Research Review By Dr. Jeff Muir©

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Date Posted:

January 2020

Study Title:

Including the Nordic hamstring exercise in injury prevention programmes halves the rate of hamstring injuries: a systematic review and meta-analysis of 8459 athletes

Authors:

Van Dyk N, Behan FP & Whiteley R

Author's Affiliations:

Aspetar Injury and Illness Prevention Program (ASPREV), Aspetar Orthopaedic and Sports Medicine Hospital, Qatar; Research Department, Aspetar Orthopaedic and Sports Medicine Hospital, Qatar; Department of Rehabilitation, Aspetar Orthopaedic and Sports Medicine Hospital, Qatar.

Publication Information:

British Journal of Sports Medicine 2019; 53: 1362–1370.

Background Information:

Hamstring injury is the most common muscle injury in many sports (1-3), and one that is often treated using eccentric strengthening exercises (4). The Nordic hamstring exercise (NHE) program is a relatively simple, eccentric hamstring exercise (partner assisted or utilizing a bench or piece of equipment where the lower leg can be secured). Recently, prospective studies have demonstrated a reduction in injuries of up to 70% with the use of preventive exercise programs such as the NHE program (5-7).

Despite this evidence, there is still debate regarding the effectiveness of such preventive exercise programs in limiting hamstring injury. Several systematic reviews have been completed evaluating these interventions; however, the methodology for these reviews has been suspect. In some cases, strict inclusion criteria – such as permitting only randomized studies written in English – limited the amount of included studies (8). Other reviews excluded studies that did not provide workload data and sports other than football, which may lead to a biased estimation of the effect of the NHE. As a result, these authors sought to complete a comprehensive systematic review and meta-analysis on the effectiveness of NHE for preventing hamstring injuries. As clinicians, preventing hamstring injuries is relevant and the results of such an investigation could certainly inform training and (pre)rehabilitation program design for athletes in many sports!

Pertinent Results:

Literature Search & Included Studies:
15 studies were identified as eligible from database searches, including 8 controlled trials (7 randomized, 1 non-randomized) and 7 cohort studies. The majority of studies (n = 13) were in male athletes, with football (soccer) the most common sport, with additional studies in rugby, baseball and ‘American football’. Sport levels ranged from amateur to professional. Across the majority of studies, players were aged 18-40, with one additional study involving youth players aged 13-18 yrs. The NHE was used in all studies, in isolation in 6 studies and in combination with the FIFA 11+ program in 4 others.

Methodology and Risk of Bias Assessment:
A high risk of performance and detection bias was identified across eligible studies (due to increased attention paid to NHE study groups and inability to blind assessors). Additionally, moderate selection bias was detected (again, primarily due to the inability to blind assessors). Attrition and reporting bias was low, as was the risk of publication bias.

Meta-analysis:
The pooled analysis included 8459 participants. The incidence of hamstring injuries for players exposed to the NHE was 0.1/1000 hours vs. 0.2/1000 hours (double!) for those undergoing usual training. Overall, a 51% reduction in hamstring injury was noted in NHE groups (RR 0.49, 95% CI 0.32 to 0.74, p = 0.0008). Heterogeneity across studies, however, was large (I2=74%).

Sensitivity Analysis:
A sensitivity analysis of only the randomized trials demonstrated only slightly altered results (RR 0.52, 95% CI 0.32 to 0.85, p=0.0008). Removal of studies with high risk of allocation, detection or attrition bias revealed, again, only a small increase in the relative risk of injury (RR 0.55, 95% CI 0.34 to 0.89, p=0.006).

Clinical Application & Conclusions:

The evidence indicates that overall, the NHE is effective in preventing hamstring injuries - reducing the risk by approximately 50%! The authors concede that the mechanisms by which NHE provides its protective effect are not yet fully understood, however. Other authors have noted increased eccentric strength and suspect that it may be responsible for the positive effect (9), although the evidence is minimal, due to the poor incorporation of NHE into regular training programs. As such, there is a need for improved understanding of the factors relating to the incorporation of the program into training and the mechanisms responsible for its effect.

