The heart rate turn point reliability and methodological aspects

Purpose: The aim of the study was to test protocol variations on the heart rate performance curve (HRPC) and the heart rate turn point (HRTP) accordin g to Conconi et al. (1996). Respiratory gas exchange variables were used to define three phases of energy supply (I, II, III). Methods: Eighteen healt hy young male subjects performed 4 tests (T1-T4). T1: initial speed of 6 km .h(-1) followed by increments of 0.6 km.h(-1) every 60 s. Subjects were tha n randomized for the next three tests. T2: initial speed 5.6 km.h(-1) follo wed by increments of 0.2 km.h(-1) every 20 s; T3: similar to T2, in the sec ond half of phase III acceleration (S) was increased. T4: like T2, at the b eginning of phase III, S was increased. No differences were found in the de gree of the deflection of the HRPC expressed as factor k(HR) between T1 (0. 228 +/- 0.225) and T2 (0.248 +/- 0.231) but a significant increase was foun d in T3 (0.533 +/- 0.248) and T4 (0.770 +/- 0.258). Results: The modificati ons of the protocol (T3 and T4) systematically influenced the deflection of the HRPC, but k(HR) was highly reproducible in all tests. Eleven subjects showed degrees of deflection in the HRPC in all tests. There were no signif icant differences for S, HR, and (V) over dot O-2 at the HRTP. An HRTP was not found in seven subjects in neither T1 or T2; however, in T3 and T4, the se seven subjects showed a deflection of HRPC resulting from the protocol. The HRTP was found to be dependent on the start of the acceleration in phas e III. In cases with a linear time course in the HRPC in T1 and T2, in T3 a n HRTP was found at 15.6 km.h(-1) and in T4 at 13.6 km.h(-1), respectively. Conclusion: The Conconi test protocol with an accelerated increase in S in the final phase of the test has a major influence on the occurrence of the HRTP in cases of near linear HRPC.