Ventilatory threshold (VT) is an important index of aerobic exercise function. The non-invasive nature of assessing VT and the fact that VT can be determined without obtaining a maximal exertion makes it broadly appealing to study in both healthy and diseased populations. Much of the understanding of the physiological and biochemical events underlying the occurrence and significance of VT is based on research involving adults. Several conclusions can be made from the studies which have examined VT in children. First, VT can be determined in a reliable manner. Second, heart rate deflection has been used as an alternative method to estimate VT and, based on limited information, appears to have reasonable accuracy. Third, although there is some evidence suggesting that VT (relative to maximal oxygen uptake [V̇O2max]) declines with maturation, the evidence is not overwhelming and it is based primarily on cross-sectional comparisons. Fourth, endurance training will increase VT in children to a greater extent than the increase in V̇O2max. Lastly, the physiological significance of VT and the metabolic consequences when exercise intensities exceeds VT are not well understood in children and are fruitful areas of research.
Anthony D. Mahon and Christopher C. Cheatham
Tracy Baynard, Viswanath B. Unnithan, Kenneth H. Pitetti, and Bo Fernhall
This study evaluated detection of ventilatory threshold (VT) in adolescents with mental retardation (MR) (17 with MR, 13 with MR and Down Syndrome (DS), mean age 17.5 years). Subjects performed an individualized treadmill VO2peak test. Two evaluators reviewed the same VT plots 6 weeks apart, using 5 different methods. VE vs. time elicited the most detectable cases (83%), but significantly fewer youth with DS exhibited a detectable VT using any combination of methods (62% vs. 100%). Only VE vs. time yielded acceptable detection rate, although this may have been influenced by the protocol used. Intra-evaluator correlation coefficients ranged from 0.91-0.97, and interevaluator reliability coefficients ranged from 0.81-0.93. These findings suggest determination of VT is difficult in this population when using an individualized treadmill protocol, especially in adolescents with DS.
Anthony D. Mahon and Paul Vaccaro
Whether the point of deflection from linearity of heart rate (HRD) coincides with ventilatory threshold (VT) has not been extensively examined in children. The purpose of this study was to assess the relationship between the VO2 measured at VT and the VO2 measured at HRD. Twenty-two boys with a mean age of 10.7 years (±1.0) performed a graded exercise test to determine VT, HRD, and VO2max. There was no significant difference between mean VO2 (ml/kg/min) at VT and at HRD (33.5±3.5 vs. 34.1±4.4; p>0.05). Linear regression analysis revealed a correlation of r = 0.76 (p<0.01) between the VO2 measured at VT and the VO2 measured at HRD. These results indicate that HRD may be an accurate predictor of VT in most but not all children, and caution should be used when interpreting the significance of HRD.
Ralph K.L. Rogers, Tony Reybrouck, Maria Weymans, Monique Dumoulin, Marc Gewillig, and Paul Vaccaro
This study assessed the relationship between the VO2 measured at ventilatory threshold (VT) and the VO2 measured at the point of deflection from linearity of heart rate (HRD). Twelve children (10 boys and 2 girls) with a mean age of 11.3 years (±4.8) performed a graded exercise test to determine VT and HRD. All children had undergone surgical repair for d-transposition of the great arteries at approximately 13 months of age. Because of failure to demonstrate HRD, the data from 4 patients were excluded from statistical analysis. For the remaining 8 patients there was no significant difference between mean VO2 (ml/kg/min) at VT and HRD (26.6 ± 6.4 vs. 26.3 ± 6.8; p > 0.25). Linear regression analysis revealed a correlation of r = 0.92 between the VO2 measured at VT and the VO2 measured at HRD. Only 8 of the 12 patients (66%) in this study satisfied criteria needed to identify the HRD. Therefore HRD may be an accurate predictor of VT in most but not all children who have had surgery for d-transposition of the great arteries.
Yagesh N. Bhambhani, Robert S. Burnham, Gary D. Wheeler, Peter Eriksson, Leona J. Holland, and Robert D. Steadward
In this study we compared the ventilatory threshold (VT) between 8 untrained and 8 endurance-trained males with quadriplegia during simulated wheelchair exercise. Each subject completed an incremental velocity test in his personal wheelchair mounted on a customized roller system designed to provide velocity and distance feedback. VT was identified by two trained evaluators using established respiratory gas exchange criteria. A significant interevaluator reliability coefficient of .90 (p < .01) was observed for the detection of VT. Relative oxygen uptake (V̇O2, ml · kg-1 · min-1) at VT and peak V̇O2 were significantly (p < .05) higher in the endurance-trained compared to untrained subjects. However, no significant difference (p > .05) was observed between the two groups when VT was expressed as a percentage of peak V̇O2. Significant correlations of .86 and .81 (p < .01) were observed between VT and peak V̇O2 in the untrained and trained groups, respectively. It was concluded that endurance training improves both VT and peak V̇O2 during wheelchair exercise in male subjects with quadriplegia but does not improve VT when it is expressed relative to peak V̇O2.
