Abstract 495: A Reappraisal of Body Mass Index and Aerobic Fitness in Young Athletic Women

Background: Lower body mass is thought to enhance athletic performance. We explored the relationship between BMI and aerobic fitness in athletic younger and older men and women. Methods: We examined 2224 patients (805 women, 1419 men) ages 17 through 91, referred to the Cardiovascular Performance Program at Massachusetts General Hospital between 2011 and 2019. Cardiorespiratory fitness (CRF; Peak V0 2 ) was assessed and expressed as %- predicted peak V0 2 , using the equation of Jones to adjust for age, height, and weight. Associations were evaluated using linear regression. Results: Mean peak VO 2 was 34.3±14.1 mL/kg/min, and median %-predicted VO 2 was 105%. We observed an inverse association between BMI and CRF in adults over 30 years old ( B = -0.043, p = 3.3x10 -33 for men, B = -0.051, p = 1.6 x 10 -13 for women) (Fig 1a) and men under 30 ( B = -0.025, p = 0.005) (Fig 1b). No linear association was found in younger women ages 17 - 29 ( B = -0.0078, p = 0.38) (Fig 1b). In contrast, a quadratic model disclosed a direct relationship at lower BMI and an inverse relationship at higher BMI (Fig 1c). An examination of high fitness young adults (defined as having %-predicted VO 2 ≥ 120%) demonstrates that fit women have mean BMI’s of 23.15 ± 2.69 (Fig 1d). Conclusion: These data highlight that BMI and fitness in younger aerobically fit women do not follow a simple linear relationship but one that is parabolic in nature. High fitness in young women occurs with highest density in the upper strata of the WHO and NIH-defined range of healthy BMI. These data support a deemphasis of weight loss generally and BMI specifically to enhance aerobic performance in athletic young women.