Muscle contractions come in two basic flavors: eccentric, also known
as negative, and concentric, or positive. Eccentric muscle contractions
involve an active lengthening of muscle fibers, which usually means the
lowering of a weight, such as when you descend to a full squat.
Concentric muscle contractions feature a shortening of muscle fibers, as
typically occurs during the raising of a weight—as when you drive up
from a squat to a standing position.
Those aren't the only types of muscle contractions. Isometric
contractions are strong but achieved without any movement. Isokinetic
contractions focus only on the positive portion of an exercise, with no
eccentric component. As you might expect, bodybuilding exercises involve
mainly eccentric and concentric contractions.
An ongoing debate among exercise scientists is whether one type of
muscle contraction is superior. One man who took a definite stand on
that issue was Arthur Jones, an eccentric genius best known for
developing the Nautilus and MedX exercise machines, as well as the
Nautilus high-intensity philosophy. He was a firm believer in the
superiority of eccentric contractions for triggering gains in muscular
size and strength. He repeatedly wrote of the importance of taking two
seconds to raise a weight and four seconds to lower it, putting the
emphasis on the negative portion of the rep. Jones eventually espoused a
negative-only style of training for maximizing strength gains. His
later exercise machines were designed to enable a user to accentuate the
negative.
While it would seem that raising a weight is more intense than
lowering it, numerous published studies show that most of the muscle
damage incurred during training comes by way of the eccentric
contractions. Apparently, lowering a heavy weight produces more damage
to muscle fibers than raising it. As such, negative contraction is
considered largely responsible for delayed-onset muscle soreness, or
DOMS, a deep muscle soreness that peaks one to two days after you train a
muscle intensely with exercises that have an eccentric component.
The advantage of eccentric contraction in this regard is that the
extensive fiber damage it causes results in a compensation effect—the
body responds by upgrading muscle protein production. The damaged muscle
fiber is not only repaired but also thickened to accommodate the
increased stress that was placed on it. The thickened fiber is
recognizable as muscle hypertrophy, or growth, and it's usually
accompanied by an increase in strength.
The process takes some time, particularly after a workout that
emphasizes negative work. Studies show that it takes a minimum of 48
hours to repair completely the damage wrought by eccentric contractions
and for larger muscles, such as the thighs, it can take as long as 72
hours. If the muscle is trained before it's fully repaired, the
potential gains can be lost, a scenario that falls under the general
heading of overtraining.
Some trainees take the repair process to questionable lengths. An
example are those who suggest that the body can take up to two to three
weeks to recover from high-intensity training marked by extensive muscle
damage. The evidence for that is more apparent in long-distance
endurance activity, such as marathon running, than in weight training.
In some cases the muscle damage incurred during a 26-mile marathon can
take as long as six months to be restored.
While all the evidence seems to point to eccentric contractions as
being the most vital type of muscle contraction for stimulating gains in
size and strength, not all studies have shown that. Some suggest the
opposite—that positive contractions are superior—which tends to confuse
the issue. A recent meta-analysis published in a leading sports medicine
journal looked back at the research to find some clarity. Twenty prior
studies that compared eccentric and concentric contractions were
examined.
The researchers noted that muscles are capable of exerting greater
absolute force during eccentric contractions and that increases in
muscular strength are associated with greater force production. Since
eccentric contraction involves less muscle fatigue, a lower
cardiorespiratory component and more metabolic efficiency, you can train
in a primarily negative mode for a longer time than you can with
primarily concentric contraction.
The analysis found that velocity of movement is a key factor. In
short, unless the speed of movement is strictly controlled during
eccentric contractions, most of the possible gains will not be realized.
In addition, intensity plays a role. Simply put, you need to train
heavy and take advantage of the fact that you can use more weight on
eccentric contraction.
The past studies that didn't favor negative contraction can be
explained. For one thing, they didn't feature enough of an intensity
factor, such as not using enough weight. Velocity was also relevant. The
negative contraction must be done considerably more slowly than the
positive. When both types of muscle contractions are done with the same
velocity, neither appears to be superior.
Many bodybuilders overlook the importance of eccentric contractions.
At Gold's Gym in Venice, California, where I train, I rarely see even
elite bodybuilders using negative techniques. In fact, the major
emphasis seems to be on the positive portion of the rep. Bodybuilders
who want to make maximum progress should heed the advice of Arthur Jones
and take two to three seconds to lift the weight and at least four
seconds to lower it—and do it on every exercise.
In addition, it makes sense to use negative-emphasis exercises to
train lagging muscle groups. Since negative contraction produces more
muscle strength, you'll be able to work them with bigger weights. That
nearly always results in more muscle and strength.
There are come caveats associated with eccentric training. The
extensive muscle fiber damage it produces leads to a few temporary
metabolic derangements. For example, it inhibits the activity of a
glucose carrier in muscle called GLUT-4, which delays the full
recuperation of muscle because glycogen is not restored. Glycogen
repletion is essential for full muscle recovery between workouts. In
practical terms, it would be foolhardy to attempt to train any
particular muscle again in less than 48 hours. If you truly emphasize
negative work in your training, it will probably lengthen the required
rest time between workouts to at least 72 hours. That may explain the
recent trend of training most muscles groups only once a week. Many have
found that more-frequent training leads to stalled progress and a
feeling of overtraining, which may be related to incomplete repair of
muscles that are trained too frequently.
Editor's note: Jerry Brainum is the author of the e-book Natural
Anabolics—Nutrients, Compounds and Supplements That Can Accelerate
Muscle Growth Without Drugs, available at JerryBrainum.com.
Roig M, et al. (2009). The effects of eccentric versus concentric
resistance training on muscle strength and mass in healthy adults: a
systematic review with meta-analysis.Br J Sports Med. 43:556-568. IM
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