Without question, there is a direct relationship between lower body strength/power and vertical jumping ability. However, other factors are at play that can enhance or inhibit ones jumping potential. Specifically, biomechanical factors such as range of motion restrictions at the ankle joint can alter jumping mechanics and reduce jump height. Recent work published in the Journal of Sports Sciences by Pappaiakovou (2013) investigated the effects of ankle joint range of motion and counter movement jump and drop jump heights. Physical education subjects were split into an inflexible group (n=15) and a flexible group (n=15). The group with greater ankle joint range of motion outperformed the inflexible group on both jumping tasks by an average of 2 cm in the counter movement jump and 3 cm in the drop jump. Additionally, for the counter movement jump, the flexible group used a greater range of motion at all leg joints while the inflexible group raised their heels off the ground and displayed a greater horizontal distance between the centre of mass of the trunk and the centre of the hip joint. With the drop jump, the flexible group showed a greater vertical shift of the body center of mass and better joint coordination. The inflexible group displayed altered mechanics (trunk angle and heel position) based on jump type.
The results of this study demonstrate the importance of assessing ankle range of motion in athletes as insufficient range of motion can have negative effects on performance and heighten injury risk. Poor ankle mobility will also affect movement efficiency in squat variations and change of direction mechanics. Restricted ankle movement can result in increased forces at the knee joint predisposing an athlete to knee injury.
Ankle mobility is often assessed by coaches or trainers as part of the overhead squat test (a component of both the Functional Movement Screen and the NASM movement screen). As an athlete performs an overhead squat, excessive external rotation at the feet or lifting of the heels off of the floor to achieve a deeper squat may be indicative of poor ankle mobility. Soft tissue work on the lower leg muscles (e.g., foam rolling) and stretching to increase dorsiflexion can be helpful in improving ankle joint range of motion. Increasing strength and power of the lower body can certainly enhance performance, but movement ability and must not be overlooked as mechanics greatly influence ones ability to express force optimally.
Pappaiakovou, G. (2013) Kinematic and kinetic differences in the execution of vertical jumps between people with good and poor ankle joint dorsiflexion. Jounral of Sports Sciences, Ahead of print.