Hours spent perfecting your golf swing or goalkicking could be a waste of time, says a US study which has found that practice doesn't always make perfect.
Researchers at Stanford University looking at the way the brain plans and calculates motion made the discovery after training monkeys torepeat a simple reaching task thousands of times.
"The nervous system was not designed to do the same thing over and over again," said Mark Churchland, postdoctoral researcher in electrical engineering and lead author of the study.
In the study, scientists rewarded the monkeys for reaching out to touch a coloured spot of light at different speeds.
Scientists monitored the promoter cortex of the monkeys' brains, responsible for movement planning, and tracked the speed of the resulting motion. Over the course of thousands of attempts, the monkeys rarely moved with the exact same speed.
Small variations in reach speed followed small variations in brain activity during movement planning, before the monkeys started reaching for the spot, according to the study, published in the journal Neuron.
Contrary to conventional wisdom that movement variability is caused by muscle activity, the scientists found that neural activity accounts for about half the variation.
In other words, training muscles to perform a certain way through practice, such as hours teeing off won't produce the same shot every time because the brain's behaviour is inconsistent.
After an initial training period, the monkeys' reach accuracy did not improve over time, suggesting that lots of practice can only improve movement control so much.
