Objectives: To examine procollagen type I N-propeptide (P1NP) and carboxy-terminal cross-linking telopeptide of type I collagen (B-CTX-1) concentrations across different phases of the menstrual (MC) and oral contraceptive (OC) cycles and in response to running. Methods: 17B-oestradiol, progesterone, P1NP and B-CTX-1 were analysed pre- and post-exercise in eight eumenorrheic females in the early-follicular (EFP), late-follicular (LFP), and mid-luteal (MLP) phases of the MC, while 8 OC users were evaluated during the withdrawal (WP) and active pill-taking (APP) phases. The running protocol consisted of 8x3 min treadmill runs at 85% of maximal aerobic speed. Results: 17B-oestradiol concentrations (pg/ml) were lower in the EFP (47.22+-39.75) compared to the LFP (304.95+-235.85; p=<0.001) and MLP (165.56+-80.6; p=0.003) of the MC and higher in the WP (46.51+-44.09) compared to the APP (10.88+-11.24; p<0.001) of the OC cycle. While progesterone (ng/ml) was higher in the MLP (13.214+-4.926) compared to the EFP (0.521+-0.365; p<0.001) and LFP (1.677+-2.586; p<0.001) of the MC. In eumenorrheic females, P1NP concentrations (ng/ml) were higher in LFP (69.97+-17.84) compared to EFP (60.96+-16.64; p=0.006;) and MLP (59.122+-11.77; p=0.002;). Post-exercise concentrations (70.71+-15.59) increased from pre-exercise (55.86+-12.86; p<0.001). For B-CTX-1 (ng/ml), lower concentrations were shown in MLP (0.376+-0.098) compared to LFP (0.496+-0.166; p=0.001) and EFP (0.452+-0.148; p=0.039). OC users showed higher post-exercise P1NP concentrations in WP (61.75+-8.32) compared to post-exercise in APP (45.45+-6; p<0.001). Comparing P1NP levels between eumenorrheic and OC users, post-exercise P1NP concentrations were higher in the EFP (66.91+-16.26; p<0.001), LFP (80.66+-16.35; p<0.001) and MLP (64.57+-9.68; p=0.002) of the MC compared to the APP of the OC cycle. Conclusion: These findings underscore the importance of studying exercising females with different ovarian hormone profiles, as changes in sex hormone concentrations affect bone metabolism in response to running, showing a higher post-exercise P1NP concentrations in all MC phases compared with APP of the OC cycle.

The authors have declared no competing interest.

NCT04458662

The IronFEMME Study took place with the financial support of the Ministerio de Economia y Competitividad, Convocatoria de ayudas I+D 2016, Plan Estatal de Investigacion Cientifica y Tecnica y de Innovacion 2013-2016 [Grant DEP2016-75387-P] funded by MCIN/AEI/10.13039/501100011033 and by ERDF A way of making Europe. IGC is supported by a grant provided by Universidad Politecnica de Madrid.

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Participants included in this study were part of the IronFEMME project, which received ethical clearance from the Research Ethics Committee of the Universidad Politécnica de Madrid.

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