This experiment aims to accomplish two goals: collect additional metabolic flexibility data with young fit adults in response to exercise; and demonstrate that automated pace guidance generated from real-time thermal-work strain monitoring and an optimized pacing policy will allow less stressful completion of a timed (60 minute) treadmill exercise of 5 miles. Each participant will undergo two treatments of first UNGUIDED followed by GUIDED exercise. The two exercise sessions will be conducted as part of a ~24 hour stay in an indirect calorimetry chamber.