Qigong operate on two levels simultaneously; they encourage the healthy flow of energy and they strengthen the structure of the body.
This process of building strength is seen by many people to arise from the energy flow alone but this is rather misleading.
Qi does not move the bones, muscles do. Nerves direct the muscles and energy fuels the entire system.
Without energy, nothing would happen, but without muscles there would be no strength.
Muscles turn energy into motion.
This is not to be confused with gym work or weight training. The degree of muscle usage in qigong must be minimal.
The aim is to employ the tendons, ligaments and fasciae for increased strength and support.
You must only use the degree of muscle strength necessary to hold the limb in place; and this is always far less than you first realise.