BRINGING SCIENCE TO TREATMENT

Acute Hamstring Injury Rehab – Get eccentric!

Patrick Gillham explores the benefits of using eccentric strengthening in rehabilitation for a quicker return-to-play following acute hamstring injuries.

West Ham’s James Collins holds his hamstring, 2016. Action Images via Reuters / Andrew Boyers

Hamstring anatomy

Figure 1: Hamstring anatomy


Sporting activities involving high demands of sprinting or excessive stretching (kicking, sliding, split positions) have been found to influence the incidence of acute hamstring injuries. Hamstring injuries are diverse in nature consisting of differing injury types, location and size. This makes recommendations regarding rehabilitation and prognosis about healing time and return-to-play notoriously difficult. It has been suggested that returnto- play timescales vary between 28-51 days following acute hamstring injuries depending on the biomechanical cause, site, and grading of soft tissue injury1. However, this is a contentious issue, which this article will explore.

Following a return to sport, the risk of re-injury is high within the first 2 weeks2. The causes have been linked with initial hamstring weakness; fatigue; a lack of flexibility, and a strength imbalance between the hamstrings (eccentric) and the quadriceps (concentric)3. The highest contributory factor however, is believed to be an inadequate rehabilitation program, which coincides with a premature return to sport4. More evidence is now highlighting the benefit of primarily using eccentric strengthening exercises in hamstring rehabilitation performed at high loads at longer musculotendon lengths5 6.

Semitendinosus (ST) , Semimembranosus (SM), and Biceps femoris long and short heads (BFLH and BFSH) make up the hamstring muscle group (see figure 1). They are involved with extension of the hip, flexion of the knee as well as providing multi-directional stability of the tibia and pelvis. All three muscles cross the posterior aspect of both hip and the knee joints making them biarticular. As a result, they have to continuously respond to large mechanical forces created by upper limb, trunk and lower limb locomotion via concentric and eccentric contractions. These forces are greatly increased during sporting activity, which is a likely culprit for their high injury frequency.

In a study at the University of Melbourne, biomechanical analysts quantified the biomechanical load (ie musculotendon strain, velocity, force, power, and work) experienced by the hamstrings across a full stride cycle during over-ground sprinting, and compared the biomechanical load across each individual hamstring muscle7.

Firstly, the hamstrings undergo a stretch-shortening cycle during sprinting, with the lengthening phase occurring during the terminal swing and shortening phase commencing just before foot strike, and continuing throughout the stance (see figure 2). Secondly, the biomechanical load on the biarticular hamstring muscles was found to be greatest during the terminal swing.

BFLH had the largest peak musculotendon strain, ST displayed the greatest musculotendon lengthening velocity, and SM produced the highest musculotendon force as well as absorbing and generating the most musculotendon power. This has ties in with other similar research, which distinguishes peak musculotendon strain as a large contributor to eccentric muscle damage, ie hamstring injury, rather than peak muscle force8; hence the recommendation of eccentric strengthening for acute hamstring rehabilitation.


 

Biomechanics during sprinting

Figure 2: Biomechanics during sprinting


Table 2: British Athletics Medical Team classification
GradingSite (see Figure 1)
1
-Pain during or after activity
-ROM normal at 24hr
-Normal power and initiation
-Pain on contraction
a-Myofascial

Myofascial injury in the peripheral aspect of the muscle
2
-Pain during activity and restricts participation
-Limitation with ROM
-Pain on contraction
-Reduced power on testing
b-Musculo-tendinous

Injury within the muscle belly most commonly at musculotendon junction (MTJ)
3
-Extensive tear
-Sudden onset of pain
-Significantly reduced ROM
-Pain on walking
-Obvious weakness on testing
c-Intratendinous

An injury which extends into the tendon
4
-Complete tear of muscle or tendon
-Sudden onset of pain
-Significant limitation to activity
-Palpable gap on palpitation
-May be less pain than Gr3

Site of injury and grading classification

In a randomised controlled trial on professional Swedish footballers9, the primary injury was located in BFLH (69%). This contrasted with 21% of the players who sustained their primary injury within SM. It was common to sustain a secondary injury to ST as well as BFLH (80%) or SM (44%). A clear majority (94%) of the primary injuries were found to be of the sprinting-type and were located in the BFLH, whereas, SM was the most common (76%) location for the stretchingtype of injury. These findings were supported in another similar article10.

Typically (see Table 1), classification for acute soft tissue injury, including hamstrings, has relied on a grading system of I (mild), II (moderate), or III (severe)11 12 13. This classification is useful in terms of coherent descriptions between different medical team members during clinical diagnosis and prognosis following acute injury. It has also been utilised as a classification system for radiological methods, such as magnetic resonance (MR) imaging, or ultrasound (US), if required for complementary confirmation of diagnosis14.

The British Athletics Medical Team proposes a new injury classification system for improved diagnostic accuracy and prognostication based on MRI features (see table 2 and figure 3)15.

Determining accurate return-to-play timescales following an acute hamstring injury has proven difficult. Injuries involving an intramuscular tendon or aponeurosis with adjacent muscle fibres (BF during high-speed running) typically require a shorter recovery period than those involving a proximal free tendon and/or MTJ (SM during dance or kicking)16.

There are also links between MRI findings as well as the area of injury, and return-to-play. More specifically, it has been hypothesised that the shorter the distance between the proximal pole of the injury and the ischial tuberosity (ie more intratendinous in nature) found on MRI findings (determined by the presence of oedema), the longer the time to return17. Likewise, the length of oedema shows a similar effect on recovery time – ie the longer the length, the longer the recovery18. In addition, the position of peak pain upon palpation following acute injury is also linked with increased recovery periods19.

