FIT 2 SIT - Are Metabolic Responses to Sitting/Light Breaks Mediated by Fitness?

The FIT 2 SIT study requires three separate study visits in total.

At visit one, we will check the participants blood pressure, height, weight, waist measurement and body fat percentage, we will also take a blood sample to measure HbA1c and cholesterol, all of which will help confirm that this participant is eligible to continue in this study (some may be excluded based on results of the above). We will also measure the amount of energy participants expend per minute while at rest and during a slow walking task (3km.h on a treadmill) using a gas mask technique. Energy responses to sitting and walking differ between individuals, therefore it is of interest to observe how each participant in this study responds to these conditions as it may help explain any potential findings of this study. For instance, introducing walking breaks (by way of reducing sitting time) may only benefit those who have consequent increases in energy expenditure as a result of these breaks. Lastly, to mark the end of the first study visit, participants will be asked to perform an exercise test based on a treadmill to assess their fitness level. whilst running a special mask covering the nose and mouth will be worn to analyse breathing, this will be connected to a machine (gas analyser) that gives information on the amount of oxygen participants breathe in and out. The point at which the amount of oxygen they breathe in remains stable despite increases in exercise difficulty is the point that we will stop the exercise test because this tells us that they have reached their exercise capacity (called V02max), and from this we can determine fitness level.

Following this first visit we will have fitness level data from all participants. Recruiting participants with a diverse fitness level will then help to elucidate the role that an individuals fitness has on their response to the following treatment conditions.

Treatment condition A is referred to as the 'sitting' condition. Here participants will remain seated throughout the whole of the 7 ½ hour test period (8am - 3:30pm) whilst watching TV/DVD's, reading, using the internet, doing paperwork etc. at their will. On arrival, participants will have a cannula (a small tube that allows us to take blood) inserted into their arm; this will stay in the arm and allow us to take regular blood samples throughout the day, without the need for multiple needles. After we take the first blood sample, participants will sit quietly for an hour. We will then provide breakfast. Whilst sitting, we will take blood samples (using the cannula) and blood pressure at 30, 60, 120 and 180 minutes after breakfast. We will then provide a lunch meal and will continue taking blood samples and blood pressure at 30, 60, 120, 180 and 210 minutes after this lunch meal. In total, we will take 11 blood samples over the 7 ½ hour testing period. Although this may sound a lot, it is equivalent to around 8-9 teaspoons of blood over the course of the day.

Condition B is the 'light activity breaks' condition. Participants will go through exactly the same process as condition A but will also be asked to do 5 minute bouts of slow walking on a treadmill every 30 minutes following breakfast and lunch. In total they will do 12 five minute walks on the treadmill throughout the 7 ½ hour test period (60 minutes of walking in total). In total, we will take 11 blood samples on the day.

With data on each participants metabolic response to a meal during A) prolonged sitting and B) during an interrupted sitting condition, we can see how fitness influenced the results.

However, at present, the absence of laboratory randomised crossover trials assessing the 'extent' to which fitness moderates the relationship between sedentary behaviour and metabolic health markers appear absent from the literature, warranting further investigation, which is why this design was chosen.