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Objective: To assess the proposed prevalence of unresponsiveness of older men and women to augment lean body mass, muscle fiber size, muscle strength, and/or physical function following prolonged resistance-type exercise training. Design/Setting/Participants: A retrospective analysis of the adaptive response to 12 (n ¼ 110) and 24 (n ¼ 85) weeks of supervised resistance-type exercise training in older ( > 65 years) men and women. Measurements: Lean body mass (DXA), type I and type II muscle fiber size (biopsy), leg strength (1-RM on leg press and leg extension), and physical function (chair-rise time) were assessed at baseline, and after 12 and 24 weeks of resistance-type exercise training. Results: Lean body mass increased by 0.9 0.1 kg (range: 3.3 to þ5.4 kg; P < .001) from 0 to 12 weeks of training. From 0 to 24 weeks, lean body mass increased by 1.1 0.2 kg (range: 1.8 to þ9.2 kg; P < .001). Type I and II muscle fiber size increased by 324 137 mm2 (range: 4458 to þ3386 mm2; P ¼ .021), and 701 137 mm2 (range: 4041 to þ3904 mm2; P < .001) from 0 to 12 weeks. From 0 to 24 weeks, type I and II muscle fiber size increased by 360 157 mm2 (range: 3531 to þ3426 mm2; P ¼ .026) and 779 161 mm2 (range: 2728 to þ3815 mm2; P < .001). The 1-RM strength on the leg press and leg extension increased by 33 2 kg (range: 36 to þ87 kg; P < .001) and 20 1 kg (range: 22 to þ56 kg; P < .001) from 0 to 12 weeks. From 0 to 24 weeks, leg press and leg extension 1-RM increased by 50 3 kg (range: 28 to þ145 kg; P < .001) and 29 2 kg (range: 19 to þ60 kg; P < .001). Chair-rise time decreased by 1.3 0.4 seconds (range: þ21.6 to 12.5 seconds; P ¼ .003) from 0 to 12 weeks. From 0 to 24 weeks, chair-rise time decreased by 2.3 0.4 seconds (range: þ10.5 to 23.0 seconds; P < .001). Nonresponsiveness was not apparent in any subject, as a positive adaptive response on at least one training outcome was apparent in every subject. Conclusions: A large heterogeneity was apparent in the adaptive response to prolonged resistance-type exercise training when changes in lean body mass, muscle fiber size, strength, and physical function were assessed in older men and women. The level of responsiveness was strongly affected by the duration of the exercise intervention, with more positive responses following more prolonged exercise training. We conclude that there are no nonresponders to the benefits of resistance-type exercise training on lean body mass, fiber size, strength, or function in the older population. Consequently, resistance-type exercise should be promoted without restriction to support healthy aging in the older population.


Mary MacKillop Institute for Health Research

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Journal Article

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