In martial arts there is much a do about Ki . The inner energy force that with proper concentration and practice you can harness . There are several schools of thought that dismiss the idea saying that it's just old wives tales and that it really doesn't exist.
Myself personally I have felt it in the presence of some of my sensei's . I can never forget the first Aikido demonstration that I watched where a rather short( around 5ft tall) lady was tossing guys( my size 6ft) around the Dojo like they were nothing for 20 minutes. She hadn't even broken a sweat .
There is a mind -body connection , and training one and not the other doesn't always enable one to achieve the balance needed to really make use and feel that Ki. Whether it is for healing the body or simply perfecting one's art(martial or otherwise) there is a balance needed.
Breath in , Breath out,