Introduction: The degenerative loss in skeletal muscle size associated with aging is often accompanied by a decrease in balance and functional mobility which may result in reduced quality of life, increased risk of falling and increased mortality rates (1). Much of our knowledge regarding the inverse relationship between poor functional outcomes and the aging process is restricted to the peripheral musculature. More recently, particular attention has started focusing on the muscles of the trunk due to their important role in performing activities of daily living (2), their association with balance and mobility in older adults (3) and falls. To date, the association between trunk muscle morphology and functional abilities has not been comprehensively explored. Therefore, the primary purpose of this study was to evaluate the association between trunk muscle morphology and functional abilities. Methodology: Sixty-four community-dwelling older adults (60 years and older) were recruited to participate in this cross sectional study. Participants underwent real-time ultrasound imaging assessment for the measurement of lower trunk muscle morphology (muscle thickness and cross sectional area CSA)). The lower trunk muscles included the anterior abdominal muscles (rectus abdominis (RA)), lateral abdominal muscles internal (the internal oblique and external obliques and transversus abdominis (LAM)) and posterior lower trunk muscles (lumbar multifidius lumbar spinal level L4/L5 and L5/S1 (LM L4/L5 and LM L5/S1). Functional outcomes were assessed using Berg Balance Test (BBT), MultiDirectional Reach Test (MDRT), Timed up and go (TUG), The 30 seconds Chair Stand Test (30sec-CST), Sit and Rise Test (SRT), Four Square Step Test (FSST), Six-minute Walk Test (6MWT) . Univariate and multivariate linear regression statistical models were used to examine the association and relationship between lower trunk muscle morphology and functional outcomes. Results: Univariate analyses revealed significant positive correlations between 6MWT, BBT, MDRT forward, 30sec-CST, SRT and RA-CSA. Moreover, MDRT backward was positively correlated with RA-CSA and LAM and with the composite trunk muscles. TUGT and FSST were also found to be positively correlated with LM L4/L5 and LM L5/S1. After adjustment for demographic variables (age, sex, BMI), the relationship between trunk muscle morphology and functional measures showed that the effects of RA-CSA was significantly and positively associated with distance covered in the 6 MWT (P < 0.001). The effect of LAM was positively and significantly associated with results from the BBT (P < 0.001). There were no associations between MDRT forward, right and left sides with lower trunk muscle morphology however, a positive and significant association was found between MDRT backward and RA-CSA (P < 0.001). RA-CSA and LM L4/L5 were significant independent predictors of the results from 30 sec-CST (P < 0.001). TUG and FSST showed a positive and significant relationship with LM L4/L5 (P < 0.001). Finally, a significant positive association between RA-CSA and SRT was found (P < 0.001). Discussion: Findings revealed positive associations between lower trunk muscle morphology and balance/functional motility. After adjusting for demographic variables, lower trunk muscle morphology was an independent predictor of static, dynamic and functional performance in older adults. Declining lower trunk muscle morphology, particularly in the anterior abdominal muscles (RA-CSA), was a common finding in this older cohort and was associated with reduced functional capacities. Thus improving trunk muscle morphology may lead to reduced balance impairments and improved functional capacities in older individuals

Keywords