Effects of Breaking up Sitting Time on Cardiometabolic Risk Markers and Cardiac Function Post Myocardial Infarction

Study design A repeated measures, randomised cross over study design will be used. All data collection will take place at the Sport and Exercise Science Laboratories, University of Bedfordshire, Polhill Avenue, Bedford, UK. After a preliminary testing session, participants will complete three, 6-hour experimental conditions in a random order: 1) uninterrupted sitting; 2) sitting interrupted with standing breaks, and 3) sitting interrupted with light intensity stepping breaks. There will be a washout period of at least 72 hours between conditions, as previous research suggests that a single session of exercise can affect blood glucose levels for the following 48 hours (Mikines, et al., 1988). Participants will be randomised to order of condition using computer generated random numbers. This will assign them a trial order using block randomization with balanced block sizes. Participants will be blinded to the trial condition until they arrive on the day of their first and second experimental conditions.

Preliminary testing Patients will first attend a preliminary testing session where they will become accustomed to light intensity stepping on the spot to the beat of a metronome and use of the Borg RPE scale. This will ensure patients are familiar with an intensity that is equivalent to an RPE of 8-11 (very light to light) that will be used in the respective experimental condition. Participants will step to different metronome paces starting at a slow pace and building up gradually every 1-2 minutes until an RPE of 8-11 is found. This imitates the intensity recommended within the warm up of CR, as recommended by BACPR. Height (cm) and weight (kg) will also be measured using a stadiometer (Harpenden 98.602, Holtain Ltd., Crymych) and digital scales (Tanita BWB0800, Tanita Corp., Tokyo, Japan) respectively, to calculate body mass index (kg/m2).

Experimental Protocol Participants will be asked to refrain from any alcohol and caffeine for 24 hours prior to each visit, as well as avoid exercise for 72 hours and complete an overnight fast. This will be explained to them during the preliminary visit. To monitor this, they will be asked prior to participation per visit whether they have fasted/ when they last ate and drank.

Participants will be asked to perform an overnight fast for at least 10 hours before arrival and minimise active travel to the laboratory (e.g. use a car for travel). They will rest for 30 minutes to achieve a steady state before baseline blood pressure (two measures with 2 minutes rest between each and the average taken) and blood samples are taken. Baseline cardiac function measures (global strain, ejection fraction and systolic volume) will be measured using an echocardiogram scan, as well as an electrocardiogram (ECG) to ensure there are no electrical contraindications to the heart which would make the participant unsuitable to complete the study intervention including ST depression / elevation or any arrythmias. Baseline mood and wellbeing measures will then be assessed using questionnaires.

Following baseline measures, a standardised breakfast will be consumed (see meals section below) and participants will then commence the experimental condition. See Figure 1 for schematic of experimental conditions.

The three experimental conditions for this study are:

1. Uninterrupted sitting for 6 hours.
2. Sitting interrupted with 5 minutes of static standing every 30 minutes.
3. Sitting interrupted with 5 minutes of light intensity stepping every 30 minutes using a metronome at the intensity determined during preliminary testing. This replicates active recovery time currently performed in a phase III CR class.

A lunch meal will be provided at 12:00 during each condition. During sitting periods, participants will be able to read books, magazines or newspapers and/or watch TV, DVDs or media streaming services. Participants will be transported to the toilets and food consumption areas using a wheelchair to ensure activity is minimised and standardised between conditions.

Standardised food and water intake Each meal will provide approximately 30% of estimated daily energy requirements. This will be calculated for each individual participant using a prediction equation based on individual's height, weight and gender. Breakfast will consist of bran flakes, whole milk, and a honey and granola bar and will consist of 54% carbohydrate, 34% fat and 12% protein. Lunch will consist of a chicken sandwich, salted crisps and jammie dodger biscuit (54% carbohydrate, 34% fat and 12% protein). The macronutrient composition of the meals are in general agreement with guidelines recommended for a balanced diet (Public Health England, 2016). Participants will be encouraged to consume their meal within 15 minutes. The time taken will be recorded in the first condition and this time will then be replicated in the latter two conditions. Water will be available for the participants ad libitum during their first experimental condition visit. This volume of intake will be recorded and the same amount provided in the following two conditions spread over the day.

Data collection Finger prick capillary whole blood samples will be collected at baseline, 30, 60, 120, 180, 210, 240, 300 and 360 minutes throughout the conditions to allow later analysis of glucose, triglycerides, HDL-C, and insulin. Blood samples will be taken after the hand is pre-warmed in warm water for approximately 5 minutes. Blood pressure and heart rate will be measured 5 minutes before each of the blood samples are taken. Cardiac function measures and mood and wellbeing will be measured at baseline and post-condition.