Introduction: Aging-related decrements in trunk muscle morphology and function are associated with decreased balance and increased falls risk (Granacher, Gollhofer, Hortobagyi, Kressig, & Muehlbauer, 2013; Granacher, Lacroix, Muehlbauer, Roettger, & Gollhofer, 2013). Previously, balance and/or resistance training of the peripheral musculature have demonstrated good efficacy for prevention of falls in older adults (Lee & Park, 2013). However, the efficacy of training the lower trunk musculature remains largely unexplored. Therefore, the purpose of this study was to assess changes in trunk muscle morphology and functional ability following a 12-week supervised multimodal exercise training program amongst healthy older individuals. Methods: We conducted a single-blinded parallel group randomised clinical trial to investigate the effectiveness of a 12-week exercise program on trunk muscle size and functional ability in healthy older individuals. Sixty-four individuals (mean [SD] age: 69.8 [7.5] years; 59.4% female) were randomised to receive a multimodal exercise program comprising walking and balance exercises with or without strength/motor control training of the trunk muscles. Lower trunk muscle size was measured using ultrasound imaging. Functional ability was assessed using the six-minute walk test, the Berg Balance test, the 30 Second Chair Stand, and the Timed Up and Go. All participants completed baseline, six-week, and 12-week assessments. Consistent with the intentionto-treat principle, all data was analysed using a linear mixed model, and the main effects of exercise group and the exercise group by time interactions explored. Results: Participants performing the trunk exercises experienced greater increases (mean difference [95% CI]) in trunk muscle hypertrophy (1.6 [1.0, 2.2]) at the end of the 12-week training program. In addition, participants performing the trunk exercises showed significantly greater improvements in their 30 Second Chair Stand (5.9 [3.3, 8.4] repetitions) and Timed Up and Go (–0.74 [–1.40, –0.03] s) performance when compared to the exercise group which did not incorporate the trunk muscle exercises. Conclusion: These findings support the inclusion of strength/motor control training of the trunk muscles as part of a multimodal exercise program in older individuals

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