Hamstring Injuries
Over the past decade high intensity running and sprint distance have increased incrementally within professional football and with this so have hamstring strains injuries (HSI). HSI are the most common noncontact injury within team sports (Ekstrand et al., 2016). HSI account for 37% of all professional football muscle related injuries and can require extensive treatment and subsequently long rehabilitation periods (Ekstrand et al., 2011). Despite a focus on HSI prevention within the literature recurrence rates remain high, 30% recur within 12 months (Orchard, 2002), with incidence rates in professional football increasing annually by approximately 2.3% between 2001 and 2014 (Ekstrand et al., 2016). Of these HSI around 80% involve the biceps femoris long head (BFLH) (Bourne et al., 2015). In football the majority of HSI occur while players are sprinting and are thought to generally occur during the late swing phase, where the hamstring muscles generate tension while lengthening to decelerate knee extension during high speed running (Schache et al., 2009). During this part of the running gait cycle, the BFLH reaches its peak length and force while undergoing a powerful eccentric contraction to decelerate the lower limb for foot contact with the ground (Schache et al., 2009).
One of the main risk factors for HSI is previous hamstring injury (Engebretsen et al., 2010). However, research has also identified that professional football players with shorter BFLH fascicles, muscle length, were reported to have a 4.1 times greater risk of sustaining a HSI (Timmins et al., 2016). Research has highlighted that resistance training, particularly eccentric training, focusing on the hamstring musculature, can increase the fascicle length of these muscles (Bourne et al., 2017a). In contrary to this, research has found that concentric hamstring training can cause fascicle shortening, which should be considered when designing any HSI prevention programme, as shorter hamstring fascicles have been linked with an increased risk of HSI (Timmins et al., 2016). Another risk factor for HSI is low levels of eccentric knee flexor strength, whilst high levels of eccentric strength have been associated with decreased hamstring strain injury risk within professional football (Timmins et al., 2016). Increasing the eccentric strength of the hamstring muscles, can be conducted by lengthening the hamstring muscles whilst it is loaded and contracted (Petersen et al., 2011). Research has indicated that HSI prevention programmes should focus on increasing hamstring fascicle lengths, increasing eccentric knee flexor strength and specifically target the BFLH as this muscle is most commonly injured (Bourne et al., 2017a; Presland et al., 2018).
Nordic Hamstring Exercise?
The Nordic hamstring exercise (NHE) has proven effective in increasing eccentric knee flexor strength (Mjølsnes et al., 2004) and reducing HSI in professional football players (Petersen et al., 2011). The NHE is a partner exercise which can be performed easily on the pitch without any specialist equipment. The NHE exercise involves the player attempting to resist a forward falling motion from a kneeling position whilst the partner anchors the players by holding their feet, by contracting the posterior chain, hamstring and glute muscles, to maximise loading in the eccentric phase of the movement (Al Attar et al., 2017).
Hamstring Activation during Nordic Hamstring Exercise
A disagreement in the S&C community has been over hamstring muscle activation during the NHE and whether it effectively activates the biceps femoris, as the movement occurs predominately around the knee joint. The biceps femoris is made up of two parts, the long head and the short head, the long head originates from the ischial tuberosity of the pelvis. The short head originates from the linea aspera on posterior surface of the femur. Together, the heads form a tendon, which inserts into the head of the fibula. Therefore, due to the fact the biceps femoris is recruited during hip extension and knee flexion there is disagreement whether the NHE is an effective exercise for developing eccentric strength within the bicep femoris. As during the NHE the muscle lengthening occurs at the knee joint and not at the hip and knee joint simultaneously, like for example during a Romanian Deadlift. There is also disagreement within the literature as to which hamstring muscles are most active during the NHE (Bourne et al., 2016; Bourne et al., 2017b; Mendiguchia et al., 2013; Ditroilo et al., 2013). Bourne et al., (2016a) has previously reported that the NHE preferentially activates the semitendinosus hamstring muscle. However, Bourne et al., (2016b) observed high levels of BFLH activity during the NHE, which suggests it still provides a powerful stimulus for adaptation within this most commonly injured muscle (Verrall et al., 2003).
Exercise Prescription
The NHE has proven effective in reducing HSI in a number of large scale randomised controlled trials (Petersen et al., 2011; Van der Horst et al., 2015; Arnason et al., 2008). Despite these findings, compliance to evidence based protocols is poor with only 11% of surveyed UEFA teams claiming to implement these NHE protocols within their programmes (Bahr et al., 2015). One of the main reasons for this may be the fact that a vast amount of the literature on the NHE has been conducted on participants in recreational sport settings, with one competitive game per week, training twice a week with no structured strength training. Many research protocols focusing on the training prescription of the NHE as a means to prevent HSI has recommended high volume protocols (three sessions per week of ~30 repetitions of NHE) (Presland et al., 2018). In a professional football environment this amount of repetitions would not be feasible where athletes are typically involved in significant training intensities and volumes, have weekly matches and following their own strength training programmes (Presland et al., (2018). Despite this, recent novel research conducted by Presland et al., (2018) investigated the effects of high or low volume NHE training on BFLH architecture and eccentric strength. Presland et al., (2018) research found low volume NHE protocols to be just as effective as high volume protocols. Specifically, Presland et al., (2018) found after a standardised 2 week training period (48 repetitions a week), 4 weeks of high volume NHE training (64-100 repetitions a week) were no more effective than a low volume protocol (8 repetitions a week) for lengthening BFLH fascicles and increasing eccentric strength. The low volume group saw BFLH fascicle lengthening of 24% after six weeks and a further 5% after training with as little as 8 repetitions for 4 weeks. This is in contrast with 23% for the high volume group who performed up to 100 repetitions per week and experienced a further 6% increase in fascicle length over 4 weeks, despite additional volume during this period. Presland et al., (2018) concluded that both high and low volume NHE training produce similar BFLH fascicle lengthening and eccentric knee flexor strength adaptations following the different training protocols. Research by Alonso‐Fernandez et al., (2018) and Bourne et al., (2017a) supported Presland et al., (2018) findings concluding that 4-10 weeks of NHE training can stimulate increases of 1.9 to 2.2 cm in BFLH fascicle length and improvements of 7%- 27% in eccentric knee flexor strength.
