393 Journal of Aging and Physical Activity, 2008, 16, 393-407 © 2008 Human Kinetics, Inc. Effect of Power-Training Intensity on the Contribution of Force and Velocity to Peak Power in Older Adults Nathan J. de Vos, Nalin A. Singh, Dale A. Ross, Theodora M. Stavrinos, Rhonda Orr, and Maria A. Fiatarone Singh Objective: To determine the effect of training intensity on the contributions of force and velocity to improvements in peak power (PP) after explosive resistance training in older adults. Methods: 112 healthy older adults (69 ± 6 yr) were randomized to explosive resistance training at 20% (G20), 50% (G50), or 80% (G80) maximal strength (1-repetition maximum) for 8–12 wk (twice weekly, 5 exercises, 3 sets of 8 explosive concentric/slow eccentric repetitions) using pneumatic resistance machines or a nontraining control group (CON). Results: Force at peak power (FPP) increased signiicantly and similarly among training groups compared with CON. Velocity at peak power (VPP) did not improve signiicantly and remained similar between all groups. Force contributed signiicantly more to PP production in G80 and G50 than in CON. The change in PP was independently predicted by changes in fat-free mass in G80 and by changes in both FPP and VPP in G50 and G20. Conclusion: Explosive resistance training in older adults results in the ability to produce higher PP outputs with heavier loads without loss of movement velocity. Moderate- to high-intensity training induced a greater relative contribution of force to PP production in this cohort. Keywords: resistance training, strength, exercise, randomized Given the faster declines in muscle power than in strength with age (Bosco & Komi, 1980; Izquierdo, Aguado, Gonzalez, Lopez, & Hakkinen, 1999; Labarque, ’T Eijnde, & Van Leemputte, 2002; Macaluso & De Vito, 2003; Metter, Conwit, Tobin, & Fozard, 1997; Skelton, Greig, Davies, & Young, 1994) and its stronger associations with functional performance and disability (Bassey et al., 1992; Bean et al., 2002; Bean et al., 2003; Cuoco et al., 2004; Foldvari et al., 2000; Hruda, Hicks, & McCartney, 2003; Suzuki, Bean, & Fielding, 2001), recent attention has been directed toward speciic resistance-training strategies to improve muscle power in older adults (Bean et al., 2002; de Vos et al., 2005; Earles, Judge, & Gun- narsson, 2001; Fielding et al., 2002; Henwood & Taaffe, 2005; Hruda et al.; de Vos, Orr, and Fiatarone Singh are with the Discipline of Exercise, Health and Performance, Faculty of Health Sciences, University of Sydney, Sydney, NSW, Australia. Singh, Ross, and Stavrinos are with Balmain Hospital, Sydney, NSW, Australia.