Welcome to the 13th edition of the Learn.Physio Research Review!

Hello! and thanks for choosing to be part of the Learn.Physio Journal Club and staying up to date with my research summaries! I hope you find them clinically useful and practical.

To kick off Issue #13, I will dive into the recent hamstring paper on the sub-types of hamstring injuries that occur in high level sprinters. It is a fascinating paper that highlights that not all hamstring injuries are created equal, and not all hamstring strains are “3-4 weekers”. Some are quite significant and take much longer than 3-4 weeks to return to full training and sport.

The 2nd paper I summarise is the latest from Ebert and colleagues from Perth, Western Australia who looked at 8 different hop tests in ACLR patients who were at 9-12 months post-op and looking to return to sport. The results are eye-opening, and you would be surprised to read how few of these ACLR patients are passing the commonly used hop tests.

Once again, I really hope you enjoy this fortnights reviews, and learn something new to take to the clinic this week.


Hamstring injuries are very common in sports that require sprinting and acceleration such as football/soccer, all rugby codes and AFL. In track and field competitions, hamstring is the most prevalent injury in competition and has significant performance and financial implications for athletes and all key stakeholders.

To help identify and better understand the different types of hamstring injuries that may present to the clinician, the British Athletics Muscle Injury Classification (BAMIC) classification system was developed. It is an MRI based classification system with clearly defined, anatomically focused classes (or grades of injury) based on the site of injury; myofascial (class a), muscle-tendon junction (class b) or intra-tendon injury (class c) and a numerical grading system from 0-4 based on the extent of the injury. See table below:

It is a reliable classification system that is associated with return to play, with a retrospective review between 2010 – 2014 reporting an increased time to return to full training and reinjury rates in injuries that extended into the hamstring intramuscular tendon (class c) (Pollock et al 2016). This has also been shown in other studies by Comin et al 2013, Brukner et al 2016, Askling et al 2007, Cohen et al 2011, van der Made et al 2018 and Eggleston et al 2020.

Given that the individual hamstring muscles have different muscle architecture and function, targeted rehab based on the specific injury subtype seems sensible. With this in mind, and based on the BMAIC injury classification framework, Macdonald et al (2019) have published a clinically reasoned, hamstring rehab approach and the link to the article (and the authors email address) can be found
The aim of this paper was to report hamstring diagnoses and outcomes between 2015 and 2019 in elite British Athletics track and field athletes following the implementation of the BAMIC and its associated targeted rehab approach.


Athletes who were included in the elite Olympic World Class Programme (WCP) were included in this study if they reported an injury to the posterior thigh during or immediately after a training session or competition between December 2015 and November 2019. All injury episodes were recorded on the Smartabase electronic medical record (EMR).

Each injury was assessed, and athlete referred for MRI scan within 7 days and rehab prescribed by British Athletics medical team. Each MRI was assessed via 3.0T MRI scanner by the same specialist musculoskeletal radiologist with the injury being classified using the BMAIC code.
The rehab of each athlete was individualised to suit their specific injury classification and other contextual factors but aligned with these 6 core values as outlined in the table below:


In summary however, there were 3 slightly different approaches based on the injured tissue:
  1. Myofascial (class a): rehab functional and expedited return to training where running based activities were the focus.
  2. Muscle-tendon junction injuries (class b): characterised by progressive strengthening and running based activities guided by objective milestones.
  3. Intra-tendon injuries (class c): characterised by a more conservative approach initially where early lengthening contractions of the tendon are avoided for the first 2 weeks to respect slower tendon healing.
Outcome measures:
Time to return to full training (TRFT) was the primary outcome measure defined as completing unrestricted sprint efforts at full pace in spikes.
Exacerbation and recurrence rates were also recorded. Exacerbation of a hamstring injury was defined as “a repeat injury to the same hamstring muscle during rehab”. Recurrence was defined as “a repeat injury to the same hamstring muscle within 3 months of return to full training”.

70 hamstring strains in 46 athletes (24 females and 22 males, mean age 24.6yrs) were included in this study.

87% of injuries occurred in sprint/power athletes with the remaining 13% occurred in endurance athletes.

18 athletes sustained more than 1 independent hamstring injury during the study period (15 athletes had 2 injuries, 2 athletes had 3 injuries and 1 athlete had 4 injuries). Important to note; not all these injuries occurred at the same location within the muscle, and not all of these injuries were deemed as recurrences or exacerbations.

