Identification of a Vo2 deflection point coinciding with the heart rate deflection point and ventilatory threshold in cycling

The purposes of this study were to compare the patterns of the work rate (WR)-Vo2 and WR-heart rate (HR) relationships in incremental cycling, to ascertain the occurrence of a Vo2 deflection (Vo2def) coinciding with the HR deflection point (HRdef ), and to determine whether the Vo2def, if present, coincides with the ventilatory anaerobic threshold (VT). Twenty-four professional cyclists performed a maximal incremental test on a wind-load cycle ergometer. Work rate, HR, Vo2, and Vco2 were recorded. The WR-Vo2 relationships obtained were linear up to submaximal WR and curvilinear thereafter and thus described a Vo2def. The WR and Vo2 at Vo2def were mathematically determined for all subjects. The ratio of DeltaWR.DeltaVo2 up to Vo2def was significantly lower than that above Vo2def (90 +/- 11 W.L.min versus 133 +/- 35 W.L.min, p < 0.0001). The WR-HR relationships obtained were linear up to submaximal WR and curvilinear thereafter. The WR and HR at HRdef were mathematically determined for all subjects. The WR values at Vo2def and at HRdef (329 +/- 32 W and 326 +/- 34 W) were significantly correlated (R = 0.96, p < 0.0001) and in good concordance (limits of agreement from -4.7% to 3.2%, Bland-Altman analysis). The Vo2 at VT was then determined for all subjects. The Vo2 values at Vo2def and at VT were significantly correlated (R = 0.99, p < 0.0001) and in strong concordance (limits of agreement from -1.9% to 1.0%, Bland-Altman analysis). In conclusion, a Vo2def coinciding with HRdef and VT was shown. This confirms that the determination of the WR-HR relationship and of HRdef is a practical and noninvasive means of identifying anaerobic threshold.     

Relationship between ventilatory threshold and muscle fiber conduction velocity responses in trained cyclists

The relationship between surface electromyography (SEMG) amplitude and the ventilatory threshold has been extensively studied. However, previous studies of muscle fiber conduction velocity (MFCV) are scarce and present insufficient evidence concerning the relationship between MFCV and metabolic responses during cycling. Based on that fact, the purpose of this study is twofold: (1) to investigate the existence of a MFCV threshold (MFCVT) during cycling and (2) to verify if this possible breakpoint is correlated with the ventilatory threshold (VT) and the SEMG threshold (SEMGT). Eight trained male cyclists (age 36.0 ± 9.7 years) performed an incremental cycling test with initial workload of 150 W gradually incremented by 20 W min^?1 until the exhaustion. Gas analyses were conducted using a breath-by-breath open-circuit spirometry and SEMG were registered from vastus lateralis in each pedaling cycle with a linear array of electrodes. A bi-segmental linear regression computer algorithm was used to estimate VT, MFCVT and SEMGT respectively in the carbon dioxide production (VCO₂), MFCV and electromyography root mean square (EMG RMS) curves. The one way ANOVA for repeated measures did not reveal any significant difference among VT (77.1 ± 7.5% of VO₂max), MFCVT (80.3 ± 10.4% of VO₂max) and SEMGT (81.9 ± 11.7% of VO₂max). The Bland and Altman procedure confirmed a good concordance between SEMGT and VT (Bias = 5.5 of %VO₂max) as well as MFCVT and VT (Bias = 5.2 of %VO₂max). The present findings suggest that muscle fiber conduction velocity threshold is a valid and reliable non-invasive tool to obtain information about ventilatory threshold in trained cyclists.     

A comparison of the point of deflection from linearity of heart rate and the ventilatory threshold in the determination of the anaerobic threshold in Indian boys

The purpose of the study was to assess whether the point of deflection from linearity of heart rate (HRD) could be used as an alternative method to determine the ventilatory threshold (VT) in Indian (Bengali) boys that represents the determination of the anaerobic threshold (AT), and also to standardize an exercise test to be effective in eliciting AT in Indian (Bengali) boys by using HRD. Twenty six (26) boys with a mean age of 12.8 (+/-1.18) years performed a graded maximal exercise test on a treadmill to determine peak VO(2), HRD and VT. The mean peak VO(2), weight related peak VO(2), peak pulmonary ventilation, and peak heart rate of the boys were found to be 1.75 l/min, 47.1 ml/kg/min, 66.9 l/min and 200.2 beats/min respectively. There were no significant differences between mean VO(2), weight related VO(2), pulmonary ventilation (VE), heart rate and respiratory exchange ratio (RER) that were measured at VT and HRD. The mean VO(2) measured at VT and HRD was found to be 1.46 and 1.45 l/min, which were about 84% and 83% of their respective peak values. Linear regression analysis revealed a correlation of 0.94 (p<0.01) between VO(2) measured at VT and VO(2) measured at HRD, so the present study indicates that the point of deflection from linearity of heart rate (HRD) may be an accurate predictor of VT in most but not all boys.     

