What Muscles Do Barbell Squats Work Out?

Squats are an effective compound exercise that, according to MuscleMagFitness.com, strengthens over 256 muscles in the body. Most of those muscles are in the lower body. In fact, the book "Serious Strength Training" refers to squats as the quintessential leg exercise. Using a barbell during the squat increases its effectiveness. By adding additional weight, the exercise becomes challenging, recruiting more muscle fibers and resulting in more strength.

For the traditional barbell squat, stand straight with your feet shoulder-width apart. Position a barbell low on the back of your shoulders and grasp the barbell with your hands close to your shoulders. Bend down by flexing your knees forward slightly and pushing your hips back until your thighs are parallel with the floor. Keep your knees in line with your feet and don't let your knees go past your toes. Extend your hips and knees to stand and return to the starting position.

The barbell squat, like all squats, targets the quadriceps or the four muscles found in the front of your thighs. This exercise targets all quadriceps muscles fairly evenly, although changing your leg stance also changes which muscles are targeted. Keeping your feet close together places emphasis on your outer quads while performing the squat with feet wider than shoulder-width targets the inner thighs more. Holding the barbell across your chest instead of your shoulders puts the focus on your quadriceps and not the posterior side of your body.

The barbell squat is also considered one of the top exercises for targeting the glute or buttocks muscles. The traditional squat elicits more gluteus maximus activation than both the horizontal and vertical leg press and similar activation to lunges, four-way hip extensions and step-ups, according to a 2006 study commissioned by the American Council on Exercise. The only exercise the study found more effective than squats for gluteus maximus activation was the quadruped hip extension. Standing with your legs further apart produces a greater activation of the gluteus maximus muscles during squats.

The other main muscles targeted by the barbell squat are the adductor magnus, or inner thighs, and the soleus, or the calves, which serve as synergists and the hamstrings, or rear thighs, and gastrocnemius, or upper calves, which act as dynamic stabilizers. To emphasize the effect on the inner thighs, you can either stand with legs wider than shoulder-width or stand with your toes pointed outwards in a 45 degree angle, otherwise known as a sumo or plie squat. To target your hamstrings, shift your weight back onto your heels and sit back as if you are sitting in a chair. To put more emphasis on your soleus and gastrocnemeus, stand with your toes elevated on a slightly elevated surface.

The barbell squat requires you to keep your core muscles engaged to keep you balanced as you lift and lower the weight. It also strengthens your rectus abdominus or main abdominal muscles as well as your obliques, or the external ab muscles. The erector spinae or lower back is also strengthened but this muscle is also at risk of injury if you squat incorrectly. Keep the barbell lower on your shoulders, focus on sitting back during the lowering phase of the exercise, and do not squat too deeply to avoid lower back pain.