Abstract
Background: Prolonged sedentary behaviour is associated with an increased risk of disease incidence and mortality, as well as a poorer cardiometabolic profile. Interrupting day time sedentary behaviour reduces postprandial glycaemia; however, the influence of interrupting evening sedentary time on health parameters has yet to be fully explored. Therefore, this thesis examines the impact of interrupting evening sitting time with short bouts of resistance exercise on postprandial metabolism, subsequent 24-hour movement patterns (sleep, sedentary behaviour and physical activity) and glycaemic control and variability. Furthermore, in order to achieve these potential health benefits, people must perform the behaviour. The COM-B model states that for behaviour change to occur, people must have the capability, opportunity and motivation. Thus, it is important to assess the perceived barriers and facilitators of incorporating these breaks in a free-living environment. Findings from which could provide information on potential behaviour change strategies to be included in the design of future interventions aimed at reducing habitual evening sedentary time.
Methods: In a randomised crossover trial, 30 adults (aged 25.4 ± 5.4 years) from three body mass index (BMI) categories (18.5–24.9 kg/m2: n=10, 25–29.9 kg/m2 n=10, ≥30 kg/m2 n=10) completed two 4-hour intervention conditions in a laboratory setting, beginning at ~1700-1730 hours: 1) Prolonged sitting, where participants sat continuously for the 4-hour period; and 2) Regular activity breaks, where participants interrupted prolonged sitting every 30 min by performing 3 min of bodyweight resistance exercises. The day prior to the session participants were fitted with a FreeStyle Libre Pro iQ continuous glucose monitor to measure interstitial glucose and an ActiGraph GT3+ accelerometer (worn on the non-dominant wrist) to measure physical activity and sleep during, and until 48-hours post-intervention. During the intervention sessions, participants were fed a standardised dinner (at 0 min) and dessert (at 120 min). Postprandial glucose and insulin response were measured in blood samples collected via intravenous cannula. Blood samples were collected hourly, with additional samples collected at 30- and 45-min after each meal. Twenty-eight participants completed individual, face-to-face semi-structured interviews at the end of the trial. Questions explored perceived barriers and facilitators to performing regular activity breaks in the evening at home. Data was analysed using inductive thematic analysis before being mapped to the components of the COM-B model.
Results: When compared to prolonged sitting, regular activity breaks lowered plasma glucose and insulin iAUC by 31.5% (95% CI -49.3% to -13.8%) and 26.6% (-39.6% to -9.9%), respectively, and interstitial mean glucose by 8.3% (-0.47 mmol/L/4h, 95% CI -0.74 to -0.20, p=0.001) during the 4-hour intervention period. During the first nocturnal period and 24-hours post-intervention there were no significant differences in interstitial mean glucose and AUC between conditions. Visual inspection of the interstitial glucose response curve showed that compared to prolonged sitting, mean glucose remained lower following regular activity breaks until ~0900 hours the following morning. Compared to prolonged sitting, regular activity breaks extended the subsequent free-living sleep period time by 29.3 min (95% CI 1.3 to 57.2, p=0.040) and time spent asleep by 27.7 min (95% CI 2.3 to 52.4, p=0.033) in the first nocturnal period after completing the intervention. There were no significant differences in sleep quality or time spent engaged in physical activity and sedentary time, over the subsequent 24- and 48-hours.
The themes identified from the qualitative interview data showed that participants found the regular activity breaksprotocol easy and acceptable. Acutely, participants reported that regular activity breaks improved subsequent sleep and focus; however, some participants experienced muscle soreness the following day. Participants perceived that having ‘awareness of the benefits’ of activity breaks, as well as reminders to take the breaks could influence their psychological capability to perform this behaviour. The perceived social opportunity to perform activity breaks at home could be influenced by whether (or not) others were performing the activity breaks. ‘Motivation’, such as working towards a goal or not wanting to interrupt their current sedentary behaviour, explained how reflective motivation could influence individuals to take activity breaks. Additionally, this theme explained how participants perceived that tiredness and reinforcement of sedentary behaviour via the nature of streaming services could hinder individuals’ automatic motivation to perform activity breaks in their habitual evening routines.
Conclusions: Interrupting evening sitting with short bouts of resistance exercise can improve postprandial metabolism in adults, regardless of weight status. Regular activity breaks extended subsequent sleep, and did not disrupt sleep quality or 24-hour movement patterns. Thus, regular activity breaks have the potential to improve cardiometabolic health through multiple mechanisms. Capability, opportunity, and motivation were all perceived to influence individuals’ ability to interrupt habitual evening sitting with regular activity breaks. A multicomponent intervention was subsequently designed to improve capability to undertake regular activity breaks in the home setting by understanding the benefits and providing reminders to interrupt sitting, opportunity by utilising social support, and motivation by creating goals and action planning.