Author(s): LATINI, D., BIZET, B., TRINCHI, M., MOGHETTI, P., BOLNER, A., MONTE, A., ZAMPARO, P. , Institution: UNIVERSITY OF VERONA, Country: ITALY, Abstract-ID: 1316

INTRODUCTION:
In vitro evidence indicates an effect of female sex hormones (i.e., estrogen and progesterone) on the microstructure of collagenic tissues [1,2]. However, if and how these changes translate into mechanical alterations in muscles and/or tendons in vivo remains debated. The current study aimed to investigate the effects of hormone levels on the mechanical properties of lower leg muscle-tendon units during maximal voluntary contractions (MVCs) and explosive isometric contractions.
METHODS:
Thirty-three active healthy women (age: 24.1 ± 2.7 years) were recruited and assigned to two groups based on oral contraceptive (OC) use: non-users (NOC; n= 18) or users (OC; n= 15, all on combined monophasic pills). The experimental session involved: blood sample collection for hormones concentration analysis, followed by strength measurements of the dominant leg to determine maximal isometric torque and rate of torque development during knee extensions and flexions, and ankle plantar- and dorsi-flexions. The mechanical behaviour of vastus lateralis, gastrocnemius medialis, tibialis anterior, Achilles (AT) and patellar (PT) tendon were investigated with ultrasound apparatuses. NOC group repeated the session in two menstrual cycle phases (follicular and luteal), while the OC group was tested only once.
RESULTS:
There were no significant differences between menstrual cycle phases and between NOC and OC groups in terms of maximal isometric torque, maximal AT or PT elongation, and belly shortening of the investigated muscles. Neither menstrual cycle phases nor contraceptive use had an effect on patellar tendon stiffness, but the Achilles tendon stiffness was reduced during the luteal phase compared to the follicular one at high torque levels (INTENSITY*PHASE p= 0.065). The stiffness of the three investigated muscles did not differ between cycle phases or groups. OC use impacted the knee extension rate of torque development, with higher values observed in OC users compared to both menstrual cycle phases (follicular, p= 0.002; luteal, p= 0.035).
CONCLUSION:
Hormonal fluctuations across the menstrual cycle only slightly affect Achilles (but not patellar) tendon behaviour, with no measurable effects on mechanical output. Oral contraceptive use did not alter the mechanical properties of the lower limb muscle-tendon structures during maximal contractions, but had a favorable impact on the explosive strength of knee extensors.

References
[1] Leblanc et al., The Journal of Steroid Biochemistry and Molecular Biology (2017)
[2] Lee et al., Journal of Applied Physiology (2015)