Physical deconditioning occurs when the body loses strength and endurance. Loss of muscle fibers from disuse results in muscle atrophy or wasting. The force of the muscle contraction declines and strength decreases.
Endurance refers to how long the muscle can contract and hold. Or in a more general sense, how long the body can keep going. Pain with use seems to occur when weakness and loss of endurance are factors.
So for example, older adults may experience aches and pains that go away by increasing their activity level. We say they are deconditioned and that exercise is the key to reconditioning.
Aerobic capacity is also part of the equation. The heart is also a muscle that can become deconditioned without the proper amount of exercise and activity. Exercise that increases the heart rate (number of times it beats in a minute) helps improve aerobic conditioning.
Some experts look at decreased body mass and increased body fat as a sign of deconditioning. Very few studies exist to actually prove or disprove the theory that deconditioning is the result of chronic pain.
It seems to make good, common sense but should be studied more closely. Finding out what kind of conditioning program works best would be helpful.