Daiyoukin (大腰筋)

On an episode of Tameshite Gatten! , they showed the current technique in improving running is utilizing the muscle named daiyoukin (大腰筋). In English, this muscle is the “Psoas major” muscle. Web site which shows this muscle is http://www.getbodysmart.com/ap/muscularsystem/thighmuscles/anteriormuscles/psoasmajor/tutorial.html