Newly released guidelines recommend increased physical activity (PA) and reduced sedentary behaviors (SB) to improve glycemia and prevent the onset and progression of type 2 diabetes (T2D). Typically, 30-60 min bouts of PA are advocated per day. Although this approach increases PA, it does not decrease the length of the sedentary periods through the day. This is important because recent epidemiological data suggest that frequently interrupting sedentary time improves glucose control even in people who achieve the recommended levels of PA. Preliminary experimental data suggest that breaking up prolonged sedentary time by performing multiple short bouts (5 min) of PA throughout the day, may improve glycemia more than performing a single continuous bout of PA, and thereby potentially be a novel strategy to prevent T2D. The improvement in glycemia was observed even when the total amount of PA and total energy expenditure were matched, suggesting that how and when PA is performed over the day may matter more than how much PA is done. However, important gaps in knowledge remain including: (1) whether similar benefits on glucose control would be observed in adults with prediabetes, a clinically relevant population that is at high risk of developing T2D; (2) whether these effects are sustained or diluted over time, and (3) what are the mechanistic underpinnings. To address these gaps, the investigators propose to measure the acute and chronic effects of PA breaks on glucose control and the underlying mechanisms in individuals at risk of developing T2D. Sedentary men and women with prediabetes (n=66, 50% F) will be randomized to either an intervention designed to interrupt SB with 5-min bouts of brisk walking performed hourly for 9 hours/day, 5 days/week (BREAK) or a control condition consisting of 45-min of brisk walking performed as a single daily continuous bout, 5 days/week (ONE). The two 3-months interventions will be matched for total active time.

Inclusion Criteria:

• Male and female
• BMI of 18.5-40 kg/m2 and weight stable over the previous 6 months.
• Age, 18-64 years old.
• Fasting glucose of 100-125 mg/dL or fasting HbA1c of 5.7-6.4%, or 2h OGTT blood glucose of 140-199mg/dL based on the American Diabetes Association criteria for pre-diabetes. Fasting glucose, HbA1c and OGTT results ordered by the participant's provider within 3-months of the screening visit will be accepted, provided they fall within the measurement of error range established by the institution's lab standards. Additionally, consistent use of Metformin (1 year) to prevent prediabetes from developing diabetes will be accepted.
• Less than 150 minutes of moderate-to-vigorous physical activity (MVPA) per week and more than 6 hours of sitting time per day, as self-reported by the volunteers using the International Physical Activity Questionnaire (IPAQ).
• Less than 6500 of steps per day as measured by a pedometer over 5 days (at least 1 weekend day).
• Passing medical and physical screening, and analysis of blood and urine screening samples.
• Low-moderate caffeine use (<3 cups/day).
• Agree to refrain from any other structured exercise than the physical activity prescribed in each arm of the study.
• Agree to eat control diets for 3 days before and during the Clinical and Translational Research Center (CTRC) visits;
• Agree to refrain from taking any over-the-counter (including nonsteroidal anti-inflammatory drugs) or prescribed medication (apart from oral contraceptives) for 3 days prior to the inpatient CTRC visits;
• Agree to wear a Fitbit® activity monitor and upload data on the website on a daily basis for the whole duration of the study.
• Agree to follow the physical activity interventions and to be randomly assigned to one of the two arms of the study.
• Agree to complete all the study procedures.

Exclusion Criteria:

• Pregnancy, breast-feeding or post-menopause for women.
• Being considered unsafe to participate as determined by the study physician.
• Ever having a history of systemic, psychiatric, neurological disease, or drug and alcohol abuse.
• History of cardiovascular disease, diabetes, uncontrolled hypertension, untreated thyroid, renal, hepatic diseases, dyslipidemia or any other medical condition affecting weight or lipid metabolism.
• Being positive for human immunodeficiency virus or hepatitis B or C.
• Taking medications affecting weight, triglycerides, energy intake/energy expenditure, or sleep in the last 3 months.
• Having abnormal blood chemistry and/or hematology as deemed significant by the study physician.
• Being a smoker or having been a smoker in the 3 months prior to their screening visit.
• Having donated over 400 mL of blood within 3 months (90 days) of screening for the study;
• Working night shifts within 1 month of and throughout the study.
• Not completing the trial days of BREAK and ONE during the screening period to assess the willingness and ability of the participant to perform each of the interventions.

A study research assistant that is not involved in the study participants' allocation process will create opaque, sealed envelopes with allocation sequences based on the randomization table created by the study statistician. The assignment of intervention to study participants will be based on the study allocation sequence generated by the statistician and the study team will enroll study participants and assign them to the interventions. The study team will be blinded until study participants' allocation (the day before visit G). After this, the study team will not be blinded to study participants' allocation as they will be responsible for assigning study participants, and for applying and monitoring the interventions. The study statistician will always be blinded.