The interacting effects of breaking up prolonged sitting with a single bout of exercise, plus regular short intervals of exercise, on blood flow to the brain and cognitive function in overweight adults

INTERVENTION: We propose a randomised cross‐over trial in 48 sedentary and overweight adults aged between 55‐80 years, to be undertaken (using a balanced orthogonal design) in two testing sites. The study will involve three acute experimental conditions (each of one day duration), separated by a minimum 7‐day washout period to account for any residual physiological effects of acute exercise that may persist for up to 72 hours. To eliminate bias, the order in which participants undertake the three experimental conditions will be determined from a computer‐generated, randomised sequence. Each experimental condition (detailed below) will be conducted in a controlled, laboratory setting to minimise the potential confounding influences and the inherent variability of less‐controlled and more‐variable ‘real‐world’ settings. In all experimental conditions participants will arrive, having fasted for 10 hours, and be seated in a comfortable lounge‐chair and instructed to minimise excessive movement and avoid all activities requiring cognitive engagement (eg: cross‐words, Sudoku). 1) Uninterrupted Sitting: Participants will sit quietly for eight hours, with breakfast and lunch provided during this period. 2) Continuous Exercise + Uninterrupted Sitting: After sitting quietly for 1 hour (steady state) participants will complete a 30 minute bout of continuous moderate‐intensity exercise on a motorised treadmill , at a predetermined power output corresponding to a range of between 65% ‐75% of maximal heart rate. Following this participants will sit quietly for the remaining 6 1/2 hours. 3) Continuous Exercise + Interrupted Sitting: Identical procedure to condition 2, however, after the continuous exercise bout, participants will remain seated for a further 30 minutes before completing a three‐minute bout of light‐intensity walking on a motorised treadmill at 3.2km.hr‐1. They will then return to the seated position. This procedure will be repeated on 12 occasions every 30 minutes for a total of 36 minutes of light‐intensity activity. The scientific rationale for the utilisation of the proposed protocol has been deliberately guided by our recently published findings (2min every 20min, total 28min) but modified slightly to accommodate the appropriate timing of the proposed testing procedures. The research group consisting of the coordinator, research nurse and assistant will be responsible for monitoring adherence to the interventions CONDITION: Cognitive Function INCLUSION CRITERIA: BMI equal or greater than 25 kg/m2 but less than 45 kg/m2 and English‐speaking PRIMARY OUTCOME: Cognitive function: Measured using a computerized battery of tests (CogState ‐ www.cogstate.com.au) that has been specifically developed for brief repeated testing of cognitive performance in clinical and research trials, with good acceptability, efficiency and stability, and minimisation of practice effects. The test battery will cover multiple cognitive domains with a primary focus on executive function (most likely to be influenced by acute exercise). The battery will comprise: 1) Identification task to assess visual attention and vigilance; 2) N‐back to assess attention and working memory; 3) Groton Maze Learning to assess executive function including spatial problem solving; 4) Detection task to assess psychomotor function and speed of processing; and 5) One card learning task to assess visual learning and memory; for a total administration time of approximately 25 minutes. SECONDARY OUTCOME: Blood measurements: Venous blood samples will be collected by a trained nurse via an in‐dwelling catheter in the antecubital vein. Between 6mL‐ 20mL (0.4 ‐ 1.3 tablespoons) will be collected on each occasion, of which a fraction will be sent immediately to Alfred Pathology (for the Baker IDI site) or University of Western Australia (UWA) for that site, for analysis of glucose, triglycerides, full blood evaluation and lipid profile. The remaining blood will be centrifuged and the plasma fraction removed and frozen at at ‐80°C for later analysis related to this trial. The cannula will be flushed with normal saline following every blood draw to maintain its patency. Blood pressure: Hourly resting brachial arterial blood pressure will be taken after a five minute rest period, three times, at one‐minute intervals, using an automated oscillometric blood pressure monitor 10 (Dinamap Vital Signs Monitor 18465X, Criticon, Florida, USA).