Effects of 12-weeks resistance training on sprint and jump performance in competitive adolescent rugby union players.Harries Simon K.; Lubans, David R.; Buxton, Anthony; MacDougall, Thomas H.J.; Callister, RobinJournal of Strength & Conditioning Research: Post Acceptance: July 17, 2017 doi: 10.1519/JSC.0000000000002119 Original Research: PDF Only Abstract Sprint performance is an important characteristic for success in many sports, including rugby union. Resistance training is used to increase muscular fitness (i.e. strength, endurance and power) and may also be effective for improving sprint and jump performances. The aims of this study were to examine the effects of resistance training using two different periodized programs (linear and daily undulating) on sprint and jump performance and explore relationships between performance measures. Sixteen male (16.9 +/- 1.0 y) adolescent rugby union players participated in 12 weeks of resistance training. A further 10 male (15.5 +/- 1.0 y) participants were recruited as a control group. Assessments of strength (box squat), 10 and 20 m sprint (electronically timed), and jump height (maximal unloaded (body mass only) and loaded (body mass + 10 kg) countermovement jumps) were conducted before and after 12 weeks training. Large to very large increases in 1RM box squat (linear: 33.9%; p < 0.001; ES = 1.64; daily undulating: 44.5%; p < 0.001; ES = 2.33) were observed after training. Small decreases were seen in 10 (linear: -1.6%; p = 0.171; ES = -0.84; daily undulating: -2.5%; p = 0.038; ES = -0.36) and 20 m (linear: -0.5%; p = 0.506; ES = -0.20; daily undulating: -1.7%; p = 0.047; ES = -0.27) sprint times. Small-to-moderate associations between changes in lower body strength and improvements in 10 and 20 m sprint times were found. Resistance training increases lower body strength in adolescent rugby union players and increases in lower body strength may transfer to improved sprinting performance with improvements following daily undulating periodized resistance training slightly superior. Copyright (C) 2017 by the National Strength & Conditioning Association.