Aim of EFEX-OA-01: To explore how running, cycling and resting acutely influence levels of collagen and proteoglycan in patients with osteoarthritis knee and in young healthy subjects, as reflected by changes in serum and urine biochemical markers originating from joint related collagens and proteoglycans.

Inclusion criteria for OA patients:

1. Kellgren-Lawrence radiological grade of 1-3 in at least one tibio-femoral joint diagnosed by screening x-ray.
2. 35 to < 75 years of age at the time of signing the informed consent form.
3. Bodyweight > 50 and < 150 kg and a BMI in the range 18,5-35 kg/m2.
4. Are male or female.
5. Is able to meet for all of the four study visits and comply with the dietary and activity restrictions.
6. Can give informed consent.

Exclusion criteria for OA patients:

Medical conditions:

1. History of arthroscopy or intra-articular administration of corticosteroids or hyaluronic acid into the target knee within 6 months before screening.
2. Kellgren-Lawrence radiological grade of 4 in at least one tibio-femoral joint
3. Previous arthroplasty of knee or hip.
4. Intention of having major surgery during the timeframe of this study.
5. OA related to eg. dysplasia, aseptic osteonecrosis, acromegaly, Paget disease, Stickler syndrome, hemochromatosis, gout, chondrocalcinosis (pseudogout) or calcium pyrophosphate deposition disease.
6. Current treatment with beta-receptor adrenergic antagonists (beta-blockers), systemic corticosteroid treatment in doses equivalent to > 10 mg of prednisolone per day, or Vitamin K antagonists, new oral anticoagulants, fractionated and non-fractionated heparin
7. Active systemic infection.
8. Active systemic inflammatory or autoimmune disease.
9. Symptomatic occlusive arterial disease e.g. claudication intermittens.
10. Heart failure > NYHA class II.
11. History of transient ischaemic attack or stroke.
12. ECG findings which, in the opinion of the investigator, compromises patient safety related to HRmax-test.
13. History of coronary artery disease, myocardial infarction, or other serious cardiovascular disease, as evaluated by the investigator.
14. Is not currently active athlete or a highly trained individual.

Inclusion criteria for healthy subjects:

1. 18 to < 75 years of age at the time of signing the informed consent form.
2. Have a bodyweight within > 50 and < 150 kg and a BMI within the range 18,5-35 kg/m2.
3. Are male or female.
4. Is able to meet for all of the four study visits and comply with the dietary and activity restrictions.
5. Can give informed consent.

Exclusion criteria for healthy subjects:

1. History of arthroscopy or intra-articular administration of corticosteroids or hyaluronic acid into the target knee within 6 months before screening.
2. Previous arthroplasty of knee or hip.
3. Intention of having major surgery during the timeframe of this study.
4. Secondary OA e.g. because of dysplasia, aseptic osteonecrosis, acromegaly, Paget disease, Stickler syndrome, hemochromatosis, gout, chondrocalcinosis (pseudogout) or calcium pyrophosphate deposition disease.
5. Current treatment with beta-receptor adrenergic antagonists (beta-blockers), systemic corticosteroid treatment in doses equivalent to > 10 mg of prednisolone per day, or Vitamin K antagonists, new oral anticoagulants, fractionated and non-fractionated heparin
6. Any known active systemic infection.
7. Any known active systemic inflammatory or autoimmune disease.
8. Symptomatic occlusive arterial disease e.g. Inermittent claudication.
9. Heart failure > NYHA class II.
10. History of transient ischaemic attack or stroke.
11. History of coronary artery disease, myocardial infarction, or other serious cardiovascular disease, as evaluated by the investigator.
12. ECG findings which, in the opinion of the investigator, compromises patient safety related to HRmax-test.
13. Is not currently active athlete or a highly trained individual.
14. X-ray verified Kellgren-Lawrence grade 1-4.
15. Is clinically suspected of having hip OA.

Other exclusions (all subjects):

1. Legal incapacity or limited legal capacity
2. Inability to communicate or cooperate with the investigator or to comply with the requirements of the entire study.
3. Are categorized as being very difficult to draw blood from, as evaluated by the investigator.
4. Current alcohol abuse and/or inability to refrain from intake of alcoholic beverages 24 hours prior to study intervention.
5. Other factors e.g. self-reported drug abuse, which in the opinion of the investigator may interfere with the study conduct.
6. Site staff, study staff members and study staff family members.
7. Other concomitant disease compromising or otherwise significantly affecting ECM turnover in the opinion of the investigator