Heart dimensions may influence the occurrence of the heart rate deflectionpoint in highly trained cyclists

Objectives-To determine whether the heart rate (HR) response to exercise in 21 highly trained cyclists (mean (SD) age 25 (3) years) was related to the ir heart dimensions. Methods-Before performing an incremental exercise test involving a ramp pro tocol with workload increases of 25 W/min, each subject underwent echocardi ographic evaluation of the following variables: left ventricular end diasto lic internal diameter (LVIDd), left ventricular posterior wall thickness at end diastole (LVPWTd), interventricular septal wall thickness at end diast ole (IVSTd), left ventricular mass index (LVMI), left atrial dimension (LAD ), longitudinal left atrial (LLAD) and right atrial (LRAD) dimensions, and the ratio of early to late (E/A) diastolic flow velocity. Results-The HR response showed a deflection point (HRd) at about 85% (V) ov er doto(2)MAX in 66.7% of subjects (D group; n = 14) and was linear in 33.3 % (NoD group; n = 7). Several echocardiographic variables (LVMI, LAD, LLAD, LRAD) indicative of heart dimensions were similar in each group. However, mean LPWTd (p < 0.01) and IVSTd (p < 0.05) values were significantly higher in the D group. Finally, no significant difference between groups was foun d with respect to the E/A. Conclusions-The HR response is curvilinear during incremental exercise in a considerable number of highly trained endurance athletes-that is, top leve l cyclists. The departure of HR increase from linearity may predominantly o ccur in athletes with thicker heart walls.