Using a total score of athleticism to guide return to sport post ACL injury

What is the current issue with return to sport testing post ACL?

Different multidimensional aspects are involved with return to sport (RTS): psychological readiness, strength level, change of direction ability, plyometric capacity, pressure from the coach / club, etc. Currently, there is no consensus on when an athlete is ready to RTS, nor on the optimal testing procedure to determine sport readiness.

Historically, discharge criteria for RTS following primary ACL reconstruction were based solely on time – after 6-9 months, you are good to go. Then strength criteria were introduced, and only lately have physical performance based criteria entered the discussion.

Current practice ^[6] involves a battery of strength and hop tests, with a limb symmetry index of 90% recommended as the pass-or-fail cut off point. However, this does not consider potential performance decrements of the uninvolved limb following injury and surgery, thus limiting the utility of this approach.

A low proportion of patients (23%) satisfy this RTS criterion, i.e., LSI ≥ 90%, but still return to play ^[7]. Perhaps more controversially, only 24% of uninjured athletes “pass” these symmetry tests  ^[4]. This may be due to the reduction in pass probability when adding multiple tests across a number of domains into a battery, thereby limiting the utility of this approach for augmenting RTS decision making.

What is a total score of athleticism, and has it been used before?

Imagine you are collecting data from several tests that seem to be fundamental to RTS following ACL reconstruction. In addition to each specific score, you are interested in reporting a global final score that could represent each athlete’s overall physical level in relation to the other members of the team. Rather than separately analysing each individual test result using pre-determined symmetry thresholds, you can create and calculate a composite score encompassing different performance characteristics for each player.

Different sports and performance settings already use standardized scores from a series of tests to create a single Total Score of Athleticism (TSA) for each player ^[5].

By averaging standardized scores (e.g., z-scores) and applying the TSA instead of just inter-limb symmetry in different tests, clinicians and coaches can examine contextualized data of individual athletes relative to their teammates. With that data, they can set benchmarks for return to sport readiness that realistically reflect the demands the athletes will face.

The use of z-scores allows clinicians to compare data across similar athletes who share the same training approach, demands, and constraints. Therefore, test scores are assumed achievable by all athletes, and thus represent realistic targets and thresholds they can work towards.

In order to define these benchmarks, injured athletes must be measured alongside their “healthy” teammates (matched controls). The benchmarks can then potentially highlight injured athletes who still display performance decrements and are not ready to RTS.

What tests would you recommend including within the TSA?

Tests must be based on research, the experience of the clinicians, and the available equipment and technology. We included strength and jump tests that are routinely used to assess an athlete’s level of physical capacity following ACL reconstruction, and that help determine readiness to RTS ^[3]. These were obtained from isokinetic strength assessment (knee extension and flexion, relative peak torque of both limbs), and from bilateral (CMJ) and single leg countermovement jump tests for jump height, relative peak power and reactive strength modified (RSImod).

We also recommend adding the single leg drop jump (SLDJ) test to better assess an athlete’s ability to efficiently store and return elastic energy.

How does the TSA score differ between those who had suffered ACL versus those who hadn’t?

The TSA was substantially lower (large effect size) than healthy controls at the time of RTS. Lower scores in strength, power and reactive strength track with reduced performance in more complex athletic skills critical to both sport and the RTS process, such as pivoting, cutting, landing, and jumping ^[1,2].

The TSA allowed us to identify which players had an ACL reconstruction and which were healthy. Simply, this means that the higher the TSA, the more likely the player has the overall profile of a healthy player.

Indeed, the odds of shifting towards a “healthy” player’s profile increase with TSA improvements (Figure 1). For every 0.5 increase in TSA, the odds of belonging to the ACL reconstructed group decrease by 49%. A change of 1 unit decreases the odds of being in the ACL group by 74%.

To understand which specific component of the total score needs specific attention, each physical characteristic can be broken down and further analysed by using z-scores and respective threshold values. Pragmatically, bars below zero represent opportunities for improvement during rehabilitation and before RTS to achieve important, safe, and specific physical quality thresholds, and to increase the TSA overall. This information can help identify one or more components to target to increase the TSA during specific rehabilitation and training cycles.

What impact does a lower TSA have on the risk of re-injury?

Among the seven ACLR players who sustained a further injury within four months of RTS, only one displayed a relatively high TSA. The other players were either in the low (4 of 7) or medium (2 of 7) TSA tertiles.

This suggests higher composite scores encompassing strength and power capacities may protect the athlete from further articular cartilage, meniscal and soft tissue injuries at the time of RTS. This also reinforces the notion that muscular strength and heightened plyometric ability are beneficial for preserving knee joint health. In particular, it is highly important that athletes fully restore their force attenuation capacity during fast sporting actions such as jumping, landing, and change of direction.

How could a TSA be developed to get a more rounded picture of an athletes readiness to RTS post ACL?

The TSA can and should encompass a broad range of aspects that practitioners first evaluate and weighting for their relevant to RTS. Possibilities include hip and ankle strength, aerobic capacity, psychological readiness and agility. Our data came only from adult male professional football players.  Practitioners should also consider how the same effects of the same variable may differ across cohorts, e.g., pediatric, adolescent, or female athletes.

To get a more rounded picture of an athlete’s readiness to RTS, include measures of bilateral and unilateral multijoint strength, such as back and front squat 3RM, and rear foot elevated split squat 3RM. I also integrate measures of single joint strength capacity through full ROM, like leg extension 5RM; hamstring capacity at inner, mid and outer range; hip dominant hamstring exercises (Romanian deadlift); and calf and abductor strength.

In addition to the CMJ, SLCMJ and SLDJ tests, I also assess single leg squat jump to isolate the concentric impulse; and the single leg tuck jump to further test the ability to attenuate and recycle higher forces. In this context, these tests reveal performance outputs and give an overall score of an athlete’s level of physical performance.

These tests can also illuminate the strategies athletes use to achieve their output. Examining force production, looking at the force-time characteristic vs. the RSI score, investigating any peak in the early phase of ground contact during the SLDJ, and examining the relationship between the hip and the ankle can all tell us how and why the athlete is doing what they are doing

These questions and analyses are excessively sophisticated if the athlete has not recovered their fundamental physical capacities. But they clearly have an impact on rehabilitation programming and RTS decision making. Assessments should still include deceleration, acceleration, change of direction and sprinting ability through drills and tests that can reveal both performance scores and movement strategies.