Comparison of heart rate deflection and ventilatory threshold during a field cross-country roller-skiing test

This study was to assess whether the point of deflection from linearity of heart rate (HRd) could be an accurate predictor of ventilatory threshold (VT2) during a specific cross-country roller-skiing (RS) test. Ten well-trained cross-country skiers performed a maximal and incremental RS test in the field and a standardized maximal and incremental treadmill running (TR) test in the laboratory. Values of oxygen uptake (VO2) and heart rate (HR) were continuously recorded during all exercises by a portable breath-by-breath gas exchange measurement system and a wireless Polar monitoring system, respectively. The VT2 and HRd points were individually determined by visual analysis during RS. Maximal VO2 (VO2 max) and HR were higher (p < 0.05) during TR (67.1 +/- 7.3 ml x min(-1) x kg(-1) and 196.0 +/- 14.1 bpm, respectively) compared with RS (64.2 +/- 7.3 ml x min(-1) x kg(-1) and 191.5 +/- 13.1 bpm, respectively). However, a high correlation (r = 0.94, p < 0.01) between TR and VO2 max was observed. Paired t-tests showed no significant differences in HR (183.6 +/- 15.1 vs. 185.2 +/- 13.9 bpm) and VO2 (55.5 +/- 7.1 vs. 55.8 +/- 6.1 ml x min(-1) x kg(-1)) at intensities corresponding to HRd and VT2 during the RS test, respectively; Pearson product-moment correlation coefficients demonstrated significant relationships for HR at the HRd and VT2 points (r = 0.99, p < 0.001) as well as for VO2 (r = 0.95, p < 0.001). Our results indicate that the specific incremental RS test is effective in eliciting HRd in the field for all skiers and is an accurate predictor of VT2. These findings give very interesting practical applications to cross-country coaches and skiers to evaluate and control specific aerobic training loads.     

Validity of the heart rate deflection point as a predictor of lactate threshold during running.

During an incremental run test, some researchers consistently observe a heart rate (HR) deflection at higher speeds, but others do not. The present study was designed to investigate whether differences in test protocols could explain the discrepancy. Additionally, we sought to determine whether the HR deflection point accurately predicts lactate threshold (LT). Eight trained runners performed four tests each: 1) a treadmill test for maximal O(2) uptake, 2) a Conconi test on a 400-m track with speeds increasing approximately 0.5 km/h every 200 m, 3) a continuous treadmill run with speeds increasing 0.5 km/h every minute, and 4) a continuous LT treadmill test in which 3-min stages were used. All subjects demonstrated an HR deflection on the track, but only one-half of the subjects showed an HR deflection on the treadmill. On the track the shortening of stages with increasing speeds contributed to a loss of linearity in the speed-HR relationship. Additionally, the HR deflection point overestimated the LT when a continuous treadmill LT protocol was used. In conclusion, the HR deflection point was not an accurate predictor of LT in the present study.     

Validity of the heart rate deflection point as a predictor of lactate threshold concepts during cycling

This paper examines the validity of the heart rate deflection point (HRDP) obtained with the updated Conconi test. Eleven male road cyclists performed 2 progressive incremental cycling tests and a 30-minute prolonged exercise test (PET). From the data obtained, comparisons were made and correlation coefficients were calculated between HRDP, the lactate threshold (LT), and the 3 mmol.L(-1) threshold (AT3). The PET at HRDP demonstrated whether or not a steady state in blood lactate concentration (BLaSS) could be maintained. Significantly lower values for power output (p < 0.01) and heart rate (HR) (p < 0.01) were found at LT compared with HRDP. No differences were found between HRDP and AT3. Only a moderate correlation for power output between HRDP and AT3 (rs = 0.69; p < 0.05) could be observed. During the PET, only 6 out of 11 cyclists reached the target time of 30 minutes, and only 4 cyclists maintained a BLaSS. We conclude that the updated Conconi test is not a valid method for assessing LT or AT3. Therefore, this method seems not suitable to evaluate endurance performance and prescribe exercise intensities in road cycling.     

