Author(s): BERNSTEIN, C., NIEDERER, D., BEHRINGER, M. , Institution: GOETHE UNIVESITÄT FRAMKFURT AM MAIN, Country: GERMANY, Abstract-ID: 1395

INTRODUCTION:
Hormonal fluctuations related to menstrual cycle phases do not seem to affect strength parameter. In contrast, data from studies in animals and postmenopausal women suggest that steroid hormones such as estrogen and progesterone may affect force generating capacity by enhancing the number and quality of cross-bridges. The ability to generate force is impaired in an estrogen-deficient state, while estrogen supplementation may restore these capacities. It is therefore conceivable that contractility varies across the menstrual cycle. However, research investigating skeletal muscle contractility across the menstrual cycle is sparse. Hence, the aim of the study was to investigate the contractility of m. rectus femoris in an eumenorrheic population.
METHODS:
Fifteen (15) regularly menstruating women not taking oral contraceptives (age 24.8 ± 3.0 yrs; body mass 59.7 ± 5.8 kg; height 1.68 ± 0.04 m; cycle length 28.2 ± 1.2 d; BMI 21.1 ± 1.3) were included. We assessed muscle contractility in in the early follicular phase, at ovulation, and in the mid-luteal phase. The onset of menses determined the early follicular phase, while a rise of luteinizing hormone in urine detected ovulation. The mid-luteal phase was set 7 to 9 days after ovulation. We used Tensiomyography (TMG-BMC Ltd., Slovenia) as a non-invasive method to assess muscle contractility by obtaining spatial and temporal parameters such as displacement of the muscle belly (Dm), contraction time (Tc), initial delay time (Td) and the velocity of contraction (Vc = Dm/(Tc+Td)) in response to a supramaximal stimulation. Repeated measurements analyses of variance were performed to detect potential between-phases differences.
RESULTS:
No between-phases differences occurred (Dm: F(2,24) =2.5, p= .103, n2p = .172, Tc: F(2,24) = 3.05, p= .0.066, n2p = .0.203, Td: F(2,24) = 0.687, p= .0.512, n2p = .054, Vc: F(2,24) = 0.687, p= .0.512, n2p = .054). However, a high inter-individual variability across the cycle phases was evident.
CONCLUSION:
Although there were no changes on a group level, the inter-individual variations indicate that muscle contractility may change across the menstrual cycle according to hormonal fluctuations in some participants but not in others. Since estrogen alters muscle properties on a molecular level, we assume that some individuals are either more responsive to hormonal fluctuations or that other factors overshadow the effects of steroid hormones on muscle properties. In conclusion, according to the current understanding, the responsiveness of muscle tissue to cycle-related hormone fluctuations needs to be assessed individually regarding the individual hormonal status.