One year of testosterone therapy in a transmasculine amateur triathlete affects hormone cycles, exercise capacity, and muscular physiology

The impact of testosterone therapy on hormone cycles, exercise capacity, and physiology of transmasculine individuals is not well understood. Existing studies report limited metrics at large time intervals between data collection. Here, we collect high-resolution temporal data from a single amateur trans male triathlete over a time period of 13 months-including one baseline month and twelve months on testosterone therapy-to characterize hormone, strength, body composition, aerobic, and training load profiles. Daily urine hormone monitoring revealed that progesterone and luteinizing hormone are the clearest metrics to predict cessation of menses. After one year, the participant increased lean body mass by 12%, average hand grip strength by 13%, jump height by 16%, and average knee isometric strength by 15%, but, in contrast with prior research, did not lose fat mass or show changes in isokinetic knee strength. While absolute VO2 max increased by 10%, relative VO2 max (e.g., normalized to body mass) only increased during corresponding peaks in training load. We provide guidelines to monitor trans males during testosterone therapy and recommendations to scale this case study to a larger population.