[Short-term exercise-based cardiac rehabilitation induced changes in cardiorespiratory, mechanical and neuromuscular responses to progressive exercise testing]. / Dissociation des réponses cardiorespiratoires et neuromusculaires à l'exercice à la suite de 4 semaines de réentraînement à l'effort chez des patients cardiaques.

Previous studies showed that changes in peak of oxygen uptake value (VO2peak) with training were poorly related to changes in Maximal Tolerated Power output (MTP) among patients with cardiovascular disease. This result could be due to a difference between cardiopulmonary adaptation to training and the skeletal muscle conditioning. OBJECTIVE: The aim of the study was to compare the responses to exercise training of electromyographic activities of vastus lateralis (rms-EMG) and respiratory parameters. METHODS: Nine cardiac patients (64.0±3.1y, 172.9±4.8cm, 83.4±16.3kg, BMI: 27.8±4.5) performed an incremental cycling exercise test to determine MTP, VO2peak and peak values of heart rate, before and after an aerobic training. Ventilatory thresholds were respectively determined as the breakpoint in the curve of carbon dioxide output against oxygen uptake plot (VT1) and the point at which the ratio of minute ventilation to carbon dioxide output starts to increase (VT2). EMGth1 and EMGth2 were defined as the first and the second breakpoints in the rms-EMG - power output relationship. RESULTS: Short-term exercise training (23.7±8.8 days) induced a significant increase in VO2peak (P=0.004), MTP (P=0.015), VT1 (P=0.001) and VT2 (P=0.001). Changes in VO2peak only attained the survival criteria (3.5±2.9mLmin-1kg-1). No significant differences (P>0.05) existed between mean power values of VT1 and EMGth1 (60.5±4.1 vs. 59.2±9.6% of MTP, respectively), or between VT2 and EMGth2 (78.3±5.7 vs. 80.2±5.2% of MTP). After training, EMGth1 occurred significantly before VT1 (60.5±6.2 vs. 64.8±4.8% of MTP, P=0.049). CONCLUSION: This might be taken into account for prescribing exercise rehabilitation according initial clinical limitations of patients.

Exercise-based Cardiac Rehabilitation in Coronary Disease: Training Impulse or Modalities?

To compare the effects of 2 short programs with similar training load (TL), based on combined aerobic - resistance training (CT) or aerobic training (AT) on cardiorespiratory responses, 32 patients with coronary heart disease (CHD: 63.8±8.0y, 1.73±0.06 m, 84.8±15.9 kg, Left Ventricular Ejection Fraction: 0.53±0.8) performed 4 weeks of exercise rehabilitation based on CT (n=16) or AT (n=16). Maximal tolerated power (MTP), peak values of oxygen uptake (VO2peak) and heart rate (HRpeak), anaerobic threshold (VT1) were determined during an incremental cycling exercise test before and after training periods. TL, quantified using the session rating of perceived exertion, did not differ between both modalities (CT: 4 438±572 vs. AT: 4 346±592 AU, p=0.300). Improvements in VO2peak were larger after CT (+36.4±24.7% of pre-training VO2peak, i. e., +4.4±2.3 mL.min-1.kg-1, n=14) than observed after AT (+20.1±9.1% of pre-training VO2peak, i. e., +2.6±1.0 mL.min-1.kg-1, n=12) (p=0.014). Additionally, CT significantly improved power (54.6±23.8 vs. 75.1±21.2 watts, p=0.001) and VO2 associated at VT1 (VO2: 9.8±2.5 vs. 12.6±2.9 mL.min-1.kg-1, p=0.001). This might be taken into account when prescribing exercise rehabilitation for CHD patients with different initial clinical limitations.

[Is there a disassociation of ventilatory and electromyographic thresholds in patients with heart disease during a graded cycling exercise?] / Concordance et dissociation des seuils de fatigue électromyographiques et des seuils ventilatoires chez le patient en réadaptation cardiaque.

