During the past decades, considerable emphasis has been directed to analyzing the potential role of caffeine on substrate use and exercise performance. Research shows that caffeine ingestion prior to exercise has beneficial effects on submaximal exercise capacity and time trial protocols. This effect is mediated by an increase in plasma free fatty acids and intramuscular triglyceride utilization, preserving muscle and liver glycogen. Generally, a dose between 4 - 9 mg/kg body mass is administered to athletes in order to observe a positive or ergogenic effect. Caffeine ingestion (6 mg/kg) improved exercise performance in a long duration protocol (2 hours + ~ 30 min time trial) regardless of the administration time (1 hour before or during exercise). Lower doses of caffeine (~ 1.5 mg/kg), when added to a carbohydrate solution increased exercise performance in a similar fashion. In rats, caffeine has been shown to have a biphasic action on postprandial glucose metabolism. When ingested before a meal, hepatic glycogenesis is blunted. Its ingestion during and after a meal allows glycogenesis to occur. Manipulating meal and caffeine timing before low intensity exercise, comparable to every-day life activities, is of great interest in assessing substrate use and muscular efficiency. it would be also interesting to see how this meal or caffeine timing manipulation influence the energetics of different phenotypes.

Research shows that caffeine ingestion prior to exercise has beneficial effects on moderate to high exercise performance. Generally, a dose between 4 - 9 mg/kg body mass is administered to athletes in order to observe a positive effect.

The aims of the study are the following: first, to investigate the effect of caffeine and/or meal on energy supply (% from fat and carbohydrate) during low intensity exercise. Second, to investigate the effect of timing and order of the above on energy supply before, during, and after exercise. Lastly, to assess exercise efficiency following the above protocols (work accomplished relative to the calories spent to accomplish the work).

Healthy, untrained male and female subjects will be recruited for this study. Subjects will be excluded if they had a previous history of any limitation on physical ability, cardiovascular disease, taking supplements or medicine that might affect their metabolic rate, claustrophobic, or unstable bodyweight during the past 6 months. Subjects will be defined as sedentary, with a maximum of 30 minutes of moderate physical activity per day (assessed by questionnaire) excluding daily activities.

During the first visit, participants will be informed about the experiment protocol, if agreed, they should give a written consent, answer a questionnaire (lifestyle), and get anthropometric and body composition measurements.

On the day of testing, subjects will come to the laboratory at 08:00 fasted. All participants will be requested to avoid physical activity, caffeine, and dietary supplements in the 24h prior to testing.

Energy expenditure is measured by indirect calorimetry. Briefly, participants will sit in a comfortable seat, using a ventilated hood with baseline energy expenditure. During this period, the participant is instructed to relax and avoid movements. Heart rate monitoring is included using a heart rate belt. Participants then complete the following protocols on five separate days (separated by at least 48 hours) in a randomized order:

Protocol 1:

A standardized meal (2 slices of toast bread + butter + Jam ~ 500 kcal) + caffeine (~200 mg) will be given to the participant. 2 hours later resting energy expenditure is measured using a facemask for 10 min while seated on a cycle ergometer. The participant will be asked to pedal at 60 revolutions per minute for 5 min per load at 20 watts (W), 35W, 50W, 65W, 80 W respectively.

Protocol 2:

A standardized meal will be given to the participant. 2 hours later caffeine will be given followed by the same protocol mentioned above.

Protocol 3:

Caffeine will be given to the participant. 2 hours later a standardized meal will be given followed by the same protocol mentioned above.

Protocol 4:

Caffeine will be given to the participant. 2 hours later the same protocol mentioned above will be applied.

Protocol 5:

A standardized meal will be given to the participant. 2 hours later the same protocol mentioned above will be applied.

Manipulating meal and caffeine timing before low intensity exercise, comparable to every-day life activities, is of great interest in assessing energy supply and muscular efficiency in humans.

There is no risks related to the study. Exercise is maintained at a low-to-moderate level comparable to everyday life. All data related to the subjects will be coded (# and initials, i.e. A001_ELIFAR) and kept confidential.

Inclusion Criteria:

• Healthy male or female individual between 18 and 30 years old,
• normal weight or overweight

Exclusion Criteria:

• Subjects will be excluded if they are not covered by (University health insurance) HIP,
• subjects with the previous history of any limitation on physical ability,
• Subjects with cardiovascular disease,
• Subjects taking supplements or medicine that might affect their metabolic rate,
• claustrophobic,
• Subjects with unstable body weight during the past 6 months.