Desirable difficulties

Desirable difficulties is a concept developed by Robert Bjork, a cognitive psychologist at UCLA in the United States. It refers to conditions that make movements feel harder and lead to more mistakes during practice, yet help people perform better when they try again later or in a new situation.

The key is to distinguish what practice looks like from the results of learning. When practice goes smoothly, it can feel as though you are learning well, but that smoothness often comes from repeating the same movement several times in a row. You can read more about the difference between performance during practice and long-term learning in Performance versus learning.

In motor learning, these three approaches are common examples.

• Mixing up practice — Instead of repeating one movement in a block, alternate between several movements. The degree to which the preceding and following movements interfere with each other in this way is called Contextual interference. You can compare the approaches in Blocked and random practice. This topic has been widely studied since Shea and Morgan's 1979 experiment.
• Changing conditions during practice — This is Variable practice, which involves changing the distance, speed, direction, or equipment. It contrasts with Constant practice, in which the same movement is repeated only in the same place.
• Reducing feedback — Rather than providing results after every trial, provide them only occasionally, or let learners sense how they did for themselves. This relates to how Knowledge of results and knowledge of performance are provided.

In learning more generally, practicing at spaced intervals rather than all at once (Distributed and massed practice) and recalling what you have learned without looking at the material are also presented as related approaches.

All three approaches lead to more mistakes and a less fluent feeling during practice. Even so, they are reported to offer an advantage when trying again a few days later or using a skill in an unfamiliar situation. The effects of high contextual interference on memory retention have also been examined in systematic reviews and meta-analyses.

Difficulty is not always a good thing. If a task is too easy, there is nothing to learn; if it is too difficult, the learner cannot complete it at all, so practice cannot continue. The appropriate level depends on the learner's experience and the complexity of the task. When first learning, a natural progression is to learn the basic movement pattern first, then add conditions one at a time as it becomes more familiar.

Difficulty itself is not the goal, either. The basic principle is to establish safety and an understanding of the task before adjusting the conditions.

• Mix things up instead of repeating the same movement in a row. In basketball, try shooting from several positions instead of taking twenty shots from one spot. The same principle applies to playing an instrument, golf, or tennis when you alternate pieces, clubs, or strokes.
• Change the conditions. Make small changes to the stair height, ball speed, surface you stand on, or hand position.
• Try again after an interval. Several short sessions spread over a few days stay with you longer than cramming everything into one day.
• Get a sense of how you did before receiving feedback. Before immediately watching a video or listening to your coach, ask yourself, “How did that go?”
• Do not get impatient if you feel clumsy during practice. A temporary drop in scores or success rates is common with this approach.