Rotation of a limb segment away from (ER) or toward (IR) the body's midline.
ER/IR describes rotational movement of a joint, most commonly the shoulder or hip, around its long axis: external rotation turns the limb outward, internal rotation turns it inward. In clinical and research contexts these are usually assessed as paired isometric or isokinetic strength values (e.g., ER/IR ratio) or range-of-motion measures, both used to screen for muscular imbalance or injury risk. Normative ratios (e.g., ~66-75% for shoulder ER/IR strength) vary by population, testing position, and velocity, so absolute cutoffs should be interpreted cautiously.
This guide was auto-drafted and is pending editorial review.