Accentuating the eccentric.
Strength training, performed with the proper equipment and the proper regimen, has improved performance, helped prevent injury, and lengthened careers.
The benefits are numerous, yet, ironically, many athletes fail to maximize them. They continue to make the same mistakes in the weight room, such as poor form, using too much weight, exercising too frequently, neglecting certain vital body parts, and - perhaps the greatest mistake of all - failing to emphasize eccentric contraction.
Every lift consists of a concentric contraction and an eccentric contraction.
In the concentric phase of the lift, the muscle shortens and contracts while applying force. This is considered the "positive" portion of the repetition.
In the eccentric phase, the muscle is forced into a lengthened state while resisting both gravity and the weight placed upon it. It is thus considered the "negative" phase of the lift.
In a bench press, for example, the concentric/positive phase occurs when the weight is raised to a straight arm position over the chest, while the eccentric/negative phase occurs when the weight is slowly lowered back to chest level. Without this eccentric contraction, the weight would come down directly upon the chest.
Too often a trainee will raise the weight concentrically and then quickly lower it without accentuating the eccentric contraction. The athlete will emphasize the lifting movement because he does not understand the necessity of slowly lowering it.
This will usually happen in competition when the athlete is straining to out-lift the opponents. He begins to weight-throw instead of weight-lift and no good will come of it.
Research has shown that a combination of concentric and eccentric contractions will produce a better workout than a concentric-only workout.
William Kraemer, in reviewing the work done by Dudley, et. al. - having three groups of athletes do a leg press and a leg extension, with Group 1 doing concentric only, Group 2 doing double concentric only (using twice as many positive reps), and Group 3 doing both concentric and eccentric contractions - concluded that Group 3 achieved significantly greater strength gains in both exercises.
Kraemer then reviewed the work done by Hather, et. al. on the muscular adaptational differences within the subjects of the Dudley experiment.
He concluded that Group 3 (combination of concentric and eccentric contractions) produced greater muscle size in both Type 1 and Type 2 muscle fibers, whereas Group 1 (concentric only) produced no changes in muscle size, and Group 2 (double concentric) increased only the size of the. Type 2 fibers.
Concentric and eccentric training also appears useful for strength maintenance during periods of reduced training.
In another study, Dudley found that such training produced lower strength losses during periods of detraining. The concentric-only group produced strength losses much more rapidly than the concentric/eccentric group did.
This kind of strength maintenance is important in avoiding injury during reduced training periods, in-season competition, and post-season rest.
A popular cadence in exercising is to raise the weight on a two-cadence count and lower it on four. The eccentric segment takes a little longer for several reasons.
First, it is during this phase that the prime mover (main muscle) is lengthening and stretching. Just as we avoid the use of fast ballistic movements during a flexibility exercise, we try to avoid a fast downward movement of the weights.
During a stretch, a ballistic movement will activate a safety mechanism called the stretch reflex - which we don't want to happen, since it inhibits further muscular stretching and produces a contraction.
A slow eccentric contraction will allow the muscle to safely enter its pre-stretch which is a slight reversal in movement just prior to muscle contraction. The prestretch allows a greater amount of muscular force to develop during the concentric contraction. The lack of a prestretch will compromise the full strength potential that can develop from training.
This slowly controlled eccentric contraction will also prevent the athlete from dropping the weight. A quick drop will produce a "bounce", as frequently seen in a bench press, where the weight is bounced off the chest just prior to execution.
While this bounce will allow more weight to be lifted, it will do so at the expense of the joints and connective tissues.
Since a muscle is 40% stronger during the eccentric phase, it is easier to lower a given weight than to raise it.
In attempting to equate the effort on both the raising and lowering of a specific weight, the athlete should understand that the slower lowering speed will make the muscle work harder. Since a slower lifting speed is more difficult, the greater strength of an eccentric contraction will allow a safe but intense contraction to occur.
The drawback with eccentric contractions is that they produce muscle soreness, which slows recovery time. This soreness worsens in the days after exercise, and as Priscilla Clarkson mentioned in an article in Sports Science Exchange: "Biopsies taken immediately after eccentric exercise showed only small focal areas of damage, whereas biopsies taken 2-3 days after the exercise showed larger areas of disruption and other abnormalities".
Strength recovery from repetitive eccentric exercise is also lengthened. Clarkson asserts that there is little restoration of strength during the first 24-48 hours after exercise and that full recovery sometimes takes 7-10 days.
Strength training prior to proper recovery will lead to reduced performance and possible injury.
The importance of the eccentric contraction may also raise questions about the benefits of exercises such as power cleans and clean and jerks. These lifts require a quick concentric stage followed by a quick, if not drop, of the weight to the starting position.
The benefits of such fast lifts have long been debated and the aforementioned research may raise additional questions on whether such exercises are the optimal choice in strength development.
This could be the reason why so many athletes continue to suffer injuries despite regular training regimens. By over-emphasizing the concentric and under-emphasizing the eccentric contractions, they fail to safely achieve optimal strength gains and are thus unable to fully prepare for the physical demands of their sport.
A recent article in the American Journal of Sports Medicine proved this. It revealed that sprinters with a history of hamstring injuries demonstrated weaker eccentric contractions than those performed by their uninjured peers.
As strength coaches, we have to ensure the maximum benefits from our conditioning programs. Increased emphasis on the eccentric phase of strength training can help make this happen.
The improvements in muscle size and strength will produce greater power, reduce the chance of injury, and minimize strength losses during periods of reduced training.
* William Kraemer: "Involvement of Eccentric Muscle Action May Optimize Adaptation to Resistance Training," Sports Science Exchange, November 1992
* Priscilla Clarkson: "To Much Too Soon: The Aftermath of Overexertion," Sports Science Exchange, January 1990
* Ted Lambrinides: "Information Update," H.I.T. Newsletter, #3, 1995
Michael Johnson Director of Strength Training Westfield (NJ) YMCA
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|Title Annotation:||muscle contraction in weightlifting|
|Publication:||Coach and Athletic Director|
|Date:||Jan 1, 1996|
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