This study explores the impact of high-intensity exercise during fasting on energy metabolism and cognitive function in healthy adults. Changes in respiratory exchange ratio, blood substances, and cognitive performance will be measured after 24 and 34 hours of fasting with and without exercise in a randomized crossover design.

Inclusion Criteria:

• 18-40 years old.
• Body mass index: 18.5-30.0 Kg/m2.
• Stable body weight (5kg range within the last 3 months)
• Being able to consume all the food items provided as part of the study.
• Not having change the time zone or have shifted sleeping hours equivalent to more than 3 hours on the previous 2 weeks.

Exclusion Criteria:

• Diagnosed with any chronic condition that, in the research team's opinion or based on the American College of Sports Medicine guidelines, could contraindicate the implementation of 34-hour fasting periods and/or high-intensity exercise.
• Diagnosed with a chronic endocrine, digestive, rheumatic, neurological, cardiac, pulmonary, autoimmune, or infectious condition that affects energy metabolism.
• Presenting any signs or symptoms of illness that, in the research team's opinion or based on the American College of Sports Medicine guidelines, could contraindicate the implementation of 34-hour fasting periods and/or high-intensity exercise.
• Pregnant or breastfeeding.
• Using medications or supplements that may alter energy metabolism.
• Currently undergoing or having undergone any type of nutritional intervention or treatment in the past 3 months.
• Engaging in more than 5 hours per week of habitual moderate-to-vigorous cycling.
• Any other condition that, in the research team's opinion, discourages participation in the study.