Dangers of practising knees?

[Mr Punch]

Practising full-speed kicks in mid-air can make a mess of your knees.

Is practising full-speed knees safe?

[Ming Yue]

I don't see why not, unless you're practicing against a cinder block wall.

at full speed, throwing a knee at a chest level target will certainly challenge your balance if you don't connect with something.

[MasterKiller]

Practice full speed everything against the heavy bag.