The isokinetic assessment of muscle strength in rugby union players.

Strength is an important requirement in the game of rugby union. Activities such as tackling, scrummaging, rucking, mauling make upper body strength essential for success at the higher levels of competition. This aspect of strength has been assessed by a variety of weight lifting tests but no tests based on a sport specific movement have been developed for rugby.The aim of this study therefore was to develop a test to measure the upper body strength of rugby union players. Isokinetic assessment of shoulder abduction and adduction strength was identified as providing a sport specific measurement based on the muscle actions involved in the rugby tackle.A pilot study was conducted to assess the reliability of the isokinetic assessment of shoulder abduction and adduction. Test re-test measurements of concentric and eccentric strength at 1.08 rad-s[-1] and 2.16 rad-s[-1] in the dominant and non-dominant shoulder were made on 10 male subjects, 1 week apart. Intra-class correlation (ICC) ranged from r = 0.80 to 0.97 and the standard error of measurement (SEM) ranged from +/- 3.2Nm to +/- 14.9Nm. The most reliable measure was the average torque at 2.16 rad-s[-1] in the dominant shoulder (concentric abduction r = 0.96, SEM +/- 3.2Nm; eccentric adduction r = 0.97, SEM +/- 4.2Nm).Isokinetic shoulder strength was measured in 29 male rugby union players at three stages of the season, the pre-season training stage (PS), at the start of the competitive season (SS) and midway through the league season (MS). 19 subjects completed all 3 tests. Measurements were made of concentric abduction and eccentric adduction of the dominant shoulder at 2.16 rad-s[-1].There were no significant differences between test measures taken at different stages of the season. Values for eccentric adduction were significantly greater than those for concentric abduction (P<0.001). Within the group changes in strength between tests were weakly correlated with initial strength (PS-SS, concentric abduction r = -0.48, p<0.05 and SS-MS, eccentric adduction r = -0.53, p<0.05) but not with the number of weight training sessions undertaken.A comparison of strength between positional roles showed that forwards were significantly stronger than backs in absolute terms but that there was no significant difference when the strength was expressed relative to body weight.The results of this study demonstrate that the isokinetic assessment of shoulder abduction and adduction provides a reliable measure of upper body strength in rugby union players.The use of this test to measure strength during the season has shown that the playing and training activities of the players produced no consistent effects on shoulder strength. The greater absolute strength of forwards is related to their greater body mass, rather than to differences in positional roles.The mean of the PS, SS and MS measures can be used to provide normative data for shoulder strength in rugby union players.