When I ask a young child to jump as high as he can, he generally squats really low. Others bend over at the waist, flexing their hips to generate power. Is this the best way to jump? Do elite jumpers squat before jumping or flex at their hips?
This is a slow-motion video of Javale McGee dunking two balls in the 2011 NBA Dunk Contest. He plants his take-off leg around :36.
As he plants, he is extended at his hips. His torso is almost completely vertical.
The second video is a slow-motion video of Demar Derozan’s “Showstopper” dunk from the 2011 NBA Dunk Contest.
Again, as he takes off at around :26, his torso is erect and there is very little flexion at his knee or his hips.
If Derozan and McGee, obviously two gifted jumpers, do not flex into a deep squat or bend over to flex their hips, are we teaching young athletes the wrong way to jump?
Below is a clip of repeat hurdle jumps.
In these repeat jumps, you can see that he does not flex his knees or hips greatly on the ground contact. The focus is to get off the ground as quickly as possible. The athlete wants to use the force of the landing to propel him into the air (Stretch-Shortening Cycle) rather than absorbing the force.
In these examples, we see leg stiffness. “In its simplest sense, stiffness is the relationship between the deformation of a body and a given force,” (Butler, R.J., Harrison P. Crowell III, H.P., & Davis, I.M., 2003). In this case, the deformation would be flexion at the ankle, knee or hip and the given force is the ground reaction force on the plant leg.
“It appears that increased stiffness is associated with increased velocity, jump height and economy. Several studies suggest that forefoot landings are associated with an increase in knee stiffness and rearfoot landings are associated with increased ankle stiffness,” (Butler, R.J., Harrison P. Crowell III, H.P., & Davis, I.M., 2003).
However, while many accept that increased stiffness improves performance based on the greater use of stored energy from the stretch-shortening cycle, others argue that stiffer landings lead to more injuries. In fact, one widely accepted factor in the increased incidence of non-contact ACL injuries in females compared to males is the more erect landing. Therefore, if we focus on vertical stiffness in the lower body to improve performance, are we putting athletes at greater risk for injury?
There is an on-going study to see if an eccentric training intervention can improve vertical stiffness and if this vertical stiffness can decrease the valgus motion at the knee.
However, until then, how should one teach jump landing? Most teach the soft landing with greater joint compliance. However, is this the best way to develop an athlete? Is it a step in the athletic development process to prevent injuries in young athletes who lack the eccentric strength to land with greater vertical stiffness? Is the landing more situation-specific depending on whether the player wants to rebound off his landing (stiff) or absorb the force and stick the landing (soft landing)?