Does Previous Knee Injury Impact Performance & What Can We Do About It? - Part III

In last week's discussion we discussed the Johnson et al study looking at the most common mechanism for injury in NFL players.  In this study, one of the results that came out was there was no association between injury mechanism and time of play.  This would indicate that fatigue does not play a role in athletes suffering a non-contact ACL injury or at least football players suffering a non-contact ACL injury.  This week, we are going to look into this discussion a little closer.

Currently this is a hot debate in the world of ACL injury prevention.  Studies are not clear one way or the other whether or not fatigue plays a role.  Santamaria et al in the Journal of Orthopedic and Sports Physical Therapy performed a systematic literature review which showed that the current body of literature was not clear on whether or not fatigue impacted biomechanics or injury rates.  One of the problems that the authors cited is there is no consistency in what researchers use for a fatigue protocol.  Some use the traditional treadmill test we use in VO2max testing, others use a percentage of max leg press while others use a timed run test.  The literature really is all over the place, so how do we truly know how mechanics are impacted if we are not even sure if we are bringing subjects into a truly fatigued state?

We know from Brazen et al work in the Clinical Journal of Sports Medicine 2010 that fatigue does impact movement during single leg landing.  In this study, the authors fatigued subjects and varified this using a percentage of maxEMG.  Once the subjects EMG level fell below a certain percentage the athlete was considered to be fatigued.  The athlete's biomechanics were measured pre/post fatigue in single leg drops.  What their results showed was that as an athlete's fatigue increased, there was an increase in frontal plane motion of the knee and higher peak vertical ground reaction forces.  Both of these factors are associated with increase in risk for lower kinetic chain injuries.

But this protocol is not being utilized across all studies and there is a plethora of other studies out there that are not showing fatigue plays a role.  So, one of the most logical things would be is to standardize the way we assess fatigue in studies.  The fatigue protocol we use in our setting is the FAST-FP (functional agility short term fatigue protocol).  Reason we use this particular protocol is the result of the Cortes et al study in the Journal of Sports Science in 2012.  In this study, the authors compared two protocols to see which had a larger impact on the lower kinetic chain biomechanics.  Specifically, which one resulted in altering mechanics as to indicate or reveal movement patterns which put our athletes at risk for injury.  This protocol is fairly simple and only takes 4 minutes.  During this, the athlete performs:

• 20 second step up/step down to a 31 cm step at 220 btm
• L drill with cones place 5 yards apart
• Counter movement jumps - the athlete jumps 5 times up to a tape on the wall representing 80% max vertical height jump
• Agility ladder - the athlete performs high knees up and down the 5 yard agility ladder.  First and third time is forward, second and forth time it is lateral.  

This whole process takes about 4 minutes.  The following video demonstrates an athlete going through one round of the FAST-FP.

So, we obviously need to standardize the way we implement a fatigue protocol in the research.  Maybe once we do this we can then see if there is an impact on injury rates following fatigue.  That aside, if you look at the literature on when an injury occurs during a game or competition, the literature  again is not clear on if this does in fact play a role.

Take the following "real life" case into consideration.  A 17 year old female soccer player playing high level club soccer.  She is competing in a tournament on Saturday and Sunday.  On Saturday she is a starter and plays in 3 games with the last game being a hard fought battle that concludes at 10 PM at night.  By the time she gets back to the hotel and in bed it is almost midnight and she is back on the field for the first game starting at 7 AM.  First play of the first game she tears her ACL.

Now, according to the literature, if we took her case and how this is currently analyzed, she tore her ACL in the first play of the game and therefore fatigue did not play a role.  However, any of us who have been athletes and who have dealt with a situation like this can attest, you are very fatigued at this point.  You have played hard for three games the day before, did not get much rest and are now playing higher level teams in the play off portion of the tournament.  But, according to the literature, this is not a fatigued player.

My point being, does fatigue not play a role OR have we simply not figured out a way to accurately assess that in the literature.  For me, I believe the later.  Sometimes we don't need a paper to tell you if you smash your finger with a hammer it is going to hurt.  It makes sense that fatigue would play a role.  I know when I am tired I move less efficiently and that my performance is impacted.  Although that is only an N of 1, it still follows general exercise physiology and biomechanical principles.

Next week, we will close out this discussion by talking about what do we do about this.  We know what the mechanism is, that it plays a role on future performance and that fatigue plays a role, but what do we do with all that information.  Stay tuned to find out next week.  Please make sure to check out our new website at www.iceperform.com.

Dr. Nessler is a practicing physical therapist with over 20 years sports medicine clinical experience and a nationally recognized expert in the area of athletic movement assessment.  He is the founder | developer of the ViPerform AMI, the ACL Play It Safe Program, Run Safe Program and author of a college textbook on this subject.  Trent has performed >5000 athletic movement assessments in the US and abroad.  He serves as the National Director of Sports Medicine Innovation for Select Medical, is Vice Chairman of Medical Services for USA Obstacle Racing and movement consultant for numerous colleges and professional teams.  Trent is also a competitive athlete in Brazilian Jiu Jitsu.