Brunico, Italy
Friday 29th August 2014

During pre-season, one of the big debates between clinicians operating in different sports, is what tests should be included in their physical & physiological screening protocols.

I remember several years ago, whilst working in the English Premier League, that our team’s testing battery took seven staff members three days to execute.  

The process could certainly have been considered very thorough, however, looking back I would argue how relevant some of the tests were to football players in general, never mind relative to specific positions of play.  In addition, I do not recall much of that data ever being referred to again or the tests being repeated throughout the course of the year.

In stark contrast to my experiences in professional football (or soccer for my North American friends), my experience of working a pre-season training camp for an NFL team five years later, was that physical screening was conspicuous by its absence.  

I spent most of my time in the training room, so never noticed whether the conditioning coaches were conducting their own profiling process, however, given that there were only two of them for what started off as a camp for 83 athletes, I am guessing they didn’t have the time to dedicate to such activities.

Nowadays, my approach to testing is to only test what: 

  1. is relevant; 
  2. is specific to the athlete’s training or matchplay demands; 
  3. will be useful to refer back to when compiling injury prevention programmes, rehabilitation programmes or return to play criteria
  4. can be retested at various points throughout the year to establish progress or review risk of injury

Screening is an uninspiring activity in my opinion, a necessary but rather mundane aspect of the job & those of you working in professional sport will vouch for me when I say that the players don’t look forward to it either.  

As a result, you don’t want to be the clinician or coach that can’t succinctly explain why each test in the battery has been included & what the benefit of the test is going to bestow upon the player at a later date.

To this extent, I now ensure that each test employed is supported by research, demonstrating its validity, reliability & relevance, with a brief “reason for inclusion” description written next to each exercise that is detailed on the testing sheets given out to players & staff.

The focus for each screening programme will vary according to the sport you intend to use it in. 

There’s no point in including a thorough shoulder screen when profiling a population of out-field football (soccer) players, whereas this will be a critical aspect during the profiling of a tennis player, basketball player, or football (soccer) goalkeeper.

The data I was responsible for collecting during my time with the Football Association illustrated the fact that posterior thigh injuries were the most prevalent of all in professional soccer in England, a finding mirrored in studies of injury epidemiology in Australian Rules Football & rugby.

As such, hamstring testing takes on a major significance in football (both codes), rugby & Australian rules protocols & has to consider the explosive nature of the games, the kicking component of the skill sets involved & the requirement to quickly accelerate, decelerate & change direction.  

Given that isokinetic testing of the hamstring is often conducted in a seated position, which doesn’t reflect a functionally relevant position for a kicking or running action & as such is not well supported as a predictor for hamstring injury, I do not include these tests in routine profiling (Chumanov et al, 2012).

Chumanov, E.S. et al (2012).  Hamstrings are most susceptible to injury during the late swing phase of sprinting.  Br J Sports Med; 46(2): pp90  

Instead, I prefer to evaluate the eccentric hamstring strength & the ratio of isometric:eccentric strength, which can be tested using a hand-held dynamometer whilst lying prone with more pertinent relative positions of the trunk/hip/knee/ankle.

Goossens et al (2014) reported that in a population of 81 freshmen physical education teaching students, lower maximum eccentric hamstring strength & a higher isometric:eccentric hamstring strength ratio were significant risk factors for hamstring injury over the course of an academic year.

Goossens, L. et al (2014).  Lower eccentric hamstring strength & single leg hop for distance predict hamstring injury in PETE students.  Eur J Sports Sci; 5: p1-7

Considering the studies that have reported significant findings of hamstring injuries in relation to eccentric hamstring strength (Fousekis et al, 2011; Opar et al, 2012; Opar et al, 2013; Opar et al, 2014), this finding is not a major surprise.

Fousekis, K. et al (2011).  Intrinsic risk factors of non-contact quadriceps & hamstring strains in soccer: A prospective study of 100 professional players.  Br J Sports Med; 45: pp709-714   

Opar, D.A. et al (2012).  Hamstring strain injuries.  Factors that lead to injury & re-injury.  Sports Med; 42: pp209-226

Opar, D.A. et al (2013).  Knee flexor strength & biceps femoris electromyographical activity is lower in previously strained hamstrings.  J Electromyography & Kinesiol; 23: pp696-703

Opar, D.A. et al (2014).  Eccentric hamstring strength & hamstring injury risk in Australian footballers.  Med Sci Sports Exerc; Published Ahead of Print

That said, not all studies that have looked for a relationship between eccentric hamstring strength & risk of hamstring injury have reached the same conclusion.  Engebretsen et al (2010) used the Nordic Hamstring Strength test & did not find any significant differences between injured & non-injured soccer players.  

Neither did Bennel et al (1998) find any significant difference when comparing the isokinetic eccentric hamstring strength in injured & non-injured Australian Rules Players.  I have, however, already mentioned my concerns with the relevance of testing players in a high-seated position, as opposed to a position with a more relevant relationship between the angles of the trunk/hip/knee/ankle.

Engebretsen, A.H. et al (2010).  Intrinsic risk factors for hamstring injuries among male Soccer players:  A prospective cohort study.  Am J Sports Med; 38: pp1147-1153 

Bennel, K. et al (1998).  Isokinetic strength testing does not predict hamstring injury in Australian rules footballers.  Br J Sports Med; 32: pp309-314

Systematic reviews by Prior et al (2009) & Foreman et al (2006) investigating risk factors for hamstring injury reported further inconsistent findings relating to the predictive values of hamstring strength.  

