ReviewThe role of neuromuscular inhibition in hamstring strain injury recurrence
Introduction
Hamstring strains are amongst the most common and problematic injuries in a wide range of sports that involve high speed running. They are the primary injury in Australian football (Gabbe et al., 2002, Orchard and Seward, 2002, Orchard and Seward, 2009, Orchard and Seward, 2010, Seward et al., 1993), soccer (Ekstrand and Gillquist, 1983, Ekstrand et al., 2010, Hawkins et al., 2001, Woods et al., 2002, Woods et al., 2004) and the sprint events in track & field (Drezner et al., 2005, Sugiura et al., 2008, Yeung et al., 2009), while also accounting for a high proportion of lost playing time in cricket (Orchard and James, 2003, Orchard et al., 2002, Stretch, 2003), rugby union (Brooks et al., 2005a, Brooks et al., 2005b, Brooks et al., 2005c, Brooks et al., 2006), Gaelic football (Newell et al., 2006, O’Sullivan et al., 2008), American football (Elliott et al., 2011, Feeley et al., 2008, Meeuwisse et al., 2000) and hurling (Murphy et al., 2010).
High rates of injury recurrence are arguably the most troublesome aspect of hamstring strains because recurring injuries often result in substantially more lost playing time than the original insults (Brooks et al., 2006, Ekstrand et al., 2011, Koulouris et al., 2007) and because the hamstrings remain at elevated risk of injury recurrence for longer than other strained muscles (Orchard and Best, 2002). There is also evidence for a significant rate of recurrence across consecutive seasons (Carling et al., 2011, Hagglund et al., 2006, Verrall et al., 2006). Hamstring strain recurrence rates of 16–60% have been reported in American football (Elliott et al., 2011, Heiser et al., 1984), rugby union (Brooks et al., 2006), soccer (Ekstrand et al., 2011), the sprint events in track and field (Drezner et al., 2005, Yeung et al., 2009) and in Australian football (Orchard and Seward, 2010). A long-term program of compulsory injury reporting in the Australian Football League (AFL) indicates that same-season hamstring re-injury rates have averaged 23% in the last 10 seasons (Orchard and Seward, 2010). However, this figure almost certainly underestimates true recurrence rates as it does not take into account lost pre-season training time.
Statistics on first and recurrent hamstring strain injuries indicate that injury prevention and rehabilitation practices are not as effective as athletes and coaches would like them to be. We argue that the current understanding of injury risk factors is inadequate and that neuromuscular inhibition of the hamstrings, previously ignored in literature and underemphasised in rehabilitation programs, may at least partially explain high hamstring injury recurrence rates. The objectives of this review article are to (i) discuss factors relating to hamstring strain injury recurrence and (ii) discuss the potential role of neuromuscular inhibition in these recurrences.
Section snippets
The persistence of risk factors
A number of modifiable and non-modifiable risk factors are proposed to predispose athletes to hamstring strains (Copeland et al., 2009, Croisier, 2004a, Devlin, 2000, Opar et al., 2012a). Modifiable factors include hamstring weakness (Croisier et al., 2008, Orchard et al., 1997, Sugiura et al., 2008, Yeung et al., 2009), poor flexibility (Bradley and Portas, 2007, Witvrouw et al., 2003) and fatigue (Brooks et al., 2006, Ekstrand et al., 2011, Woods et al., 2004), while the non-modifiable
Is rehabilitation sabotaged by neuromuscular inhibition?
The following section discusses the putative role of neuromuscular inhibition in hamstring strain injury recurrence (Opar et al., 2012a). A conceptual framework for the proposed relationship between neuromuscular inhibition and several maladaptations associated with hamstring strain injury recurrence is shown in Fig. 2.
The early stages of conventional hamstring rehabilitation are characterised by the avoidance of excessive muscle stretch, initially because stretch may exacerbate scar formation (
Conclusion
The persistence of risk factors and the development of maladaptations following hamstring strain injury may explain injury recurrence. Several post-hamstring injury maladaptations have been identified in the literature, which, if not specifically addressed during rehabilitation, potentially contribute to injury recurrence. It is proposed that pain-driven neuromuscular inhibition of hamstring voluntary activation occurs following hamstring strain injury, and that this inhibition has a
Conflict of interest
None declared.
Acknowledgements
No external contributors were involved nor was any financial assistance provided for the completion of this project.
Jackson Fyfe completed his Bachelor of Exercise Science (Hons) at Australian Catholic University in Melbourne, Australia investigating chronic neuromuscular inhibition following hamstring strain injury. He is currently undertaking his PhD within the College of Sport and Exercise Science at Victoria University, Melbourne, Australia.
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Jackson Fyfe completed his Bachelor of Exercise Science (Hons) at Australian Catholic University in Melbourne, Australia investigating chronic neuromuscular inhibition following hamstring strain injury. He is currently undertaking his PhD within the College of Sport and Exercise Science at Victoria University, Melbourne, Australia.
David Opar completed his B. App. Sci (HM) (Hons) at RMIT University, Melbourne, Australia and completed his PhD at Queensland University of Technology, Queensland, Australia. His thesis, supervised by Dr. Anthony Shield and Dr. Morgan Williams, focused on alterations to neuromuscular hamstring function in previously injured athletes. Currently he is a Lecturer in Exercise Science at Australian Catholic University, Melbourne, Australia.
Morgan Williams completed a PhD at ACU in Melbourne, Australia. He is currently a Senior Lecturer in Sports Science at the University of Glamorgan, Wales, UK.
Anthony Shield has an interest in the applications of eccentric exercise with a current focus on hamstring strain injury. He completed his PhD at Southern Cross University, Australia and is currently a Senior Lecturer in the School of Exercise and Nutrition Sciences at Queensland University of Technology.