The knowledge gap on sedentary behavior and sedentary breaks includes whether detrimental effects of sedentary behavior can be fully attenuated by 1.) sedentary breaks 2.) physical activity or 3.) both combined. Specifically, when breaking sedentary time which physical activity pattern- and intensity modifies the negative effects of sedentary behavior on glucose- and lipid metabolism? This lack of quantitative evidence calls for prospective experimental studies investigating the physiological and biological impacts of sedentary behavior, as well as the effectiveness of different strategies to reduce sedentary time. Thus, quantifying effects of the intensity, frequency, volume and investigating the patterns of sedentary breaks and/or physical activity on predefined outcomes is of importance.

Aims:

Our primary aims are to investigate the effects of breaking up sedentary time on glucose- and lipid metabolism and thus examine whether pattern for sedentary bouts and breaks and physical activity intensity during sedentary breaks matter. Specifically, the aims of the PhD-project are to provide knowledge on the following questions:

• How does different patterns of accumulation of sedentary bouts and breaks acutely influence glucose- and lipid metabolism under iso-caloric conditions?

The participants will undergo 4 different trial conditions of which all are iso-caloric, but with different intervals of sitting and executing moderate physical activity by treadmill walking corresponding to 45-55% of their individual VO2max/peak values, estimated from the individual's pre-test. The total duration of sedentary- and physical activity time will be identical in each trial condition. This study has a is randomized cross-over design. If found eligible from step 1 and 2 in the inclusion process, participants will be invited to a final screening day in our lab. Eligible participants then consenting to joining the study will continue on to 4 trial days. Due to possible acute rise in insulin for up to 48 hours, a 5-14 day washout period between trials will be used to avoid carryover effects. In the washout periods between experimental conditions the participants will resume their habitual life activities and behaviours, i.e., diet and physical activity patterns. However, from visit 2, during washout the participants will wear accelerometers (ActiGraph GTX3+, Pensacola, FL) during waking hours to objectively measure sedentary time and physical activity. Average sedentary time (hour/day) and time spent in , light-, moderate- and vigorous physical activity intensity (min/day) will be derived. During the main trial days, the participants may read or work on a personal computer during the sedentary time in the respective trial conditions. The sample size calculations with glucose as the primary outcome, are based on the study by Dunstan et al. (2012). They estimated that 19 paired observations were needed to secure a power of 0.90 in order to detect the smallest expected effect size between the interventions, when using a two-tailed test with a significance level of 5%. To account for the possibility of dropouts the sample size in the present project is set to recruit 30 participants, with 25 participants completing the trials, and thus planning for 80% power

Inclusion Criteria:

• Predominantly sedentary occupation.
• Physical activity: equal or less tham 150 minutes /week
• Nonobese. Central adiposity: Waist circumference equal or less than 102 cm for men and equal or less than < 88 cm for women. BMI < 30 km·m2

Exclusion Criteria:

• Shift-work
• Smoking
• Pregnancy
• Current use of medication, except from hormonal contraceptives.
• No presence of any co-morbidity (e.g. diabetes type 2, cardiovascular or cardiorespiratory disease, or other conditions known to affect carbohydrate and lipid metabolism - thyroid-, -liver or kidney).
• Systolic /diastolic resting blood pressure: > 140/90 mmHg
• Fasting blood glucose concentration: > 6.1 mmol/L
• Abnormal total cholesterol, LDL, LDL or triglyceride concentrations (> 50% above recommendations)