The difference between S1 and S2 was not significant, but the difference between S2 and S3 was significant for all groups, except between IND and NON. In cases where HRTP could be determined (N = 34), power output at HRTP and LTP2 was not significantly different and highly correlated (R = 0.90, P < 0.001) (Fig. 3B), similar to HR at HRTP and LTP2 (R = 0.93, P < 0.001) (Fig. 3C).
Several attempts have been undertaken to identify possible causes for these differences in HR response pattern, but neither plasma catecholamine response (27), parasympathetic receptor blockade (30), nor pH (20) or lactate response (27) was able to explain the phenomenon of HR deflection in young healthy subjects. Additionally, the HR response pattern was shown to be highly reproducible independent of the methodology applied (18,31). A review of the concept of the heart rate deflection point was presented previously (3).
A possible explanation may be found in studies showing a similar HR response by intervention, as reported by Gaesser and Rich in 1985 (8), who described an unexpected finding that caffeine significantly reduced submaximal exercise HR without changes in maximal HR. These authors were unable to explain the discrepancy; however, the results were consistent. The submaximal heart rates have been suggested to be mediated by baroreceptors, which is in agreement with a simulation study by Pessenhofer et al. (23). It was also reported by Graham (11) that caffeine may enhance the release of calcium or to lessen the accumulation of potassium, which was shown to be related to the kHR2 (19). This effect was suggested to be related to the ability of caffeine to interfere or block the action of adenosine. Andros and Gerber (2) studied the effect of adenosine on the reduced heart rate in the elderly. They suggested that the cardiac tissue in older human either produces more adenosine to β-adrenoceptor stimuli or is more responsive to adenosine, but from their data they were not able to demonstrate a significant effect as described by Gaesser and Rich (8). These results are rather speculative regarding the nonregular HR response in young and healthy subjects.
In conclusion, the HR response in incremental cycle ergometer exercise is neither linear nor uniform between LTP1 and Pmax. The more the HR response is linear or even inverted, especially in older subjects and patients, the more the linear %HRmax method overestimates target HR for training. Therefore, the HRmax method should be adapted to more accurately reflect the relationship between HR and power output. The use of turn points such as the LTP2 or the HRTP may be recommended for exercise training prescription.
Address for correspondence: Peter Hofmann, Ph.D., Institute of Sports Sciences, KF-University of Graz, Mozartgasse 14/1, A-8010 Graz, Austria; E-mail: Peter.Hofmann@kfunigraz.ac.at.
1. American College of Sports Medicine. ACSM’s Guidelines for Exercise Testing and Prescription. Philadelphia: Lippincott Williams & Wilkins, 2000, pp. 145–147.
2. Andros, E. A., and J. G. Gerber. The effect of adenosine on the reduced heart rate response to exercise in the elderly. J. Gerontol. 53A: M87–M91, 1998.
3. Bodner, M. E., and E. C. Rhodes. A review of the concept of the heart rate deflection point. Sports Med. 30: 31–46, 2000.
4. Brooks, G. A., TH. D. Fahey, T. P. White, and K. M. Baldwin. Exercise Physiology: Human Bioenergetics and Its Applications. Mountain View, CA: Mayfield, 2000, p. 675.
5. Bunc, V., and J. Heller. Comparison of the ventilatory threshold in young and adult trained and non-trained subjects. In: Physical Activity for Life: East and West, South and North, B. Svoboda and A. Rychtecky (Eds.). Aachen, Germany: Meyer & Meyer, 1995, pp. 117–120.
6. Conconi, F., G. Grazzi, I. Casoni, et al. The Conconi test: methodology after 12 years of application. Int. J. Sports Med. 17: 509–519, 1996.
7. Froelicher, V. F., and J. N. Myers. Exercise and the Heart. Philadelphia: W. B. Saunders, 2000, p. 363.
8. Gaesser, G. A., and R. G. Rich. Influence of caffeine on blood lactate response during incremental exercise. Int. J. Sports Med. 6: 207–211, 1985.
9. Gilman, M. B., and C. L. Wells. The use of heart rate to monitor exercise intensity in relation to metabolic variables. Int. J. Sports Med. 14: 339–344, 1993.
10. Godsen, R., T. Carrol, and S. Stone. How well does the Polar Vantage XL Heart Rate Monitor estimate actual heart rate? Med. Sci. Sports Exerc. 23: S14, 1991.
11. Graham, T. Caffeine and coffee: a useful supplement? News Sport Nutr 6: 1–7, 1998.
12. Hofmann, P., V. Bunc, H. Leitner, R. Pokan, and G. Gaisl. Heart rate threshold related to lactate turn point
and steady state exercise on cycle ergometer. Eur. J. Appl. Physiol. 69: 132–139, 1994.
