ntroduction: Age-related decrements in trunk muscle size and strength are associated with decreased balance and increased falls risk. The effectiveness of balance and/or resistance training of the peripheral musculature for falls prevention in older adults have been well-demonstrated. However, little is known about the effect of exercise programs targeting trunk musculature on functional ability in older adults. Our study sought to explore the effectiveness of a 12-week supervised multimodal exercise program comprising walking and balance exercises, with or without trunk strengthening/motor control exercises on trunk muscle size, strength, and functional ability in healthy older adults. Methods: Our study was a single-blinded parallel group randomized controlled trial. We recruited healthy older adults (≥60 years), with no history of lumbar surgery or medical conditions impeding safe participation in an exercise program. Sixty-four older adults (mean (SD) age: 69.8 (7.5) years; 59.4% female) were randomized to receive a 12-week supervised multimodal exercise program comprising walking and balance exercises with or without trunk strengthening/motor control exercises. Trunk muscle size and strength were assessed using ultrasound imaging and HUMAC NORM isokinetic dynamometer, respectively. Functional and balance outcomes were assessed using 30-second Chair Stand Test, Sitting and Rising Test, Berg Balance Scale, and Multi-Directional Reach Test. All data was analyzed using a linear mixed model. Results: After 12 weeks of the exercise program, the trunk strengthening/motor control exercise group experienced larger increases in trunk muscle hypertrophy (1.6[1.0,2.2]cm) and composite trunk strength (172.6[100.8,244.5]N); as well as improved 30-Second Chair Stand Test (5.9[3.3,8.4]repetitions), Sitting and Rising Test (1.2[0.22,2.2]points), Forward Reach Test (4.2[1.8, 6.6]cm), and Backward Reach Test (2.4[0.22,4.5]cm) outcomes, compared to the walking-balance exercise group. Conclusion: This randomized controlled trial shows that including trunk strengthening/motor control exercises into a 12-week supervised multimodal exercise program confers additional benefits to balance and walking training in healthy older adults.

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