The study will require 4 meetings for each subject: a 30-minute meeting to explain the project; a meeting of 2 hours (glucose tolerance test, at rest); a one-hour meeting (maximum oxygen consumption test (VO2max) during an exercise conducted on an electromagnetically braked cycle ergometer, and a meeting of about 4 hours for experimentation (120-min exercise on a stationary bicycle with ingestion of a solution carbohydrates or sweetened water, and a 20-km time trial).
Visit #1 - Pre-participation (screening visit) Following an initial contact by phone or email, the subject will be invited to individual meetings which will last about 15 minutes. During the meeting, one of the project managers will check the eligibility of the potential subject in the study and, if eligible, will present him the details of the protocol specifying the discomforts and risks involved. The participant will be required to fill a Physical Activity Readiness Questionnaire (PAR-Q) and will be given a copy of the consent form. We will request the name and contact details of a person to contact in case of emergency, this information will be recorded and preserved in the subject matter. A period of at least three days will be allocated to make the decision whether to participate in the study or not. If the participant decides to participate in the study, he will be invited for the second visit (oral glucose tolerance test) and on this occasion will sign the consent form.
Visit #2 - Oral glucose tolerance test (OGTT) This test will be performed at Exercise Physiology Laboratory at the Department of kinesiology from the University of Montreal under the procedure commonly used for these tests. This procedure requires the ingestion of 300 mL of water containing 75 g of glucose in the morning (around 8am) after 12 hours of fasting, and blood samples and on the tip of a finger at 0, 60 and 120 minutes for the measurement of blood glucose. Subjects with higher blood glucose than 5 mmol/L before ingestion of glucose and greater than 8 mmol/L after ingestion (60 or 120 min) will not be considered for the study. These glucose tolerance standards are more stringent than those of the World Health Organization, because the objective of this test is not a diagnosis on glucose tolerance or a prognosis of its future development, but just n include in the study subjects who have good glucose tolerance.
Visit #3 - Maximum oxygen uptake testing: cycling VO2max This test will be conducted in the Exercise Physiology Laboratory at the Department of kinesiology from the University of Montreal. Exercise involves pedaling a stationary bike at a power output (resistance) gradually increasing until reaching VO2max. During the execution of the test, the subject is wearing surface electrodes to measure heart rate, a mouthpiece and nose clip to measure the volume of expired gas as well as the oxygen and carbon dioxide content to determine the consumption oxygen and carbon dioxide production. This type of testing is routinely used in our laboratory. The test can be stopped at any time by the will of the subject. For this test, guidelines established by the Exercise Physiology Laboratory at the Department of kinesiology from the University of Montreal will be followed. These guidelines are based on recommendations of ethics and safety of the "American College of Sports Medicine".
4- Experimentation The tests will be conducted at the Exercise Physiology Laboratory at the Department of kinesiology from the University of Montreal. The exercise is carried out on stationary cycle ergometer. It lasts 120 minutes at a power output corresponding to 60% of the VO2max obtained during the maximal test. A volume of a carbohydrate solution (120 g, 6% carbohydrate by volume) or sweetened water will be administered to the subject before (571 mL) and during exercise (286 mL every 30 minutes). The following solutions will be administered in a balanced, randomized, double-blind model: maple sap, maple syrup, glucose, a commercial sports drink and water with a glucose trace (0.001% carbohydrate by volume). Under conditions where only a trace of water or glucose are administered, a natural sweetener (stevia) will be added to obtain a sweet taste similar to other conditions. Carbohydrate solutions will all be artificially enriched in 13C. The volume ingested after 30 minutes of exercise will be artificially enriched in deuterium (D2O, 8g incorporated in the ingestion of 286 mL).
