To examine the role that lower extremity segmental length plays on vertical jump displacement. Previous research examining the relationship between segmental limb length and vertical jump ability revealed poor correlations. However, prior research did not use a reliable method to measure jump height (Davis et al, 2006). Thirty-one subjects participated (males = 21, females = 9) with a mean a 21.3 + 1.3 years. All subjects were physical active and engaged in general exercise. Measurements included height, weight, thigh length, shank (shin) length, truncated foot length, total foot length, and maximum vertical jump height. Segmental limb lengths were measured according to methods previously described. All measures were repeated twice for reliability analysis. The Just Jump mat (Probotics Inc.) was used to measure vertical jump height. This jump measure yields reliable and valid data. The Just Jump estimates vertical jump height, based on the gravitational affect of a projectile using the following: y = 2[0.5(g)(t2)], where y = vertical displacement, g = acceleration from gravity (−9.81 m/s2), and t = time of fall from peak height. Subjects were instructed to jump as high as possible three times on the Just Jump mat. Each of the scores were recorded and the highest vertical jump value was used in the analysis. Statistical analysis included reliability analysis using the intraclass correlation coefficient (ICC) as well as Pearson's correlation to test the relationship between maximum vertical jump height and the different segmental limb lengths. In addition, segmental length ratios (e.g., thigh:tibia, thigh:foot, height:foot, etc), were also tested for relationships with vertical jump height. Reliability of the segmental data and the vertical jump data were very good with all ICC values exceeding 0.75. The ICC for vertical jump measures was 0.96. Statistical analysis demonstrated that maximum jump height and segmental lengths were gender dependent. Therefore, analysis was separated by gender. For males, maximum jump height was significantly (p < 0.05) correlated with tibial length (r = −0.33) as well as the ratio of femur:tibia length (r = 0.39) and height:tibial length (r = 0.40). For females, truncated foot length was correlated with jump height (r = −0.44), as well as the ratios of femur:truncatedfoot length (r = 0.43), tibia:truncated foot length (r = 0.52) and height:truncated foot length length (r = 0.48). While long limb segments potentially produce greater torque, this is offset by an increase in angular inertia. Long segments may create a challenge to generate angular velocity for vertical jumping. The fact that truncated foot length (females) and tibial length (males) were negatively correlated with jump height suggest that limb length may influence vertical jump ability. These findings contradict earlier research. However, this present study used a reliable method of vertical jump height, while the previous research used a questionable method to measure this key outcome. Athletes with long feet (relative to height) and/or long tibia length (relative to height) may be at a mechanical disadvantage for vertical jump ability. Screening such athletes in order to consider additional jump training may allow these athletes to maximize their jumping potential.
