Weight training can activate muscles without loading the joints by using very light weights that challenge the muscle to a minor degree.

“the ultimate weight training would be to activate the muscle without loading the joint and you can do that you can activate the muscle and not load the joint when you use very light weights but enough weight that the muscle gets challenged just just even the most minor degree because once it's challenged you can then over flex that muscle you can voluntarily flex the muscle beyond so you need an just enough weight to initiate the muscle activation and contraction and that's usually not very much at all and then the joints not being loaded the muscles being activated and you're getting a much safer workout”