Exercise-meal Timing and Postprandial Glucose Control

Healthy volunteers will undergo an informed consent and screening visit to determine their eligibility. Participants who are included will then be assigned to one of the three studies (walking, standing, or circuit-exercises) and then come to the lab on 5 consecutive mornings to undergo a pre-trial visit and 4 experimental trial visits (A, B, C, and D). The order of the experimental trial visits will be randomized in a counter-balanced, cross-over design.

Screening visit: Having read the participant info sheet, a study investigator will discuss the project with the potential participant who will have the chance to ask any questions. Informed consent will be sought and a General Health and Physical Activity Questionnaire will be completed. Body weight, height, resting heart rate, blood pressure, and waist circumference will be measured, and blood measures of glycated hemoglobin, triglycerides, and cholesterol will be taken.

Pre-trials visit: Participants will come to the laboratory to receive an accelerometer physical activity monitor, a continuous glucose monitor, and to complete a physical activity bout (walking, standing, or stair climbing, depending on which study they are enrolled). Over the next 5 consecutive days, participants will be instructed to maintain their normal diet and activity habits, to record their dietary intake, to refrain from vigorous exercise and alcohol, and continue wearing the accelerometer and continuous glucose monitoring devices at all times.

Experimental trial A: Following an 8-10 hour overnight fast, participants will come to the lab and will be given a 500 calorie meal-replacement drink to consume within 10 minutes. They will remain in a seated position for 2 hours and then complete the physical activity bout (30-min walk, 30-min stand, or 10-min circuit-exercises) after which they may leave the lab. Resting and post-activity heart rate and blood pressure will be recorded.

Experimental trial B: Following an 8-10 hour overnight fast, participants will come to the lab and complete the physical activity bout. Immediately after this they will be given a 500 calorie meal-replacement drink to consume within 10 minutes and will remain in a seated position for 2 hours, after which they may leave the lab. Resting and post-activity heart rate and blood pressure will be recorded.

Experimental trial C: Following an 8-10 hour overnight fast, participants will come to the lab and will be given a 500 calorie meal-replacement drink to consume within 10 minutes. Immediately after finishing the meal they will complete the physical activity bout and then remain in a seated position until 2-hours has passed since ingesting the meal. After this time they may leave the lab. Resting and post-activity heart rate and blood pressure will be recorded.

Experimental trial D: Following an 8-10 hour overnight fast, participants will come to the lab and will be given a 500 calorie meal-replacement drink to consume within 10 minutes. Thirty minutes after finishing the meal they will complete the physical activity bout and then remain in a seated position until 2-hours has passed since ingesting the meal. After this time they may leave the lab. Resting and post-activity heart rate and blood pressure will be recorded.

After the final trial, the accelerometer and continuous glucose monitoring devices will be collected and the participant's role in the study will end.

Inclusion criteria

• Age 18-65 years.
• Body Mass Index 18-30 kg/m2.
• Generally healthy.

Exclusion criteria

• Smoking.
• Pregnancy, or planning to become pregnant, or a nursing mother.
• More than 2 kg weight change during the last month.
• Diabetes.
• Evidence of, or being treated for, cancer or infectious/non-infectious chronic hematological, pulmonary, cardiac, hepatic, renal, or gastrointestinal diseases.
• Any contraindication to exercise