How often?
Today's gear heads hit a muscle group once a week.
Powerlifters commonly do the bench, squat and deadlift once per week each and also several assistance exercises for each lift on the day.
The pre-steroid oldtimers hit a muscle group it 2-3 times a week with 6-12 sets per workout.
So, maybe that's right for natties.
I don't recall hearing about torn pecs in the 70s and early 80s.
I do think the use of anabolics nowadays without building a solid base from time spent natural training has something to do with the current frequency of pec tears.
The connective tissues just never get the chance to toughen up before being subjected to heavy loads.