Preliminary evidence indicates that age-related changes in trunk muscle morphology and function are associated with decreased balance and increased falls risk. However, the associations between trunk muscle morphology, strength, and functional ability, as well as the trainability of these muscles are not well established. Therefore, the aims of this thesis were to identify the relationships between trunk muscle morphology, strength, and functional ability and to determine the effects of exercise training on these outcomes in healthy older adults.
We initially undertook a systematic review to determine the effect of exercise training on trunk muscle morphology. Our results identified motor control and machine-based exercises targeting the trunk muscles resulted in the largest change in the trunk muscle morphology.
Using a cross-sectional design, we then explored the relationships between trunk muscle morphology, strength, and functional ability in 64 older adults. Our results showed anterior and lateral abdominal and posterior trunk muscle size and strength were positively associated with functional ability.
Finally, we conducted a randomised clinical trial investigating the effectiveness of a 12-week exercise programme on trunk muscle size, strength, and functional ability. 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. Participants performing the trunk strengthening exercises experienced larger increases (mean difference [95%CI]) 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 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), Backward Reach Test (2.4 [0.22, 4.5] cm), and Timed Up and Go Test (-0.74 [-1.4, -0.03] seconds) outcomes.
These findings further our understanding regarding 1) the relationships between trunk muscle morphology, strength, and functional ability and 2) appropriate exercise prescription aimed at improving these outcomes in older individuals
