Opposition or contralateral, in regards to body movement or mechanics, means that opposite sides of the body work together to coordinate the right arm and left leg, and then the left arm and right leg. Ipsilateral refers to same side coordination.
Cross crawl refers to movements in which we use opposition such as walking, climbing, crawling, walking, running, and swimming. These are intentional cross-lateral activities, which you cross the mid-line of the body. Touching the hand to the opposite knee or foot.
This type of movement builds the connection between the right and left hemispheres of the brain. This allows for the electrical impulses and information to pass freely between the two hemispheres. This is essential for physical coordination as well as cerebral activities, such as reading, listening, teaching or learning a skill, and hand-eye coordination.
The cross crawl technique is an easy way to activate brain development and the nervous system. It gives motor and sensory stimuli needed to take control of bodily functions, thereby preventing or rehabilitating health problems. Exercises from martial arts such as Tai Chi (kung fu), qigong and yoga focus greatly on contralateral and ipsilateral movements throughout their curriculum.
United Martial Arts Association 