Exercise prescription was generally based on the determination of ventilatory thresholds (VT1, VT2) during cardiopulmonary exercise testing (CPX). Changes in surface electromyographic activity (EMGth1, EMGth2) were also related to VT1 and VT2 in healthy subjects. OBJECTIVE: To observe the occurrence of EMGth1 and EMGth2 and whether these events accompany VT1 and VT2 during CPX in cardiac patients (CP). METHOD: Thirty-four CP (62.1±7.3years, 172.1±6.3cm, 81.3±15.3kg, BMI: 27.3±4.1) performed a cycle CPX at a 60-rpm cadence. VT1 was determined as the breakpoint in the curve of carbon dioxide output against oxygen uptake plot (V-slope method). VT2 was defined as the point at which the ratio of minute ventilation to carbon dioxide output starts to increase. The root mean square of electromyogram (rms-EMG) was on-line calculated from the real time bipolar surface electromyographic signals recorded from the vastus lateralis. EMGth1 and EMGth2 were defined as the first and the second breakpoints in the rms-EMG-power output relationship. RESULTS: Peak values of oxygen uptake (16.3±4.6mL·min-1·kg-1) and heart rate (106.7±13.8bpm) were reached at 112.9±38.5w (PMT). VT1 and VT2 occurred at 71.1±25.9w (62.5±5.5% PMT) and 87.9±28.6w (78.0±5.1% PMT). All subjects presented two breakpoints in the rms-EMG curve, EMGth1 at 68.0±24.7w and EMGth2 at 88.5±30.1w, i.e. 60.0±7.6 and 78.6±5.0% of PMT. EMGth1 occurred significantly before VT1 (P=0.004, small effect size). No significant difference was observed between EMGth2 and VT2 (P=0.13, small effect size). CONCLUSION: The EMGth1 occurrence before VT1 suggested a role of skeletal muscle conditioning on ventilatory responses, which should be taken into account in cardiac rehabilitation program prescription.

Who runs the fastest? Anthropometric and physiological correlates of 20 m sprint performance in male soccer players.

The aim of the present study was to examine the relationship of 20 m sprint performance with anthropometrical and physiological parameters in male soccer players. A hundred and 81 soccer players from the region of Athens (age 23.4 ± 5.0 yrs, body mass 73.4 ± 7.7 kg, height 180.0 ± 5.9 cm, body fat (BF) 14.4 ± 3.6%), classified into quartiles according to 20 m sprint time (group A, 2.84-3.03 s; group B, 3.04-3.09 s; group C, 3.10-3.18 s; group D, 3.19-3.61 s), participated. Soccer players in group A were younger and had better performance in vertical jumps and in the Wingate anaerobic test (WAnT, p < 0.05). Sprint time correlated to age (r = 0.27), body mass (r = 0.23), body height (r = 0.20), BF (r = 0.23), vertical jumps (-0.58 ≤ r ≤ -0.50) and the WAnT (-0.45 ≤ r ≤ -0.30, p < 0.05). In summary, the magnitude of correlations of sprint time with measures of lower limbs muscle strength and power (WAnT and jumps) was larger than with anthropometric measures (body mass and BF).

[Muscle retraining or aerobic endurance training? What will improve the aerobic capacity of patients with coronary disease in the only 4 weeks?]. / Modalités ou charge de réentraînement: quelle modalité choisir pour améliorer l'aptitude aérobie du patient coronarien en seulement 4 semaines?

OBJECTIVE: The aim of this study was to compare the effects of 4 weeks of CT and AT, which training impulse (total external workload and perceived exertion), are similar on power associated at VO2 peak (pVO2 peak) and cardiorespiratory responses of patient with CAD. METHOD: Eighteen male with CAD (62 ± 7 years, 175 ± 2 cm, 84 ± 16 kg, fraction of ejection = 0.49 ± 0.16) performed 4 weeks of CT (n = 9) or AT (n = 9). pVO2 peak, maximal and first ventilatory threshold values of oxygen uptake (VO2 peak, VO2-vt) and heart rate (HRmax, HR-vt) were measured before and after training session. Total training impulse (exercise rehabilitation and other paramedical actions) were evaluated and harmonized between AT and CT according to Foster et al. formula (1996) RESULTS: No significant difference were found in training impulse between AT and CT (3650 ± 220 vs 3497 ± 190 U, P = NS). VO2 pic increased after AT (16.9 ± 4.4 vs 18.9 ± 4.9 mL O2/min/kg, P < 0.05) and remained unchanged after CT (17.7 ± 7.8 vs 17.8 ± 7.2, P = NS). Four weeks of training induced significant increase in pVO2 peak, VO2-vt and FC-vt, expressed in absolute or relative value (P < 0,05), without any difference between AT and CT modalities (P = NS). CONCLUSIONS: Improving pVO2 pic following an exercise training does not necessarily preclude an improvement in coronary VO2 pic. pVO2 peak was not improved with the same cardiorespiratory adaptations between AT and CT. Thus, there seems important to measure gas exchanges of subject with CAD during the incremental test and identify the respective part of muscular and cardiorespiratory functions in exercise exhaustion.

