Force plates offers a great solution to show objective metrics on how force is produced during a variety of movements including jumping. They not only show how high an athlete jumps, but how they jump. Dual force plates are even more informative since they provide objective feedback on how one limb performs versus the other. This is important since research has shown a 15% or greater lower limb asymmetry has been associated with greater risk of sport injury. However, it should be noted that there will be inherent asymmetries due to the nature of certain sports and positions that are more one side dominant such as pitchers and fencers as an example.
A deeper dive into the asymmetry will provide more context and what interventions can possibly be implemented to decrease the risk of injury.
To simplify things, a jump can be broken down into 3 phases. Loading (downward movement before jumping), takeoff (the moment your feet leave the ground), and landing (the moment your feet return to the ground).
To help understand asymmetries, it can be broken down into two categories: capability and tendency.
Capability refers to an athlete’s ability to perform a movement. Using a countermovement jump as an example; this does not mean they would perform a perfect jump with 0% asymmetry every single jump but they have the physical ability to do it.
Tendency refers to an athlete’s inclination and shows if they favor one side versus the other or if they tend to be more symmetrical.
To provide a visual of capabilities and tendencies during the three phases of a jump:
The below graph shows the loading phase (the first frame from the photo above).
Capability: This athlete was not able to produce a jump where he was closer to 0% (his closest jump to 0% was 9.7% favoring his right side).
Tendency: This athlete's inclination is to favor his right side (11.7%).
The below graph shows the takeoff phase (the second frame from the photo above).
Capability: This athlete was not able to produce a jump where he was closer to 0% (his closest jump to 0% was 12.6% favoring his right side).
Tendency: This athlete's inclination is to favor his right side (13.3%).
The below graph shows the landing phase (the third frame from the photo above).
Capability: This athlete has the ability to be more symmetrical (his closest jump to 0% was 0.6% to his left.
Tendency: This athlete's inclination is to favor his right side (15.7%).
Overall, this information tells us this athlete tends to favor his right side on all phases of a jump and he has not shown an ability to be symmetrical in all phases of a jump except for the landing phase.
What interventions can we possibly administer from this information? Depending on their deficits, there can be an emphasis on single leg and/or double leg exercises. To improve loading capabilities, exercises such as landings and eccentrics can be prescribed. To improve takeoff capabilities, exercises such as jumping, single leg jumps, and assisted jumps can be prescribed. To improve landing capabilities, exercises such as balance drills, landing mechanics, and decelerations can be prescribed.