Look Before you Jump – Key Vertical and Horizontal Jump Testing Metrics after ACL Reconstruction
Jump testing is frequently included throughout the process after ACL reconstruction (ACLR) to track the changes in physical competency throughout rehabilitation but also to inform return to play decision making. Jump height and jump distance are the most used outcomes with limb symmetry index thresholds normally set at 90% prior to discharge. However, recent research has highlighted the difference between vertical and horizontal jump performance after ACLR and the additional deficits highlighted by biomechanical analysis over performance variables alone. This piece by Enda King and Roula Kotsifaki will highlight the key differences between tests and key metrics to consider when jump testing after ACLR.
Horizontal Jump Overview
The single leg hop for distance is the most reported functional test in the literature after ACLR. However, a recent systematic review showed ongoing deficits in biomechanical measures despite high levels of symmetry in hop distance (1). In addition, horizontal hop distance symmetry commonly resolves before symmetry of vertical jump height does. This is achieved by athletes frequently using a “hip strategy” to maximise jump performance in the presence of ongoing deficits at the knee/quadriceps. The work contribution of the hip, knee, and ankle during the single hop for distance after ACLR has been described previously (2).
The knee work symmetry between limbs during the propulsion phase – that defines the hop distance- was only 69% despite achieving 97% hop distance symmetry. The reduced knee work was compensated for by greater hip work during the propulsion phase of the jump. Of even greater interest is that the knee work contributes less than 15% to the horizontal jump compared to the hip and ankle which is approximately 45% each.
How far you hop horizontally is determined almost 90% by the work done at the hip and ankle!! However, when it comes to the subsequent landing, knee work contributes over 65% to the landing strategy and therefore landing is much more demanding on any residual knee deficits than the propulsion phase but this information is lost when looking at hop distance alone.
As hop distance is easy to measure it is often retained in testing batteries despite “hiding” many biomechanical deficits. However, the single leg hop for distance is one of the best tests to challenge knee function during landing, highlighted by deficits in knee work with compensations at both hip and ankle. For that reason, it should be an important part of training and testing after a knee injury providing biomechanical analysis can be carried out.
The most commonly used vertical tests are countermovement jumps and drop jumps which express explosiveness and plyometric ability, respectively. In a clinical setting, jump height is a more sensitive metric than hop distance to evaluate an athlete’s status during rehabilitation and at the time to return to sport after ACLR. Vertical performance metrics like jump height and reactive strength index can better identify interlimb asymmetries than horizontal jumps. Athletes at the time of RTS presented 97% symmetry in hop distance but 83% and 77% symmetry in jump height during a single leg countermovement jump and a single leg drop jump, respectively (3).
These findings are explained in part by the different demands on knee function between horizontal and vertical jumps. In healthy individuals, the relative knee work contribution in the concentric phase was three times greater during the vertical hop than during the horizontal hop (4). The greater knee work contribution during vertical hops likely explains why performance deficits are more readily apparent than during horizontal hops in those with knee impairments.
While most horizontal jump tests reported after ACLR are single leg tasks, both double and single leg tests are commonly utilised in vertical tests providing additional information and different strategies to analyse. Whereas the hip and ankle commonly compensate for the knee in single leg tasks, the healthy limb assumes a greater amount of responsibility during double leg jumps as is evident in a range of ground reaction force variable derivatives.
Recent data indicated that elevated deficits were present for the eccentric, concentric and landing-phase impulse 9 months after surgery, and that those deficits were greater in bone–patellar tendon–bone than hamstring autografts (5). These deficits have been shown not to improve between 6 and 9 months despite improvements in quadriceps strength, highlighting the importance of specificity of training and testing to highlight and resolve deficits post ACLR (6).
Drop jumps place a greater demand on the ankle and less on the hip than countermovement or horizontal jumps but are still very demanding on the knee joint (2). Single leg drop jump height is frequently the last jump performance metric to recovery post ACLR with an asymmetry in 20-30% for jump height and reactive strength index at 9 months after surgery despite > 90% symmetry in single leg hop distance (7, 8)
Again, deficits in knee work are highly prevalent and greatly influence performance. Not only have ongoing biomechanical asymmetry been reported at 9 months post ACLR (7), but that those asymmetries are greater than in healthy athletes (8). In addition, both single and double leg drop jump performance and biomechanics have been shown to be diminished in athletes who go on to injure their contralateral previously healthy ACL after return to play highlighting the importance of including drop jump testing post ACLR (9).
In clinical practice, recovery of horizontal jump symmetry often precedes that of countermovement or drop jump symmetry due to the difference in demands on the knee/quadriceps between the propulsion phase of the tests. When it comes to both horizontal and vertical jump testing, biomechanical analysis will add additional information over jump performance alone and should be utilised when assessing rehabilitation status or making return to play decisions after ACLR.
In horizontal jumps, the landing phase is more demanding than the jump on knee function and should be the main focus of your assessment. In double leg vertical jumps, asymmetry in vertical ground reaction force derivatives highlight residual compensations and functional deficits that do not resolve over time unless specifically addressed during rehabilitation.
Drop jump testing shows persistent performance and biomechanical deficits at return to play and may highlight those at risk of additional ACL injury. With affordable force plate solutions increasingly available, a pair of uniaxial force platforms can give valuable information to track athletes’ progression during rehabilitation and evaluate jump performance and ground reaction forces at the time to RTS. While whole body biomechanical analysis will highlight joint specific deficits, ground reaction force variables and curves can be informative regarding jump strategy and residual deficits as highlighted in the videos below.
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- Kotsifaki A, Korakakis V, Whiteley R, et al. 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;54(3):139-53.
- Kotsifaki A, Whiteley R, Van Rossom S, et al. Single leg hop for distance symmetry masks lower limb biomechanics: time to discuss hop distance as decision criterion for return to sport after ACL reconstruction? Br J Sports Med 2022;56(5):249-56.
- Kotsifaki A, Van Rossom S, Whiteley R, et al. Single leg vertical jump performance identifies knee function deficits at return to sport after ACL reconstruction in male athletes. Br J Sports Med 2022
- Kotsifaki A, Korakakis V, Graham-Smith P, et al. Vertical and Horizontal Hop Performance: Contributions of the Hip, Knee, and Ankle. Sports health 2021;13(2):128-35.
- Miles JJ, King E, Falvey É C, et al. Patellar and hamstring autografts are associated with different jump task loading asymmetries after ACL reconstruction. Scandinavian journal of medicine & science in sports 2019;29(8):1212-22.
- Costley JAE, Miles JJ, King E, et al. Vertical jump impulse deficits persist from six to nine months after ACL reconstruction. Sports biomechanics 2021:1-19.
- King E, Richter C, Franklyn-Miller A, et al. Whole-body biomechanical differences between limbs exist 9 months after ACL reconstruction across jump/landing tasks. Scandinavian journal of medicine & science in sports 2018;28(12):2567-78.
- King E, Richter C, Franklyn-Miller A, et al. Back to normal symmetry? Biomechanical variables remain more asymmetrical than normal during jump and change-of-direction testing 9 months after anterior cruciate ligament reconstruction. The American journal of sports medicine 2019;47(5):1175-85.
- King E, Richter C, Daniels KA, et al. Can Biomechanical Testing After Anterior Cruciate Ligament Reconstruction Identify Athletes at Risk for Subsequent ACL Injury to the Contralateral Uninjured Limb? The American journal of sports medicine 2021;49(3):609-19.
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