The squat does not just work your legs, but also your hips and core musculature. The squat builds strength and power, improves your vertical jump and burns fat. This requires consistent training, effort and dedication as well as a basic understanding of how to apply the squat to your training program. A knowledge of the specific muscle actions involved in squatting will help you use this exercise to the fullest. Consult a health care professional before beginning any strength training program.
Eccentric Muscle Actions
The eccentric muscle action is the lengthening phase, or lowering aspect in the squat. When you are headed down to the bottom position, you are engaging in the eccentric portion of the squat. The term eccentric does not apply to the muscle itself, only an action that applies to muscles. As you squat, your quadriceps and hamstrings, the muscles on the front and back of your thighs, stretch and so do your hips. The degree of stretch and recruitment of your hips is directly proportional to the depth of your squat, according to a 2002 study published in the "Journal of Strength and Conditioning Research."
Quadriceps
The quadriceps is a group of four muscles on the front of your thigh responsible for extending your knee joint. Every time you straighten your leg, your quadriceps contract, or shorten. It is this pulling action by which a muscle generates force. This is termed the concentric action. When descending into the bottom position of the squat, your quadriceps must stretch, and this is the eccentric action. This stretching helps generate force, and it is possible to overload the eccentric motion through the use of heavy weights. This sort of overload during the eccentric phase can lead to greater gains in muscle size, according to a 2010 study published in the "European Journal of Applied Physiology."
Hamstrings
Your hamstrings, or the muscles on the back of your thigh, also lengthen when squatting. Your hamstrings lengthen not because of the flexing at your knee joint, but because of the flexing at your hip joint, which is where the eccentric action of your hamstrings occur. This is even greater if you lean forward, but you should avoid doing this when squatting, as it places extra strain on your lower back. There is less hip flexion than there is knee flexion in the squat, which is why there is less hamstring activity, compared with quadriceps activity.
Isometric Contractions
An isometric contraction is a muscular contraction in which no movement takes place. An example of this would be tensing your upper back to hold the barbell in place when squatting. If movement takes place in your upper back, which should be stable, you may experience difficulty. Isometric contractions should also occur when squatting in your abdominals and obilques, the muscles of your stomach and sides, which support your torso when squatting. By drawing air into your stomach and aggressively tightening these muscles, you can increase the pressure in your core, which should help you avoid leaning forward. So while both eccentric and concentric actions take place to complete the squat, a very important isometric contraction can help improve your squat and reduce your risk of injury.
References
- "Journal of Strength and Conditioning Research"; The Effect of Back Squat Depth on the EMG Activity of 4 Superficial Hip and Thigh Muscles; A. Caterisano, et al.; August 2002
- "European Journal of Applied Physiology"; Effects of Strength Training with Eccentric Overload on Muscle Adaptation in Male Athletes; B. Friedmann-Bette, et al.; March 2010
- "Medicine and Science in Sports and Exercise"; Effects of Technique Variations on Knee Biomechanics During the Squat and Leg Press; R.F. Escamillia, et al.; September 2001
- "Ergonomics"; The Effect of an Abdominal Belt on Trunk Muscle Activity and Intra-abdominal Pressure During Squat Lifts; S.M. McGill, et al.; February 1990
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