Non-exercise micro-interventions to mitigate sedentarism induced poor health

Grant, Dale Mathew (2020) Non-exercise micro-interventions to mitigate sedentarism induced poor health. Doctoral thesis (PhD), Manchester Metropolitan University.

Preview

Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (14MB) | Preview

Abstract

Introduction: Displacing sedentary behaviour (SB) with light intensity physical activity (LIPA) enhances health in older adults. However, neither the underpinning physiologic mechanisms nor any impact of LIPA pattern are clear. Therefore, the current thesis investigated the effects of chronically displacing SB, with two distinct patterns of LIPA (intermittent vs continuous) on musculoskeletal health outcomes in older women. It was hypothesised that both LIPA implementations would improve health, with SB fragmentation (SBF) resulting in greater enhancements. Methods: Thirty-six community-dwelling older women were recruited (73±5 years). Following lifestyle (physical behaviour & diet) and health (body composition, muscle morphology, strength, activation capacity and physical function) assessments, participants were allocated to either: 1) SBF (2 minutes LIPA for every 30 minutes SB) (n = 14), 2) continuous LIPA (45–50-minute LIPA bout) (n = 14), or 3) control (n = 8). Assessments were repeated at week 8. Results: SB displacement with LIPA was successfully implemented and overwhelmingly perceived as palatable and achievable. Irrespective of prescribed pattern, displacing SB with LIPA resulted in enhanced physical function, plantar flexor (PF) isometric maximum voluntary contraction (iMVC), thoracic spine bone mineral density (BMD), and increased intake of nutrients promoting anabolism. Interestingly, increased PF iMVC was mediated via divergent neuromuscular adaptation pathways, dependant on prescribed LIPA pattern (SBF: reduced dorsiflexor antagonist coactivation, LIPA: increased PF activation capacity), and occurred irrespective of apparent PF maladaptation (reduced gastrocnemius medialis muscle volume). Furthermore, SBF reduced habitual dietary glucose intake and increased intake of nutrients promoting bone health. Accordingly, significantly greater increases in leg BMD and trends toward greater peak handgrip strength were observed following SBF. Conclusions: Ultimately, the results from the current thesis suggest some advantage of intermittent vs continuous LIPA implementation. Notably, despite its conventional designation as suboptimal, 8-weeks of LIPA implementation enhances overall musculoskeletal health in older adults.