There are two points and many of you are missing the main one.
CAS want's people to take responsibility and do 3 periods of physical activity per week. full stop.
CinC says it is up to stn cdrs to see this happens. full stop
He goes on to say that stn cdrs will delegate to flt cdrs who will appoint PTLs.
Nowhere does it say 3 x 50 minutes exercise
However to use PTLs to monitor such exercise and to mandate that it will be 50 minutes implies that it will be work.
I believe there is also an insurance issue involved; for instance I believe the rules are different if you break your ankle doing voluntary jockstrapping on a Saturday, as opposed to organised sport.
In the winter, for day workers, there are no daylight hours for out of hours running. Many jockstrappers run at lunchtimes in lieu of lunch but surely you cannot 'cancel' lunch and substitute sports instead.
The CAS's wishes are feasible. The implementation may not be feasible and may create both administative overload, especially for the PTLs, and as people have said, as soon as it is mandated it becomes DUTY.
Now there could be one benefit. If the morning wave was cancelled 3 times per week it would be a big efficiency saving - very green.