Physical intelligence is the brain’s ability to figure out how to perform physical skills better and better. It learns by doing. 

But we forget. We lose skills we don’t use. That results in losing basic life skills if we withdraw from life. The more we pull back from activities that might result in injury the less capable we become over time. We have to find a way to stretch ourselves in what we already know or in learning new activities. 

Exercise is not enough. We need unpredictable environments. An opponent across the net. An unstable trail. Something that engages the brain in adapting skills to accommodate new information. We retain physical skills and we exercise the brain.