In my work with fearful children who have movement difficulties I am always amazed at how quickly and easily a child can be shifted from fearfulness to courage in the face of physical challenges. As one 6-year-old put it "I have leant to face my fears".
The same child had also learned to enjoy working his muscles hard and to interpret sensations of tiredness in his muscles as a good thing - because "it means that my muscles are working hard enough to make them stronger".
He had learned to put in the extra effort needed to complete a task when his muscles were starting to tire, and the pleasure of pushing himself hard to reach a goal or meet a challenge.
Michael was nearly five when he first came to see me. He tolerated the assessment tasks for about 20 minutes - then started to whine and wanted to leave. So we switched to games. We played being chased by a lion and did shuttle runs across the room, with me shouting loud warnings about the lion catching me and encouragement to run faster. When we stopped I encouraged him to feel his heart beating. Yes, it was beating very, very fast because that is what hearts do when one runs. He wanted his mom to feel his heart, and then wanted to feel my heart beating fast. After a little rest he wanted to run again - so that he could feel his heart again.
His perception of his heart beating fast had shifted from being a signal of an anxiety-provoking situation to the sensation of effort, exercise and excitement. (You do have to realize that I make a great deal of fuss about escaping from that lion that is chasing us.)
We also did some jumping from one big cushion to another - big jumps across a river. He did a few, then refused to do any more. So we had a conversation about what his knees felt like when he jumped. And my response was "That is what knees feel like when you jump". His mom reported that in the car on the way home Michael was very excited about feeling his knees. "Mom" he said "I can feel my knees". He also did a lot of jumping at home in the week that followed.
Bibliography selected list of scientific papers that relate to different aspects of behavioral inhibition: brain mechanisms, assessment, parental factors and risk factors.