Nearly all martial arts have some form of supplemental strength and conditioning exercises. Karate has hojo undo, boxing has road work, Brazilian jiu-jitsu has ginastica natural. These can be more separate from the art, as with barbell training in judo, or more integrated, such as sumo's shiko.
What kind of strength and conditioning work is used in tai chi?
For instance, how are stance work, forms, and other methods arranged for maximum benefit to tai chi skill? What attributes are worked on, other than the presupposed technical skill?