Author(s): GUISADO CUADRADO, I., ROMERO-PARRA, N.1,2, PEINADO, A.B.1 , Institution: UNIVERSIDAD POLITÉCNICA DE MADRID, Country: SPAIN, Abstract-ID: 726

INTRODUCTION:
Exercise guidelines to improve bone strength generally include resistance-based exercises (1). Beyond mechanical stimulus, sex hormones may also have an effect on bone health, as in vitro studies have demonstrated the influence of 17β-oestradiol on osteocyte function (2). Thus, this study investigated the acute effects of eccentric resistance exercise on procollagen type I N-propeptide (P1NP) and carboxy-terminal cross-linking telopeptide of type I collagen (β-CTX-1) concentrations in premenopausal females.
METHODS:
Nine eumenorrheic females and ten oral contraceptive (OC) users performed an eccentric-based resistance exercise (10x10 repetitions of back squats with a 4-second eccentric phase) in three of the menstrual cycle (MC) phases [early follicular (EFP), late follicular (LFP) and mid luteal (MLP)] and in the two OC cycle phases [withdrawal (WP) and active pill-taking (APP)], in a randomized testing order. β-CTX-1 and P1NP, 17β-oestradiol and progesterone were assessed pre- and post-exercise. MC and OC cycle phases were confirmed by serum sex hormone analysis.
RESULTS:
17β-oestradiol (pg·ml-1) was lower in EFP (36.635±29.930) compared to LFP (224.807±233.813; p=<0.001) and MLP (161.445±110.082; p<0.001) and higher in the WP (24.857±29.428) compared to APP (12.717±13.357; p=0.004). While 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). 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 ovarian hormonal profiles, 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, MLP vs APP (p=0.027). Exercise time effect showed lower β-CTX-1 concentrations 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.
CONCLUSION:
Eccentric resistance training decreased β-CTX-1, showing its potential to protect against acute bone resorption. This study underscores the need to understand the characteristics of resistance training for optimal bone health in active females. β-CTX-1 was lower in the MLP compared to LFP of the MC, which may indicate that progesterone can reduce β-CTX-1 without modifying P1NP concentrations. Finally, ovarian hormonal profile influence bone (re)modelling markers, decreasing bone formation in OC users, indicating the need to investigate long-term effects on bone structure and strength.

Funding: Grant DEP2016-75387-P funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe".

References
1. Beck BR, et al. (2017). doi: 10.1016/j.jsams.2016.10.001
2. Klein-Nulend J. et al (2015). doi: 10.1016/j.jbiomech.2014.12.007