Recruitment difficulties.

There is ample evidence that exercise therapy is beneficial with respect to pain in patients with osteoarthritis of the knee. However, the pain relieving mechanisms are unknown. To enhance the efficacy of exercise therapy a deeper understanding of the involved mechanisms is needed.

Different exercise types may affect the pain sensitivity differently. It is hypothesized that non-specific exercises (i.e. exercises that does not involve the knee) reduces the processing of pain in the central nervous system (central sensitivity) to knee joint pain in healthy subjects. It is also hypothesized that exercises that involve the knee (i.e. specific knee exercises) reduce the sensitivity of pain receptors in the knee (peripheral sensitivity) in healthy subjects.

Healthy volunteers are recruited and randomised to one of four interventions: 1: Muscle strengthening exercises involving the thigh muscles; 2: Muscle strengthening exercises involving the shoulder muscles; 3: Cardio-vascular fitness exercises; or 4: Control (no exercises). The active interventions include exercises three times per week for 12 weeks. Pain sensitivity and a range of explanatory variables is measured before the interventions, after 4 weeks and after 12 weeks.

Inclusion Criteria:

• Age between 18 and 35 years
• Untrained (i.e. less than 2 hours of organised exercise per week in the last 6 months - physical activity related to transportation (e.g. bicycling) is not included)
• Generally healthy according a medical exam at screening, history
• Willing and able to participate in all measurements
• Willing and able to attend all training sessions
• Willing to keep the habitual activity and amount of training constant (ie screening activity and training volume).
• 20 ≤ body mass index (BMI) ≤ 28 kg/m2
• Speak, read and write Danish

Exclusion Criteria:

• Pregnant or breastfeeding
• Current or previous symptoms of autoimmune disease (eg, inflammatory bowel disease, multiple sclerosis, lupus, rheumatoid arthritis)
• Planned surgery during the study period
• Current or former musculoskeletal injuries or illnesses, including but not confined to:
• Ligament Injuries
• Meniscus Injuries
• Osteoarthritis
• Patellofemoral Pain Syndrome
• Backache
• Neck pain
• tendinopathy
• Current or past diagnosis, signs or symptoms of significant cardiovascular disease, including but not limited to:
• Ischemic heart disease
• Arteriosclerosis
• Medical conditions that contraindicate exercise, including but not limited to:
• Chronic or congenital heart disease
• Asthma
• Chronic Obstructive Pulmonary Disease
• Past or current diagnosis, signs or symptoms of significant neurological disease, in-incl. but not limited to:
• Blood clot in brain
• Stroke
• Clinically significant head trauma within the last year
• Peripheral neuropathy
• Epilepsy or seizures
• Impaired balance
• Alcohol or drug abuse within the past 5 years
• Past or current diagnosis, signs or symptoms of major psychiatric disorder
• Regional pain syndromes like fibromyalgia
• Regional pain caused by lumbar nerve root or cervical radiculopathy with or at risk for developing it