Effect of a short-term intermittent exercise-training programme on the pulse wave velocity and arterial pressure: a prospective study among 71 healthy older subjects.

AIMS OF THE STUDY: Stiffening of large arteries has been associated with increased cardiovascular outcomes among older subjects. Endurance exercises might attenuate artery stiffness, but little is known about the effects of intermittent training programme. We evaluate the effect of a short Intermittent Work Exercise Training Program (IWEP) on arterial stiffness estimated by the measure of the pulse wave velocity (PWV). METHODS AND SUBJECTS: Seventy-one healthy volunteers (mean age: 64.6 years) free of symptomatic cardiac and pulmonary disease performed a 9-week IWEP that consisted of a 30-min cycling twice a week over a 9-week period. Each session involved six 5-min bouts of exercise, each of the latter separated into 4-min cycling at the first ventilatory threshold alternated with 1-min cycling at 90% of the pretraining maximal tolerated power. Before and after the IWEP, the following measurements were made: carotid-radial PWV and carotid-femoral PWV with a tonometer and systolic and diastolic blood pressure. RESULTS: Training resulted in a non-significant decrease of the carotid-radial PWV, a significant decrease of the carotid-femoral PWV from 10.2 to 9.6 m/s (p < 0.001) (that was no longer significant after adjustment for mean arterial pressure) and a significant decrease in both systolic and diastolic blood pressure, respectively, from 129.6 ± 14.9 mmHg to 120.1 ± 14.1 mmHg (p < 0.001) and from 77.2 ± 8.8 mmHg to 71.4 ± 10.1 mmHg (p < 0.001). CONCLUSION: The present results support the idea that a short-term intermittent aerobic exercise programme may be an effective lifestyle intervention for reducing rapidly blood pressure and probably central arterial stiffness among older healthy subjects.

Comparison of 2 portable respiratory gas analysers.

The aim of this study was to compare respiratory measures taken simultaneously using the Cosmed K4b(2) and Cortex Metamax II portable metabolic systems. 10 trained male cyclists performed a graded exercise cycle test to exhaustion (40w.3 min (- 1)) under standardized conditions. The measured respiratory variables were significantly correlated between both devices: r=0.97 and 0.98 (n=10, p<0.01) for oxygen uptake ( V˙O(2)) and ventilation (VE), respectively. Further Bland and Altman plots revealed a good level of agreement for measures of V˙O(2) expressed in mL.min (- 1) [- 670 to 486] (mean bias of - 91.7, i. e., - 3.1%) or in mL.min (- 1).kg (- 1) [- 7.3 to 9.0] (mean bias of 0.85, i. e., 2.3%) and V(E) [- 23.1 to 18.2] (L.min (- 1), mean bias of - 2.4, i. e. - 4.1%). However, poor agreement was found for measures of carbon dioxide (VCO(2), mL.min (- 1)) [- 280 to 1 394] (mean bias of 671 i.e., 20.3%). VCO(2) at maximal exercise intensity was also significantly (p<0.01) greater in the Cortex compared to the Cosmed system. The higher measured CO(2) concentrations led to significantly (p<0.01) higher calculated respiratory exchange ratio (RER) values with the Cortex device. In conclusion, there was satisfactory agreement between the Cosmed K4b(2) and Cortex Metamax II systems for most respiratory measures; however there was a poor level of agreement between VCO(2) and calculated RER measurements between the 2 systems.

