The present cross-sectional study is part of a larger study of the same population. The main aim was to investigate vascular function in Norwegian female elite long-distance runners.17 (link) Overlap includes age, height, weight, training data, fat mass, hormone levels and the LEA in Female Questionnaire (LEAF-Q). Power analysis was done for the main outcome, endothelial function, in the overall study on vascular function. However, in addition, post hoc power analysis has been performed for the primary objective of the current study and presented in the results section. Written information about the study was distributed to female runners in the top 20 long-distance running statistics lists in Norway in 2019 and announcements on social media. Recruitment focused on long-distance running (footraces ranging from 5 km to half-marathon), including trail running. According to the recently published paper from McKay et al,18 (link) 10 runners qualified as ‘elite’ by competing at the international level (including track, road and trail running), and 5 runners competed at the national level, representing ‘highly trained’ runners.18 (link) The whole runners’ group will be referred to as ‘elite runners’ hereafter. A control group of physically inactive women was recruited among students at the University of Oslo. The inclusion criteria were age 18–35 years, healthy, non-smoking and nullipara. Training criteria were a minimum of 8-hour endurance training weekly for the runners and a maximum of 2-hour training weekly for the controls. Sixteen runners and 17 physically inactive women were recruited between October 2019 and January 2020. All participants signed written informed consent. One runner and two controls were withdrawn from the study due to injury or challenges during the COVID situation. The final analysis included 15 runners and 15 controls. Both study groups were Caucasian.
The study was conducted during three different test days. The overall study17 (link) included vascular function tests, performed on the first test day. In addition, the participants answered the LEAF-Q.19 (link) At the second visit, all blood samples were collected. The BMD and maximal oxygen consumption (VO2max) were measured at the third visit.