Rugby union is a team-sport in which collisions and impact forces play a decisive role. In this regard, momentum-based measurements (the product of mass and velocity of a body in a given movement) are frequently used by practitioners. Generally, sprint momentum (SM; the product of sprinting speed and athlete's body mass) is the most commonly considered momentum-based measure by coaches and sport scientists, either to differentiate playing positions or to examine player performance. However, recently, jump squat momentum (JSM) has been suggested as a complementary momentum-based measure because of its strong relationship with SM. In this study, we compared the body mass; half-squat 1 repetition maximum (HS 1RM), in both absolute and relative terms (i.e., relative strength [RS]); sprinting speed and momentum; and JSM of 21 rugby backs and forwards using an independent t test. As expected, forwards are significantly heavier and stronger and exhibit higher SM and JSM than backs (p = 0.02). By contrast, backs are faster in linear sprints over both 10- and 30-m (p < 0.001) and exhibit higher values of RS (p < 0.05). Furthermore, irrespective of the playing position, RS was significantly different between the "low" and "high" RS groups (p < 0.001). Despite these marked differences, all players achieved their greatest magnitudes of JSM at an average of 40% HS 1RM. Strength and conditioning coaches interested in increasing JSM and its related metrics (e.g., SM) in rugby players could use this specific loading range to prescribe JS loads during their strength-power training sessions.
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