The influence of playing level on the biomechanical demands experienced by rugby union forwards during machine scrummaging

This study investigated machine scrummaging at different playing levels in rugby union and analysed kinetic factors that might influence performance and injury risk. Thirty-four forward packs from six different playing levels scrummaged against an instrumented scrum machine under real environmental conditions. Applied forces were measured in three orthogonal directions. The peak (SD) of the overall compression forces during engagement ranged between 16.5 (1.4) kN (International-Elite) and 8.7 (0.1) kN (Women), while sustained compression forces spanned between 8.3 (1.0) kN (International) and 4.8 (0.5) kN (Women). The peak of the overall vertical force during the initial engagement phase was between 3.9 (0.7) kN (Elite) and 2.0 (1.0) kN (School), and the range of lateral forces was between 1.8 (0.3) kN (International) and 1.1 (0.3) kN (School). Forces measured across all playing levels, particularly during initial engagement, were generally higher than those measured in the most commonly cited previous studies. This increase may be due to a combination of changes in modern scrummaging technique, changes in players' anthropometrics, and experimental conditions that better respect ecological validity. The magnitude of the measured forces is in the range of values that studies on cadaveric specimens have indicated as potentially hazardous for (chronic) spine injuries.