Changes in Hormone Cycles and Exercise Capacity During Testosterone Therapy in a Transmasculine Triathlete: A Case...

The impact of testosterone therapy on the 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 points.

High-resolution temporal data were collected from a single amateur trans male triathlete over 13 months-including one baseline month and 12 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 associated with cessation of menses. After 1 yr, the participant increased lean body mass by 12%, average hand grip strength by 16%, jump height by 16%, and average knee isometric strength by 18%, but did not lose fat mass or show changes in isokinetic knee strength. Fluctuations in running fitness and maximum oxygen consumption ( $\dot{V}{O}_{2max}$ ) were associated with both training and testosterone levels, with future work needed to untangle their relative contributions.

This study provides the most comprehensive characterization of the impacts of testosterone therapy on hormone cycles, exercise capacity, and physiological changes in a single person to date, as well as observations to help inform the design of larger cohort studies.