Exercises characterized by the application of a quick muscle stretch followed by rapid muscle shortening enabling muscle(s) to achieve maximal rates of force development. They are intended to improve reactive/explosive muscle performance.

肌肉在离心(拉长)收缩之后紧接着进行向心(缩短)收缩的力量练习称为超等长练习,比较典型的是"跳深",即从高处跳下再向上跳起的动作,此时的股四头肌、臀大肌、小腿三头肌等在落地时做离心收缩,向上跳起时做向心收缩.
超等长收缩（plyometric）通过肌肉快速stretch和shortening 使肌肉获得最大力度，趋向于改变肌肉的反应力/爆发力。