The relationship between cardiorespiratory fitness and chronic pelvic pain in women with endometriosis: a preliminary cross-sectional analysis

Introduction: Endometriosis is an inflammatory condition that causes endometrial tissue deposits outside of the uterus, including the ovaries, pericardium and brain. The condition is associated with chronic pelvic pain(CPP) and often results in reduced participation in physical activity and social activities, leading to decreased quality of life(QOL).Increasing cardiorespiratory fitness(CRF) has been established as a treatment in other inflammatory conditions including fibromyalgia and arthritis, with exercise often employed to manage chronic pain.A possible mechanism being the upregulation of analgesic opioid-receptors. The association between CRF and CPP in endometriosis has yet to be explored. The aim of this study was to determine the relationship between CPP and CRF in endometriosis.

Methods: Ten women(age=24.7±5.16) surgically diagnosed with endometriosis were included in this preliminary analysis.CPP was assessed using a 100mm visual analogue scale, recorded as average pain experienced in the week before testing.CRF was measured as the maximum oxygen uptake(VO2max,mL/kg/min), via indirect calorimetry using an individualised graded exercise test with continuous monitoring of ventilation, oxygen and carbon dioxide concentrations. All outcome measures were collected on two occasions, separated by 24-hours accounting for biological variability.

Results: There was a trend towards a positive relationship between CPP and CRF(r=0.09,p=0.805).High CRF was classified as above the mean CRF of 29.01mL/kg/min, whereas low CRF was classified as CRF below the mean. Those with a low CRF reported pain that is 6.6%lower than those with a high CRF, but with no significant difference between-groups.

Discussion: CPP associated with endometriosis has significant effects on a person’s QOL.While increasing CRF has been shown to reduce CPP in other conditions, current results suggest that a higher CRF is associated with higher CPP.High-intensity exercise is a key factor in increasing CRF but in turn could lead to an increased expression of pro-inflammatory markers associated with chronic pain. This could possibly explain the increased CPP found in those with high CRF in the present study. This finding has important implications in how exercise is prescribed in clinical settings to elicit optimal pain management. Despite a small sample size resulting in a lack of statistically significant results(p>0.05), the health-related QOL burden associated with CPP merits these results clinically significant. The preliminary results of this study support the need to continue investigation into the relationship between CRF and CPP. This investigation is currently underway, expected completion is September 2021.