Influence of muscle-tendon unit structure, function, and menstrual cycle phase in dancers’ physical performance

Pessali-Marques, Barbara (2020) Influence of muscle-tendon unit structure, function, and menstrual cycle phase in dancers’ physical performance. Doctoral thesis (PhD), Manchester Metropolitan University in collaboration with Lancashire Cotton Mills Ltd.

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Abstract

Flexibility and jump are crucial capabilities for dancers but reaching good performance in both is a challenge. Given that muscle-tendon stiffness (SMTU) might affect both these capabilities and that muscle structure and concentration of female hormones across the menstrual cycle may affect SMTU, this thesis aimed to determine the factors that might affect SMTU and, therefore, physical performance in female dancers, especially through the menstrual cycle. A piece of equipment to measure and train flexibility in highly flexible participants was developed and validated. Then, fifteen young adult dance students under oral contraception, eleven dance students without contraception and twenty non-dancers without contraception completed several laboratory-based tests. Participants underwent semitendinosus and rectus femoris ultrasound imaging, flexibility and vertical jump tests including electromyography, kinematics, and pain mixed-method assessment. Participants also provided serum/saliva samples on test days, including ovulatory, follicular and luteal phases. An intervention involving stretching the most flexible limb allowed evaluation of limb asymmetries and impact on function. Results showed no statistical structural and functional differences between dancers and non-dancers. Asymmetries in flexibility, but SMTU, between limbs, were found for all groups. Those asymmetries appear to not influence jump performance. Four-series of passive constant torque stretch was not sufficient to cause or increase any asymmetry or to affect SMTU. Stretching did not change jump height, muscle activation and kinematics of vertical jumps. Dancers presented irregular menstrual cycle with the change in hormone across the phases being associated with changes in key outcome variables. Thus, oestrogen and relaxin appear to be positively correlated to muscle laxity while progesterone is positively correlated to SMTU. This thesis’ results will provide data for the development of training strategies to improve performance and potentially decrease injuries in dancers. Additionally, contributing to research on hormonal factors in female performance and, therefore, women’s health.