How often each should I train each muscle group?
The amount of times per week that you train each muscle group will depend on a number of factors. If you're just starting out, and you're exercising and weight lifting two to three times a week, it's probably at a low to moderate intensity. In such cases, you can probably exercise each of the muscle groups each time you go out, for example a Monday, a Wednesday, and a Friday. As you get more advanced, you start segmenting the body parts when you work out. You may do all pushing muscles one day and all pulling muscles the next, then take a break and then repeat that cycle if you do it four days a week. Or you may do all upper body one day and all lower body the next, then take a break; and then all upper body and then lower body. Advanced body builders, for example, will work out five to six days a week and they may only work one body part a day. Monday they're doing arms, Tuesday they're doing legs, Wednesday they're doing back and chest and so on; one each day. Due to the volume and the intensity of their workout being so great, it actually takes a whole week to recover to where they're ready to do it again. So, how frequently you do the resistance or the strength training is dependent on a number of factors; your ability, your health, your time, your commitment, and your goals.