The influence of sedentary behaviour on muscle-tendon properties and resultant postural balance in older adults

Wullems, Jorgen Antonin (2018) The influence of sedentary behaviour on muscle-tendon properties and resultant postural balance in older adults. Doctoral thesis (PhD), Manchester Metropolitan University and Katholieke Universiteit Leuven.

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Abstract

In recent years, sedentary behaviour (SB) has been identified as a health risk, independent of physical activity (PA). With the population becoming increasingly sedentary, detailed analysis of its effects is required. It is proposed that in the elderly, arguably the most sedentary age group, SB might adversely affect musculoskeletal health hence leading to poorer physical functioning, less independence and higher risk of falling. Hence, this thesis aimed to study the associations between SB and muscle-tendon properties in older adults (aged ≥60 years). To do so, a machine learning algorithm was applied onto thigh-mounted accelerometry data. Algorithm performance was acceptable for a wide spectrum of physical activity intensities, and its concurrent validity was good. Then, a cross-sectional study on 105 older adults included a 7-day habitual activity monitoring week, and assessed gastrocnemius medialis (GM) muscle-tendon morphology, architecture, function, fatigue indices, mechanical and material properties, and postural balance. From the accelerometer data, both total amount and patterns of SB were extracted. Analysis of these outcomes ranged from simple comparison of general SB levels to compositional data analysis. Multiple linear regression models showed a few associations linking SB with detrimental outcomes with GM muscle properties (dimension, strength and force). Similarly, isotemporal substitution yielded a limited number of significant potential relative effects of SB behaviour alterations. GM tendon mechanical, material and morphological properties also showed associations. Interestingly, negative associations between SB and postural balance in this group of older adults were also identified. Overall, this thesis presents novel data from detailed analyses on SB and intrinsic muscle-tendon properties in older adults. Regardless of the somewhat limited associations between sleep and PA-independent SB outcomes and GM muscle-tendon properties in older adults, the negative relationship with a task associated with habitual physical independence (i.e. postural balance) warrants further investigation of SB in elderly.