Forces generated in rugby union machine scrummaging at various playing levels

We studied the kinetics of machine scrummaging in rugby union by assessing three-dimensional forces and analyzing factors that might contribute to performance and influence injury risk during scrum engagement. Thirty-four forward packs from six different playing levels performed machine scrummaging trials against an instrumented scrum machine under real environmental and normal scrum engagement conditions. The peak (SD) of the overall compression forces during engagement ranged between 16.5 (1.4) kN (International and 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). The forces measured across all playing levels, particularly during engagement, were generally higher than those measured in the most commonly cited previous studies. The current study allowed the formation of a more comprehensive picture of scrummaging biomechanics, of the differences between different playing levels and of potential injury factors.