Samantha G. Fawkner, Neil Armstrong, David J. Childs, and Joanne R. Welsman
The purpose of this study was to assess the reliability of the ventilatory threshold using visual analysis (TVent) and a computerised v-slope method (TV - slope) with children. Twenty-two children completed 2 ramp incremental cycling tests to voluntary exhaustion. Oxygen uptake (V̇O2) at TVent was derived independently by two observers using plots of V̇E/V̇CO2, V̇E/V̇O2, PETO2 and PETCO2, V̇E and RER as a function of time. V̇O2 at TV - slope was determined by both observers using linear regression analysis of the plot of V̇CO2 against V̇O2. A TV – slope was determined for each test, although a TVent could not be found by one of the observers in 7 of the 44 tests. Inter-observer reliability was slightly better for TV - slope, and both methods had similar test-retest coefficients of repeatability (0.19 and 0.22 L • min−1, TVent and TV - slope, respectively). Although TV slope may be the method of choice, investigators should consider the 95% limits of agreement when interpreting their data.
Anthony D. Mahon and Melinda L. Marsh
This study examined the occurrence of a V̇O2 plateau at maximal exercise, and whether ventilatory threshold (VT) differend between children who do and children who do not achieve a V̇O2 plateau at maximal exercise. After performing a graded exercise test on a treadmill to assess VT and V̇O2max, the children were divided into a plateau group (n = 14) and a nonplateau group (n = 12). There were no differences with respect to the V̇O2 at VT (36.7 ± 3.4 vs. 37.9 ± 5.4 ml · kg−1 · min−1) and V̇O2max (51.6 ± 5.4 vs. 54.6 ± 3.6 ml · kg−1 · min−1) in the plateau and nonpiateau groups, respectively. The mean HR, RER, and RPE at maximal exercise were also similar between groups. These results indicate that VT and V̇O2max are similar in children regardless of the occurrence of a V̇O2 plateau at maximal exercise. Furthermore, a plateau in V̇O2 during a maximal exercise test is not mandatory for assessment of V̇O2max in this age group.
Laurent Mourot, Nicolas Fabre, Aldo Savoldelli, and Federico Schena
To determine the most accurate method based on spectral analysis of heart-rate variability (SA-HRV) during an incremental and continuous maximal test involving the upper body, the authors tested 4 different methods to obtain the heart rate (HR) at the second ventilatory threshold (VT2). Sixteen ski mountaineers (mean ± SD; age 25 ± 3 y, height 177 ± 8 cm, mass 69 ± 10 kg) performed a roller-ski test on a treadmill. Respiratory variables and HR were continuously recorded, and the 4 SA-HRV methods were compared with the gas-exchange method through Bland and Altman analyses. The best method was the one based on a time-varying spectral analysis with high frequency ranging from 0.15 Hz to a cutoff point relative to the individual’s respiratory sinus arrhythmia. The HR values were significantly correlated (r 2 = .903), with a mean HR difference with the respiratory method of 0.1 ± 3.0 beats/min and low limits of agreements (around –6/+6 beats/min). The 3 other methods led to larger errors and lower agreements (up to 5 beats/min and around –23/+20 beats/min). It is possible to accurately determine VT2 with an HR monitor during an incremental test involving the upper body if the appropriate HRV method is used.
Gregory B. Dwyer and Anthony D. Mahon
Little is known about the responses to graded exercise in athletes with cerebral palsy (CP). This study compared the ventilatory threshold (VT) and peak VO2 among athletes with CP during treadmill and cycle ergometry exercise. Six (4 men, 2 women) track athletes with CP volunteered to participate in the study. Graded exercise tests on a treadmill and cycle ergometer were performed on separate days to assess VT and peak VO2. Paired t tests were used to compare the two exercise modes. The VT, expressed as a percentage of peak VO2, was significantly higher on the cycle ergometer than on the treadmill. The absolute VO2 at the VT was similar during both testing modes, and peak VO2 was significantly higher on the treadmill than on the cycle ergometer. Similar to responses seen in able-bodied individuals, the VO2 at VT was similar during both modes of exercise, while the peak VO2 was 10% lower on the cycle than on the treadmill. Cycle ergometer peak VO2 in these athletes was higher than previous reports of individuals with CP for the cycle ergometer.
Oliver Faude, Tim Meyer, and Wilfried Kindermann
The work rate (WR) corresponding to ventilatory threshold (VT) is an appropriate intensity for regenerative and low-intensity training sessions. During incremental ramp exercise, VO2 increase lags behind WR increase. Traditionally, a VO2 time delay (t d) of 45 seconds is used to calculate the WR at VT from such tests. Considerable inaccuracies were observed when using this constant t d. Therefore, this study aimed at reinvestigating the temporal relationship between VO2 and WR at VT.
20 subjects (VO2peak 49.9 to 72.6 mL · min–1 · kg–1) performed a ramp test in order to determine VT and a subsequent steady-state test during which WR was adjusted to elicit the VO2 corresponding to VT. The difference in WR and heart rate at VT was calculated between the ramp and the steady-state test (WRdiff, HRdiff) as well as the time delay corresponding to WRdiff during ramp exercise.
Mean values were t d = 85 ± 26 seconds (range 38 to 144), WRdiff = 45 ± 12 W (range 23 to 67), HRdiff = 1 ± 9 beats/min (range –21 to +15). The limits of agreement for the difference between WR at VT during ramp and steady-state exercise were ± 24 W. No signifi cant influence on t d, WRdiff, or HRdiff from differences in endurance capacity (VO2peak and VT; P > .10 for all correlations) or ramp increment (P = .26, .49, and .85, respectively) were observed.
The wide ranges of t d, WRdiff, and HRdiff prevent the derivation of exact training guidelines from single-ramp tests. It is advisable to perform a steady-state test to exactly determine the WR corresponding to VT.