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Is your hopping distance <90% symmetrical? You might be 4x at risk of an ACL injury.


The Scenario: Recurring knee injury. Seems to happen at least once a year. I don’t get it – I’m in good shape, I’m aware of my form. I spend time warming-up before activity and foam roll and lacrosse ball smash every day. My glutes are good and strong and I’ve passed every balance test my physio throws at me. Why does this keep happening?


Before we talk about hop testing and hop training, we first need to talk about outcome measures.


Outcome measures are a way of determining your progress. Maybe it’s by seeing how much more you can move, or how much stronger your muscle is getting. Maybe it’s seeing if your balance time is longer or if the weight you can squat is more than it was 4 weeks ago. Outcome measures are a basic foundation of physiotherapy – without measuring progress how can we know with certainty that you’re getting any better? Without outcome measures, how can we know if what we’re doing is helping? The answer is – we can’t.


So we measure things.


But does performing well on a mobility, or strength, or balance or squatting test predict your ability to perform in your actual sport?


In some cases... not really.


John Breech of CBS sports wrote a short article published online in February 15, 2015 outlining how bad legendary QB Tom Brady’s performance was during the 2000 NFL combine – a week-long “interview” where NFL prospects have their physical and mental skills and abilities tested with the goal of impressing enough to be drafted. In the article John references Tom Brady’s now infamously slow 40-yard dash time of 5.28 seconds – good enough for the slowest among active NFL starting quarterbacks. To put it into perspective, the average 40-yard dash time for NFL QBs, according to Topher Doll of SB Nation is 4.93 seconds.1 Tom’s vertical jump also didn’t impress - demonstrating only 24.5 inches – when the average QB can demonstrate 31.33.2


Is a bad combine performance from an eventual elite professional athlete a one-off? Doesn’t seem so. In 2006 Frank Kuzmits and Arthur Adams from the University of Louisville, Kentucky sought to investigate the correlation between the NFLs combine results and success within the league.3


Here’s how they did it. A total of 306 player combine results were analyzed with each player encompassing 1 of 3 positions: quarterback (QB), wide receiver (WR) and running back (RB). Data from 10 different combine tests (10-, 20- and 40-yard dash times, bench press, vertical jump, broad jump, three-cone drill, 20- and 60-yard shuttle, and the Wonderlic Personnel Test) were used. Player success within the league was measured using a combination of draft order, salary earned, and games played, with each player position also having a unique measure of success: QBs (QB rating), WRs (average yards per reception) and RBs (average yards per carry) during the first 3 years of their career. They analyzed data over a 6 year span from 1999 to 2004 and then statistically correlated every combine variable to see if anything from the combine could predict success in the league.


Only 14 of the 230 correlations showed any significance. That is, only 14 variables had the odds of occurring more frequently vs random chance. Not a single WR combine variable correlated with any measure of success. Only 1 QB combine variable was correlated with success and that correlation actually went in the “wrong direction” (they found that a slower 40-yard dash time had some correlation with a QBs rating, however this only correlated for the QBs first year).


Due to the overwhelmingly low level of correlations present, the authors concluded that the combine “clearly lacks any meaningful degree of predictive [ability]”.


But all of this isn’t to highlight the shortcomings of the NFL combine – it’s to raise the question: are we measuring the right things? Does this happen in physiotherapy too? ie. Is what we’re measuring during your rehab help predict your chance of success? Or how about predicting the likelihood of you experiencing a recurring injury?


Let’s look at a study performed at the University of Wisconsin by Lace Luedke and her colleagues in 2015.4 Lace took 68 injury-free competitive highschool cross-country runners and measured their isometric hip abduction, knee flexion, and knee extension strength before the 2014 competitive season. Athletes were then followed over the season to identify any occurrences of knee or shin injuries. Although some relationships were found in the ability to predict knee injuries, using the strongest hip and knee strength values had zero ability to predict the likelihood of experiencing a shin injury.


Now what about hopping? How good is hopping ability at predicting a future injury?


Turns out… pretty good.

Sue Barber and her team from the Cincinnati Sports Medicine Research Department were one of the first to show that hop testing could be used as a screening procedure for return to sporting activities.5 In 1987 Barber and her team looked at hop testing in 2 groups of people. Group 1: 93 people with no history of lower extremity injuries and Group 2: 35 people with non-surgically treated ACL tears.


