岔气，又称运动岔气或运动急性胸肋痛，指的是体育运动，特别是跑步中，胸肋部产生的疼痛。岔气多发生在右下肋部，在运动停止后会自然消失。腹部按摩、缓慢深呼吸或腹式呼吸能加速其缓解。

岔气目前没有统一的解释。可能的原因有下列几个：

Side stitch (also called a side ache, a side cramp, a side crampie, a side sticker or simply a stitch) is an intense stabbing pain under the lower edge of the ribcage that occurs while exercising. It is also referred to as exercise related transient abdominal pain (ETAP). Some people think that this abdominal pain may be caused by the internal organs (like the liver and stomach) pulling downwards on the diaphragm, but that theory is inconsistent with its frequent occurrence during swimming, which involves almost no downward force on these organs. If the pain is present only when exercising and is completely absent at rest, in an otherwise healthy person, it is benign and does not require investigation. There are a variety of published ways of alleviating the symptoms including adjusting at what point in a runner's stride they inhale.