The subjective perceived effort of physical activity is measured with Borg Rating of Perceived Exertion Scale (Borg's RPE scale).

Borg´s RPE measures physical activity intensity. Perceived exertion of how hard the individual feels the body is working. The individual experienced physical sensations during physical activity (increased heart rate, increased breathing or breathing rate, increased sweating and muscle fatigue)

The scale goes from 6 "No effort at all" to 20 "Maximum effort" .

Medical examination according to the 2017 criteria for Hypermobility Spectrum Disorder or HSD/hEDS (hEDS Diagnostic Checklist).

Include assessment of joint mobility according to the Beighton scale (described below), physical examination of the diagnostic criteria for hEDS, family history of hEDS, and presence of musculoskeletal pain and joint dislocations.

The Beighton scale assesses 9 joints for hypermobility. Hyperextension in elbow joint bilaterally >10 degrees, hyperextension in knee joint bilaterally > 10 degrees, hyperextension of the fifth finger bilaterally > 90 degrees, ability to move the thumb towards the forearm bilaterally and trunk flexion in standing (palm completely on the surface).

A total of 9 points is possible, generally hypermobility is achieved at 6 points for children and adolescence.

Back ground data like age, sex ,onset, diagnosis, date of diagnosis, HSD/hED, family history of hypermobility, pain, physical activity habits, the impact of pain on school attendance, and other chronic diseases will be collected through a questionnaire.

The questionnaire consists of 14 questions, of which 11 are multiple-choice questions, two with numerical rating scale answer options and one pain drawing.

Back ground data of the caregiver concerning education, type of employment and marital status, family history of pain, the caregiver's experience of the child's pain and physical activity level will be collected through a questionnaire.

The questionnaire consists of 16 questions, of which 15 are multiple-choice questions, and one pain drawing.

Functional Disability Inventory (FDI) is a self-report inventory consisting of 15 items that are graded on a five-point scale, ranging from 0 to 4 ("No Trouble" to "Impossible"). The FDI assessed difficulties with the performance of daily activities in home, school, recreational, and social domains. Participants are asked to rate how much difficulty they had completing various tasks, "in the past few days". The sum of answers creates a total score (range 0-60) with higher scores indicating greater pain-related disability. The FDI was created for use in children and adolescents 8-17 years old with recurrent abdominal pain.

Participation will be measured using the Frequency of Participation Questionnaire (FPQ). The question is developed to measure the child's participation in all areas of the International Classification of Functioning, Disability and Health.

FPQ consists of 14 questions about participation in everyday activities such as school and leisure.

Participants indicate how often an activity is carried out. Grading from 0 ("never") to 5 ("a few times per week").

Fatigue will be measured with the Pediatric Quality of Life Inventory (PedsQL) Multidimensional Fatigue Scale.

PedsQL Multidimensional Fatigue Scale is a self-assessment form that consists of 18 statements that are graded on a five-point scale, from 0 "never a problem" to 4 "almost always a problem". The PedsQL scale consists of three subscales: General Fatigue, Sleep/Rest Fatigue, and Cognitive Fatigue. The Child/Adolescents questionnaire includes ages, 5-7, 8-12 and 13-18.

Items are reversed scored and linearly transformed to a 0-100 scale, so that higher scores indicate better outcome. To reverse score, the 0-4 scale items will be transformed to 0-100 as follows: 0=100, 1=75, 2=50, 3=25, 4=0.

Catastrophizing will be measured with the child version of the Pain Catastrophizing scale (PCS-C).

The PCS-C is a self-assessment form that consists of 13 statements that are graded on a five-point scale, from 0 "not at all" to 4 "very much". The total score is 52 points where higher scores indicate higher catastrophizing thoughts. In agreement with previous study using PCS - C to investigate movement loss in children and their parents shared the result on PCS-C in this study into low (0-14 points), between.(15-25 points) and high (26-52) estimated disaster thoughts.

Anxiety and depression will be measured with the Hospital anxiety and depression scale (HADS).

HADS is a self-assessment form developed to measure anxiety and depression in patients in somatic care. HADS consists of 14 statements with seven statements for each subscale: HADS anxiety and HADS depression that are graded on a four-point scale from 0 to 3 points. The participant should decide how often he or she has known in the last week, for example "as if something terrible will happen" or whether he or she "appreciates the same things as before". The scores from the seven different statements per sub-scale are combined and can amount to a maximum of 21 points per sub-scale. 0-7 points: Does not speak for anxiety/depression, 8-10 points: The score may be an indication of an anxiety or depression condition in the person, 11 points or more: Demonstrate a likely depression or anxiety of clinical significance.

Physical activity was measured with Axivity AX3 triaxial accelerometer (Axivity Ltd, UK).

The participants were instructed to wear it attached to the right thigh with medical tape for seven days.

Participants will record planned physical activity and the time when they go to bed and get up parallel to the activity measurement.