The influence of hip mobility and quadriceps fatigue on sagittal spinal posture and muscle activation in rugby scrum performance.

Rugby Union scrumming puts the spine under a high degree of loading. The aim of the current study was to determine how sagittal hip range of motion and quadriceps fatigue influence force output, spinal posture, and activation of the trunk and quadriceps muscles in rugby scrumming. Measures of sagittal hip flexion/extension range of motion were collected from 16 male varsity and club first XV level participants. Sagittal spine motion (electromagnetic motion capture), trunk and quadriceps activation (electromyography), and applied horizontal compressive force (force plate) were measured during individual machine scrumming. Participants performed a 5-trial scrum block involving 5 s of contact with 1-2 min recovery between each trial. They then performed a fatiguing protocol (wall sit to failure) and immediately returned to the scrum machine to perform another five trials. Though there was no significant influence of fatigue on the horizontal compressive force applied during contact (P = .83), there was a 52% increase in cervical flexion (P < .001), as well as decreased (18-23% lower) abdominal and erector spinae muscle activation (P < .05). Furthermore, quadriceps activation decreased (12-25% lower) over the course of the initial scrum block but increased (13-15% higher) in the post fatigue block (P < .05). Although athletes were able to maintain force output following the fatiguing wall sit task, there is the potential that they may be at an increased risk of spinal injury due to the combination of increased flexion and high-applied compressive force; a combination which has been shown to increase the likelihood of intervertebral disc herniation.