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Using BODITRAK to Measure and Assess the Single Leg Jump

T
o introduce myself, I am currently a physical therapist at Orthopedic Institute in Sioux Falls, SD. I work primarily with an orthopedic and sports medicine clientele. I work with athletes of multiple sports, ages, and skill levels. My deep passion is working with golfers. I have experience working with amateurs of all ages and skills as well as professionals. I went to PT school at Mayo Clinic, worked throughout Minnesota before moving to Sioux Falls, SD. A large part of my continuing education training has been golf related, part of this does include a TPI Medical 3 certification.

Through TPI and its partners, I became aware of BodiTrak. I have seen it used, have seen the benefit, and wanted one for myself. However, I needed to convince my supervisors of its use outside of golf to justify the cost. Of course I use it for golfers, however something that isn’t as well known, is its use for other types of athletes in the rehabilitation setting. Here, I am going to explain how we use BodiTrak to train and assess athletes following lower extremity (LE) injuries and/or surgeries. Specifically, we will look at how we use it for the single leg vertical jump.

It is well documented that the single leg vertical jump test is a simple and important LE test for strength and power in the rehabilitated leg. This is one measure commonly used to ensure they are ready to return to competition. An acceptable standard for return to play is 90% of jump height on the injured limb compared to the contralateral limb. This is commonly measured via the Vertec and jump mats that calculate height based on time in the air.  These methods only show you jump height. Mixed with a 2D video, you can assess their lower extremity alignment, amount of knee flexion, etc to ensure they are safe.  By using the ground reaction force (GRF) measurement on BodiTrak, you can get a specific force output (Body weight), 2D video analysis, all the while looking at pressure distribution of their foot in real time throughout the motion. It has been shown that using GRF is a valid measurement to assess LE force and has excellent intrasession and intersession reliability. (McElveen, Riemann, & Davies, 2010).

It is not uncommon to see athletes within acceptable ranges using the Vertec, then demonstrate poor loading strategies with a single leg squat and single leg vertical jump when using BodiTrak. This is because good athletes are excellent at utilizing compensation patterns to maximize performance. This puts them at large risk of future injuries.  You can see an example of this in the screenshots below with a recent Division 1 soccer player I’m working with recovering from an ACL reconstruction.

She was measured at 1.9x BW on her right (surgical) leg, and 2.6x BW on left leg at 5 months post surgery. Obviously, earlier than the expected time frame to return to play and expected to be less than 90%. However, this gave us a lot of information as to how she is loading that leg, which otherwise we would not know without BodiTrak.

The graph above is a representative example of force development strategies between an athlete’s injured and healthy limbs.  As you can see, the general force development trends of both legs are similar, but there are important distinctions in the data, in particular when used for return-to-play assessment:

  1. TAKEOFF PHASE: Notice that the athlete generates roughly the same total vertical force with each leg (~2.1x BW in healthy limb vs 1.9x BW in injured limb), but the strategy of force development is quite different.  With the healthy limb, the athlete generates force quickly and consistently, marked by the orange line climbing steeply (from ~0.2 to ~2.2) in a short period of time.  The athlete is less assertive with their injured limb, evidenced by more gradual & ‘hesitant’ rate of force development.  
  2. AIRTIME: Similar (~95%) between healthy and injured limb.  Using an athlete’s relative jump performance as rehab stage indicator would show an acceptable comparative range.
  3. LANDING PHASE: Notice how the orange line of the healthy side stabilizes at ‘1x BW’ approximately 1s sooner (on a 4s total recording) than the blue line of the injured side. Time to stabilization is an often-used assessment of performance in return to play.

As coaches or clinicians, we need to understand the how, not just the how much.  Determining an athlete’s readiness to return to play using just airtime/jump height/DVF can be helpful, but offers an incomplete picture. By looking at the underlying data on BodiTrak, we can identify key markers around the ‘how’ – insight that contributes to a comprehensive, objective assessment.

Among some hip and knee alignment issues in my soccer client, we found that we need to work more on proper loading with the single leg squat. A recent article by BodiTrak discussed coaching a squat. The pressure moves into the rearfoot when descending and due to a plantarflexion torque at transition, the pressure shifts to the forefoot. By utilizing the pressure map feature, we could see her left leg at her lowest point just prior to transition, she loads 58% into her rearfoot and 42% into her forefoot. At the same point on the right leg (surgical) she has 37% in rearfoot and 63% in forefoot. Throughout the loading phase, she never loads more than the 37% in her rearfoot. This pattern was true for multiple trials.

This particular patient is able to make excellent adjustments in alignment and muscle activation after instruction to the point her 2D analysis showed an excellent SL loading pattern in preparation for a jump. However, 2D analysis doesn’t show her loading strategy in her foot. If we continued to rehab without this knowledge, there is a good chance this would go uncorrected and would lead to poor loading anytime she would load this leg. As a soccer player, you need to think about rapid change of direction with forward/backward movement and with lateral movement in which you need to plant and load onto the surgical leg. This also applies to anytime she is jumping and landing which is typically off balance and forces use of one leg over the other. All of this would increase her overall risk of re-injury, which, as research would suggest, she is already at a higher rate of re-injury. Anything I can do as a physical therapist to reduce her risk of future injury is beneficial. BodiTrak provides me with a cost effective way to gather critical information as to how the foot interacts with the ground that your standard measuring devices are unable to provide.

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Works Cited

McElveen, M. T., Riemann, B. L., & Davies, G. J. (2010). Bilateral Comparison of Propulsion Mechanics During Single-Leg Vertical Jumping. Journal of Strength and Conditioning Research , 24 (2), 375-381.