Background:

Although physical activity is recommended as a therapeutic approach for endometriosis, there is limited evidence on the interaction between endometriosis and skeletal muscle health and function.

Case presentation:

The participant was diagnosed with stage II endometriosis via laparoscopic surgery in 2020. She was undergoing treatment with Dienogest. The study spanned nine consecutive weeks, during which we assessed both functional and structural skeletal muscle parameters, including muscle stiffness, maximal strength, and muscular fatigue outcomes. Saliva samples were collected to analyze estradiol and cortisol concentrations at rest, immediately after, and 30 min following the fatiguing protocol.

Resting estradiol concentrations were within the expected range with a mean value of 2.48 pg/mL (±1.24). estradiol levels did not change significantly following the fatiguing protocol [F (2, 16) = 0.113, p = 0.893, η_p² = 0.014]. A significant negative relationship between estradiol concentrations and muscle stiffness, both in a relaxed (r = –0.68, p = 0.044) and contracted state (r = –0.763, p = 0.017) was evident.

Mean resting cortisol concentrations were 5.87 nmol/L (±2.18), and significantly decreased after the fatiguing protocol [F (2, 16) = 18.2, p < 0.001, η_p² = 0.695]. Pearson’s correlation showed a significant positive association between cortisol concentrations and eccentric peak torque (r = 0.723, p = 0.028).

Conclusions:

A diminished hormonal response to physical strain was evident. From these results, we propose the hypothesis that the function of the hypothalamic-pituitary-adrenal (HPA) axis may be impaired following prolonged stress. Muscle stiffness of M. rectus femoris was negatively influenced by estradiol concentrations. Hence, estradiol may modulate muscle stiffness, potentially independent of the underlying pathology.