The power output/heart rate relationship in cycling: test standardization and repeatability

The purpose of this study was to update and standardize the test for determining the power output/heart rate (PO/HR) relationship in cycling.

The current protocol was developed in the laboratory using a wind-load cycling simulator. Five hundred incremental tests were carried out by 290 male cyclists during a 2-yr period (1995-1997). The subjects' own bicycles, equipped with a standard crankset with a built-in power measuring system, were used for testing. The test protocol consisted of time-based increments in cadence that were uniform up to submaximal speeds and progressively greater in the final phase.

The PO/HR relationship obtained was linear at low to submaximal PO and curvilinear from submaximal to maximal PO. A method was developed for the mathematical identification of the point of transition from the linear to the curvilinear phase (deflection point or heart rate break point). In 484 of the 500 tests performed, the deflection was independent of the final acceleration (PO at deflection 318.4 +/- 42.4 W, PO at final acceleration 351.6 +/- 43.2 W, P < 0.001), whereas in 16 tests the deflection and the start of the final acceleration coincided. To evaluate test repeatability and precision, 15 subjects repeated the test twice within a few days. No significant differences were found for the heart rate at deflection, power output at deflection, or slope of the linear part of the PO/HR relationship obtained in the two tests.

It is concluded that the deflection point obtained by determining the PO/HR relationship on a wind-load simulator is not an artifact dependent on the incremental test protocol but rather a repeatable physiological phenomenon.