Hamstring Injuries

How do hamstring injuries occur, what are their risk factors and how can we prevent them?

Hamstring strain injuries (HSI) are the most common type of injury in sports involving repeated bouts of sprinting, particularly soccer and Australian Rules football (5). Hamstring injuries also have a high recurrence rate and are therefore a continued topic of discussion within physiotherapy. Understanding why these injuries occur and how we can prevent them is a fascinating discussion which we will delve into below:

Mechanism:

Mechanisms of hamstring strain injury likely involve a combination of high muscle-tendon unit forces (active or passive), extensive muscle-tendon unit lengthening beyond moderate lengths, and high-velocity movements. (8)

Hamstring strains can be generalized into 2 broad categories, sprint and stretch mechanisms. Hamstring strains within running are the most common and typically result in injuries to the biceps femoris group, whilst stretching injuries typically result in injury to the semimembranosus. (2)

A stretch-type injury to the hamstrings is caused by extensive hip flexion with an extended knee. Hamstring injuries during sprinting are most likely to occur due to excessive muscle strain caused by eccentric contraction during the late swing phase of the running gait cycle. (6)

Risk factors:

Non-modifiable (7):

Older age
History of HSI (Athletes who have any history of HSI are 2.7 times more likely to sustain an HSI than those without, and they are ~5 times more likely if the previous HSI occurred in the same season)
ACL Injury (athletes with a history of ACL injury have a 70% increase in risk of HSI)
Calf Strain Injury (previous calf strain injury increases the risk by 50%.)

Modifiable:

Reduced hamstring fascicle length (3)
Reduced eccentric hamstring strength qualities and endurance were associated with an increased risk of HSI
Playing position impacted the risk of index HSI in football, American football and rugby.
Positions that can have larger running demands resulted in a greater risk of index HSI in football (midfielders, defenders and forwards vs goalkeepers) (7)
Lack of readiness to return to play post-injury (4)
Between leg strength imbalances

Hamstring Prevention and Rehabilitative Strategies:

Eccentric Hamstring Strengthening:

Progressive eccentric loading has been shown to increase hamstring strength and long head of the biceps femoris muscle fascicle length in relatively brief periods of rehabilitation after acute HSI. (8)
Progressions from eccentric exercises such as single-leg diver exercises to bilateral sliders and ultimately Nordic hamstring exercises are great ways to progressively expose the tissue to loading. (8)
Strengthening programs with Nordic exercises significantly increase hamstring strength, increase muscle thickness, and decrease imbalance ratios in female and male players. A significant reduction in injury incidence and severity in professional players has been observed in players performing routines incorporating progressive Nordic exercises. (4)
Exercise programs involving Nordic hamstring exercises are shown to reduce injury rates by up to 51% across multiple sports in different athletes. (10)

High-Speed Running:

Returning to high-speed running with gradual reloading is arguably one of the most important aspects of injury prevention and rehabilitation, given that it is fundamental to performance in many sports and a common mechanism for HSI. (8)
Running exposure is a modifiable risk factor for HSI. The risk of subsequent HSI is elevated in athletes exposed to greater high-speed running loads, especially with sudden increases. (7)
Graduated exposure may also be advantageous for resilience to injury mechanisms such as sprinting. (7)
A typical running program commences with a light jog when the individual can tolerate pain-free walking. Progressions are then made from a light jog all the way up to high-speed running. The timeframe in which this occurs is dependent on the significance of the hamstring injury, ranging from multiple days to multiple weeks. Below is a summation of the progressions we can utilise to progress an individual back to high-speed running.

(8)

Other aspects to incorporate in preventative and rehabilitative programs:

Balance training (1)
Core Stability training (1)
Progressive agility training (9)
Hip Extensor strengthening (8)
Hamstring Endurance training (7)

Conclusion:

Hamstring strains, although common, remain an area that plagues the sporting population. Like most injuries, hamstring strains are multifactorial and require a detailed individual approach. With that said by understanding the risk factors and mechanisms above we can get a clearer picture of how and why these injuries occur.

Hamstring programs incorporating eccentric loading and high-speed progressions have the best overall research in reducing hamstring injuries. With that said there is no one size fits all model and assessing the individual and addressing specific limitations that arise is an extremely important component that cannot be overlooked in achieving the best results possible.

References:

Biz, C., Nicoletti, P., Baldin, G., Bragazzi, N. L., Crimì, A., & Ruggieri, P. (2021). Hamstring Strain Injury (HSI) Prevention in Professional and Semi-Professional Football Teams: A Systematic Review and Meta-Analysis. International journal of environmental research and public health, 18(16), 8272.
Bourne, M. N., Duhig, S. J., Timmins, R. G., Williams, M. D., Opar, D. A., Al Najjar, A., Kerr, G. K., & Shield, A. J. (2017). Impact of the Nordic hamstring and hip extension exercises on hamstring architecture and morphology: implications for injury prevention. British Journal of Sports Medicine, 51(5), 469.
Bourne, M. N., Timmins, R. G., Opar, D. A., Pizzari, T., Ruddy, J. D., Sims, C., Williams, M. D., & Shield, A. J. (2018). An Evidence-Based Framework for Strengthening Exercises to Prevent Hamstring Injury. Sports Medicine, 48(2), 251.
Chavarro-Nieto, C., Beaven, M., Gill, N., & Hébert-Losier, K. (2023). Hamstrings injury incidence, risk factors, and prevention in Rugby Union players: a systematic review. The Physician and sports medicine, 51(1), 1–19.
Cuthbert, M., Ripley, N., McMahon, J. J., Evans, M., Haff, G. G., & Comfort, P. (2020). The Effect of Nordic Hamstring Exercise Intervention Volume on Eccentric Strength and Muscle Architecture Adaptations: A Systematic Review and Meta-analyses. Sports medicine (Auckland, N.Z.), 50(1), 83–99.
Danielsson, A., Horvath, A., Senorski, C., Alentorn-Geli, E., Garrett, W. E., Cugat, R., Samuelsson, K., & Hamrin Senorski, E. (2020). The mechanism of hamstring injuries – a systematic review. BMC musculoskeletal disorders, 21(1), 641.
Green, B., Bourne, M. N., van Dyk, N., & Pizzari, T. (2020). Recalibrating the risk of hamstring strain injury (HSI): A 2020 systematic review and meta-analysis of risk factors for index and recurrent hamstring strain injury in sport. British journal of sports medicine, 54(18), 1081–1088.
Hickey, J. T., Opar, D. A., Weiss, L. J., & Heiderscheit, B. C. (2022). Hamstring Strain Injury Rehabilitation. Journal of athletic training, 57(2), 125–135.
Rudisill, S. S., Kucharik, M. P., Varady, N. H., & Martin, S. D. (2021). Evidence-Based Management and Factors Associated With Return to Play After Acute Hamstring Injury in Athletes: A Systematic Review. Orthopaedic journal of sports medicine, 9(11), 23259671211053833.
van Dyk, N., Behan, F. P., & Whiteley, R. (2019). Including the Nordic hamstring exercise in injury prevention programmes halves the rate of hamstring injuries: a systematic review and meta-analysis of 8459 athletes. British journal of sports medicine, 53(21), 1362–1370.