Presland et al., (2018) Nordic hamstring exercise training protocols.
| High Volume Intervention | |||||
|
Week |
Frequency | Sets | Reps |
Total Reps |
|
|
1 |
2 | 4 | 6 |
48 |
Standardised Training Protocol |
|
2 |
2 | 4 | 6 |
48 |
|
|
3 |
2 | 4 | 8 |
64 |
Varied Volume Training Period |
|
4 |
2 | 4 | 10 |
80 |
|
|
5 |
2 | 5 | 10 |
100 |
|
|
6 |
2 | 5 | 10 |
100 |
|
|
Sum |
440 |
||||
| Low Volume Intervention | |||||
|
Week |
Frequency | Sets | Reps |
Total Reps |
|
|
1 |
2 | 4 | 6 |
48 |
Standardised Training Protocol |
|
2 |
2 | 4 | 6 |
48 |
|
|
3 |
1 | 2 | 4 |
8 |
Varied Volume Training Period |
|
4 |
1 | 2 | 4 |
8 |
|
|
5 |
1 | 2 | 4 |
8 |
|
|
6 |
1 | 2 | 4 |
8 |
|
|
Sum |
128 |
|
|||
Practical Applications
Presland et al., (2018) findings are very important for practitioners, as the addition/replacement of 8 NHE repetitions into a strength and conditioning programme without NHE is easily attainable and would result in minimal increases in overall training load. However, when integrating this protocol within a players strength and conditioning programme it is important to note that Presland et al., (2018) prescribes a ‘standardised training period’ in both the high volume and low volume interventions consisting of 48 total NHE repetitions a week, which must be completed prior to the varied volume training period (8 NHE per week). Therefore, it may be recommended that the ‘standardised training period’ is performed in the last two weeks of the off-season programme prior to the players returning for the new season (Johnson, 2018). This would allow the players sufficient time to recover between performing the higher volume NHE combined with their off-season programme as they will still have a reduced overall training load. When following Presland et al., (2018) NHE protocol it is important to note that at the end of the 6 week programme the NHE should not be stopped. After a detraining period of only two weeks BFLH fascicle length were found to decrease 15%-17%. Therefore, the NHE should be maintained throughout the season following a progressive loading periodisation.
Summary
To conclude there is a plethora of literature to support the use of the NHE within any strength and conditioning programme aimed at decreasing the risk of HSI. NHE should be maintained throughout the season as reversal of adaptation can occur in as little as 2 weeks. Once the NHE can be performed sufficiently by a player for the required sets and repetitions, additional external weight should be utilised in order to maintain progressive overload. Another benefit of the NHE is that no specialised equipment is needed to perform the movement, therefore, it makes the NHE very user friendly and easy to perform regularly and consistently. Finally, the NHE should not be the only strength exercise performed during a HSI prevention programme, instead it should form part of the core exercises utilised by the strength and conditioning coach.
Example: Strength Training Programme
| Exercise | Sets | Reps |
Rest |
|
1A. Back Squat |
3 | 5 |
2-3mins |
| 2A. Split Squat | 3 | 5 |
2-3mins |
|
3A. RDL |
3 |
5 |
2-3mins |
|
4A. Lateral Lunge |
3 |
5 |
2-3mins |
|
5A. Nordics |
2 | 4 |
2mins
|
| 5B. SL Slide Eccentric Outs | 2 |
6 |
Key: RDL = Romanian Deadlift, SL = Single Leg
Ian Jones MSc BSc (hons) ASCC
References
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Alonso‐Fernandez, D., Docampo‐Blanco, P., & Martinez‐Fernandez, J. (2018). Changes in muscle architecture of biceps femoris induced by eccentric strength training with nordic hamstring exercise. Scandinavian journal of medicine & science in sports, 28(1), 88-94.
Alt, T., Nodler, Y. T., Severin, J., Knicker, A. J., & Strüder, H. K. (2018). Velocity‐specific and time‐dependent adaptations following a standardized Nordic Hamstring Exercise training. Scandinavian journal of medicine & science in sports, 28(1), 65-76.
Arnason, A., Andersen, T. E., Holme, I., Engebretsen, L., & Bahr, R. (2008). Prevention of hamstring strains in elite soccer: an intervention study. Scandinavian journal of medicine & science in sports, 18(1), 40-48.
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