Effect of increasing energy cost on arm coordination in elite sprint swimmers.

The purpose of this study was to analyze the changes in stroke parameters, motor organization and swimming efficiency with increasing energy cost in aquatic locomotion. Seven elite sprint swimmers performed a 6×300-m incremental swimming test. Stroke parameters (speed, stroke rate and stroke length), motor organization (arm stroke phases and arm coordination index), swimming efficiency (swimming speed squared and hand speed squared) and stroke index were calculated from aerial and underwater side-view cameras. The energy cost of locomotion was assessed by measuring oxygen consumption and blood lactate. Results showed that the increase in energy cost of locomotion was correlated to an increase in the index of coordination and stroke rate, and a decrease in stroke length (p<.05). Furthermore, indicators of swimming efficiency and stroke index did not change significantly with the speed increments (p<.05), indicating that swimmers did not decrease their efficiency despite the increase in energy cost. In parallel, an increase in the index of coordination IdC and stroke rate were observed, along with a decrease in stroke length, stroke index and hand speed squared with each increment, revealing an adaptation to the fatigue within the 300m.

Effects of a short-term personalized Intermittent Work Exercise Program (IWEP) on maximal cardio-respiratory function and endurance parameters among healthy young and older seniors.

OBJECTIVE: The aim of this study was to evaluate the efficiency of a short-term Intermittent Work Exercise Program (IWEP) among healthy elderly subjects. STUDY DESIGN AND SETTING: This longitudinal prospective study took place at the Strasbourg University Hospital geriatric department. STUDY PARTICIPANTS: One hundred and fifty older volunteers, previously determined as being free from cardiac and pulmonary disease, were separated into two age groups: the "young senior" (60.2 ± 3.1 yr) and the "older senior" groups (70.8 ± 5.2 yr). These groups were then subdivided by gender into the "young female senior", "young male senior" "older female senior" and "older male senior" groups. INTERVENTION: Before and after the IWEP, all subjects were asked to perform an incremental cycle exercise to obtain their first ventilatory threshold (VT1), maximal tolerated power (MTP), peak oxygen uptake (VO2peak) and maximal minute ventilation (MMV). The IWEP consisted of a 30-min cycling exercise which took place twice a week, and was divided into six 5-min stages consisting of 4 min at VT1 intensity and 1 min at 90% MTP. MEASUREMENTS: An assessment was made of the effects of the IWEP on maximal cardio-respiratory function (MTP, VO2peak, MMV) and endurance parameters (VT1, heart rate [HR] measured at pretraining VT1 and lactate concentrations at pre-training MTP). RESULTS: This short-term training program resulted in a significant increase of MTP (from 13.2% to 20.6%), VO2peak (from 8.9% to 16.6%) and MMV (from 11.1% to 21.8%) in all groups (p<0.05). VT1 improved from 21% at pretraining to 27%, while HR at pre-training VT1 as well as lactate concentrations at pre-training MTP decreased significantly in all groups (p<0.05). The post-training values for VO2peak and MMV of the "older seniors" were not significantly different (p>0.05) from the "young seniors" pre-training values for the same parameters. CONCLUSION: The most striking finding in this study is that after only 9 weeks, our short-term "individually-tailored" IWEP significantly improved both maximal cardio-respiratory function and endurance parameters in healthy, previously untrained seniors.

Swim specialty affects energy cost and motor organization.

The purpose of this study was to analyse the effect of swimmer specialty on energy cost and motor organization. The stroking parameters (velocity, stroke rate, stroke length, stroke index) and the index of coordination (IdC) of 6 elite sprinters were compared with those of 6 elite long-distance swimmers during an incremental swimming exercise test (6x300 m separated by 30 s of passive recovery) that progressively increased the energy cost. Energy cost ( C), with its aerobic ( Caero) and anaerobic ( Canaero) components, was determined by measuring oxygen uptake (VO2) and blood lactate ([La]). Motor organization was assessed by analysis of video recordings from aerial and underwater side-view cameras. The results showed that throughout the test, both groups increased C, Canaero, stroke rate and IdC and decreased Caero and stroke length (all P<0.05). On the mean of the 300-m sets, sprinters had higher values for C (14.8 VS. 12.9 J x kg (-1).m (-1)), Canaero (33.8 VS. 23.4%), [La] (5.9 VS. 3.1 mmol x L (-1)), stroke length (2.31 VS. 2.28 m) and IdC (-11.2 VS. -21.7%) and lower values for Caero (66.2 VS. 79.6%), VO2 net (2 825 VS. 2 903 mL x min (-1)), stroke rate (0.55 VS. 0.62 Hz) and stroke index (2.96 VS. 3.19 m (2) x s (-1)) than long-distance swimmers (all P<0.05). For the same relative intensity, sprinters accumulated more lactate and swam more slowly than long-distance swimmers; they showed greater change in their arm coordination but their swimming economy was lower.

