Effects of Reducing Prolonged Sitting on the Endothelial Function in Overweight/Obese Adults

This randomised crossover trial in overweight or obese adults will involve two acute experimental conditions (each of 6 hours duration), to examine the impact of prolonged uninterrupted sitting, or breaking up sitting with brief bouts of simple resistance activities (3 minutes every 30 minutes) on endothelial function. Twenty five inactive and injury-free participants aged between 35-75 years will be recruited. Participants will visit the Physical Activity Laboratory at Baker IDI on 3 separate occasions. Participants will first attend a familiarisation session 3-7 days prior to the commencement of the experimental trial, in order to ensure optimal safety and to allow orientation with the testing procedures and measurement devices. During this visit, the study staff will familiarize participants with simple resistance activities, ensuring they are comfortable with the exercises and suitable technique and movement consistency are achieved. Anthropometric measurements (weight, height and waist circumference) will also be obtained. Activity intensity levels will be monitored and assessed using heart-rate monitoring, and the Borg rate of perceived exertion scale (RPE – numbered scale from 6-20) and visual analogue scales (VAS – continuous scale from ‘extremely easy’ to ‘extremely difficult’). Each participant will then complete two experimental conditions in a laboratory setting, supervised by the study staff to ensure adherence to the experimental conditions. The two conditions will be separated by a minimum 5-day washout period to account for any residual physiological effects of the intervention. Participants will be advised to wear appropriate footwear and clothing to allow sufficient range of motion at the knee and hip (45 degrees to 90 degrees for half-squats or knee raises). In all experimental conditions participants will be seated in a comfortable lounge-chair and have access to a television, DVD player and reading materials such as newspapers and magazines. They will be instructed to minimise excessive movement, but will be allowed to visit the toilet when necessary. Before starting the experimental conditions, participants will sit for the first one hour, during which baseline measurements will be taken. Participants will be then given a standardised breakfast meal of croissant with ham & cheese, Pine and mango juice with a choice of Corn flakes or Sultana bran (with Milk). This will comprise 33% of estimated daily energy requirements, with a macronutrient profile of 53-55% energy from carbohydrate, 12-15% energy from protein, and 30-33% energy from fat. The two experimental conditions are- 1) Uninterrupted Sitting (control condition): Participants will sit quietly for 5 hours. 2) Simple Resistance Exercises and Interrupted Sitting: Identical procedure to Condition 1, however, participants will complete a 3 min bout of simple resistance activities every 30 minutes. The activities will be allocated into nine 20 second segments, alternating between body weight half squats, calf raises and brief gluteal contractions in-between single leg knee raises (total exercise time equals to 27 mins). This interchange between movements will provide rest for the corresponding muscle groups between each activity segment. To ensure appropriate standardisation, participants will complete each activity in a controlled manner within their range of motion (knee or hip 45 to 90 degrees for half-squats or knee raises), while synchronizing the tempo of each activity to a demonstration video playing. To minimise any potential diet-induced variability in the metabolic profile, participants will be provided with a standard ‘food pack’, containing a dinner meal for the night prior to each experimental condition, as well as lunch and dinner following each condition. All food packs will be matched for macronutrient composition (as % of total energy intake, with a macronutrient profile of 53-55% energy from carbohydrate, 12-15% energy from protein, and 30-33% energy from fat). Participants will be instructed to consume only the food items within the food pack for each meal. The lunch (based on 27 % estimated energy requirements-consisting of bread roll with a choice of Turkey/Cheese/Cranberry/Lettuce roll or Ham/Cheese/Cranberry/Lettuce roll or Turkey/Cheese/Mayonnaise/Lettuce roll or Ham/Cheese/Mayonnaise/Lettuce roll with a choice of Lemonade or Fanta) will be consumed before leaving the laboratory, and the dinner meals (based on 40% estimated energy requirements-consisting of Mongolian beef, apricot muesli bar and roasted cashews) between 7-9pm in the evening. Participants will be instructed to only consume the food contained in the packs, and to perform their habitual pattern of daily activities for the next 24 hours. The meals will be self-selected from pre-selected options and will be the same meal for both conditions. Before leaving the laboratory on the experimental days, participants will be fitted with both a 24 hour ambulatory blood pressure monitor (ABPM) and a continuous glucose monitoring system (CGMS). Participants will be asked to keep these devices on overnight after each trial to assess what happens to their blood glucose and blood pressure during this period. This will require them to take 3 blood samples with a finger prick blood taking device provided by the research staff. The next morning before breakfast participants will simply remove both devices (tape and all), put in a pre-prepared envelope and mail it back to Baker IDI (unless collected by researchers).