Cross education is a phenomenon where a person working only one limb will notice a corresponding increase in strength and coordination in the other extremity. While the resting limb will not develop strength as quickly as the one the person is exercising, it will experience some improvement. People can turn this to their advantage in a number of settings, including during injury recovery when they may have to rest a limb to reduce the risks of further injury or complications.
In a simple example of cross education, a person could start lifting weights with the right arm only. The right arm would bulk up and develop muscle strength, and so would the left, to a lesser degree. A variety of exercise techniques can draw upon cross education, such as alternating exercise on either side of the body to give limbs a chance to rest. The resting limb does not go into complete stasis because it is still receiving signals, and will stay warmed up while the person works the other side of the body.
The body exhibits bilateral symmetry and the two halves have a number of connections. When someone works one side of the body, the nerves on the other side experience stimulation. Neurological activity can create muscle strength as well as contributing coordination training. On the spinal cord level, signals will stimulate both sides of a set of nerve roots, not just one, when people are working one side of the body. The brain also appears to be involved in cross education, as it plays a role in developing motor skills, including strength and coordination.
For people with injuries, cross education allows them to work out to retain strength, coordination, and skill without injuring the affected limb. A trainer can work with the patient to develop an appropriate exercise plan. This technique can also be useful for building up strength in a weaker limb; the patient focuses on exercising that limb and not working the stronger one, building up more equal strength and coordination over time. The low-level stimulation of the strong limb prevents atrophy.
The mechanics of cross education are still a subject of study. While people have been able to document the process, the precise mechanism of action is somewhat unclear. People like athletic trainers and physical therapists can both use this phenomenon in their work. Exercise classes and programs sometimes also integrate some level of cross education, depending on the nature of the program and its goals.