Injury location:
43% of all injuries occurred in the distal 1/3 of the hamstring, 31% proximal 1/3 and 26% in the central 1/3. An isolated injury to the Biceps Femoris Long Head was the most frequently occurring structural injury (70% of reported cases), followed by 19% to the semimembranous.

Injury occurrence:
71% of injuries occurred during training, 24% in competition and 4% during competition warm-up. Of interest, injuries that were sustained in competition took on average 28 days to return to full training compared with 17 days sustained during training. It should be noted that class c (intra-tendon) injuries occurred more frequently in competition than training.

In 54% of injuries, they occurred during >90% maximal velocity with 27% occurring during 50-90% maximal velocity. Interestingly, 8% occurred during jumping.
37% of athletes described the injury occurring during stance phase of the running cycle, 26% at terminal swing and 19% reported a gradual sub-acute onset of symptoms post training or competition.
Time to return to full training:
For the primary outcome measure, there was a highly significant difference in TRFT between class c injuries (intra-tendon) vs class a (myofascial) and class c (intra-tendon) vs class b (muscle-tendon junction) injuries. There was no significant difference between class a and class b injuries.



Only 2 repeat injuries were recorded during this 4-year study (one index 1a and one index 2b). This gives a re-injury rate of 2.9% in this elite group.
There were 2 key findings from this study of elite British track and field athletes.

Firstly, this paper clearly showed that implementing the targeted rehab approach based on the BMAIC injury classification, hamstring reinjuries and exacerbations were very low at nearly 3%. Even more impressive was that none of these 2 reinjuries occurred in the intra-tendon part of the hamstring unit which is often reported as a common site of reinjury. In general, hamstring reinjury rates usually range from 12-25% (Pollock et al 2016, Eggleston et al 2020 and van der Made et al 2018). Mendiguchia et al 2017 also had a low reinjury rate in their study on elite level football/soccer players, however their study was limited to grade 1 muscle injuries.

The second key finding was that TRFT was much significantly delayed in type c injuries (intra-tendon) with the median TRFT for 2c or 3c hamstring injuries were 35 days and 51.5 days respectively. This was in stark contrast to other types of injuries to myofascial tissue or the muscle-tendon junction (ranging from a median TRFT of 12-19 days).

What is more impressive is that none of the type 2c or 3c injuries recorded in this cohort had surgery or received PRP injection to their injured tendons to expediate the return to full training and competition process. This speaks volumes of the high-quality rehab plans developed by the medical team, physio team and high-performance team of British Athletics and the coordinated efforts between all of the key stakeholders including the athletes themselves and coaching staff. This is highlighted by the fact that during the studies original paper from 2010-2014 (when the targeted rehab approach was not performed), mean TRFT for 3c injuries was 84 days compared to the current study (when the targeted rehab approach was introduced from 2016) had a mean TRFT of 48 days.

This contrasts with what is becoming more commonplace, especially here in Australia with AFL footballers, who are more likely to have surgery to an injured hamstring intra-tendon to speed up the return to sport process. Given the return to sport timeframes that we’re seeing here in Australia in AFL footballers ranges from 7-12 weeks, this paper may give medical staff, physios and high-performance staff within these AFL organisations some serious food for thought.
This was a well conducted study that highlights 2 key points of hamstring injury and rehab. Firstly, the hamstring intramuscular tendon results in a significant time away from full training and competition activities. However, when managed with a targeted rehab approach, with a multi-disciplinary team who are all on the same page, it can result in a faster return to full training (than what is currently published), with low rates of reinjury and without the need for surgery or PRP injections.

