULTS: Normal training significantly improved their velocity associated with VO2max (20.5+/-0.7 vs 21.1+/-0.8 km x h(-1), P = 0.02). As a result of improved running economy (50.6+/-3.5 vs 47.5+/-2.4 mL x min(-1) x kg(-1), P = 0.02), VO2max was not significantly different (71.6+/-4.8 vs 72.7+/-4.8 mL x min(-1) x kg(-1)). Time to exhaustion at vVO2max was not significantly different (301+/-56 vs 283+/-41 s) as was performance (i.e., distance limit run at vVO2max: 2052.2+/-331 vs 1986.2+/-252.9 m). Heart rate at 14 km x h(-1) decreased significantly after NT (162+/-16 vs 155+/-18 bpm, P < 0.01). Lactate threshold remained the same after normal training (84.1+/-4.8% vVO2max). Overload training changed neither the performance nor the factors concerning performance. However, the submaximal heart rate measured at 14 km x h(-1) decreased after overload training (155+/-18 vs 150+/-15 bpm). The maximal heart rate was not significantly different after NT and OT (199+/-9.5, 198+/-11, 194+/-10.4, P = 0.1). Resting plasma norepinephrine (veinous blood sample measured by high pressure liquid chromatography), was unchanged (2.6 vs 2.4 nm x L(-1), P = 0.8). However, plasma norepinephrine measured at the end of the vVO2max test increased significantly (11.1 vs 26.0 nm x L(-1), P = 0.002). CONCLUSION: Performance and aerobic factors associated with the performance were not altered by the 4 wk of intensive training at vVO2max despite the increase of plasma noradrenaline.

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PubMed1998

The V(O2) slow component for severe exercise depends on type of exercise and is not correlated with time to fatigue.

The purpose of this study was to examine the influence of the type of exercise (running vs. cycling) on the O2 uptake V(O2) slow component. Ten triathletes performed exhaustive exercise on a treadmill and on a cycloergometer at a work rate corresponding to 90% of maximal VO2 (90% work rate maximal V(O2)). The duration of the tests before exhaustion was superimposable for both type of exercises (10 min 37 s +/- 4 min 11 s vs. 10 min 54 s +/- 4 min 47 s for running and cycling, respectively). The V(O2) slow component (difference between V(O2) at the last minute and minute 3 of exercise) was significantly lower during running compared with cycling (20.9 +/- 2 vs. 268.8 +/- 24 ml/min). Consequently, there was no relationship between the magnitude of the V(O2) slow component and the time to fatigue. Finally, because blood lactate levels at the end of the tests were similar for both running (7.2 +/- 1.9 mmol/l) and cycling (7.3 +/- 2.4 mmol/l), there was a clear dissociation between blood lactate and the V(O2) slow component during running. These data demonstrate that 1) the V(O2) slow component depends on the type of exercise in a group of triathletes and 2) the time to fatigue is independent of the magnitude of the V(O2) slow component and blood lactate concentration. It is speculated that the difference in muscular contraction regimen between running and cycling could account for the difference in the V(O2) slow component.

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PubMed1996

Effect of protocol on determination of velocity at VO2 max and on its time to exhaustion.

The velocity associated with the achievement of VO2 max during an incremental treadmill test (v VO2 max) has been reported to be an indicator of performance in middle distance running events. Previous study has shown the reproducibility of the time to exhaustion (time limit: tlim) at v VO2 max performed by well-trained males in the same condition at one week of interval (Billat et al., 1994b). It is essential in studies involving tlim at v VO2 max that the v VO2 max be precisely determined, or else the measured tlim will be meaningless. The purpose of this study was to examine the influence of the stage duration and velocity incrementation on the velocity at VO2 max and, consequently, on the two times to exhaustion (tlim) associated with the two v VO2 max generated by the two protocols. v VO2 max was determined in 15 trained male endurance athletes as the lowest speed at which VO2 max was attained in speed-incremented 0%-slope treadmill tests. For one test, increments were 1.0 km.h-1 and stages were 2 min in duration; for the other test, increments were 0.5 km.h-1 and stages were 1 min in duration. Results of paired means t-tests revealed no difference in v VO2 max obtained using the two protocols. v VO2 max was 20.7 +/- 1.0 km.h-1 with the 1.0 km.h-1 x 2 min protocol and 20.8 +/- 0.9 km.h-1 with the 0.5 km.h-1 x 1 min protocol. In addition, VO2, VCO2, VE, VE/VO2 and respiratory exchange ratio at the submaximal intensities that were common to both protocols (e.g., 17.0 km.h-1, 18.0 km.h-1, 19.0 km.h-1, 20.0 km.h-1) did not differ. Times to exhaustion at the two v VO2 max demonstrated a high degree of inter-individual variability (coefficients of variation were 35% and 45%) but did not differ (345 +/- 120 s versus 373 +/- 169 s). These results demonstrated that small changes in protocol have no significant impact on the value of v VO2 max and in consequence on tlim v VO2 max.

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