How to master and manipulate the most fundamental element in weight lifting.
By Timothy C. Fritz
Bodybuilding is all about muscle -- finding ways to exhaust it, then feeding it, and finally letting it rest so it can grow
bigger and stronger than ever. To complete this cycle repeatedly, you must constantly seek new ways to train, explore the
latest nutritional recommendations and do the research necessary to distinguish fact from fiction. Focusing on this big
picture can help keep your growth on the fast track.
Though you need to keep your long-term goals in sight, equally important is periodically zeroing in on the fundamentals: the
essential elements that will carry you forward. None of these elements is more basic than the repetition. You perform
hundreds, perhaps thousands, of them each week, but how often do you stop to consider what's actually happening each time you
The more you know about the factors that influence a rep -- including the underlying physiology -- the better you'll
understand how your muscles work. Once acquired, this wisdom can be applied to every exercise you perform, enabling you to
build muscle more effectively and efficiently.
At the most rudimentary level, a rep comprises three phases: the concentric contraction (lifting the weight), the transition
and the eccentric contraction (lowering the weight). For most exercises, the concentric phase comes first, although on
exercises such as the squat and bench press, you actually descend through the eccentric half to assume the real start
A common misconception is that a muscle contracts during the first half of the movement and then relaxes as you return the
weight to the start position. In fact, a muscle contracts during both phases. The difference is that the muscle shortens
during the concentric half and lengthens during the eccentric half.
A contraction is initiated by impulses sent via nerves from the brain and spinal column to muscle cells. A single nerve, or
neuron, is connected to several muscle cells, or fibers. Collectively, the neuron and the fibers it innervates constitute a
motor unit. When a nerve fires, all muscle fibers constituting the unit contract. Each muscle comprises many such motor
units, of course, but only during maximal contraction do they all fire simultaneously. During a less-than-maximal movement,
only a certain number of motor units respond at one time, depending upon the force and motor skills required.
PHASE ONE: The Concentric Contraction
Closing the Gap
During the concentric contraction, the working muscle shortens, pulling the bones on either side of the joint being used
closer together. (Picture your forearm and upper arm coming together when you curl a dumbbell.) At the start of this
concentric contraction, only a small number of motor units are activated, generating minimal force. As more force is
required, additional motor units are called upon.
If the weight being lifted is relatively light, many motor units will remain inactive; only a fraction of the total muscle
contracts. However, if the weight is heavy, the muscle is fatigued or both, the muscle must recruit as many motor units (and
fibers) as possible to accommodate the demands being placed upon it. The amount of force that a muscle is able to generate
increases with the number of motor units that are utilized.
Use a rep speed at which the movement is completely controlled -- with no swinging -- to get maximum recruitment. If you let
momentum do some of the work for you, you won't use as many muscle fibers to lift the weight. Breathing is another important
aspect of any rep. As a rule of thumb, exhale during the concentric contraction, the period of greatest exertion.
PHASE TWO: The Transition
Stuck in the Middle with You?
At the end of the concentric contraction, a muscle is in its shortest position. Some exercise physiologists and many
bodybuilders recommend that you pause here for a second or two to contract the working muscle as intensely as possible, a
technique called peak contraction. "During my precontest phase, I rely heavily on peak contraction, particularly for biceps
and triceps," says Garrett Downing, winner of the heavyweight division at the 1999 NPC USA Championships.
"For example, holding something like a triceps extension at the bottom, as opposed to just lightly 'tapping' there, gives me
more of a pump and makes my muscles look harder and more striated. It's definitely an asset."
Two-time Mr. Olympia Larry Scott agrees. "I believe peak contraction has a lot of physiological benefits in terms of
activating hard-to-hit muscle fibers, establishing new neural pathways and so forth," he says. "More fundamentally, it helps
you get more in touch with your body. I use it for every bodypart, not just arms."
Others question the need to stop at any point during the rep. Steven Fleck, PhD, CSCS, former head of the physical
conditioning program for the U.S. Olympic Committee, believes that using the appropriate resistance is more important than
generating a peak contraction. "If the weight is light, you can never reach maximal contraction," he says. "But if you manage
the resistance right, you'll get near-maximal contraction at some point during the range of motion."
Your best bet is probably to include peak contraction as a tool in your training program without relying on it to produce
maximum stimulation and contraction. Instead, depend on heavy weights to promote the highest levels of contraction, activate
the highest number of fibers and hence fatigue your muscles.
PHASE THREE: The Eccentric Contraction
Letting It Down Slow
Whether or not you pause at the end of the concentric half of the rep, eventually you have to return the weight to the start
position. This half of the rep is called the eccentric phase, which many bodybuilders mistakenly treat as an afterthought. As
you lower a dumbbell during a curl, for example, the biceps lengthens, even though it's still contracted to some degree.
(Were it not for this contraction, the weight would simply fall back to the start instead of returning in a controlled
During the eccentric phase, nerve impulses continue to signal motor units to fire, even though fewer motor units are
incorporated than during the concentric contraction. As a result, more stress is placed upon each of the activated muscle
This has important implications for muscle soreness and tissue breakdown, key issues in muscle-building. "One of the theories
of size development is that you must have some minute muscle damage followed by an inflammatory response," explains Fleck.
"The inflammatory response is one of the triggers for protein synthesis, which results in more muscle.
With normal weight training, during an eccentric contraction you lower the same weight with fewer muscle fibers, and that
means that each fiber involved has to sustain greater force. Therefore, a higher percentage is damaged." In theory, increased
muscle-fiber damage could lead to increased growth. Greater tissue damage would also explain the increased incidence of
delayed-onset muscle soreness often associated with eccentric training.
Research confirms that the eccentric component of a lift may be just as important as the concentric phase for promoting
muscle growth. One study showed that, when compared to normal (concentric and eccentric phase) weight training,
concentric-only training required twice as many repetitions to produce similar results.1 Breathing is as important during the
eccentric phase as it is during the concentric phase. Inhale during the eccentric phase or between reps.
Full Range of Motion
Combining the concentric and eccentric phases of the rep produces an exercise's range of motion. To ensure maximal
contraction and promote joint flexibility, you want to fully utilize this. Limiting factors can include joint properties and
body composition, both of which will provide a natural "stopper," letting you know when you've taken a movement far enough.
Movements that fall short at either end of the range of motion will limit the number of muscle fibers involved, and may
actually lead to decreased flexibility. Exercising through a full range of motion is safe as long as the rep is slow and
One Final Rep
Although you needn't -- and shouldn't -- contemplate muscle physiology each time you lift, you can benefit greatly from a
basic understanding of what happens when you complete a repetition. Realize that the eccentric contraction is at least as
important as the concentric contraction when it comes to building muscle. Remember to breathe naturally and execute movements
through a full range of motion in a slow, controlled manner.
Maintain tension (contraction) in the working muscle during the entire movement, and don't feel like you have to stop at the
midpoint of the rep to accentuate the contraction, although don't hesitate to do it if it feels good. If each set you perform
consists of intelligent reps based on good form, your training sessions will quickly peak, as will your muscles.
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