The challenge is now for 99% of us who do not work in elite settings, who do not have readily available imaging facilities, to try and identify clinically the intra-tendon subtypes from the myofascial (class a) and muscle-tendon junction (class b) types of injuries. Given that over half of intra-tendon tears occurred in this population at >90% maximal speed running, there is 1 clue that might lead us to be suspicious that we have an intra-tendon tear on how hands. The other clue may be that the athlete reports a run of recurrences in a short window of time (3 months).
Nevertheless, we should always treat the person sitting in front of us, and not the scan, and guide rehab in a progressive manner. We should also aim to work closely with the athletes S&C coach and head coach to ensure a smooth transition from the early days following injury back to the training field. If you are looking to learn more about hamstring rehab, take Dr Peter Brukner and Dr Ryan Timmins Hamstring Masterclass here
If you're enjoying our research review, check out our newly released Hamstring Masterclass featuring Dr Peter Brukner and Dr Ryan Timmins
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Depending on which country live in and healthcare system you have, approximately 90% of patients who have an ACL injury will undergo ACL reconstruction (ACLR) (Paterno et al 2014). However, it is not perfect, with 2nd ACL injuries (inclusive of both ipsilateral graft and contralateral side) occurring in approximately 1 in 5 patients aged under 25yrs of age (Wiggins et al 2016), with this number increasing to approximately 1 in 3 patients aged under 20yrs of age (Webster & Feller 2016).

To identify those at increased risk of sustaining a 2nd ACL injury, functional hop tests are commonly employed with the distance of the hop on each leg being converted to a number called the limb symmetry index (LSI).

For distance or height tests, the equation is injured limb / uninjured limb x 100; and for timed hop tests the equation is uninjured limb x injured limb x 100 due to the anticipated faster time that the uninjured limb will complete the task.

The usual “cut-off score” that is used in the literature is 90% and in considered the standard of what healthy normal athletes can do, which is what we want our ACLR athletes eventually strive to do. However, it is unknown the 90% cut-off is to different hop tests, and it has also been questioned that the LSI score can over-estimate the patient’s ability to return to sport due to the de-conditioning that has been observed in the contralateral limb (Wellsandt et al 2017 and Patterson et al 2020).

Another criticism of the current “standard” hop tests is that they assess straight forward movement and may not be sufficient to detect residual and persistent side to side differences in more challenging sport specific tasks including vertical hopping/landing and medial/lateral hoping and landing.

It must be said that hop tests are only one component of the return to sport test battery following ACLR (quads and hamstring strength and psychological readiness also equally important), but it is important that we try to identify ideal hop tests to assess higher levels of function. Therefore, the purpose of this study was to investigate 8 different hop tests in ACLR patients to see if additional hop tests to the “standard hop tests” can identify any lingering functional impairments at a time (9-12 months post-op) when athletes are looking to return to sport following ACLR.


50 ACLR patients (34 males and 16 females) who all had primary hamstring autograft repairs were included in this cross-sectional study.  The mean age of the 50 patients was 28 years of age and on average 10 months post-op ACLR. Patients were included if they were:

  • 9-12 months post-op ACLR.
  • 16-50 years of age.
  • not experiencing any ongoing problems with either knee.
  • not experiencing any other musculoskeletal pain or dysfunction that would affect their ability to perform hop test battery.
  • had no recollection of prior significant injury or surgery to contralateral leg.
  • had returned, or planned on returning to level 1 sports (according to Noyes Sports Activity Rating Score).

Hop test battery

Patients performed a 5min warm-up on stationary bike and an additional 5-10mins of their own preferred stretching routine if they chose. Patients then completed 8 hop tests undertaken in a pre-determined, randomised order. After familiarisation, each hop test was performed on the uninjured limb first, alternating between the uninjured limb and ACLR limb until the valid number of tests were recorded (all hop tests required 3 valid hops on each leg, except for 6m timed hop test and timed speedy hop test which both required only 2 valid hop tests each leg). Rests between each hop test was standardised to minimise effects of fatigue (2mins rests between hop tests), but each individual hop within each hop test was conducted and performed at the patient’s discretion. Arm swing was permitted in all hop tests.

The 8 hop tests included were:

1) Single Leg Hop for Distance
2) 6m time Hop Test
3) Triple Hop for Distance
4) Triple crossover hop for distance
5) Single medial hop for distance
6) Single lateral hop for distance
7) Single leg counter-movement jump for height
NB: jump height was measured via an accelerometer fixed firmly around the waist via Velcro strap, immediately superior to the greater trochanter
8) Timed speedy hop test


For all 8 hop tests, the best score out of the valid trials on each leg was used for data analysis, with an LSI being calculated for each hop test.
The mean LSIs for the following hop tests were as follows:

