Effect of eccentric-based resistance exercise on bone (re)modelling markers across the menstrual cycle and oral contraceptive cycle.

Purpose: To investigate the acute effects of eccentric-based resistance exercise and sex-hormone fluctuations on P1NP and β-CTX-1 concentrations in premenopausal females.

Methods: Nine eumenorrheic females and ten oral contraceptive (OC) users performed eccentric-based resistance exercise, consisted of 10 × 10 repetitions of parallel back squats with a 4-s eccentric phase, in the early-follicular (EFP), late-follicular (LFP) and mid-luteal (MLP) phases of the menstrual cycle (MC) or in the withdrawal (WP) and active pill-taking (APP) phases of the OC cycle.

Results: 17β-oestradiol (pg·ml^-1) was lower in EFP (36.63 ± 29.93) compared to LFP (224.81 ± 233.81; p ≤ 0.001) and MLP (161.45 ± 110.08; p < 0.001) and higher in WP (24.857 ± 29.428) compared to APP (12.72 ± 13.36; p = 0.004). Progesterone (ng·ml-1) was higher in MLP (8.30 ± 5.23) compared to EFP (0.33 ± 0.33; p < 0.001) and LFP (0.21 ± 0.18; p < 0.001), no significant differences were observed between the WP and APP. In eumenorrheic females, β-CTX-1 (ng·ml^-1) was lower in MLP (0.395 ± 0.126) compared to LFP (0.472 ± 0.137; p = 0.044). Comparing MC vs OC phases, eumenorrheic females had higher P1NP levels (ng·ml^-1) compared to OC users: EFP (62.54 ± 13.13) vs APP (50.69 ± 8.91; p = 0.034), LFP (67.32 ± 18.96) vs WP (52.16 ± 10.72; p = 0.047), LFP vs APP (p = 0.025), MLP (67.51 ± 19.34; p = 0.049) vs WP, MLPvsAPP (p = 0.027). Exercise time effect showed lower β-CTX-1 concentrations 2 h post-exercise (MC: 0.376 ± 0.114, p < 0.001; OC: 0.340 ± 0.156, p = 0.030) compared to pre-exercise (MC: 0.485 ± 0.137; OC: 0.428 ± 0.188) in all participants.

Conclusions: β-CTX-1 concentrations were lower in the mid-luteal phase, emphasising the importance of standardizing bone marker measurements to a specific MC phase. OC users exhibited reduced P1NP levels, underscoring the need to investigate synthetic and endogenous hormones' impact on long-term bone structure and strength. Trial registration The study was registered at Clinicaltrials.gov NCT04458662 on 2 July 2020.