Menstrual Cycle Related Fluctuations in Circulating Markers of Bone Metabolism at Rest and in Response to Running in Eumenorrheic Females.

This study examined potential fluctuations in bone metabolic markers across the menstrual cycle both at rest and after a 30-min bout of continuous running at 80% of V̇O. Resting and post-exercise (0, 30, 90 min) sclerostin, parathyroid hormone (PTH), carboxy-terminal cross-linking telopeptide of type I collagen (β-CTXI), and procollagen type 1 N propeptide (PINP) were assessed in 10 eumenorrheic women (age: 21 ± 3 y, BMI: 23.2 ± 3.0 kgm) during the mid- to late-follicular (FP: day 8.0 ± 1.4) and mid-luteal (LP: day 22.0 ± 2.5) phases of the menstrual cycle. Ovulation was determined using ovulation kits and daily measurement of oral body temperature upon awakening. Menstrual cycle phase was subsequently confirmed by measurement of plasma estradiol and progesterone. On average, resting estradiol concentrations increased from 46.3 ± 8.9 pg·mL in the FP to 67.3 ± 23.4 pg·mL in the LP (p = 0.015), and resting progesterone increased from 4.12 ± 2.36 ng·mL in the FP to 11.86 ± 4.49 ng·mL in the LP (p < 0.001). At rest, there were no differences between menstrual cycle phases in sclerostin (FP: 260.1 ± 135.0 pg·mL; LP: 303.5 ± 99.9 pg·mL; p = 0.765), PTH (FP: 0.96 ± 0.64 pmol·L; LP: 0.79 ± 0.44 pmol·L; p = 0.568), β-CTXI (FP: 243.1 ± 158.0 ng·L; LP: 202.4 ± 92.3 ng·L; p = 0.198), and PINP (FP: 53.6 ± 8.9 μg·L; LP: 66.2 ± 20.2 μg·L; p = 0.093). Main effects for time (p < 0.05) were shown in sclerostin, PTH, β-CTXI and PINP, without phase or interaction effects. Sclerostin increased from pre- to immediately post-exercise (45%; p = 0.007), and so did PTH (43%; p = 0.011), both returning to resting concentrations 30 min post-exercise. β-CTXI decreased from pre- to post-exercise (20%; p = 0.027) and was still below its pre-exercise concentrations at 90 min post-exercise (17%; p = 0.013). PINP increased immediately post-exercise (29%; p < 0.001), returning to resting concentrations at 30 min post-exercise. These results demonstrate no effect of menstrual cycle phase on resting bone marker concentrations or on the bone metabolic marker response to intense exercise.