  • single leg hop for distance 95%
  • 6m time hop test 95%
  • triple hop test 96%
  • triple crossover hop for distance 95%
There were no significant differences between each other. However, they collectively were all significantly greater than the other 4 hop tests:
  • medial hop for distance 87%
  • lateral hop for distance 87.5%
  • single leg counter movement jump 83%
  • timed speedy hop test 86.5%
  • Of importance was the result that the single leg countermovement jump LSI result was significantly lower than every other hop test.
Other notable results:
  • there were no significant differences between males and females for any of the 8 hop tests.
  • only 36% of the cohort passed the 90% LSI cut-off standard for the 4 commonly used hop tests in clinical practice (single leg hop for distance, 6m timed hop test, triple hop for distance and triple crossover hop test).
  • only 5 patients (10%) demonstrated at least 90% on all 8 hop tests.

There was a lot of findings to come away from this really interesting paper looking at hop test performances in ACLR athletes who were in that 9–12-month post-op window when they are typically looking to return to pre-injury levels of sport.

One of the most notable findings was that only 36% of the cohort were able to pass the commonly used hop tests by clinicians to determine if they are ready to do so. Two papers recently showed that returning to sport without passing a battery of clinical tests (including these hop tests) significantly increased the risk of 2nd ACL injuries and other knee injuries (Kyrtitis et al 2016 & Grindem et al 2016).

Despite only 36% of the cohort passing the 4 common hop tests, the results did show that, patients were much more likely to pass these tests, but much more likely to fail on the less commonly used tests (medial hop, lateral hop, single leg countermovement jump and timed speedy hop test).

Given that these less commonly used tests are more challenging and require different movement strategies compared to the straight-line hop tests, these results will hopefully allow researchers to explore in the future if there is a correlation between >90% LSI and <90% on these “new hop tests” and risk of 2nd ACL injuries.

Another key finding was the overall poor performance on the single leg countermovement jump test at a mean score of 83% LSI across the entire cohort; with only 9 people (18%) able to achieve a 90% LSI on this test. Given that most team sports require the athlete to leap vertically in the air and land on 1 or 2 legs, it appears from these results that vertical plyometric work during rehab is not being adequately performed. Once again, I think that this test needs to be incorporated into future research papers and looking at there is a correlation between performance on this test and risk of 2nd ACL injury.

The authors acknowledged some of their own limitations such as a taking care with generalising this data to patients outside of 16-50years of age, as well as patients who have had primary ACLR with other harvest tissue than hamstring grafts or have 2 or more ACLRs. They also understand that LSI outcome measure is far from perfect and can over-estimate one’s ability to return to sport. They also highlight that hop tests only provide one part of the discharge process and that isokinetic strength testing, psychological readiness assessment and/or biomechanical analysis can and should also form part of the comprehensive return to sport battery.

For me, personally I would have loved to see in the paper the actual distances and times the patients hopped to get an idea of their performance levels so that we can interpret ACLR performance data to healthy controls (where possible). And as much as I love the single leg countermovement jump test as a hop test, the challenge for us clinicians are to be able to reliably measure the single leg countermovement jump test in the clinic without the need for expensive technology.
In summary, this was a brilliant insight to the performance of ACLR patients on common, and not-so-common hop tests to help guide the decision about returning to sport in a group of ACLR athletes at a time when most are quite close to returning to sport.

The 4 common hop tests were easily passed with mean LSI scores of at least 95% on each of the 4 hop tests. The problem was that the more physically and mentally challenging “not-so-common” hop tests, were less likely to be passed with most patients not meeting the 90% cut-off score on each of the other 4 hop tests – with the single leg counter movement jump test being the least likely to pass (18% of patients passed).

The big question that hopefully we will get to answer one day is, do any of these “not-so-common” and more challenging hop tests predict the likelihood of 2nd ACL injury in the future? Only time will tell.

If you are looking to learn more about ACLR rehab and improve your post-op ACLR management, take our online ACLR course
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The below paper is full text reference for your own reading. References cited throughout this article can be found in the reference section of this paper

Research Review 1

Pollock N, Patel A, Chakraverty J, et al. Time to return to full training is delayed and recurrence rate is higher in intratendinous (’c’) acute hamstring injury in elite track and field athletes: clinical application of the British Athletics Muscle Injury Classification. Br J Sports Med 2016;50:305–10.

Comin J, Malliaras P, Baquie P, et al. Return to competitive play after hamstring injuries involving disruption of the central tendon. Am J Sports Med 2013;41:111–5.

