The purpose of this study was to verify the use of a single test to obtain annual training guidelines applicable to multiple modes of training. Eight triathletes (4 females, 4 males) were tested 3 times during their training year (Phase I; Phase II; Phase III) on a treadmill and cycle ergometer. Cardio-respiratory variables were calculated at standardized percentages of maximal oxygen uptake (VO_2max; 50-100%). VO_2max differences between tests reached 6% in every testing session (p ≤ 0.01). VO_2max was stable for both tests throughout the season. The ANOVA (3 phases x 2 tests x 6 intensities) demonstrated that there was a significant difference for heart rate (HRs; p ≤ 0.05) between tests in Phase I only. However, the nonparametric sign test did not show any significant differences in any phase. These results demonstrated that triathletes could use the relationship between HR and % VO_2max collected during a treadmill or a cycle ergometer test to obtain interchangeable reference HRs for monitoring their running and cycling training bouts in high volume and/or high intensity phases of their training year.