260 International Journal of Sports Physiology and Performance, 2007;2:260-269 © 2007 Human Kinetics, Inc. Kilduff, Owen, Kingsley, and Cunningham are with the Dept of Sports Science, University of Wales Swansea, Singleton Park, Wales SA2 8PP, UK. Bevan is with Ospreys Rugby, Landore, Swansea SA1 2FA, UK. Bunce and Bennett are with Welsh Rugby Union, Vale of Glamorgan, CF72 8JY, UK. Optimal Loading for Peak Power Output During the Hang Power Clean in Professional Rugby Players Liam P. Kilduff, Huw Bevan, Nick Owen, Mike I.C. Kingsley, Paul Bunce, Mark Bennett, and Dan Cunningham Purpose: The ability to develop high levels of muscle power is considered an essential component of success in many sporting activities; however, the optimal load for the development of peak power during training remains controversial. The aim of the present study was to determine the optimal load required to observe peak power output (PPO) during the hang power clean in professional rugby players. Methods: Twelve professional rugby players performed hang power cleans on a portable force platform at loads of 30%, 40%, 50%, 60%, 70%, 80%, and 90% of their predetermined 1-repetition maximum (1-RM) in a randomized and balanced order. Results: Relative load had a significant effect on power output, with peak values being obtained at 80% of the subjects’ 1-RM (4466 ± 477 W; P < .001). There was no significant difference, however, between the power outputs at 50%, 60%, 70%, or 90% 1-RM compared with 80% 1-RM. Peak force was produced at 90% 1-RM with relative load having a significant effect on this variable; however, relative load had no effect on peak rate of force development or velocity during the hang power clean. Conclusions: The authors conclude that relative load has a significant effect on PPO during the hang power clean: Although PPO was obtained at 80% 1-RM, there was no significant difference between the loads ranging from 40% to 90% 1-RM. Individual determination of the optimal load for PPO is necessary in order to enhance individual training effects. Key Words: force platform, relative intensity, peak rate of force development, force–time curve The ability to develop high levels of muscle power is considered an essential component of success in many sport activities. For example, Sleivert and Taingahue 1 reported negative correlations between relative peak power output (PPO) during the split squat and 5-m-sprint time (r = –.65) and relative PPO during the traditional squat and 5-m-sprint time (r = –.66), which might indicate that increasing PPO will lead to an improvement in sprinting performance, a primary performance outcome