The aim of this study was to assess the effectiveness of a multimodal exercise program to increase trunk muscle morphology and strength in older individuals, and their associated changes in functional ability. Using a single‐blinded parallel‐group randomized controlled trial design, 64 older adults (≥60 years) were randomly allocated to a 12‐week exercise program comprising walking and balance exercises with or without trunk strengthening/motor control exercises; followed by a 6‐week walking‐only program (detraining; 32 per group). Trunk muscle morphology (ultrasound imaging), strength (isokinetic dynamometer), and functional ability and balance (6‐ Minute Walk Test; 30 second Chair Stand Test; Sitting and Rising Test; Berg Balance Scale, Multi‐Directional Reach Test; Timed Up and Go; Four Step Square Test) were the primary outcome measures. Sixty‐four older adults (mean [SD]; age: 69.8 [7.5] years; 59.4% female) were randomized into two exercise groups. Trunk training relative to walking‐balance training increased (mean difference [95% CI]) the size of the rectus abdominis (2.08 [1.29, 2.89] cm2), lumbar multifidus (L4/L5:0.39 [0.16, 0.61] cm; L5/S1:0.31 [0.07, 0.55] cm), and the lateral abdominal musculature (0.63 [0.40, 0.85] cm); and increased trunk flexion (29.8 [4.40, 55.31] N), extension (37.71 [15.17, 60.25] N), and lateral flexion (52.30 [36.57, 68.02] N) strength. Trunk training relative to walking‐balance training improved 30‐second Chair Stand Test (5.90 [3.39, 8.42] repetitions), Sitting and Rising Test (1.23 [0.24, 2.23] points), Forward Reach Test (4.20 [1.89, 6.51] cm), Backward Reach Test (2.42 [0.33, 4.52] cm), and Timed Up and Go Test (−0.76 [−1.40, −0.13] seconds). Detraining led to some declines but all outcomes remained significantly improved when compared to pre‐training. These findings support the inclusion of trunk strengthening/motor control exercises as part of a multimodal exercise program for older adults.

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