Study Methods:

One author searched the following databases: MEDLINE via PubMed, CINAHL via Ebsco, and OpenGrey from January 1950 to August 2018. Searches included search terms such as “Nordic” and “Russian”, coupled with the OR operator. Additional keywords “hamstring” and “injur*” were added and combined with previous search terms using the AND operator.

Eligible participants were any athlete participating in any sport. Interventions included NHE or any program that included NHE; outcomes included incidence or rate of hamstring injuries.

Initial searches were conducted in duplicate; a third investigator facilitated group consensus on disagreements. Two investigators conducted full-text reviews and imported results into RevMan, v5.3.

Methodological quality was evaluated using the Cochrane risk of bias tool. Data analysis was performed as per Cochrane methodology (10). A random-effects model was used for the meta-analysis, based on the expectation of diverse populations. Sensitivity analyses included analyzing only high-quality studies; removing studies with a high risk of allocation, detection or attrition bias; and examining pooled effects when excluding each study individually.

Study Strengths / Weaknesses:

Strengths:
  • The authors used comprehensive search criteria and included cohort studies (with comparison groups) as well as randomized trials (permitting more data to be analyzed compared to prior papers on this topic).
  • Pooling of data and sensitivity analyses allowed for robust meta-analysis of data.
  • The authors used Cochrane methodology to assess risk of bias and analyze data.
Weaknesses:
  • Moderate selection and high performance bias were identified in the included studies. Note, blinding subjects and assessors is not really possible with this sort of intervention. As a further result, detection bias was also possible in these studies (blinded assessors would help with this).
  • Substantial variability was noted across NHE training protocols.
  • The risk of initial vs. recurrent hamstring injury differs and could affect the impact of NHE on said injury.

Additional References:

  1. Ekstrand J, Hägglund M, Waldén M. Injury incidence and injury patterns in professional football: the UEFA injury study. Br J Sports Med 2011; 45: 553–8.
  2. Hägglund M, Waldén M, Ekstrand J. Risk factors for lower extremity muscle injury in professional soccer: the UEFA Injury Study. Am J Sports Med 2013; 41: 327–35.
  3. Opar DA, Williams MD, Shield AJ. Hamstring strain injuries. Sports Medicine 2012; 42: 209–26.
  4. Al Attar WSA, Soomro N, Sinclair PJ, et al. Effect of injury prevention programs that include the nordic hamstring exercise on hamstring injury rates in soccer players: a systematic review and meta-analysis. Sports Med 2017; 47: 907–16.
  5. Petersen J, Thorborg K, Nielsen MB, et al. Preventive effect of eccentric training on acute hamstring injuries in men’s soccer: a cluster-randomized controlled trial. Am J Sports Med 2011; 39: 2296–303.
  6. van der Horst N, Smits DW, Petersen J, et al. The preventive effect of the Nordic hamstring exercise on hamstring injuries in amateur soccer players: a randomized controlled trial. Am J Sports Med 2015; 43: 1316–23.
  7. Arnason A, Sigurdsson SB, Gudmundsson A, et al. Risk factors for injuries in football. Am J Sports Med 2004; 32: 5–16.
  8. Goode AP, Reiman MP, Harris L, et al. Eccentric training for prevention of hamstring injuries may depend on intervention compliance: a systematic review and metaanalysis. Br J Sports Med 2015; 49: 349–56.
  9. Harøy J, Thorborg K, Serner A, et al. Including the copenhagen adduction exercise in the FIFA 11+ Provides missing eccentric hip adduction strength effect in male soccer players: a randomized controlled trial. Am J Sports Med 2017; 45: 3052–9.
  10. Higgins JPT, Green S. Cochrane handbook for systematic review of interventions version 5.1. 0: The Cochrane Collaboration. 2011.