Fig. 1.

After an overnight fast and ≥36 h after the last exercise, the participant arrived for a dual energy X-ray absorptiometry (DEXA) scan, oral glucose tolerance test (OGTT), and skeletal muscle biopsy for each condition. Prestudy days occurred 5 days before the beginning of the Colorado Trail Race (CTR) and the control period (CON). The participant stopped competing at the CTR at 7:00 PM, was transported to Colorado State University, and was studied 36 h after exercise at 7:00 AM. Pre-CON was conducted 45 days after Post-CTR. The ²H₂O labeling started 1 day before the CTR and CON by consuming 2 × 50 ml/day of ²H₂O followed by 6 days of 1 × 50 ml/day of ²H₂O consumed each morning. This labeling scheme required the participant to carry 6 days of ²H₂O during the CTR.