Incidence of overweightness and obesity have increased dramatically in both adults and children since the mid-1970's. In children, the rate has more than tripled as documented by government agencies. The associated metabolic health risks of obesity are well known, but the risks associated with joint and ligament health remain relatively unknown, especially among overweight children participating in youth sporting activities. The purpose of this study was to investigate the influence of body composition and segmental mass variability on upper extremity ligamentous and joint injuries in youth throwing athletes. 19 youths (age: 14.0 + 1.20 yrs; height: 67.21 + 3.86 in; mass: 68.37 + 18.84 kg) were asked to throw 10 pitches at game speed into a net placed in front of them. Kinetic values at the shoulder and elbow joints were calculated using a VICON motion analysis system. Participant's body and segmental mass and composition were analyzed using a DEXA scan. The study utilized a multivariate correlation (Pearson product correlation; p < .05) and regression framework to investigate the relationship between whole body and throwing arm segmental body mass and composition measures to kinetic variables about the shoulder and elbow. Pearson product correlations revealed significant (p < .01) and positive correlations between each of the peak moment variables about the shoulder (internal rotation moment: 71 + 14 Nm, horizontal adduction moment: 94 + 17 Nm) and elbow (varus moment: 68 + 12 Nm) with each of the whole body and throwing segmental mass variables (body fat percentage: 19.30 + 8.13%; throwing arm mass: 4.1 + 1.30 kg; throwing arm fat percentage: 17.9 + 9.81%; throwing arm length: 26.7 + 2.12 in.), indicating body mass, total fat, arm length, segmental mass, and segmental fat are strongly correlated to peak moment generation about the throwing shoulder and elbow. Lean mass had a marginal significant (p < .1) effect on peak moment generation at the shoulder and elbow. The multivariate regression results showed similar results as the correlations, indicating a strong positive and significant (p < .01) relationship between each of the mass variables to that of the moment variables about the shoulder and elbow. Results suggest, as expected, that body and segmental mass play a significant role in peak moment generation about the throwing shoulder and elbow. Participants who had a greater percentage of fat mass produced greater injury correlated moments about the shoulder and elbow. Further, it should be noted, the segmental lean mass variables indicate that individuals who are fitter (i.e. have better muscle development or less fat mass) may have a reduced injury potential than that of individuals who may have a higher fat composition and less relative muscle mass. The importance of youth fitness levels has been widely documented in previous years. However, there remains a dearth of information on the impact of increased segmental fat mass on musculoskeletal injury risks in youth athletes. The current data set provides evidence that the increased mass due to accumulated fat potentially plays a crucial role in the elevation of shoulder and elbow injuries in youth throwing. Further, coaches should focus not only on improper mechanics, but also on improving the overall fitness level of their athletes.