In many sports, greater height and arm span are purportedly linked to athletic success. While variation in body proportions has been explored across an array of scientific disciplines, studies focusing on humans of tall stature outside of clinical cases are limited. We investigated body size proportions in a sample of elite athletes, employing data on recruits for the National Basketball Association (NBA, n=2,990), mixed martial arts (MMA) fighters (mixed-sex, n=1,284), as well as a control sample of healthy young adults who are not professional athletes, represented here by male (n=4,082) and female (n=1,986) recruits for the United States Army, to test two hypotheses: 1) There is a significant difference in arm span to height ratios between elite professional athletes and the control population, and 2) There is a significant relationship between arm span to height ratio and athletic success within the NBA and MMA. We find that NBA players are significantly taller, with absolutely and relatively wider arm spans than MMA fighters and the control population. Additionally, we find that basketball players are significantly more likely to be drafted earlier in the NBA, and MMA fighters are significantly more likely to have a better loss to win ratio, if their arm span to height ratio falls above the regression line. However, we note that arm span and height, as well as athletic success, are impacted by a myriad of factors, and some of the most successful professional athletes do not have particularly long arms relative to their height.