This study was designed to 1) determine the relative frequency of occurrence of a heart rate deflection point (HRDP), when compared to a linear relationship, during progressive exercise, 2) measure the reproducibility of a visual assessment of a heart rate deflection point (HRDP), both within and between observers 3) compare visual and computer-assessed deflection points. Subjects consisted of 73 competitive male cyclists with mean age of 31.4 ± 6.3 years, mean height 178.3 ± 4.8 cm. and weight 74.0 ± 4.4 kg. Tests were conducted on an electrically-braked cycle ergometer beginning at 25 watts and progressing 25 watts per minute to fatigue. Heart Rates were recorded the last 10 seconds of each stage and at fatigue. Scatter plots of heart rate versus watts were computer-generated and given to 3 observers on two different occasions. A computer program was developed to assess if data points were best represented by a single line or two lines. The HRDP represented the intersection of the two lines. Results of this study showed that 1) computer-assessed HRDP showed that 44 of 73 subjects (60.3%) had scatter plots best represented by a straight line with no HRDP 2)in those subjects having HRDP, all 3 observers showed significant differences(p = 0.048, p = 0.007, p = 0.001) in reproducibility of their HRDP selection. Differences in HRDP selection were significant for two of the three comparisons between observers (p = 0.002, p = 0.305, p = 0.0003) Computer-generated HRDP was significantly different than visual HRDP for 2 of 3 observers (p = 0.0016, p = 0.513, p = 0.0001). It is concluded that 1) HRDP occurs in a minority of subjects 2) significant differences exist, both within and between observers, in selection of HRDP and 3) differences in agreement between visual and computer-generated HRDP would indicate that, when HRDP exists, it should be computer-assessed.

KEY WORDS: Conconi, anaerobic threshold, lactate threshold.