Impact of short-term aerobic interval training on maximal exercise in sedentary aged subjects.

BACKGROUND: Ageing is known to be associated with a decrease in peak oxygen consumption (VO2peak) and maximal tolerated power (MTP). Regular physical exercise is the most appropriate to improve aerobic capacity, but its effect still remained discussed in old people. DESIGN: The aim of this study was to determine whether a short interval training session would be associated with improvements in exercise efficiency in aged subjects in both genders. METHODS: In all, 19 women and 16 men (65.4 +/- 4.9 years) performed a cycle incremental exercise test before and after a 9-week period of aerobic interval training (twice a week, 30 min session where 6 x 4-min at the first ventilatory threshold alternated with 1-min at the second ventilatory threshold) with cycle ergometer. Minute ventilation (MV), O(2) uptake (VO(2)) and CO(2) output (VCO(2)) were measured breath-by-breath and by an open-circuit metabolic cart. RESULTS: Before training, maximal values of MV (MMV), VO2peak, heart rate, systolic blood pressure, MTP, blood lactate at MTP recovery and the power at the first (pVT(1)) and second ventilatory thresholds (pVT(2)) were higher in men compared with women. Nine weeks of interval training induced a significant increase in MMV, VO2peak, MTP, pVT(1) and pVT(2) and decrease in systolic blood pressure in the same way in men than in women, without any significant effect on their maximal heart rate values. CONCLUSIONS: These findings suggest that the age-related declines in aerobic index are attenuated by a short exercise interval training sessions in women and men.

Comparison of analyses of respiratory gases made with the K4b2 portable and Quark laboratory analysers in horses.

Measurements of minute ventilation (VE) and expired oxygen and carbon dioxide fractions (FeO2 and FeCO2) were measured at rest and during exercise in seven warmblood horses performing two consecutive standardised incremental treadmill exercise tests at submaximal speed, using the portable K4b2 telemetric unit and the laboratory Quark metabolic cart in random order. Oxygen consumption (VO2) and carbon dioxide production (VCO2) were estimated using the Haldane equation. There were no significant differences between the measurements made with the two devices. However, VE was overestimated when the horses were cantering at 10 m/s in comparison with values available in the literature.

Health benefits of physical activity in older patients: a review.

As the number of elderly persons in our country increases, more attention is being given to geriatric healthcare needs and successful ageing is becoming an important topic in medical literature. Concept of successful ageing is in first line on a preventive approach of care for older people. Promotion of regular physical activity is one of the main non-pharmaceutical measures proposed to older subjects as low rate of physical activity is frequently noticed in this age group. Moderate but regular physical activity is associated with a reduction in total mortality among older people, a positive effect on primary prevention of coronary heart disease and a significant benefit on the lipid profile. Improving body composition with a reduction in fat mass, reducing blood pressure and prevention of stroke, as well as type 2 diabetes, are also well established. Prevention of some cancers (especially that of breast and colon), increasing bone density and prevention of falls are also reported. Moreover, some longitudinal studies suggest that physical activity is linked to a reduced risk of developing dementia and Alzheimer's disease in particular.

Cardiorespiratory responses during running and sport-specific exercises in handball players.

