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In strength training, the squat is a compound, full body exercise that trains primarily the muscles of the thighs, hips and buttocks, quads (vastus lateralus medialis and intermedius), hamstrings, as well as strengthening the bones, ligaments and insertion of the tendons throughout the lower body. Squats are considered a vital exercise for increasing the strength and size of the legs and buttocks, as well as developing core strength. Isometrically, the lower back, the upper back, the abdominals, the trunk muscles, the costal muscles, and the shoulders and arms are all essential to the exercise and thus are trained when squatting with proper form.
Squats are one of the three lifts in the strength sport of powerlifting.
Muscles engaged 
- Primary Muscles
- Secondary Muscles (Synergists/Stabilizers)
- Erector Spinae, Transverse Abdominus, Gluteus medius/minimus (Abductors), Adductors, Soleus, Gastrocnemius
The movement begins from a standing position. Weights are often used, either in the hand or as a bar braced across the trapezius muscle or rear deltoid muscle in the upper back. The movement is initiated by moving the hips back and bending the knees and hips to lower the torso and accompanying weight, then returning to the upright position.
Squats are commonly performed to varying depths. Squatting below parallel qualifies a squat as deep while squatting above it qualifies as shallow. Some authorities caution against deep squats; though the forces on the ACL and PCL decrease at high flexion, compressive forces on the minisci and articular cartilages in the knee peak at these same high angles. This makes the relative safety of deep versus shallows squats difficult to determine.
As the body gradually descends, the hips and knees undergo flexion, the ankle dorsiflexes and muscles around the joint contract eccentrically, reaching maximal contraction at the bottom of the movement while slowing and reversing descent. The muscles around the hips provide the power out of the bottom. If the knees slide forward or cave in then tension is taken from the hamstrings, hindering power on the ascent. Returning to vertical contracts the muscles concentrically, and the hips and knees undergo extension while the ankle plantarflexes.
Two common errors include descending too rapidly and flexing the torso too far forward. Rapid descent risks being unable to complete the lift or causing injury. This occurs when the descent causes the squatting muscles to relax and tightness at the bottom is lost as a result. Over-flexing the torso greatly increases the forces exerted on the lower back, risking a spinal disc herniation.
Another error where health of the knee joint is concerned is when the knee is not aligned with the direction of the toes. If the knee is not tracking over the toes during the movement this results in twisting/shearing of the joint and unwanted torque affecting the ligaments which can soon result in injury. The knee should always follow the toe. Have your toes slightly pointed out in order to track the knee properly.
Various types of equipment can be used to assist with squats. A power cage can be used to reduce risk of injury and eliminate the need for a spotting partner. Bar path should be dictated by stabilizing muscular and skeletal anatomy and not by the use of upright fixed supports. The Smith machine also removes use of the hips from the movement which turns the exercise into something resembling a leg press instead of a true squat. Other equipment used can include a weight lifting belt to support the torso and boards to wedge beneath the ankles to improve stability and allow a deeper squat (some shoes also have wooden wedges built into the sole to mimic this). Heel wedges and related equipment are discouraged by some as they are thought to worsen form over the long term. However, weightlifting shoes generally have an elevated, incompressible sole which has a similar effect as a wedge. The barbell can also be cushioned with a special padded sleeve used if the weight becomes uncomfortable for the lifter.
World records 
The heaviest Raw (unequipped) Squat (no additional equipment except knee wraps) is held by Robert Wilkerson (USA) with a best of 453.59 kg (1000 lb)  beating the previous record set by Ethan Moore (USA) of 451 kg (995 lb).
The squat has a number of variants, some of which can be combined:
- Back squat – the bar is held on the back of the body at the base of the neck or lower across the upper back. In powerlifting the barbell is often held in a lower position in order to create a lever advantage, while in weightlifting it is often held in a higher position which produces a posture closer to that of the clean and jerk. These variations are called low bar and high bar, respectively.
- Box squat – at the bottom of the motion the squatter will sit down on a bench or other type of support then rise again. The box squat is commonly utilized by power lifters to train the squat. Pausing on the box creates additional stimulus in the hips and glutes. Some people believe this form of isometric training allows for greater gains in the squat compared to a traditional Olympic style squat, while others contend that the increased spinal loading creates more opportunity for injury.
- Front squat – the weight (usually a barbell) is held in front of the body across the clavicles and deltoids in either a clean grip, as is used in weightlifting, or with the arms crossed and hands placed on top of the barbell.
- Hack squat – a barbell is held in the hands just behind the legs; known in Germany as Hacke (heel [squat]) because the barbell would sit behind the ankles, popularised in the English-speaking countries by early 1900s wrestler Georg Hackenschmidt. Also called a rear deadlift.
