Jackson, JK, Shepherd, TR, and Kell, RT. The influence of periodized resistance training on recreationally active males with chronic nonspecific low back pain. J Strength Cond Res 25(1): 242-251, 2011-The most common musculoskeletal health issue is chronic nonspecific low back pain (CLBP). CLBP increases pain and disability, which reduces quality of life (QoL). Generally, pain, disability, and QoL are improved with a moderate volume and intensity of physical activity. Recently, periodized resistance training (PRT) was shown to be effective at improving CLBP in sedentary young, middle-age, and older adults. The purpose of this study was to determine if PRT would increase strength, reduce pain and disability, and improve QoL in recreationally active, moderately trained middle- and older-age males. Forty-five male subjects were divided according to age into 1 of 3 groups: (a) middle-age exercise (ME), (b) old-age exercise (OE), or (c) control (C). All subjects suffered from CLBP and were considered to be moderately trained, participating in recreational ice hockey for 60 minutes, 2 times per wk−1 for ∼5 months/year along with other recreational activities. The study ran for 16 weeks (3-week familiarization and 13 weeks of testing and PRT) with 5 repetition maximum testing at baseline and weeks 8 and 12. The PRT program systematically and progressively overloaded all major muscle groups (whole-body workout). The results indicate that middle- and old-age recreationally active males with CLBP respond similarly in magnitude to PRT, with improvements in all outcome measures (strength, pain, disability, QoL) across all time points of the study. Clinical significance (≥25%) in outcome measures was reached on most variables for the ME and OE groups. The results suggest that PRT may be effectively applied as rehabilitation for moderately trained recreational athletes with CLBP.