To determine whether a 4-a-side handball (HB) game is an appropriate aerobic stimulus to reach and potentially enhance maximal oxygen uptake (V O(2)max), and whether heart rate (HR) is a valid index of V O(2) during a handball game. Nine skilled players (21.0+/-2.9 yr) underwent a graded maximal aerobic test (GT) where V O(2)max and HR-V O(2) relationship were determined. V O(2), HR and blood lactate ([La](b)) were recorded during a 2 x 225 s (interspersed with 30s rest) 4-a-side handball game and were compared to those measured during an 480-s running intermittent exercise (IE). Mean V O(2) tended to be higher in handball compared to IE (93.9+/-8.5 vs. 87.6+/-7.4% O(2)max, p=0.06), whereas HR was similar (92.3+/-4.9 vs. 93.9+/-3.9% of the peak of HR, p=0.10). [La](b) was lower for handball than for IE (8.9+/-3.5 vs. 11.6+/-2.1 mmol l(-1), p=0.04). Time spent over 90% of V O(2)max was higher for handball than for IE (336.1+/-139.6s vs. 216.1+/-124.7s; p=0.03). The HR-V O(2) relationship during GT was high (r(2)=0.96, p<0.001) but estimated V O(2) from HR was lower to that measured (p=0.03) in handball, whereas there was no difference in IE. 4-a-side handball game can be used as a specific alternative to IE for enhancing aerobic fitness in handball players. Nevertheless, the accuracy of HR measures for estimating V O(2) during handball is poor.

Fatigue responses in exercise under control of VO2.

To examine the fatigue response during an exhaustive heavy exercise performed under control of oxygen uptake (SS@V.O (2)Delta50) or power output (SS@pDelta50), eleven trained male subjects performed an incremental test to determine the peak of the oxygen uptake value (V.O (2peak)) and lactate threshold and two exhaustive steady-state cycling exercises at the intermediate value between the lactate threshold and V.O (2peak) (SS@V.O (2)Delta50 and SS@pDelta50). The control of V.O (2) induced an oscillation of the power output, which lowered the average power output (276 +/- 47 vs. 315 +/- 40 W, p = 0.004) and cancelled the slow component of oxygen kinetics. However, all subjects reached maximal cardiac output (CO) and heart rate (HR) values which were sustained almost two times longer in SS@V.O (2)Delta50 compared to SS@pDelta50 (979 +/- 854 vs. 475 +/- 236 s, p = 0.046 for CO and 1050 +/- 890 vs. 513 +/- 288 s, p = 0.037 for HR). Furthermore, SS@pDelta50 elicited V.O (2peak) but not SS@V.O (2)Delta50 (4963 +/- 434 vs. 4723 +/- 460 mL . min (-1), p = 0.026). Finally, the time spent at the maximal CO and HR values is correlated with time to exhaustion at V.O (2)Delta50. In conclusion, the cause of fatigue does not seem to have the same origin during exhaustive supra-lactate threshold exercise under control of V.O (2) (V.O (2)Delta50) compared to constant power output (pDelta50), while both elicit the maximal HR and CO values.

Ventilatory thresholds assessment from heart rate variability during an incremental exhaustive running test.

The present study examined whether the ventilatory thresholds during an incremental exhaustive running test could be determined using heart rate variability (HRV) analysis. Beat-to-beat RR interval, V(.-)O (2), V(.-)CO (2) and V(.-) (E) of twelve professional soccer players were collected during an incremental test performed on a track until exhaustion. The "smoothed pseudo Wigner-Ville distribution" (SPWVD) time-frequency analysis method was applied to the RR time series to compute the usual HRV components vs. running speed stages. The ventilatory equivalent method was used to assess the ventilatory thresholds (VT1 and VT2) from respiratory components. In addition, ventilatory thresholds were assessed from the instantaneous components of respiratory sinus arrhythmia (RSA) by two different methods: 1) from the high frequency peak of HRV ( FHF), and 2) from the product of the spectral power contained within the high frequency band (0.15 Hz to fmax) by FHF (HF x FHF) giving two thresholds: HFT1 and HFT2. Since the relationship between FHF and running speed was linear for all subjects, the VTs could not be determined from FHF. No significant differences were found between respective running speeds at VT1 vs. HFT1 (9.83 +/- 1.12 vs. 10.08 +/- 1.29 km x h (-1), n.s.) nor between the respective running speeds at VT2 vs. HFT2 (12.55 +/- 1.31 vs. 12.58 +/- 1.33 km x h (-1), n.s.). Linear regression analysis showed a strong correlation between VT1 vs. HFT1 (R (2) = 0.94, p < 0.001) and VT2 vs. HFT2 (R (2) = 0.96, p < 0.001). The Bland-Altman plot analysis reveals that the assessment from RSA gives an accurate estimation of the VTs, with HF x FHF providing a reliable index for the ventilatory thresholds detection. This study has shown that VTs could be assessed during an incremental running test performed on a track using a simple beat-to-beat heart rate monitor, which is less expensive and complex than the classical respiratory measurement devices.

