Thank you for your interest in this research study. The purpose of this study is to learn more about the best time of day to exercise for weight loss. We want to understand if morning exercise and evening exercise result in similar amounts of weight loss. If you join this research study, you will participate in a monitored exercise program for 7 months and then continue to exercise on your own for an additional 6 months. Your total study participation will last for 13 months.


If you participate you will be randomly assigned to one of two study groups: morning exercise or evening exercise. Exercise will take place at the Anschutz Health and Wellness Center (AHWC) Exercise Facility. The morning exercise group will complete all exercise sessions during a specified 3-4 hour window in the morning. The evening exercise group will have to complete all of their exercise sessions during a 3-4 hour window in the late afternoon/evening. You will NOT be able to choose which group you are assigned or change your group assignment. You will be asked not to participate in any other physical activity or weight management programs for the duration of the 13-month study.


The aerobic exercise program is progressive in duration and intensity. Throughout the 13-month study, you will be asked to exercise 4-5 days per week during your assigned exercise window (morning or evening). At the start of the program you will be exercising for around 20-30 minutes per exercise session. The program will progress each week and by around month 3, you will be required to exercise between 40-80 minutes per exercise session. The duration of the exercise sessions will be based on the number of calories you burn during each exercise session. In general, individuals that weigh more will burn more calories in a shorter amount of time and their exercise sessions will be shorter than individuals with lower body weights. All exercise will be aerobic in nature. This means you will be using treadmills, stationary cycles, ellipticals, and other cardiovascular equipment for your exercise. Exercise sessions will be verified using heart rate monitors and a phone application. You will be asked to attend monthly exercise behavioral support sessions as well as several 1:1 feedback support sessions. Your gym membership at the AHWC will be provided to you at no cost. To remain in the study (and continue to receive the benefit of the gym membership) you must complete >85% of the prescribed exercise sessions.


During the 7-month supervised exercise phase, you will be required to complete 3 exercise sessions per week at the AHWC exercise facility and one session per week on your own. After you complete the 7-month supervised exercise intervention, you will be asked to continue to do 4-5 exercise sessions per week on your own during your assigned exercise window (morning or evening) for another 6 months using your heart rate monitor. We will continue to provide you with a membership to the AHWC exercise facility during this time.


Prior to joining the study you will be asked to complete a screening visit to confirm your eligibility. This visit will last approximately 1-2 hours. You may be asked to fast before you come in for your first study visit for a blood draw. This means you cannot eat anything, or drink anything except for water for 12 hours before your appointment. When you fast, you may feel lightheaded, dizzy, and/or weak. During the 13-month research study, you will also undergo periodic assessments of your body weight, body composition, fitness, metabolic rate, blood laboratory values, sleep, diet, mood, and activity patterns (1-2 study assessment visits, occurring at 0, 3.5, 7 and 13 months).


Before you come in to learn more about the study, it would be helpful to see if you are likely to qualify to be in the study. In order to do this, we would like to ask you some eligibility questions, which will include questions about your health history, including questions about your mental health and drug and alcohol use. It should take about 15-20 minutes to go through these questions. Some of the questions may make you uncomfortable; you do not have to answer any question that you would not like to answer, but without answers to these questions, we will not be able to determine if you are eligible to participate in the study. We will collect your name and contact information, but we will use an identification code (rather than your name) on the form we use to record your answers. If you do not enroll in this study, we will keep the information collected during this pre-screening secure. We are also required to give you the number of COMIRB, the Ethics Board that oversees our research: it is (303) 724-1055, in case you have any questions or concerns for them.


If you have any questions about the screening questions, please call contact the study team at


If you have no questions at this time, please begin answering the questions below.

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