Direct result of an injury—A disability results directly from an injury if the injury is a substantial factor in bringing the disability about.

Gainful work means full-or part-time activity that actually is compensated or commonly is compensated.

Medical certainty—A fact exists to a degree of medical certainty, when, pursuant to a medical assessment, the fact is demonstrated by convincing evidence.

Permanently disabled—An individual is permanently disabled only if there is a degree of medical certainty (given the current state of medicine in the United States) that his disabled condition—

(1) Will progressively deteriorate or remain constant, over his expected lifetime; or

(2) Otherwise has reached maximum medical improvement.

Product of an injury—Permanent and total disability is produced by a catastrophic injury suffered as a direct and proximate result of a personal injury if the disability is a direct result of the personal injury.

Residual functional capacity means that which an individual still is capable of doing, as shown by medical (and, as appropriate, vocational) assessment, despite a disability.

Totally disabled—An individual is totally disabled only if there is a degree of medical certainty (given the current state of medicine in the United States) that his residual functional capacity is such that he cannot perform any gainful work.