Squats have been utilized for centuries to increase life / athletic performance. Squatting is a complex multi-joint movement that requires muscular symmetry, coordination, and strength. An inability to perform a squat, especially a full range of motion (ROM) squat, is a good indication of stiffness and possible asymmetry within the body. Asymmetry is muscular imbalance between the right and left side (halves); usually one side is more dominant and developed than the other. During squats, muscular length-tension relationships are constantly changing. The constant changing between muscular groups makes squatting exceedingly difficult because it requires coordination, stability, strength, balance, and soft tissue elasticity. However, it is core stability and strength that allows the body to coordinate and stabilize the extremities. Due to the complexity of a squat, squats are often considered one of the most difficult exercises to perform.
There are numerous forms of squats: box squats, back squats, front squats, Bulgarian split squats, dumbbell squats, stability ball wall squats, single leg squats, pistol squats, and so on. However, the discussion that clearly creates the most confusion and debate is not what type of squat to utilize, but rather if it's advantageous to perform full range of motion (ROM) squats or parallel squats.
1) The basics...
Full ROM squats require maximal knee flexion and extension (i.e. the knee bends and extends to its furthest point). Generally speaking, power lifters perform parallel squats and Olympic lifters perform full ROM squats; however, some perform both forms. Both squatting techniques should maintain an upright torso and not allowing the knees to pass the front of the foot. During a full ROM squat, the knees will pass in front of the foot slightly.
Squats are a total body, with emphasis placed upon the legs, compound exercise that requires a high degree of mastery. During squats multiple-joints are worked. The hamstrings, quadriceps, and glutes are the agonist (primary) and synergist (secondary) muscles activated during the squatting movement.
2) The Muscles... example is sprinting and jumping.
The hamstring muscles act as agonist (prime movers) during squats. A main muscle within the hamstring group, the biceps femoris, seems to be activated during both full ROM and parallel squats; however, full ROM squats seem to edge out the parallel squats in biceps femoris activity. Hamstrings play a pivotal role in the speed athletes or persons are capable of running at. An athlete's ability to sprint at faster speeds is directly related to the amount of force (concentric contractions) that the hamstring muscle can create.
The Gluteus maximus seems to be most active as an agonist muscle during the bottom part of a full ROM squat. During sprinting the Gluteus muscle is responsible for generating force upon the ground. World class sprinters, or athletes that are fast, generally have strong Glutes with significant muscle mass. This muscle adaptation allows them to generate high force upon the ground during sprinting. The parallel squat fails to activate the gluteus muscles in comparison to a full ROM squat.
Various studies have shown the quadriceps group to be active during both forms of squatting. The parallel squats seem to activate more of the quadriceps group and less of the gluteal muscles. However, during a full ROM squat, the rectus femoris muscle of the quadriceps group seems to be worked more than during a parallel squat. This muscle is largely responsible for the eccentric (downward) portion of a sprint. A stronger more stable muscle will allow for increased speed and performance.
3) Performance... example is sprinting and jumping.
A German case study showed an 8% increase in vertical jumping ability for those whom performed full ROM squats. In contrast, the test group that performed parallel or quarter squats showed results of a 0% increase in vertical jumping ability (5). During jumping movements, the Gluteus group is highly active. In order to jump higher a stronger gluteus muscle is required. Full ROM squats will increase the strength and power of the Gluteus muscle. Once below parallel, either during a back or front squat (assuming form is correct), the gluteus muscles acts as an agonist to move the body back up. One technique is a bottom squat. Attempt to squat below parallel and pause at the bottom squat position. Hold this position for 1-2 seconds and explosively stand back up. This technique can be highly successful in activating the gluteus muscle.
The quadriceps muscles are highly active during the ground contact phase of a sprint. During this phase, the quadriceps stabilize the leg and body, controlling the high degree of force placed upon the one leg / knee upon landing. If the quadriceps are developed the sprinter will be able to quickly move from the eccentric portion to concentric portion (i.e. landing to horizontal propulsion). This intermediary phase is known as the amortization phase (4). It is crucial that this phase be kept short by activating the muscles and tendons in a spring like mechanism, known as the stretch shortening cycle. If the eccentric motion is slowed down by an unstable or weak quadriceps muscle than the amortization phase will be longer and less power will be generated. As a result, the athlete will move slower.
The full ROM squat, as well as the parallel squat, place emphasis on the quadriceps group. However, the full ROM is greater because it recruits the gluteal muscles more than the parallel squat. For this reason, amongst numerous other health and injury prevention reasons, I find the full ROM to be the preferred squat technique.
Performance is necessary, but if you cannot stay healthy you will never be successful. Read part II of Range of Motion Squats vs. Parallel Squats to learn how they relate to injury prevention and health.
Sources
1. Athletic Body in Balance
By, Gary Cook
2. American College of Sports Medicine
3. NASM Essentials of Personal Fitness Training (3rd edition)
By, National Academy of Sports Medicine
Editors: Michael A. Clark, Scott C. Lucett and Rodney J. Corn
© 2008
4. The Essentials of Strength Training and Conditioning (3rd edition).
By, National Strength and Conditioning Association
Editors: Thomas R. Baechle and Roger W. Earle
© 2008, 2000, 1994
pages 416-417
5. Ten Things We've Learned About Squats by Charles Poliquin Group