It will be interesting to see if Bruce goes into the opening and closing of the internal organs, or whether he goes into more detail about changing the tendons and ligaments. If I remember correctly, the opening and closing of the internal organs basically follows from the cavities. The tendons and ligaments become more important after these are working well.
It is one of those chicken and egg moments where you get better access to the ligaments and tendons which helps with the internal organs which further helps with the ligaments and tendons.
For example, the lungs aren’t really worked without the ligaments and tendons. First I don’t work the lung directly. They are more like a passive sack. It’s the diaphragm that;s important to good breathing. Although the diaphragm is just a large strangely shaped muscle, it is the ligaments and tendons that attach it to bone that become important. In fact it is also the ligaments and tendons of the ribs that become important as well. This is where they are actively used to boost opening and closing for power.