The squat is a fundamental movement pattern -- it's hard to imagine getting through the day without doing at least a few squats. Standing up out of a chair, getting in and out of your car and even sitting on the toilet are all movements involving squats. As well as being such a regular movement for most people, squats are also an important and beneficial leg exercise used by bodybuilders, weightlifters and other athletes and exercisers looking to develop high levels of fitness, strength and performance.
Core is the term used to describe the muscles that support your spine, specifically your rectus abdominis, erector spinae, obliques and transversus abdominis. When you perform weighted squats, these muscles must work hard to ensure your lumbar spine is held in the right position and that your lower back does not round. A strong core is essential for heavy squats, as it can help prevent injury.
Located on the back of your thigh and running from the base of your pelvis to just below the back of your knee, your hamstrings are responsible for controlling hip extension when you squat. There are three muscles that make up the hamstrings: biceps femoris, semimembranosus and semitendinosus. Working together, they act as a brake as you descend and then powerfully contract to extend your hip and help you stand back up. Tight hamstrings can result in a rounding of your lower back, so flexibility is important as well as strength.
Your gluteus maximus is a large and powerful muscle that does a lot of work when you squat. Located on the back of your hip and essentially your butt, your gluteus maximus works with your hamstrings and controls your hip. Like your hamstrings, your glutes help control your descent and are then involved in extending your hips to push you back upward. Squats are an effective butt-building exercise.
Located on the front of your thigh and running from your hip to below your knee, your quadriceps are your primary knee extensor muscles. Known as the quads for short, four muscles make up your quadriceps: rectus femoris, vastus intermedius, vastus lateralis and vastus medialis. These muscles are the ones you are most likely to feel after a high-rep set of squats.
While there are a number of primary muscles involved in squatting, there are also several secondary muscles that help make this exercise possible. The muscles on the inside and outside of your hips and thighs, your adductors and abductors, work to ensure your knees track over your feet and do not swing inward or outward. Your upper-body muscles must also work very hard to hold and support the barbell on the front or back of your shoulders -- depending on whether you perform front or back squats. While squats are normally classed as a leg exercise, so many muscles are involved in a secondary capacity that squats are almost a whole-body exercise.