Analysing The Vertical Jump
by Nizar Abu-Hamdeh
This article contains a detailed technique analysis of the vertical jump, based on pictures taken from high speed camera recordings of skilled vertical jumpers. Some of the recommendations may initially result in lower vertical jump heights, because changes in technique have to be practiced to be integrated into a fluid movement. Slight deviations to the suggestions presented may be appropriate due to differences in body structure. However, most tips are easily integreble and can immediately improve performance and lower the risk of injury.
The Stance
Before initiating the movement, the feet should be placed directly under the hips so that they can most effectively push the hips and upper body upward as the legs are straightened during the upward movement in preparation for the flight phase. If the feet are placed wider than hip width apart, the forces generated through leg extension will cross the body. As a result, vertical velocity is wasted as only a portion of the forces generated are used for take-off.
The Crouch Phase
While descending into the crouch, the trunk inclines forward and the ankle, hip and knee joint angles decrease so that the extensor muscles of the respective joints are placed on eccentric stretch to develop tension.
If the arms are used, there is extension in the shoulder joints as the arms are whipped down. Whipping the arms down as the bottom position is approached increases the load on the leg muscles so that they can respond with more force in the upward movement.
The eccentric contraction of the extensor muscles switches to an isometric contraction to stop the downward movement in preparation for the upward movement, at that time the muscular contraction switches to concentric.
The Push Off Phase
After the downward movement is stopped, hip joint extension should occur through contraction of the gluteus maximus and hamstrings to raise the upper body so that the center of gravity of the trunk is directly above the knees and feet when knee extension and then plantar flexion take place to propel the body upward.
When the arms are used, they should forcefully swing forward and upward after the bottom position is approached. Swinging the arms upward and forward leads to greater vertical velocity because they un-weight the athlete when they approach an approximately 45 degree angle in front of the body. Because the body is momentarily lighter, the forces generated through knee extension and plantar flexion become greater; this in turn can propel the athlete higher.
In knee joint extension, the thighs moves away from the shins as the legs straighten to generate vertical velocity needed for takeoff. The major muscle group involved in this action is the quadriceps femoris, which, due to having to accelerate the whole body weight minus the lower legs, provide the main force for pushing the body upward.
In the ankle joint, the gastrocnemius and soleus are involved in plantar flexion, the final joint action in preparation for the take-off. In this action, the heels move away from the balls of the foot as the whole body is raised. This action provides the final push to maximize the vertical velocity needed for the highest possible jump and should occur after the legs are almost completey extended .
The Flight Phase
The legs should be completely straight, the trunk should be in line with the legs and the toes should point to the ground after the ground is left. If the arm swing was used in the jump, the arms should be overhead or shoulder level. Following these points should assure that all the necessary joint actions were executed conciously and forcefully.
The Landing
The feet should be under the hips as the athlete lands to help the leg muscles handle the landing forces efficiently. The landing should take place on the balls of the feet, followed immediately by the heels and then by ankle-, knee-, and hip joint flexion. For safety reasons, the toes should not point down as the athlete lands as this can lead to excessive jamming of the foot bones, which can result in foot injuries.
Landing with the underside of the foot approximately 45° to the horizontal results in a quick occurence of the ball-heel or midfoot contact. This allows for the arch of the foot to withstand most of the landing forces, an important point for injury prevention.
Notes:
As the legs are straightened, the leg actions overlap to some extent. Nonetheless, for an optimal vertical jump it is necessary that hip, knee and ankle joint extension should follow in this sequence. Hip joint extension should come first to make the trunk move upward to an optimal position so that the knee and then ankle musculature can create the vertical velocity needed to propel the body as high as possible. If knee and ankle extension occur too early, the resistance under which the quadriceps and gastrocnemius must contract increases which results in less vertical velocity for take-off.