13. Hofmann, P., R. Pokan, K. Preidler, et al. Relationship between heart rate threshold, lactate turn point
and myocardial function. Int. J. Sports Med. 15: 232–237, 1994.
14. Hofmann, P., R. Pokan, P. Schmid, et al. Load dependent myocardial function and heart rate performance curve in healthy young and older subjects. Int. J. Sports Med. 17: 13, 1996.
15. Hofmann, P., W. Niederkofler, R. Pokan, and S. P. von Duvillard. Individual physical working capacity. Med. Sci. Sports Exerc. 29: S204, 1997.
16. Hofmann, P., R. Pokan, F-J. Seibert, R. Zweiker, and P. Schmid. The heart rate performance curve during incremental cycle ergometer exercise in healthy young male subjects. Med. Sci. Sports Exerc. 29: 762–768, 1997.
17. Hofmann, P., R. Pokan, S. P. von Duvillard,and P. Schmid. Letter to the editor re: Conconi et al.: the Conconi test: methodology after 12 years of application. Int. J. Sports Med. 18: 397–398, 1997.
18. Hofmann, P., R. Pokan, and S. P. von Duvillard. Influence of step length during incremental exercise on the heart rate performance curve. Med. Sci. Sports Exerc. 30: S242, 1998.
19. Hofmann, P., F. J. Seibert, A. Öhlknecht, K. M. Sudi, R. Pokan, and P. Schmid. Relationship between blood potassium level and the deflection of the heart rate performance curve. Int. J. Sports Med. 19: 25, 1998.
20. Hofmann, P., F. J. Seibert, R. Pokan, M. Golda, D. Wallner, and S. P. von Duvillard. Relationship between blood pH, potassium, and the heart rate performance curve. Med. Sci. Sports Exerc. 31: S150, 1999.
21. Leitner, H., P. Hofmann, and R. Pokan. Application of fuzzy logic in the determination of the anaerobic threshold in performance diagnostics. Int. J. Sports Med. 15: 351, 1994.
22. Meyer, T., H. H. Gabriel, and W. Kindermann. Is determination of exercise intensities as percentages of VO2max
adequate? Med. Sci. Sports Exerc. 31: 1342–1345, 1999.
23. Pessenhofer, H., A. Meier, G. Schwaberger, and N. Sauseng. Verification of hypotheses about the physiological basis of the Conconi test by model simulation. Int. J. Sports Med. 12: 119, 1991.
24. Pollock, M. L., and D. H. Schmidt. Heart Disease and Rehabilitation. Champaign, IL: Human Kinetics, 1995, p. 148.
25. Pollock, M. L., G. A. Gaesser, J. D. Butcher, et al. The recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in healthy adults. Med. Sci. Sports Exerc. 30: 975–991, 1998.
26. Pokan, R., P. Hofmann, K. Preidler, et al. Correlation between deflection of heart rate/performance curve and myocardial function in exhaustive bicycle ergometry. Eur. J. Appl. Physiol. 67: 385–388, 1993.
27. Pokan, R., P. Hofmann, M. Lehmann, et al. Heart rate deflection related to lactate performance curve and plasma catecholamine response during incremental cycler ergometer exercise. Eur. J. Appl. Physiol. 70: 175–179, 1995.
28. Pokan, R., R. Enne, P. Hofmann, et al. Performance diagnostics in aging women and men. Int. J. Sports Med. 19: 28, 1998.
29. Pokan, R., P. Hofmann, S. P. von Duvillard, et al. The heart rate performance curve and left ventricular function during exercise in patients after myocardial infarction. Med. Sci. Sports Exerc. 30: 1475–1480, 1998.
30. Pokan, R., P. Hofmann, S. P. von Duvillard, et al. Parasympathetic receptor blockade and the heart rate performance curve. Med. Sci. Sports Exerc. 30: 229–233, 1998.
31. Pokan, R., P. Hofmann, S. P. von Duvillard, et al. The heart rate turn point
reliability and methodological aspects. Med. Sci. Sports Exerc. 31: 903–907, 1999.
32. Pokan, R., P. Hofmann, S. P. von Duvillard, et al. Exercise testing in cardiovascular diseased patients: lactate turn points versus gas exchange variables. Med. Sci. Sports Exerc. 32: S143, 2000.
33. Shephard, R. J., and H. S. Miller. Exercise and the Heart in Health and Disease. New York: Marcel Dekker, Inc., 1999, pp. 275–294.
34. Weltman, A., J. Weltman, R. Rutt, et al. Percentages of maximal heart rate, heart rate reserve, and VO2
peak for determining training intensity in sedentary women. Int. J. Sports Med. 10: 212–216, 1989.
35. Weltman, A., D. Snead, R. Seip, et al. Percentages of maximal heart rate, heart rate reserve, and VO2max
for determining endurance training intensity in male runners. Int. J. Sports Med. 11: 218–222, 1990.