Identification of a VO2 deflection point coinciding with the heart rate deflection point in professional rugby players

Background. In 1982 Conconi et al. (1) proposed a noninvasive test for identifying the anaerobic threshold through the determination of the speed/heart rate (S/HR) relationship in running. The S/HR relationship was determinate also in cycling, rowing, swimming, skating, cross country ski. This relationship was linear from low to submaximal speeds and curvilinear from submaximal to maximal speeds (Smax). The passage from the linear to the curvilinear phase (speed deflection, Sd) coincided with the beginning of a sharp accumulation of blood lactate: this is an indirect way to determine the anaerobic threshold. Aim. To compare the patterns of the S/oxygen consumption (S/VO2) and S/HR relationship during maximal incremental running test in rugby players, and to evaluate the occurrence of an oxygen consumption deflection point (VO2def) coinciding with the heart rate deflection point (HRdef). Subjects and Methods. 18 professional male rugby players (age 21-30). All athletes performed a maximal incremental cardiopulmonary running test on treadmill. After adequate warm up at least 15 minutes at moderate intensity follow by short speed variations of ten to fifteen seconds. Test started at 7 km/h and speed was increased by 0.3 km/h every 30 seconds until a Borg score 18-19/20 RPE then they started the final acceleration (0.5-1 km/h every 20 seconds) until exhaustion; Figure 1. The oxygen uptake as a function of speed was determined and the S/VO2 as well as the S/HR relationships were mathematically analyzed. The ventilatory threshold (VT) was calculated by the V-slope method. Data are represented as mean ± standard deviation; Table 1. Results. The analysis of S, VO2 and HR showed no difference between HRdef and VO2def data (P>0.05, T Test). Table 2. The pattern of the S/VO2 relationships was similar to that of the S/HR relationship, that is linear up to submaximal exercise intensity and curvilinear thereafter and thus describing a VO2 flattening (VO2def); Fig 2. HRdef was mathematically determined in all subjects while VO2def and VT were mathematically determined in 12 and 11 of the 18 participant respectively. The S values at VO2def and at HRdef were strongly correlated (R=0.92, P<0.0001; Fig. 3) and in good concordance (limits of agreement from -0.7 to 0.8 km/h, Bland-Altman analysis; Fig. 4). The VO2 values at VO2def and at VT were strongly correlated (R=0.96, P<0.0001; Fig. 5) and in good concordance (limits of agreement from -766 to 444 km/h, Bland-Altman analysis; Fig. 6). Conclusions. A VO2def coinciding with HRdef was shown in the most part of cases. These results demonstrate that exercise intensity above HRdef is at least partially independent by the aerobic mechanism of ATP re-synthesis, providing evidence that the determination of the S/HR relationship and HRdef could be a practical and non-invasive means of identifying the transition to anaerobic mechanisms in rugby players.