Analysis of heart rate deflection points to predict the anaerobic threshold by a computerized method

Many studies have used the heart rate deflection points (HRDPs) during incremental exercise tests, because of their strong correlation with the anaerobic threshold. The aim of this study was to evaluate the profile of the HRDPs identified by a computerized method and compare them with ventilatory and lactate thresholds. Twenty-four professional soccer players (age, 22 ± 5 years; body mass, 74 ± 7 kg; height 177 ± 7 cm) volunteered for the study. The subjects completed a Bruce-protocol incremental treadmill exercise test to volitional fatigue. Heart rate (HR) and alveolar gas exchange were recorded continuously at ≥1 Hz during exercise testing. Subsequently, the time course of the HR was fit by a computer algorithm, and a set of lines yielding the lowest pooled residual sum of squares was chosen as the best fit. This procedure defined 2 HRDPs (HRDP1 and HRDP2). The HR break points averaged 43.9 ± 5.9 and 89.7 ± 7.5% of the VO2peak. The HRDP1 showed a poor correlation with ventilatory threshold (VT; r = 0.50), but HRDP2 was highly correlated to the respiratory compensation (RC) point (r = 0.98). Neither HRDP1 nor HRDP2 was correlated with LT1 (at VO2 = 2.26 ± 0.72 L·min(-1); r = 0.26) or LT2 (2.79 ± 0.59 L·min(-1); r = 0.49), respectively. LT1 and LT2 also were not well correlated with VT (2.93 ± 0.68 L·min(-1); r = 0.20) or RC (3.82 ± 0.60 L·min(-1); r = 0.58), respectively. Although the HR deflection points were not correlated to LT, HRDP2 could be identified in all the subjects and was strongly correlated with RC, consistent with a relationship to cardiorespiratory fatigue and endurance performance.     

The relationship between anaerobic threshold and heart rate linearity during cycle ergometry

Recent studies have demonstrated there is a definitive deflection in the heart rate response to incremental velocity work that coincides with the anaerobic threshold. These studies were conducted with elite athletes who performed the specific activities in which they were trained. The purpose of this study was to determine if the same relationship in heart rate and ventilatory response to increasing velocity was evident in nine untrained healthy subjects aged 22 to 36 years performing leg ergometry under controlled laboratory conditions. All subjects began pedaling at 50 rpm with an initial power output of 100 W. Pedaling rates were increased by 5 rpm every 30 s. This increment was equivalent to a power increase of 11.1 W. The subjects cycled to the point of exhaustion or until they could no longer maintain the pedaling speed at the higher velocities. Heart rate and expiration gases were collected at 30-s intervals. The results indicated that the heart rate and ventilatory response to increasing velocity as previously reported under field conditions does not exist under laboratory conditions. While there was a definitive and statistically significant inflection in the ventilatory response to increasing velocity, heart rate remained linear. Therefore, caution should be used when determining the anaerobic threshold from the single measure of heart rate response.     

Utility of the Conconi's heart rate deflection to monitor the intensity of aerobic training

The Conconi's heart-rate deflection point (HRd) in the heart rate (HR)/speed curve is often used to set aerobic training loads. Training could either be set in percentage running speed or HR at HRd. In order to establish the limits and usefulness of various aerobic-training modalities for intermediate athletic level (physical-education students), acute responses were analyzed while running for a typical 40-minute training session. Speed, HR, lactate, and cortisol were thus recorded during training at 90 and 100% of running speed (RS: n = 14) and HR (HR: n = 16) at HRd (90% running speed [RS90], 100% running speed [RS100], 90% HR [HR90], and 100% HR [HR100]). During constant HR training, RS decreases while HR drifts upward during constant RS training. Half of the subjects can not finish the 40-minute RS100 session. For HR90, RS90, HR100, and RS100, average intensities are 67, 69, 74.9, and 77% maximal aerobic speed (multistage test), respectively. This study indicates that (1) training at HR100 and RS100 is more appropriate to improve high-intensity metabolic capacities (increased cortisol and lactate) while RS100 is too difficult to be maintained for 40 minutes for subjects at that level at least, (2) training at HR90, however, is better to improve endurance and capacity to do a large amount of work considering cortisol and lactate homeostasis, and (3) training at a constant HR using a HR monitor is a good method to control the intensity of the training with subjects not used to pacing themselves with the split-time approach.     