Furthermore, there have been attempts to clarify the link between grading of acute hamstring injury and return-to-play. In a prospective cohort study on 207 professional footballers with acute hamstring injuries, 57% were grade I, 27% were grade II, and 3% were grade III. Grade I injuries returned to play within an average of 17 days. Grade II was 22 days, and grade III was 73 days. Eighty four percent of these injuries affected the BF, 11% SM, and 5% ST, but there was no significant difference in lay-off time for injuries to the three different muscles20. This has been compared to 5-23 days with grade I-II injuries, and 28-51 days for grade I-III in other studies respectively21 22.

Table 1: Typical classification
GradingClinical Findings
I (Mild)-Small quantity of muscle fibres involved
-Minor swelling Discomfort
-No or only minimal loss of strength
-No or only minimal restriction of movement
II (Moderate)-Tear of significant number of muscle fibres
-Pain and swelling
-Pain reproduced on muscle contraction
-Reduced power
-Movement limited by pain
III (Severe-Tear occurs across entire cross-section of the muscle/tendon
-Commonly a tendinous avulsion
-Often requires surgical opinion

Letter classification dependent on anatomical site of muscle injury

Figure 3: Letter classification dependent on anatomical site of muscle injury


Rehabilitation – eccentric strengthening

Several researchers have argued the benefits of eccentric strengthening following an acute hamstring injury versus concentric when aiming to reduce timeframes for return-to-play23 24 25 26 27 28. The crux of this argument is that with the majority of acute hamstring injuries occurring during eccentric loading (terminal swing or stretching), the rehabilitation ‘should mirror the particular situation that lead to the injury’29. This quotation was taken from a study, which showed a significant difference between an eccentric and concentric rehabilitation programme following acute hamstring injuries in elite and non-elite footballers.

This study was a randomised controlled clinical trial on 75 footballers in Sweden, which reported that using eccentric strengthening versus concentric the time to return-to-play was reduced by 23 days. This was irrespective of the type of injury or the site of injury. The outcome measure was the number of days to return to full– team training and availability for match selection. This article will now explore this study in greater depth.

Two rehabilitation protocols were used, and initiation began five days following injury. All players had sustained a sprinting-type (high speed running/ acceleration) or stretching-type injury (high kicking, split positions, glide tackling). Exclusion criteria included previous hamstring injuries, trauma to posterior thigh, ongoing history of low back problems, and pregnancy.

All players underwent an MRI investigation 5 days following the injury, to expose the severity and site of injury. A player was judged to be fit enough to return to full-team training using the active ‘Askling H-test’ (see figure 4). A positive test is when a player experiences any insecurity or apprehension when performing the test. The test should be completed without full dorsiflexion of the ankle.


The Askling H-test

The Askling H-test

Figure 4: The Askling H-test


Seventy two percent of players sustained sprinting-type injuries, whilst 28% were stretching-type. Of these, 69% sustained injury to BFLH, whereas 21% was located in the SM. Injuries to ST were only sustained as secondary injuries (48% with BFLH, and 44% with SM). Ninety four percent of sprinting-type injuries were located in the BFLH, while SM was the most common (76%) location for the stretching-type injury.

The two rehabilitation protocols used were labelled L-protocol and the C-protocol. One aimed at loading hamstrings during lengthening (L-protocol), and the other consisted of exercises with no emphasis on lengthening (C) (see boxes 1 and 2). Each consisted of three exercises which could be performed anywhere and were not dependent of advanced equipment. They also aimed at targeting flexibility, trunk/pelvic stability as well as specific strength training to the hamstrings. All were performed in the sagittal plane with speed and load progressed throughout.


Box 1: C-Protocol

-Standing contract/relax hamstring stretch – twice every day, 3 sets x 4 repetitions.

-Standing cable/resistance band hip extension with injured limb – once every day, 3 sets x 6 repetitions.

-Supine single-leg pelvic lift using body weight on injured limb – Once every 3rd day, 3 sets with x8 repetitions.


Box 2: L-Protocol

-‘The Extender’ on injured limb (slow knee extensions to the point just before pain) – Twice daily, 3 sets x 12 repetitions.

-‘The Diver’ standing on injured limb (performed slowly with simultaneous upper and lower limb movement) – Once every other day, 3 sets x 6 repetitions.

-‘The Glider’ with injured leg in front using friction sock/ sliding matt for sliding leg (movement back to standing is completed using the arms. Progression with distance of slide and speed performed) – Once every 3rd day, 3 sets x 4 repetitions.


Findings

The time to return was significantly shorter in the L-protocol compared with the C-protocol, averaging 28 days and 51 days respectively. Time to return was also significantly shorter in the L-protocol than in the C-protocol for injuries of both sprinting-type and stretching-type, as well as for injuries of different injury classification. There are questions, however, over whether the C-protocol is specific enough for hamstring activation to create a legitimate comparison.

Summary and clinical implications

Acute hamstring injuries most commonly occur during sprinting (terminal swing) or stretching (kicking, sliding, lunging/split positions). BFLH is involved more often in sprinting-type injuries as a result of terminal swing. This is possibly due to its absorption of the largest peak musculotendon strain across all four hamstring muscles. Injuries can be classified from Grade I-III or perhaps more specifically Grade 1-4 for severity and a-c depending on site of injury. This based on MRI findings. The closer the site of injury is to the proximal hamstring tendon, the longer the return-to-play period. Using eccentric strengthening exercises in rehabilitation programmes will promote a faster return-to-play. For example, ‘The Extender’, ‘The Diver’, or ‘The Slider’. To enable a thorough rehabilitation process, clinicians need to take into account the initial hamstring weakness, any lack of flexibility, previous hamstring injuries, age, fatigue, and strength imbalances between hamstring (eccentric) and quadriceps (concentric) contraction.

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