Recalibrated FRIEND equation for peak oxygen pulse is accurate in endurance athletes: the NOODLE study.

Peak oxygen pulse (OP) is an important index of cardiorespiratory fitness (CRF). The FRIEND database is a global source of reference values for CRF. However, no reference equation is tailored for endurance athletes (EA) to predict OP. Here, we adjusted the well-established FRIEND equation for OP to the characteristics of the EA population. 32 (34.0%) female EA and 62 (66.0%) male well-trained EA underwent maximal cardiopulmonary exercise test on a treadmill. V̇O was 4.5 ± 0.5 L min in males and 3.1 ± 0.4 L min in females. OP was 23.6 ± 2.8 mL beat and 16.4 ± 2.0 mL beat for males and females, respectively. Firstly, we externally validated the original FRIEND equation. Secondly, using multiple linear regression, we adjusted the FRIEND equation for OP to the population of EA. The original FRIEND equation underestimated OP for 2.9 ± 2.9 mL beat (P < .001) in males and 2.2 ± 2.1 mL beat (P < .001) in females. The updated equation was 1.36 + 1.07 (23.2 · 0.09 · age - 6.6 [if female]). The new equation explained 62% of the variance and significantly predicted OP (R = 0.62, β = 0.78, P < .001). The error of the EA-adjusted model was 0.1 ± 2.9 mL beat (P = .82) and 0.2 ± 2.1 mL beat (P = .65) for males and females respectively. Recalibration of the original FRIEND equation significantly enhances its accuracy among EA. The error of the EA-adjusted model was negligible. A new recalibrated equation should be used to predict OP in the population of EA.