From couch to Ironman 70.3: A three-year case study of weight loss and cardiometabolic adaptation revealed through continuous wearable monitoring.

This single-participant case study leverages 1,146 days of continuous monitoring to describe a three-year weight loss and fitness transformation in a highly motivated young adult male who achieved a 27.8% reduction in body weight and completed an Ironman 70.3 triathlon. Daily resting heart rate (RHR), heart rate variability (HRV; RMSSD), HRV coefficient of variation (HRV-CV), sleep, and physical activity were analyzed. Clinical biomarkers were evaluated, and body composition (DEXA) and maximal oxygen consumption ( ˙VO2max) were assessed after weight loss; dietary intake was not recorded. From May 2022 to May 2025, body weight decreased from 122.3 ± 1.0 to 88.3 ± 0.6 kg. Wearable data showed improvements in RHR (69.5 ± 3.9 to 53.6 ± 3.3 bpm), HRV (40.6 ± 9.7 to 75.5 ± 14.0 ms), HRV-CV (18.9 ± 6.6 to 17.5 ± 3.5%), and physical activity (12.0 to 38.6 hours/month). Clinical biomarkers improved, including fasting glucose (102 to 82 mg/dL), triglycerides (134 to 74 mg/dL), low-density lipoprotein (89 to 72 mg/dL), and high-density lipoprotein (33 to 42 mg/dL). Post-weight-loss  ˙VO2max (46.9 ml/kg/min) and body fat (21.6%) compared favorably with age- and sex-based norms. Sustained behavior change was associated with substantial weight loss and favorable cardiometabolic adaptations. These findings illustrate the potential of long-term wearable monitoring to capture behavior-driven cardiometabolic changes during weight loss in real-world settings.