1 of 9 Kerin F, et al. Br J Sports Med 2022;56:608–615. doi:10.1136/bjsports-2021-104171 Its not all about sprinting: mechanisms of acute hamstring strain injuries in professional male rugby union—a systematic visual video analysis Fearghal Kerin , 1,2 Garreth Farrell, 3 Peter Tierney , 4 Ulrik McCarthy Persson, 5 Giuseppe De Vito, 6 Eamonn Delahunt 7 Original research To cite: Kerin F, Farrell G, Tierney P, et al. Br J Sports Med 2022;56:608–615. ► Additional supplemental material is published online only. To view, please visit the journal online (http://dx.doi. org/10.1136/bjsports-2021- 104171). 1 Fearghal Kerin, Leinster Rugby, Dublin, Ireland 2 Fearghal Kerin, University College Dublin, Dublin, Ireland 3 Leinster Rugby, Dublin, Ireland 4 Sports Science, Football Association, London, UK 5 School of Public Health Physiotherapy & Sports Science, University College Dublin, Dublin, Ireland 6 Department of Biomedical Sciences, University of Padova School of Sciences, Padova, Veneto, Italy 7 School of Public Health, Physiotherapy and Sports Science, University College Dublin, Dublin, Ireland Correspondence to Fearghal Kerin, Fearghal Kerin, Leinster Rugby, Dublin 4, Ireland; Fearghal.Kerin@leinsterrugby.ie Accepted 10 January 2022 Published Online First 19 January 2022 © Author(s) (or their employer(s)) 2022. No commercial re-use. See rights and permissions. Published by BMJ. ABSTRACT Objectives The mechanisms of hamstring strain injuries (HSIs) in professional Rugby Union are not well understood. The aim of this study was to describe the mechanisms of HSIs in male professional Rugby Union players using video analysis. Methods All time-loss acute HSIs identifed via retrospective analysis of the Leinster Rugby injury surveillance database across the 2015/2016 to 2017/2018 seasons were considered as potentially eligible for inclusion. Three chartered physiotherapists (analysts) independently assessed all videos with a consensus meeting convened to describe the injury mechanisms. The determination of the injury mechanisms was based on an inductive process informed by a critical review of HSI mechanism literature (including kinematics, kinetics and muscle activity). One of the analysts also developed a qualitative description of each injury mechanism. Results Seventeen acute HSIs were included in this study. Twelve per cent of the injuries were sustained during training with the remainder sustained during match-play. One HSI occurred due to direct contact to the injured muscle. The remainder were classifed as indirect contact (ie, contact to another body region) or non-contact. These HSIs were sustained during fve distinct actions—’running’ (47%), ’decelerating’ (18%), ’kicking’ (6%), during a ’tackle’ (6%) and ’rucking’ (18%). The most common biomechanical presentation of the injured limb was characterised by trunk fexion with concomitant active knee extension (76%). Fifty per cent of cases also involved ipsilateral trunk rotation. Conclusion HSIs in this study of Rugby Union were sustained during a number of playing situations and not just during sprinting. We identifed a number of injury mechanisms including: ’running’, ’decelerating’, ’kicking’, ’tackle’, ’rucking’ and ’direct trauma’. Hamstring muscle lengthening, characterised by trunk fexion and relative knee extension, appears to be a fundamental characteristic of the mechanisms of acute HSIs in Rugby Union. INTRODUCTION Hamstring strain injuries (HSIs) are the most prev- alent muscle injury sustained by professional field- sport athletes. 1–6 They have been shown to account for 12% of all injuries in elite Rugby Union (‘rugby’) and soccer with recurrence rates of 23%–30% reported. 7 8 Two distinct types of HSIs have been described in the published literature; those that occur during sprinting (sprint-type) and those that occur as a result of an ‘over-stretch’ (stretch-type). 9 It is generally agreed that the sprint type of HSIs is sustained via an eccentric overload during the terminal swing phase of high velocity running. 10 During this phase of running, the biceps femoris long head exhibits the greatest elongation of the hamstring muscles, reaching almost 110% of its resting length. 11 The semimembranosus and semi- tendinosus muscles lengthen to 107% and 108% of their resting lengths, respectively. 11 Askling et al 12 demonstrated that all first-time acute HSIs sustained by sprinters primarily involved the biceps femoris long head. The stretch type of HSIs typi- cally occur as a result of an over-stretch in a posi- tion of knee extension and trunk flexion, 13 which may be compounded by hip abduction. 14 This has been shown to more frequently involve the semi- membranosus muscle (83%). 15 HSIs are the most commonly sustained non- contact lower limb injury in rugby, 7 particularly among ‘backs’ for whom they have the highest injury incidence (0.30 injuries/1000 hours). Rugby Union is a collision sport, which requires players to tackle, evade, kick and sprint. 16 17 There are 15 players on a team—seven backs and eight forwards. Backs are typically lighter and quicker and are expected to carry out more sprinting and high-speed running than forwards, who in addition to running, may be expected to participate in more tackling, grappling and set-piece activities. 7 As a result, although the majority of HSIs in rugby have consistently been shown to occur during high-speed running, 7 18 19 the demands of the sport may provide an environment for which both the sprint-type and stretch-type HSIs can occur. In Australian football players, 81% of HSIs occur during high-speed running, with the remaining 19% during kicking, 20 while it has long been suggested that another common mechanism of injury involves picking the ball from ground. 21 Video analysis is currently used in Rugby Union to assist match officials in making on-field deci- sions as well as in determining the severity of head injuries through the head injury assessment process. 22 Retrospective video analyses have been published describing the mechanisms of anterior cruciate ligament injuries and shoulder dislocations in rugby. 23 24 Serner et al, 25 to our knowledge, are the only research group to describe the mecha- nisms of acute muscle injuries using a video analysis approach—they reported on 17 adductor longus strains sustained by professional football (soccer) players. If the prevalence of HSIs in Rugby Union Protected by copyright. on July 5, 2022 at Universita Di Padova Biblioteca Pinali. http://bjsm.bmj.com/ Br J Sports Med: first published as 10.1136/bjsports-2021-104171 on 19 January 2022. Downloaded from