Transfer effect of strength and power training to the sprinting kinematics of international rugby players.

Increasing lower-body strength is often considered to be important for improving the sprinting speed of rugby players. This concept was examined in a group (n = 40) of international rugby players in a 2-part study. The players were tested for body mass (BM), 1 repetition maximum power clean (PC), and front squat, as well as triple broad jump and broad jump. In addition, speed over 40 m was tested, with timing gates recording the 0- to 10-m and 30- to 40-m sections to assess acceleration and maximal velocity. Two video cameras recorded the 2 splits for later analysis of sprinting kinematics. The players were divided into a fast group (n = 20) and a slow group (n = 20) for both acceleration and maximal velocity. In the second part of the study, a group (n = 15) of players were tracked over a 1-year period to determine how changes in strength corresponded with changes in sprinting kinematics. The fast groups for both acceleration and maximal velocity showed greater levels of strength (d = 0.5-1.8), lower ground contact times (d = 0.8-2.1), and longer stride lengths (d = 0.5-1.3). There was a moderate improvement over 1 year in PC/BM (0.08 kg·kg, p = 0.008, d = 0.6), and this had a strong relationship with the change in maximal velocity stride length (r = 0.70). Acceleration stride length also had a large improvement over 1 year (0.09 m, p = 0.003, d = 0.81). Although increasing lower-body strength is likely important for increasing sprinting speed of players with low training backgrounds, it may not have the same effect with highly trained players.