Functional training has its origins in rehabilitation.
Physical therapists developed exercises that mimicked what patients did at home or work in order to return to their lives or jobs after an injury or surgery.
Thus if a patient's job required repeatedly heavy lifting, rehabilitation would be targeted towards heavy lifting, if the patient were a parent of young children, it would be targeted towards moderate lifting and endurance, and if the patient were a marathon runner, training would be targeted towards re-building endurance.
Functional training involves mainly weight bearing activities targeted at core muscles of the abdomen and lower back. Most fitness facilities have a variety of weight training machines which target and isolate specific muscles. As a result the movements do not necessarily bear any relationship to the movements people make in their regular activities or sports. Functional training attempts to adapt or develop exercises which allow individuals to perform the activities of daily life more easily and without injuries.
Functional training may lead to better muscular balance and joint stability, possibly impacting the number of injuries sustained and individual's performance in a sport. The benefits may arise from the use of training that emphasizes the body's natural ability to move in three anatomical planes of motion. In comparison, though machines can often be safer to use, they restrict movements to a single plane of motion, which is an unnatural form of movement for the body and may potentially lead to faulty movement patterns or injury.
Many athletes equate strength training with bodybuilding; accordingly, individuals involved in endurance or flexibility-based sports do not strength train for fear of gaining too much bulk and losing flexibility, or mimic the training of bodybuilders without adapting workouts to their specific sports. As a result, training can lack the performance benefits that strength training could provide.