Self-paced VO2max tests (SPV) are a fairly recent development in cardiorespiratory testing. SPV’s have been considered valid for measuring VO2max, however, other measurements such as ventilatory threshold (VT) are also important when completing such cardiorespiratory testing and have not been adequately studied. It has been suggested that VT cannot be measured during SPV.
PURPOSE: The purpose of this study was to determine whether the first VT (VT1) and second VT (VT2) could be identified during an SPV and how it compared to VT1 and VT2 determined during a Bruce protocol. It was hypothesized that VT1 and VT2 could be determined during SPV and would not be different than the VT1 and VT2 identified during the Bruce protocol.
METHODS: 10 healthy, recreationally active subjects (9 male, 1 female, 25.4 ± 9.0 years) completed SPV and Bruce protocols on the same treadmill in random order. Gas sampling was processed as 15 breath moving averages. VT1 and VT2 were determined by identifying breaks in the VE, VE/VO2, PETO2, VE/VCO2 and PETCO2 versus time slopes as well as the VE versus VCO2 slope. The researcher analyzing VT was not involved in testing and was blind to the protocol. VT1 and VT2 was expressed as a percentage of the maximal VO2 (%VO2max) attained during the respective protocol. Paired t-tests were used to identify differences between protocols for VO2max, VT1 and VT2.
RESULTS: VO2max was not different between Bruce and SPV protocols (55.5 ± 5.5 vs 56.6 ± 4.5 ml*kg-1*min-1, respectively, p = 0.15). Five tests (4 during SPV) produced atypical slopes and VT2 identification was difficult. VT1 occurred at a higher %VO2max in SPV (41.1 ± 8.1 SPV vs 32.2 ± 7.4 Bruce, p = 0.005) as did VT2 (86.4 ± 7.5 SPV vs 67.8 ± 8.9 Bruce, p < 0.001).
CONCLUSIONS: SPV allowed subjects to alter their pace and their ventilatory responses making it more difficult to identify VT. Higher VT in SPV is in contrast to recent research. The magnitude of difference in VT may be due to both the difficulty in identifying VT in SPV and also the potential for SPV to allow subjects to alter their metabolic requirements and postpone anaerobiosis. Measurement of blood lactate throughout testing is needed to aid in the validation of VT in SPV.