Assessment of ventilatory thresholds from heart rate variability in well-trained subjects during cycling.

The purpose of this study was to implement a new method for assessing the ventilatory thresholds from heart rate variability (HRV) analysis. ECG, VO2, VCO2, and VE were collected from eleven well-trained subjects during an incremental exhaustive test performed on a cycle ergometer. The "Short-Term Fourier Transform" analysis was applied to RR time series to compute the high frequency HRV energy (HF, frequency range: 0.15 - 2 Hz) and HF frequency peak (fHF) vs. power stages. For all subjects, visual examination of ventilatory equivalents, fHF, and instantaneous HF energy multiplied by fHF (HF.fHF) showed two nonlinear increases. The first nonlinear increase corresponded to the first ventilatory threshold (VT1) and was associated with the first HF threshold (T(RSA1) from fHF and HFT1 from HF.fHF detection). The second nonlinear increase represented the second ventilatory threshold (VT2) and was associated with the second HF threshold (T(RSA2) from fHF and HFT2 from HF.fHF detection). HFT1 , T(RSA1), HFT2, and T(RSA2) were, respectively, not significantly different from VT1 (VT1 = 219 +/- 45 vs. HFT1 = 220 +/- 48 W, p = 0.975; VT1 vs. T(RSA1) = 213 +/- 56 W, p = 0.662) and VT2 (VT2 = 293 +/- 45 vs. HFT2 = 294 +/- - 48 W, p = 0.956; vs. T(RSA2) = 300 +/- 58 W, p = 0.445). In addition, when expressed as a function of power, HFT1, T(RSA1), HFT2, and T(RSA2) were respectively correlated with VT1 (with HFT1 r2 = 0.94, p < 0.001; with T(RSA1) r2 = 0.48, p < 0.05) and VT2 (with HFT2 r2 = 0.97, p < 0.001; with T(RSA2 )r2 = 0.79, p < 0.001). This study confirms that ventilatory thresholds can be determined from RR time series using HRV time-frequency analysis in healthy well-trained subjects. In addition it shows that HF.fHF provides a more reliable and accurate index than fHF alone for this assessment.

Influence of acute moderate hypoxia on time to exhaustion at vVO2max in unacclimatized runners.

Eight unacclimatized long-distance runners performed, on a level treadmill, an incremental test to determine the maximal oxygen uptake (VO2max) and the minimal velocity eliciting VO2max (vVO2max) in normoxia (N) and acute moderate hypoxia (H) corresponding to an altitude of 2,400 m (PIO 2 of 109 mmHg). Afterwards, on separate days, they performed two all-out constant velocity runs at vO2 max in a random order (one in N and the other in H). The decrease in VO2max between N and H showed a great degree of variability amongst subjects as VO2max decreased by 8.9 +/- 4 ml x min(-1) x kg)(-1) in H vs. N conditions (-15.3 +/- 6.3 % with a range from -7.9 % to -23.8 %). This decrease in VO2max was proportional to the value of VO2max (VO2max vs. delta VO2max N-H, r = 0.75, p = 0.03). The time run at vVO2max was not affected by hypoxia (483 +/- 122 vs. 506 +/- 148 s, in N and H, respectively, p = 0.37). However, the greater the decrease in vVO2max during hypoxia, the greater the runners increased their time to exhaustion at vVO2max (vVO2max N-H vs. tlim @vVO2max N-H, r = -0.75, p = 0.03). In conclusion, this study showed that there was a positive association between the extent of decrease in vVO2max, and the increase in run time at vVO2max in hypoxia.