- Overhead squat – a barbell is held overhead in a wide-arm snatch grip; however, it is also possible to use a closer grip if balance allows.
- Zercher squat – the bar is held in the crooks of the arms, on the inside of the elbow. One method of performing this is to deadlift the barbell, hold it against the thighs, squat into the lower portion of the squat, and then hold the bar on the thighs as you position the crook of your arm under the bar and then stand up. This sequence is reversed once the desired number of repetitions has been performed. Named after Ed Zercher, a 1930s strongman.
- Bulgarian squat – performed much like a split squat, but the foot of the non-lifting leg is rested on a knee-high platform behind the lifter.
- Split squat – an assisted one-legged squat where the non-lifting leg is rested on the ground a few 'steps' behind the lifter, as if it were a static lunge.
- Belt squat – is an exercise performed the same as other squat variations except the weight is attached to a hip belt i.e. a dip belt
- Sissy squat – a squat with several sorts (dumbbell, weight plate, smith machine, barbell, bodyweight). In the most common variant, a dumbbell is held behind the legs while the heels are lifted off the ground and the torso remains flat while the lifter leans backwards; sometimes done with a plate held on the chest and one arm holding onto a chair or beam for support. Unlike most other squat variations, Vince Gironda promoted sissy squat as a rectus femoris isolation exercise.
- Smith squat - a squat using a smith machine. Hack squats can be done easily this way, as in the picture.
- Trap bar squat – a trap bar is held with hands at the sides.
- Bodyweight squat – done with no weight or barbell, often at higher repetitions than other variants.
- Overhead squat – a non-weight bearing variation of the squat exercise, with the hands facing each other overhead, biceps aligned with the ears, and feet hip-width apart. This exercise is a predictor of total-body flexibility, mobility, and possible lower body dysfunction.
- Face the wall squat – performed with or without weights. It is primarily to strengthen the vertebrae tissues. In the Chinese variant (面壁蹲墙) weights are not used. Toes, knees and nose line up almost touching the wall. Advanced forms include shoeless, wrists crossed behind the back, and fists in front of forehead, all performed with toes and knees closed and touching the wall.
- Hindu squat – done without weight where the heels are raised and body weight is placed on the toes; the knees track far past the toes.
- Jump squat – a plyometrics exercise where the squatter engages in a rapid eccentric contraction and jumps forcefully off the floor at the top of the range of motion.
- Pistol or pistol squat – a bodyweight squat done on one leg to full depth, while the other leg is extended off the floor. Sometimes dumbbells or kettlebells are added for resistance. (aka single leg squat).
Injury considerations 
Although the squat has long been a basic element of weight training, it has in recent years been the subject of considerable controversy. Some trainers allege that squats are associated with injuries to the lumbar spine and knees. Others, however, continue to advocate the squat as one of the best exercises for building muscle and strength. Some coaches maintain that incomplete squats (those terminating above parallel) are both less effective and more likely to cause injury than a full squat (terminating with hips at or below knee level).
See also 
- Rippetoe, Mark (2007). Starting Strength: Basic Barbell Training, p.8. The Aasgaard Company. p. 320. ISBN 0-9768054-2-1.
- "Bodyweight Squat". acefitness.org. American Council on Exercise. Retrieved 27 March 2011.
- Brown, SP (2000). Introduction to exercise science. Lippincott Wims & Wilkins. pp. 280–1. ISBN 0-683-30280-9.
- Kellis, E, Arambatsi, F, Papadopoulos, C. Effects of load and ground reaction forces and lower limb kinematics during concentric squats. J Sports Sci 23: 1045-1055, 2005. 10 Feb 2013
- Clarkson, HM, and Gilewich, GB. Musculoskeletal Assessment: Joint Range Of Motion And Manual Muscle Strength. Baltimore, MD: Williams and Wilkins, 1999. pp 374. 10 Feb 2013
- Bompa, Di Pasquale & Cornacchia, 2002, p. 121, 125.
- McRobert, S (1999). The Insider's Tell-All Handbook on Weight-Lifting Technique. CS Publishing. ISBN 9963-616-03-8.
- Jonas Rantanen Breaks World Record Squat. SeriousPowerLifting. Retrieved 2013-03-15.
- "Powerlifting watch. Raw world records".
- Bompa, Di Pasquale & Cornacchia, 2002, p. 120.
- Cornacchia, Lorenzo; Bompa, Tudor O.; Di Pasquale, Mauro G.; Mauro Di Pasquale (2003). Serious strength training. Champaign, IL: Human Kinetics. ISBN 0-7360-4266-0.
- A basic guide to squatting correctly.
- "Bodyweight Squat". acefitness.org *Workout Exercises and Routines. American Council on Exercise. Retrieved 27 March 2011.