Baseline measurements
Baseline data were collected 1 or 2 days before the start of the event, after a minimum resting period of 24 h. At baseline, body height and weight (Seca 888 scale, Hamburg, Germany) were measured to calculate body mass index (BMI). All participants completed a general questionnaire on demographics, level of education, smoking and medication use, and the validated Short Questionnaire to Assess Health enhancing physical activity (SQUASH)(25). IBD walkers completed an extended general questionnaire with additional questions on type and extent of IBD, age of disease onset, number of flare-ups and previous IBD-related surgeries. Participants’ heart rate was measured every 5 km during the first exercise day using a 2-channel ECG chest band 130 system. Heart rate (HR) was used to estimate exercise intensity as a percentage of the maximum HR (exercise intensity = measured HR / expected maximal HR x 100%), where expected max HR = 208 –132 (0.7 x age))(26).