An aid to the determination of the ventilatory threshold

Detection of the ventilatory threshold during an incremental load exercise test by eye can be difficult. Although various alternative methods employing information other than the ventilation can be used to assist in determining the ventilatory threshold, they rely on underlying assumptions about the physiological basis for the ventilatory threshold. The method presented here (CUSUM) uses only the ventilation data, and therefore avoids such assumptions. Twelve subjects performed a total of 47 incremental exercise tests to exhaustion. Determinations of the ventilatory thresholds made by eye from the ventilation data (mean of three independent observers) were used as a standard for comparison with determinations using the modified V-slope method and the CUSUM method. A mean (SD) difference of 0.6 (2.84) ml·min^–1·kg^–1 was found between the standard ventilatory thresholds and those determined using the modified V-slope method. A similar comparison between the standard ventilatory thresholds and those determined using the CUSUM method yielded a difference of –0.11 (2.35) ml min^–1·kg^–1. It was concluded that the CUSUM method was a useful aid for the detection of the ventilatory threshold using the ventilation data alone.     

Using a logarithmic regression to identify the heart-rate threshold in cyclists

The purpose of this study was to establish an objective method for identifying the heart-rate threshold (HRT) in cyclists. Fifty-six male cyclists were tested on a cycle ergometer to volitional fatigue. Identification of the HRT used a heart-rate increase above a logarithmic regression line of best fit, coupled with the crossover of a linear regression line of best fit. The measures of Vco(2) and blood lactate for ventilatory threshold (VT) and lactate threshold (HLaT), respectively, were used as criterion measures to validate the HRT. Comparison of HRT with VT and HLaT showed significant associations (r = 0.98). Statistical variance between HRT, VT, and HLaT indicated no difference. From these findings, the logarithmic regression method provides an objective means to determine the HRT. Through this method, cyclists may obtain information for establishing accurate training levels and protocols.     

Transient ventilatory and heart rate responses to moderate nonabrupt pseudorandom exercise

Dynamic responses of inspired minute ventilation, CO2 and O2 end-tidal gas fractions, and heart rate were obtained from six normal human volunteers in response to a complex dynamic exercise challenge. Subjects pedalled a chair ergometer at constant frequency. The retarding torque applied to the ergometer pedals was controlled by a low-pass-filtered pseudorandom binary sequence (fPRBS), which provided a complex, nonanticipatory exercise stimulus containing sufficient high- and low-frequency energy to excite the small signal, broadband ventilatory response. The exercise range was chosen to produce a mean level of O2 consumption at or below 50% maximum O2 consumption. Cross-covariant analysis of the fPRBS exercise with breath-by-breath ventilation provided an estimate of the dynamic (impulse) response to exercise, which contained both fast phase 1 and slow phase 2 components. The initial, phase one, hyperpnea occurred within the same breath as the exercise transition and preceded a hypocapnic response. The phase one hyperpnea represented 26% of the total ventilatory response. The secondary, phase 2, hyperpnea was delayed several breaths from the onset of phase 1. It contained slower dynamics and followed a hypercapnic response. Heart rate increased abruptly during phase 1, peaked near the phase 1-to-2 boundary, and then decreased rapidly. The experimental protocol was designed to minimize the subjective response and provide an adequate stimulus for the faster time constants. Results obtained from these experiments were consistent with a nonhumoral induced phase 1 exercise hyperpnea.     

A systems model approach to the ventilatory anaerobic threshold

An analogue systems model of whole-body human bioenergetics predicts a change in kinetics of VO2 time series values as a result of exercise levels above an anaerobic threshold. Plotted VO2 results from exercising subjects appear to confirm this change. The purpose of this study is to describe the background to the systems model analogue of the anaerobic threshold and a test procedure devised to estimate this threshold. The estimate so obtained has the dual advantages of being based on model theory and of not being subject to the sort of ambient variations inherent in a single-test determination. A non-homogeneous group of eight subjects comprising a full replicate of a 2(3) factorial experimental design, with factors age, sex and training status, took part in the study. On one hand the results indicate acceptance of the systems model theory. On the other, the analogue threshold measure possesses corresponding properties to the conventional anaerobic threshold. It is higher for trained (155-214 W) than for untrained subjects (108-158 W), higher for males (149-214 W) than for females (108-170 W), and displays no evident interaction effects. Results for the VO2 time constant and for the work efficiency, display similar effects except for an interaction in the latter between age and training status. These experimental findings are regarded as confirmatory of the nature of the analogue threshold measure.     

