Normative Values for Hip Flexion Range of Motion and Strength in Professional Rugby Union Players.

Abstract

Professional Rugby Union is a multi-directional field-based team sport. It involves intermittent periods of high-speed running, changes of direction, kicking, and a high volume of collision-based activities, such as tackling, rucking, mauling and scrummaging. The physical nature of Rugby Union means that it has one of the highest incidences of injury of any team sport (Williams et al, 2013). The hip and groin region is among the most commonly injured sited in Rugby Union. In the most recent Rugby World Cup (RWC), injuries to the hip and groin accounted for 5.8% of all injuries sustained during the competition (Fuller et al, 2017). Recognised intrinsic risk factors for injury to the hip and groin include strength (or decreased strength specifically) (Tyler ert al, 2001), and range of motion (Henderson et al, 2010). Assessment of hip muscle strength and range of motion are routine and vital components in the continuous assessment and monitoring of injured and non-injured professional athletes. To date, all published data around hip strength in professional athletes has focused on hip adduction / abduction and rotational strength. To the knowledge of this author there is no published normative values on hip flexion strength and range of motion in professional rugby union players. Forty-four professional Rugby Union players were recruited for this study. All were injury free at the time of testing. A hand-held dynamometer measured peak hip flexion strength of each player by way of an eccentric break-test. Hip flexion strength was assessed on both legs with the hip flexed to 90 degrees and also at maximal available inner range of motion (beyond 90 degrees). Active hip flexion range of motion was measured using a Universal Goniometer. The principal investigator was a Chartered Physiotherapist working in professional sport with experience in both methods of assessment. For both hip flexion range of motion and hip flexion strength, percentile scores between 5 and 95% for each of the values were computed. This method produced a clinician friendly table of reference ranges and values. It also highlighted the heterogeneous make up of a professional Rugby Union team. The lowest reference strength value was 181.6 Nm while the 95% percentile range was 425 Nm. Linear regression analysis was conducted to examine the influence of variables such as; 1) playing position, 2) kicking leg, and 3) history of hip and groin pain, on the clinical measurements of hip flexion range of motion and hip flexion strength. The only significant finding from this analysis, was that if a player plays as a back , then their inner range hip flexion strength is significantly less that a player who is a backrow forward (p=0.018). All participants also completed two patient-reported outcome measures (PROM), which were; 1) The Copenhagen Hip and Groin Outcome Score (HAGOS), and 2) the International Hip Outcome Tool-33 (i-HOT 33). A linear regression anlaysis examined the influence of the variables of 1) hip flexion strength, 2) hip flexion range of motion, and 3) history of hip and groin pain, on the subsection scores of both PROMs. The results revealed that despite being injury free at the time of completing the PROMs, players who had a previous history of hip and groin pain scored significantly lower in three of the four subsections of the i-HOT 33, and three of the six subsections of the HAGOS. Ultimately this meant that despite being at full strength and available for selection, players with a history of hip and groin pain had a significantly different perspective on their health than their colleagues without a history of hip and groin pain. This study provides useful percentile ranges for hip flexion strength and range of motion for this unique cohort, that are user friendly for clinicians working with professional Rugby Union teams. The findings from this research also highlights the heterogeneity of a professional Rugby Union squad and emphasises the need for future research to examine each playing group as a separate population. This study also demonstrates the importance of using PROMs in ongoing player assessment and monitoring.