I often here you should always include the back squat in your weight lifting routine; I cringe. Being a corrective exercise specialist, I know this is a recipe for disaster as most individuals simply do not have the correct posture and biomechanics to perform this exercise effectively, or even safely. However, this post is direct to those who may already have a training base, and want to get the most out of their training program. Therefore, when it comes to exercise selection you need to determine if the exercise is accomplishing what it is intended to do, or if it is the most optimal at doing so.
The back squat is most often implemented to develop the musculature of the legs, and namely thighs for physique based athletes, or those wishing to develop muscle tissue. To assess if the back squat is good for you it may take some trial and error. I will try to give as much direction as possible. In general, taller individuals will recruit more glutes, hamstrings, and low back (posterior chain) than a shorter individual who will be able to squat more upright and recruit more quadriceps. Of course I always advocate working with a trainer or someone with experience on how to perform this exercise when assessing its applicability. The best way to test is to do the exercise, video tape it, and also assess your muscle fatigue within the workout and the delayed muscle soreness the days following. The video will help you not only check to see if your form is good, but also to assess the angle of change at your hips and knees. If your low back, glutes, and hamstrings are fatigued and pumped after your set of squats then you most likely recruited those most. Also, if your glute/ham/low back area is sore the days following your squat session, those are the muscles you taxed most from the exercise. On the contrary if you feel the aforementioned things in your quads and lower in your thighs, thats what you worked predominantly. It’s not really all that complicated.
In the end its about how your individual biomechanics work that will dictate the extent to which what muscles will be recruited. Remember, exercise selection, for all intents and purposes, is not a matter of right or wrong but rather what is a better or more optimal selection for you.