Heart rate deflection point as a strategy to defend stroke volume during incremental exercise.

The purpose of this study was to examine whether the heart rate (HR) deflection point (HRDP) in the HR-power relationship is concomitant with the maximal stroke volume (SV(max)) value achievement in endurance-trained subjects. Twenty-two international male cyclists (30.3 +/- 7.3 yr, 179.7 +/- 7.2 cm, 71.3 +/- 5.5 kg) undertook a graded cycling exercise (50 W every 3 min) in the upright position. Thoracic impedance was used to measure continuously the HR and stroke volume (SV) values. The HRDP was estimated by the third-order curvilinear regression method. As a result, 72.7% of the subjects (HRDP group, n = 16) presented a break point in their HR-work rate curve at 89.9 +/- 2.8% of their maximal HR value. The SV value increased until 78.0 +/- 9.3% of the power associated with maximal O(2) uptake (Vo(2 max)) in the HRDP group, whereas it increased until 94.4 +/- 8.6% of the power associated with Vo(2 max) in six other subjects (no-HRDP group, P = 0.004). Neither SV(max) (ml/beat or ml.beat(-1).m(-2)) nor Vo(2 max) (ml/min or ml.kg(-1).min(-1)) were different between both groups. However, SV significantly decreased before exhaustion in the HRDP group (153 +/- 44 vs. 144 +/- 40 ml/beat, P = 0.005). In the HRDP group, 62% of the variance in the power associated with the SV(max) could also be predicted by the power output at which HRDP appeared. In conclusion, in well-trained subjects, the power associated with the SV(max)-HRDP relationship supposed that the HR deflection coincided with the optimal cardiac work for which SV(max) was attained.     

Metabolic and performance responses to constant-load vs. variable-intensity exercise in trained cyclists.

We studied glucose oxidation (Glu(ox)) and glycogen degradation during 140 min of constant-load [steady-state (SS)] and variable-intensity (VI) cycling of the same average power output, immediately followed by a 20-km performance ride [time trial (TT)]. Six trained cyclists each performed four trials: two experimental bouts (SS and VI) in which muscle biopsies were taken before and after 140 min of exercise for determination of glycogen and periodic acid-Schiff's staining; and two similar trials without biopsies but incorporating the TT. During two of the experimental rides, subjects ingested a 5 g/100 ml [U-(14)C]glucose solution to determine rates of Glu(ox). Values were similar between SS and VI trials: O(2) consumption (3.08 +/- 0.02 vs. 3.15 +/- 0.03 l/min), energy expenditure (901 +/- 40 vs. 904 +/- 58 J x kg(-1) x min(-1)), heart rate (156 +/- 1 vs. 160 +/- 1 beats/min), and rating of perceived exertion (12.6 +/- 0.6 vs. 12.7 +/- 0.7). However, the area under the curve for plasma lactate concentration vs. time was significantly greater during VI than SS (29.1 +/- 3.9 vs. 24.6 +/- 3. 7 mM/140 min; P = 0.03). VI resulted in a 49% reduction in total muscle glycogen utilization vs. 65% for SS, while total Glu(ox) was higher (99.2 +/- 5.3 vs. 83.9 +/- 5.2 g/140 min; P < 0.05). The number of glycogen-depleted type I muscle fibers at the end of 140 min was 98% after SS but only 59% after VI. Conversely, the number of type II fibers that showed reduced periodic acid-Schiff's staining was 1% after SS vs. 10% after VI. Despite these metabolic differences, subsequent TT performance was similar (29.14 +/- 0.9 vs. 30.5 +/- 0.9 min for SS vs. VI). These results indicate that whole body metabolic and cardiovascular responses to 140 min of either SS or VI exercise at the same average intensity are similar, despite differences in skeletal muscle carbohydrate metabolism and recruitment.