Dec. 22 (HealthDay News) -- Brain inconsistency is why you can't reliably repeat that perfect fastball or golf swing, says a Stanford University study.

"The main reason you can't move the same way each time, such as swinging a golf club, is that your brain can't plan the swing the same way each time," study co-author Krishna Shenoy, an assistant professor of electrical engineering, said in a prepared statement.

Shenoy's research, published in the Dec. 21 issue of Neuron, includes investigation of the neural basis of sensorimotor integration and movement control.

It's as if every time the brain plans a movement, it has to start from scratch. Practice and training can help improve certain actions, but humans and other primates simply aren't wired for consistency like machines or computers.

Contrary to what's been widely believed, movement variability is not primarily a mechanical phenomenon, the researchers said. Their study of neural and muscle activity in monkeys revealed that less than half of movement inconsistency is the fault of muscles.

The researchers suggested that the human brain evolved an improvisational style of movement, because the majority of situations involving movement are unique. For example, ancient human hunters never caught and killed prey in exactly the same way or under the same conditions.

"The nervous system was not designed to do the same thing over and over again. The nervous system was designed to be flexible. You typically find yourself doing things you've never done before," study co-author and postdoctoral researcher Mark Churchland said in a prepared statement.