It’s not the reigning “king of exercises” for nothing. No single exercise is arguably as effective, not only for the intended lower-body target muscles but for all the muscles from your shoulders, chest and back down to your core, all of which fire to maintain your posture and balance as you rep.
Main Areas Targeted: Quadriceps, glutes, hamstrings, calves, core
Strengths: You need strong legs from the ankles to the hips, and back squats work the lower-body prime movers, stabilizers and synergists. The quadriceps and hamstrings are the major muscle groups that affect knee stability and motion. Quads come into play during the straightening of the knees, while hamstrings are directly related to the bending of the knees and the pushing action against the ground, such as in a short sprint. At the end of the day, squats are beneficial in developing muscular growth, strength and power, all while strengthening stabilizers and the core.
How-To: Stand with your feet about shoulder-width apart and hold a bar across your upper back. Your knees should be slightly bent and your toes turned out slightly. Keeping your head in a neutral position, abs tight and torso upright, bend at the knees and hips to slowly lower your body as if you were going to sit in a chair. Go as deep as you can handle, ideally to a point where your thighs come parallel to the floor or below while maintaining your natural lower-back arch, then forcefully drive through your heels and extend your hips and knees to return to a standing position.
The benefit of free-weight exercises is the countless variations you can come up with. Experiment with bar placement on your back (high/low), foot placement (narrow/wide) and even with range of motion. I started doing rack squats, which target the top third of the movement. It allows me to go heavier and it mimics the range of motion used in jumping.