Which statement corresponds to a muscle score of 3?

• A. 2 muscle score - active movement without gravity
• B. 3 muscle score - active movement against gravity
• C. 4 muscle score - active movement against gravity, and some resistance
• D. 5 muscle score - active movement against full resistance w/o evident fatigue ('normal strength')

Answer: (B)

In the MRC muscle strength scale, grade 3 means the muscle can move the joint through its full range of motion against gravity, but cannot resist additional external force. Gravity is the limiting factor at this level: you can lift the limb upward, but you cannot hold it against a manual resistance. This sits between moving only with gravity eliminated (grade 2) and moving against gravity with some resistance (grade 4), and between that and normal strength (grade 5). For example, elbow flexion can occur against gravity, but applying resistance would defeat the movement. Therefore, the description “active movement against gravity” matches a muscle score of 3. The other statements map to the other grades: movement only with gravity eliminated corresponds to grade 2; movement against gravity with some resistance to grade 4; and movement against full resistance to grade 5.