Brukner P, Connell D. ’Serious thigh muscle strains’: beware the intramuscular tendon which plays an important role in difficult hamstring and quadriceps muscle strains. Br J Sports Med 2016;50:205–8.

Askling CM, Tengvar M, Saartok T, et al. Acute first-time hamstring strains during high-speed running: a longitudinal study including clinical and magnetic resonance imaging findings. Am J Sports Med 2007;35:197–206.

Cohen SB, Towers JD, Zoga A, et al. Hamstring injuries in professional football players: magnetic resonance imaging correlation with return to play. Sports Health 2011;3:423–30.

van der Made AD, Almusa E, Whiteley R, et al. Intramuscular tendon involvement on MRI has limited value for predicting time to return to play following acute hamstring injury. Br J Sports Med 2018;52:83–8.

Eggleston L, McMeniman M, Engstrom C. High-Grade intramuscular tendon disruption in acute hamstring injury and return to play in Australian football players. Scand J Med Sci Sports 2020;30:1073–82.

van der Made AD, Almusa E, Reurink G, et al. Intramuscular tendon injury is not associated with an increased hamstring reinjury rate within 12 months after return to play. Br J Sports Med 2018;52:1261–6.

Mendiguchia J, Martinez-Ruiz E, Edouard P, et al. A multifactorial, Criteria-based progressive algorithm for hamstring injury treatment. Med Sci Sports Exerc 2017;49:1482–92.

Research Review 2

Ebert JR, Du Preez L, Furzer B, Edwards P, Joss B. Which Hop Tests Can Best Identify Functional Limb Asymmetry in Patients 9-12 Months After Anterior Cruciate Ligament Reconstruction Employing a Hamstrings Tendon Autograft? Int J Sports Phys Ther. 2021 Apr 1;16(2):393-403. doi: 10.26603/001c.21140. PMID: 33842035; PMCID: PMC8016443.

Paterno MV, Rauh MJ, Schmitt LC, Ford KR, Hewett TE. Incidence of Second ACL Injuries 2 Years After Primary ACL Reconstruction and Return to Sport. Am J Sports Med. 2014 Jul;42(7):1567-73. doi: 10.1177/0363546514530088. Epub 2014 Apr 21. PMID: 24753238; PMCID: PMC4205204.

Wiggins AJ, Grandhi RK, Schneider DK, Stanfield D, Webster KE, Myer GD. Risk of Secondary Injury in Younger Athletes After Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-analysis. Am J Sports Med. 2016 Jul;44(7):1861-76. doi: 10.1177/0363546515621554. Epub 2016 Jan 15. PMID: 26772611; PMCID: PMC5501245.

Webster KE, Feller JA. Exploring the High Reinjury Rate in Younger Patients Undergoing Anterior Cruciate Ligament Reconstruction. Am J Sports Med. 2016 Nov;44(11):2827-2832. doi: 10.1177/0363546516651845. Epub 2016 Jul 7. PMID: 27390346.

Wellsandt E, Failla MJ, Snyder-Mackler L. Limb Symmetry Indexes Can Overestimate Knee Function After Anterior Cruciate Ligament Injury. J Orthop Sports Phys Ther. 2017 May;47(5):334-338. doi: 10.2519/jospt.2017.7285. Epub 2017 Mar 29. PMID: 28355978; PMCID: PMC5483854.

Patterson BE, Crossley KM, Perraton LG, Kumar AS, King MG, Heerey JJ, Barton CJ, Culvenor AG. Limb symmetry index on a functional test battery improves between one and five years after anterior cruciate ligament reconstruction, primarily due to worsening contralateral limb function. Phys Ther Sport. 2020 Jul;44:67-74. doi: 10.1016/j.ptsp.2020.04.031. Epub 2020 May 8. PMID: 32447259.

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. Br J Sports Med. 2016 Aug;50(15):946-51. doi: 10.1136/bjsports-2015-095908. Epub 2016 May 23. PMID: 27215935.

Grindem H, Snyder-Mackler L, Moksnes H, Engebretsen L, Risberg MA. Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study. Br J Sports Med. 2016 Jul;50(13):804-8. doi: 10.1136/bjsports-2016-096031. Epub 2016 May 9. PMID: 27162233; PMCID: PMC4912389.


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