When it came to single leg hop testing (single leg hop for distance and single leg timed hop over 6m), 92.5% of the normal group had a symmetry value of 85% (that is, the performance of one leg was at least 85% in distance or time as compared to the other leg). This 85% cut-point was termed the limb symmetry index, or LSI. In the ACL tear group – only 50% of the group could achieve an LSI of 85%. Of these 50% that could achieve a normal performance, 100% of them complained of giving-way episodes during sporting -activities. Even more interesting, the ACL group had a 98% LSI in both a 6m shuttle-run with no pivoting, as well as a 6m shuttle-run with pivoting – another potential example of certain outcome measures having little predictive ability.


Barber and her team established in this study that those with an ACL injury, even if they could hop, were still likely experiencing giving-way episodes which could ultimately lead to a future injury. So the next question is – could a poor performance on hop testing actually predict the likelihood of an injury? In 2013, a research team from Pacific University in Hillsboro, Oregon looked to find out.6

Jason Brumitt and his team took 193 uninjured Division III athletes and had them perform a single leg hop for distance test before the start of their competitive season. Three hops were performed on each leg with the distance measured from the start line to the back of the landed heel. A successful hop required the athlete hold the landing position for 5 seconds. From the start until the end of their season, if an athlete experienced an injury, it was recorded. In this study they found that when females had a pre-season side-to-side single leg hop distance difference greater than 10%, they were 4 times more likely to experience a foot or ankle injury during that season.


So Brumitt and his team have now established that poor single leg hopping performance can be predictive of experiencing an injury. Now the final question remains – can training single leg hopping help prevent injury recurrence?


It turns out, absolutely.


In 2016 a research team out of the Aspetar Orthopaedic and Sports Medicine Hospital in Doha, Qatar looked at 158 professional athletes who had received an ACL reconstruction, participated in a rehab program that included hop training, and then successfully returned to professional competition.7


Three hop tests were analyzed – a single leg hop for test for distance, a single leg triple hop test for distance, and a single leg triple crossover hop for distance. Unlike the 85% LSI that Barber used in 1987, these authors required an LSI of at least 90% to merit a pass.


When this LSI was not achieved – they found that an athlete was 4.1 times more likely to re-rupture their ACL.


Now there are a lot of reasons for potentially why your hopping might not be the best: poor balance?8 Not enough ankle bending/dorsiflexion mobility?9,10 Not enough knee bending during a hop landing leading to increased shock transmission to the knee?11 It’s up to a trained physiotherapist and a solid thorough assessment to find out.


Recurring knee pain despite consistent self-maintenance? Has your hopping been analyzed or trained? Maybe it’s time it was.


References:


  1. Doll, T. (2013, February 12). Some clarification is in order: average speed by position. Retrieved from: https://www.milehighreport.com/2013/2/12/3969128/some-clarification-is-in-order-average-speed-by-position

  2. Willman, D. Retrieved from: http://nflsavant.com/combine.php

  3. Kuzmits FE and Adams AJ. “The NFL combine: does it predict performance in the National Football League?” Journal of Strength and Conditioning 2008,22(6);1721-1727.

  4. Luedke LE, Heiderscheit BC, Williams DSB, Rauh MJ. “Association of isometric strength of hip and knee muscles with injury risk in high school cross country runners.” The International Journal of Sports Physical Therapy 2015,10(6):868-876.

  5. Barber SD, Noyes FR, Mangine RE, McCloskey JW, Hartman W. “Quantitative assessment of functional limitations in normal and anterior cruciate ligament-deficient knees.” Clinical Orthopaedics and Related Research 1990,255;204-214.

  6. Brumitt J, Heiderscheit BC, Manske RC, Neimuth PE, Rauh MJ. “Lower extremity functional tests and risk of injury in division III collegiate athletes.” The International Journal of Sports Physical Therapy 2013,8(3);216-227.

  7. Kyritsis P, Bahr R, Landreau P, Miladi R, Witvrouw E. “Likelihood of ACL graft rupture: not meeting six clinical discharge criteria before return to sport is associated with a four times greater risk of rupture.” British Journal of Sports Medicine 2016,50(15);946-951.

  8. Plisky PJ, Rauh MJ, Kaminski TW, Underwood FB. “Star excursion balance test as a predictor of lower extremity injury in high school basketball players.” JOSPT 2006,36(12);911-919.

  9. Fong C-M, Blackburn JT, Norcross MF, McGrath M, Padua DA. “Ankle-dorsiflexion range of motion and landing biomechanics.” Journal of Athletic Training 2011,46(1);5-10.

  10. Backman LJ and Danielson P. “Low range of ankle dorsiflexion predisposes for patellar tendinopathy in junior elite basketball players. A 1-year prospective study.” American Journal of Sports Medicine 2011,39(12);2626-2633.

  11. Applequist BC. “Shock attenuation in landing” (2012). UNLV Theses, Dissertations, Professional Papers, and Capstones. 1705.

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