This force is directly opposite the line of pull of the muscle or tendon. In general, this pressure is applied near the distal end of the lever in which the muscle is inserted. At this grade the patient moves the part against gravity into the test position. Consideration must be made for the size of the patient and the cross-sectional area of the functional muscle group tested. The pressure exerted against a child whose wrist extensors are tested will be much less than that against an adult whose knee extensors are tested.
Substitution is when a muscle or muscle group attempts to compensate for a weak or paralyzed muscle.
These substitutions appear similar to normal movements. The examiner must learn to identify these substitutions by placing the part in the test position and by using proper patient positioning as much as possible. The former action allows even inexperienced examiners to detect the sudden shift of the body part, which accompanies the substitution for muscle weakness. Placing the patient in the proper position tends to block known substitution patterns by resisting body shifting and turning the body part to use gravity. Gravity is a form of resistance affecting the testing of trunk, neck and extremity muscles.