Monday, July 15, 2013

Predicting Hamstring Injuries in Collegiate and Professional Football Players

In the July issue of the American Journal of Sports Medicine, there was a great research study published called Isokinetic Concentric Quadriceps and Hamstring Strength Variables From NFL Scouting Combine Are Not Predictive of Hamstring Injury in First – Year Professional Football Players.  This study begins to address the question of whether or not the methodology we currently use in pre-participation physicals is truly assessing or providing us with the information we are seeking.  Questions like this have plagued those of us that work in the sports medicine realm for years.  How do you predict something that has never occurred?  Is the current methodology we use in pre-participation physicals truly predicative of athletic injury? 

Whether your sport is football, soccer, basketball or baseball, hamstring injuries are common place amongst all the sports.  There are many causative factors for these but we know that once one does occur, the likelihood of re-injury is high.  In football, since most of these occur during pre-season (78.9%) and over 70% occurring in the first month of practice, identifying those at risk is essential for player health, subsequent injuries and overall team performance.

Studies back in the late 90s and early 2000s suggested that a strength imbalance between the quadriceps and hamstrings is a predictive measure for risk of hamstring strains.  These studies suggest that a hamstring to quadriceps ratio [H/Q] of <.6 placed a player at higher risk for hamstring injury.  As such, it is an accepted standard of practice in the NFL combines, to obtain preseason Cybex isokinetic concentric strength tests for the quadriceps and hamstrings.  The purpose of this study was to do a retrospective analysis and see if this is a reliable and valid measure for hamstring injury risk. 

In this study, the authors worked with 32 NFL teams that identified players that were selected in the first 5 rounds of NFL draft who also had hamstring injuries during their first professional season.  Of these, 162 of those players with previous hamstring injuries also had Cybex data from their previous year’s combine.  They performed a retrospective analysis on the data in order to determine the sensitivity and specificity for the hamstring to quadriceps ratio, as determined by the Cybex isokinetic test, predicting hamstring injury. 

What the authors found was that the sensitivity and specificity for the hamstrings to quadriceps ratio predicting hamstring injury were .513 and .524.  From this the authors suggest there is no predictive relationship with H/Q ratios and risk for hamstring injury.  So, if this is a excepted standard of practice and it is not predictive, should we be looking at something else?  Most would say yes, but what?  That is the true question.  When looking at this test in particular, does it really test how the hamstrings function in a closed kinetic chain?  No.  Does it account for the co-contraction between the quadriceps and hamstrings that must occur during athletic activities?  No.  Does it test the mechanism of most hamstring injuries (eccentric in nature)?  No.  Based on the above, are we really surprised that this does not have a predictive value for hamstring injuries?  So how do we test?

Many believe that attempting to predict injury risk and prevent injuries should parallel tests sports performance.  The two are so closely correlated. Knowing the research behind movement assessment and it’s tie to injury prediction and prevention, would this give us a better “true and full” assessment of the athlete?  If those same mechanics that result in abnormal force attenuation along the kinetic chain were identified and improved, would this also result in improvement in force production?  Although the answer seems logical, it has yet to be proven in the research.

Albert Szent-Gyorgi, who won the Nobel Prize in 1937 for discovering vitamin C, once said “Discovery consists in seeing what everyone else has seen and thinking what no one else has thought.”

About the author:  Trent Nessler, PT, DPT, MPT.  Trent is a practicing physical therapist with 14 years in sports medicine and orthopedics.  He has a bachelors in exercise physiology, masters in physical therapy and doctorate in physical therapy with focus in biomechanics and motor learning.  He author of a textbook “Dynamic Movement Assessment™: Prevent Injury and Enhance Performance”, is associate editor of the International Journal of Athletic Therapy and Training, Member of the USA Cheer Safety Council and founder/developer of the Dynamic Movement Assessment™.


Zvijac J, Toriscelli T, Merrick S, Kiebzak G.  Isokinetic Concentric Quadriceps and Hamstring Strength Variables From NFL Scouting Combine Are Not Predictive of Hamstring Injury in First – Year Professional Football Players.  Am J Sports Med.  41:1511-1518. 2013.

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