Abstract This study examined whether low-normal serum total testosterone ( T ) is associated with bone mineral density (BMD) or bone stress injuries (BSI) in male endurance athletes. Baseline data from 46 national- to international-level Finnish athletes (age 24.8 ± 3.6 years; biathlon, cross-country skiing, orienteering, triathlon, Nordic combined, endurance running) were analyzed; 31 completed 1-year follow-up. Participants were categorized into low T (lowest quartile: 11.8 ± 1.8 nmol/L) and normal T groups (17.9 ± 3.1 nmol/L; p < 0.001). At baseline, BMD and Z -scores did not differ at any site (all p > 0.5), and BSI history prevalence was similar in low T (41.7%) and normal T groups (29.4%). The low T group had lower IGF-1 ( p = 0.031) but comparable cortisol and insulin. During follow-up, repeated-measures analysis showed a significant group-by-time interaction for T ( p = 0.001), whereas 1-year changes in BMD and Z-scores did not differ between groups. Regression models showed that increased IGF-1 independently predicted improved total body BMD ( p = 0.01). In conclusion, low-normal T in elite male endurance athletes was not associated with compromised bone health over 1 year and appeared largely reversible in the follow-up subset.
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