Prior, M. et al (2009).  An evidence-based approach to hamstring strain injury: a systematic review of the literature.  Sports Health; 1: pp154-164

Foreman, T. (2006).  Prospective studies into the causation of hamstring injuries in sport: a systematic review.  Phys Ther Sport; 7: pp101-109

Goossens et al (2014) considered a functional test in addition to the prone strength tests & investigated the predictive values of a single leg hop for distance test.  Subjects performed three single leg jumps as far as possible, maintaining the landing position for three seconds in the same footprint.  The best score of the three was recorded.

Freckleton et al (2014) investigated whether reduced hamstring muscle strength, as assessed functionally with the single leg bridge, would increase risk of hamstring injury.  

Freckleton et al (2014).  The predictive validity of a single leg bridge test for hamstring injuries in Australian Rules Football Players.  Br J Sports Med; 48: pp713-717

The single leg bridge tests the hamstring in a functional capacity similar to terminal swing, with subjects holding approximately 20ş knee flexion.  Starting with their heel on a box, they push their bottom off the ground, up into a neutral hip position.  The movement is repeated until form is lost & the maximum repetition count is recorded.

Both studies reported significant deficits in players that then went on to sustain a hamstring muscle injury over the course of the test period, although it must be noted that Freckleton et al (2014) only observed significant results in those sustaining right-sided hamstring injuries. 

Given that this pre-season, the hand-held dynamometers that were ordered did not arrive in time, I included both of these functional tests in the screening programme for the basketball team.  Given the hop for distance test has high basketball task relevance, this contributed to my decision to incorporate it into the battery of OptoJump tests that we conducted.

The majority of true hamstring muscle injuries which involve high intensity running, occur at the musculotendinous junction of the biceps femoris long head (Koulouris & Connell, 2005; Crosier et al, 2004), during the late swing phase.

Koulouris, G. & Connell, D. (2005).  Hamstring Muscle Complex:  An Imaging Review 1.  Radiographics; 25(3): pp571-586

Crosier, J.L. et al (2004).  Factors associated with recurrent hamstring injuries.  Sports Med; 34(10): pp681-695 

The next most frequent hamstring muscle to sustain injury is the semimembranosus, which often reflects a movement into extreme joint range that stretches the entire complex.  To this end, the proximal tendon may also be compromised in this type of presentation (Yu et al, 2008; Askling et al, 2006).

Yu, B. et al (2008).  Hamstring muscle kinematics & activation during overground sprinting.  J Biomech; 41(15): pp3121-3126

Askling, C. et al (2006).  Type of acute hamstring strain affects flexibility, strength & time to return to pre-injury level.  Br J Sports Med; 40(1): pp40-44

Finally, given the long tendinous characteristics of the semitendinosus, this muscle is often compromised during high plyometric loads, where the stretch-shortening demands on the tendon lead to an overload.

Despite the variety of roles played by each of the components of the hamstring muscle group, I have not seen any papers that have attempted to bias the tests to expose one muscle over the other in an attempt to more accurately predict the injury risk.  

Subsequently, whilst the tests we conducted enabled us to quickly identify the candidates with marked hamstring strength deficits, we then had to conduct more in-depth assessments to differentiate between possible causes.  

As a result, we were then able to give each player a supplementary hamstring injury prevention programme specifically designed to address their individual pathology or weakness (McAllister et al, 2014).

McAllister, M.J. et al (2014).  Muscle activation during various hamstring exercises.  J Strength & Cond Res; 28(6): pp1573-1580  

A lack of a differential diagnosis increases the likelihood that every posterior thigh pain presentation will be treated the same, with no knowledge as to whether the symptoms are the result of a muscular, neural, fascial or joint related problem.  By definition, the chances are in that sort of an environment, most of the presentations will be treated sub-optimally.

Omar et al (2013) have demonstrated reliability of a novel device used to measure eccentric hamstring strength during a Nordic hamstring exercise.  Whilst this device is not currently widely available, I will be consulting with my colleagues in Australia to ascertain their opinions once they get to use one.

Omar, D.A. (2013).  A novel device using the Nordic hamstring exercise to assess eccentric knee flexor strength:  a reliability & retrospective injury study.  J Orthop Sports Phys Ther; 43(9): pp636-640  

As a clinician, it is important for me to weigh up the available evidence & reason why I should or should not include a test in my screening programme.  

My opinion is, that whilst hamstring injuries contribute such a great percentage to the presentation of soft tissue injuries in sports such as football (soccer/Australian Rules/American) & rugby, it is worth including tests that have been shown to highlight a potential cause, whilst auditing our own results alongside ongoing research, to establish the value of continuing to include them.

Furthermore, the subjective component of the screening programme must be constructed to compliment the objective testing.  For example, the risk factors most consistently demonstrated to predispose to hamstring muscle injury are age, previous hamstring injury & previous knee injury, all of which must be ascertained during the subjective interview.

All things considered, the ongoing screening & profiling of players must be carefully planned, taking the subtleties of the specific sport into consideration.  Planning should start during the season & testing should not just be limited to the first days of pre-season…the repeat dates should also be considered from the outset.  

The programme you employ should be reviewed on each occasion & as new evidence comes to light, it should evolve to refine the information you glean from it.

I would just like to thank my colleague, James (Butterfield) at Muangthong United, in Thailand for his help in sourcing some of the papers I have referred to in this blog…”Cheers JB”!

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