The first CMJ never looks great following ACL reconstruction (patellar tendon graft autograft) and medial/lateral meniscus repair but mine is especially ugly! Luckily, I don’t get embarrassed easily.
Through this blog, I am hoping to provide a case study example of my first jump completed at 4 months post-operative, with a few metrics that I consider useful. By no means is this a comprehensive insight into the vast testing and profiling options that we can track and utilize to our advantage when rehabbing an injured patient, as other tests and metrics will be very important to monitor to round out the rehabilitation continuum.
The CMJ is a great task to examine as part of the return to sport/activity testing as it looks at the neuromuscular function of a patient and allows us to tailor specific interventions to address found limitations. Beyond return to sport testing, the CMJ has wide utility in the physical therapy setting for recreational athletes, runners, weightlifters, etc. to help find areas of improvement surrounding pain/injury. Horizontal jump testing on the turf with a tape measure just doesn’t cut it anymore, as vertical jump testing on force plates highlights deficiencies of the knees much better!
I’ll share my comparison report in an upcoming blog, but remember, the force tracings are just as important as the results!
Unweighting phase: The unweighting phase is highlighted in the yellow portion of this force-time curve. Following the weighting period, it is the start of CMJ where the patient or athlete starts to initiate the movement, and they are essentially freefalling. My CMJ force trace starts fairly evident on which side I’m favoring, with delayed and limited movement on my surgical side (left side).
Braking phase: The braking phase is highlighted in red. It is the eccentric phase of the CMJ, where the patient is actively controlling their force in the downward direction. The body must create a great deal of force to stop momentum against gravity, and this is a key area to focus on for an injured patient. A well-done CMJ would have a steep slope from the yellow to green sections, which would correlate with a high braking rate of force development (RFD). Mine is not steep and therefore, my braking RFD was low. It can be seen from my force trace that I rely more on my non-surgical side to produce my force against gravity and reduce my body's momentum.
One of my favorite metrics to look at is the L/R average braking force, as this will give insight into how symmetrical a patient is producing their force against gravity. My L/R average braking force was 21% in favor of my non-operative side. Ideally, with time and training, we start to see this drop well below 10% asymmetry. My force at minimum displacement (the amount of force at the very bottom of the braking phase, right before the transition to propulsion) was 30% lower than my pre-injury data, and my braking net impulse was 15% different. Check out our metric database here to learn more about these metrics: Hawkin Metric Database.
Propulsive Phase: This phase is highlighted in green. It involves the concentric portion of the CMJ, where the patient is pushing upward into the plates. Here, I have a bimodal peak (meaning a double peak), where my highest force is in the propulsive phase, not at the lowest point in my jump (the end of the braking phase), which has shown to likely be a more optimal profile. This would be expected 4 months post-op, as patients can be limited by pain and tolerance to movement, as well as limited neuromuscular activation.
Research shows significant differences in propulsive impulse for those with ACL reconstruction, as these patients will not effectively translate the energy from the braking phase to the propulsive phase. My L to R average (avg) propulsive force was 136% different compared to the baseline. My left average propulsive force was 715N and my R average propulsive force was 879N. Not a whole lot of pushing was coming from my L side.
Jump height: My jump height was 30% lower than the baseline.
Landing Phase: This is the phase highlighted after flight time. Once again, it was very easy to pick up which side I wanted to land on. Most patients and athletes will have a learned preference for the leg they land on. Landing with 902N at peak landing force on my L leg and 1672N on my R leg is not a preference. I knew I was going to have a large asymmetry here, but my body was fully in protection mode.
Strategy metrics: Most of the metrics I previously highlighted are outcomes and drivers. The strategy metrics I’ll highlight now are countermovement depth and time to takeoff. Interestingly, my countermovement depth was deeper than my baseline tests. I see a lot of patients who have more shallow depth during their first jump, typically due to pain or aversion to loading. My guess is that the strategy I took to develop more force was to try to sit lower into the movement, as my neuromuscular activation is limited. My time to takeoff (the time from the weighting phase to the flight phase) was also much slower, and therefore my mRSI (jump height divided by time to takeoff) decreased. Again, a neuromuscular limitation.
It’s important to consider that this is likely your patient’s first time jumping on the plates and possibly their first time completing a CMJ. Let your patients get comfortable with the plates and the jumps and utilize their findings to help guide your exercise selection.
I wish I had a reason for why my force trace wasn’t pretty given that I’ve jumped many times before.
References
1. Kotsifaki A, Korakakis V, Whiteley R, Van Rossom S, Jonkers I. Measuring only hop distance during single leg hop testing is insufficient to detect deficits in knee function after ACL reconstruction: a systematic review and meta-analysis. Br J Sports Med. 2020 Feb;54(3):139-153. doi: 10.1136/bjsports-2018-099918.
2. McHugh MP, Hickok M, Cohen JA, Virgile A, Connolly DAJ. Is there a biomechanically efficient vertical ground reaction force profile for countermovement jumps?.TranslSportsMed.2021;4:138–146. https://doi.org/10.1002/tsm2.200
3. Labban W, Manaseer T, Golberg E, Sommerfeldt M, Nathanail S, Dennett L, Westover L, Beaupre L. Jumping into recovery: A systematic review and meta-analysis of discriminatory and responsive force plate parameters in individuals following anterior cruciate ligament reconstruction during countermovement and drop jumps. J Exp Orthop. 2024 Apr 2;11(2): e12018. doi: 10.1002/jeo2.12018. PMID: 38572392; PMCID: PMC10986632.