Estimation bias: body mass and body height in endurance athletes The Body Mass Index (BMI) is a known variable that correlates with performance in endurance charges.The BMI is calculated on the basis of body size and body weight. We have a comparison of 1,607 athletes, including 255 women and 1.352 men, a comparison between the results for body weight and body size that tells us the athletes and the effectively measured values. Men like women underestimated their body weight and overestimated their body size, so the BMI was too low. Especially older athletes (> 35 years) have underestimated body weight and overestimated the body size so that it came to a significant difference in the BMI between the communicated numbers and the effectively measured numbers. All results can be found under https://pubmed.ncbi.nlm.nih.gov/23409596/