Table 3

Description of analysed measures

 Distance from the padsSet-upDistance between the front row players C7 and the scrum machine pads at the onset of movement
 Maximum engagement speedEngagementFront row centre of mass maximum velocity during the initial engagement phase. The front row centre of mass has been defined as the weighted average of the centres of mass of the trunk of the three front row players
 Peak compression forceEngagementMaximum of the compression force during engagement
 Positive forward impulseEngagementArea under the compression force curve, calculated between the time of engagement and the instant when the force drops down to the value of the sustained push
 Negative forward impulseEngagementArea between the level of average sustained push and the compression force curve, calculated from the end of the positive impulse interval to the beginning of the sustained push phase
 Average sustained pushSustained pushAverage value of the compression force over the sustained push phase
 Peak vertical forceEngagementPeak vertical force during engagement (always downward/negative)
 Average sustained vertical forceSustained pushAverage value of the vertical push over a 1 s interval from the end of engagement
 Range of lateral forceEngagementRange of lateral forces during engagement
 Average sustained lateral forceSustained pushAverage value of the lateral push over a 1 s interval from the end of engagement
 HIEngagementBased on the ‘spine in line’ principle and on the assumption that potential risk for the upper spine may come from the concurrency of high forces and increased neck angles
The HI is a combination of forces (typically acting through the shoulder and base of the neck) and neck deviations (ie, absolute neck angle in the horizontal plane) averaged over the duration of the engagement phase and across the front five players, who are the ones with spine constrained on both ends (see online supplement 2 for a detailed description). HI is not a validated metric but a proposed quantity which includes kinematic and kinetic factors likely related to the generation of undesired stresses on the spine (eg, bending in compression). HI varies between 0 and 1, where the higher the value, the higher the average hazard on the front five forwards
In addition, forces and angle-deviations coupling varies throughout the engagement phase. This change can be calculated at each time, and its maximum value can be taken into account as the worst combination in terms of hazard over the engagement phase (maximum hazard measure)
  • Please refer to figure 2 for an annotated graphical representation of force parameters/phases.

  • Phases of scrummaging (see also figure 2): engagement (ie, interval between the onset of forces and 1 s after the peak of compression force); sustained push (ie, 1 s interval from the end of the engagement, with the exception of Fold-in for which the last 1 s was considered). Force measures are the total force generated by the forward pack, that is, the sum of forces measured by the four instrumented beams of the scrum machine.

  • HI, hazard index.