An Examination of Neck Strength, Endurance, Neck Pain and Neck Stiffness in Rugby Union Players

Abstract

Background: Rugby is a high speed collision sport during which the neck is often exposed to loads that place it at risk of injury. When injuries do occur they range from catastrophic injuries where permanent spinal cord damage may result, through to minor injuries where the primary symptom is neck pain (NP). As a potential preventative strategy it has been proposed that neck muscle strength and endurance may play a role in the prevention or mitigation of minor neck injury. Aims: The overall aim of this thesis was to explore the efficacy of a neck specific exercise intervention in improving neck neuromuscular function (neck muscle strength and endurance) and alleviating or minimizing symptoms of minor neck injury (neck pain and stiffness). To evaluate the efficacy of this intervention, a testing apparatus and an experimental protocol capable of reliably measuring neck strength and endurance were designed and developed. In order to address these aims, the thesis was constructed around a number of independent but linked research projects. Methods: A sequential multi-study approach was used to examine neck strength, endurance, NP and neck stiffness (NS) in rugby players. A critical review of the literature examined the existing neck injury surveillance data and potential factors or mechanisms that may play a role in the occurrence of neck injuries. A retrospective online survey was employed to examine the impact neck injuries sustained while playing rugby have on the subsequent health of retired players. A custom testing apparatus was designed and built to examine neck strength and endurance in a simulated contact posture, and its reliability established. This apparatus was then used with a cohort of amateur forwards, backs and healthy controls to examine the effect of a 20-week competitive season on neck neuromuscular performance. Evidence gathered from the thesis studies was used to design a neck exercise intervention for rugby players. The efficacy of this intervention was then examined in a cohort of professional rugby players using measures of neuromuscular function and perceived neck dysfunction (NP and NS) over a competitive season and compared with a group of players who did not receive the intervention. Results: Neck pain and NS proved to be frequently reported current health complaints for retired professional rugby players. The majority of players surveyed sustained a neck injury (79%) during their careers. Of these, 91% reported currently experiencing symptoms of either NP and/or NS. These findings indicate that most professional players will sustain a neck injury and that this injury, or the accumulation of microtrauma in the neck region over their careers will have long-term health and disability consequences. The testing apparatus developed assessed the neck isometrically in a simulated contact position. Assessment of neck strength over a single session revealed that, in the adopted body position, neck strength in the four examined directions could be reliably assessed using three trials (ICC(3,1): 0.86-0.94). To explore the test re-test reliability of the device, neck strength and endurance were assessed over three separate trials. The relative and absolute reliability for extension and flexion strength (ICC(3,1): 0.92-0.97; SEM: 11.27-15.27 N), and endurance (ICC(3,1): 0.98; SEM: 8.55-12.53 s) demonstrate that the apparatus can be used to reliably measure these parameters over time. Over a competitive season neck strength and endurance was assessed in amateur rugby players and healthy controls. At the end of the competitive season improvements in strength for forwards and backs were observed (p= 0.01-0.05), while the control group remained unchanged. No changes for the endurance measures were observed for the three groups over the season, which is likely attributable to the high individual variability found in these measures. Thus, participation in a season of amateur rugby appears to impose a physical stress on the neck musculature which leads to strength adaptation for amateur players. Proxy measures of neck dysfunction, NP and NS, were recorded at the start and end of the season. Both forwards and backs, reported increased NP (p= 0.01-0.04), while only the backs reported increased NS over the season (p= 0.01-0.02). These results suggest that despite improvements in neck strength over the season, both forwards’ and backs’ perceived neck function was impaired, while controls reported no change. A neck specific exercise intervention consisting of exercises intended to improve neck muscle strength, endurance, and coordination, along with impulse loading of the neck, was administered to a professional rugby team. In the intervention group neck strength (p= 0.01-0.03) and endurance (p= 0.01) was found to improve over the competitive season. In contrast, a professional control team that did not receive the intervention, displayed significant decreases in post-season neck strength and endurance, which coincided with increases in worst NP (p= 0.05) and average NS (p= 0.02). Despite the observed improvements in neck strength and endurance over the season in the intervention group, NP and NS scores remained unchanged. This data suggests that playing professional rugby imposes a large physical and perceived stresses on the neck, as evidenced by the impaired neck strength and endurance, and the increased post-season NP and NS scores. The prescription of and adherence to a neck strengthening exercise programme resulted in improvements in neck strength and endurance over a season, but did not change self-reported NP or NS. However, in this study the neck exercise intervention did prevent increases in symptom severity when compared to controls. Conclusion: Collectively, this corpus of work presents a number of interlinked studies relating to the exploration of neck strength, endurance, NP and NS in rugby players. The results from this research indicate that neck injuries sustained during a player’s career will likely impact on their subsequent health once retired. In comparison to other regions of the body the neck is a primary area of current pain and stiffness for retired professional players. In conclusion, the performance of neck specific exercises may provide a feasible strategy to reduce the occurrence of minor neck injuries in rugby players, which may improve their long-term health outcomes relating to neck disability and increase functionality in retirement.