Blade explained pretty clearly, muscle fibres tend to grow better when strectched under contraction. However it is not a state that can be maintained for too long, thus the 2 weeks at the end of the fives.
<div></div><div id="QUOTEHEAD">QUOTE</div><div id="QUOTE">That being the case, let the weight "stretch" the contracted muscle. Its not about fatigue or fighting gravity. It's about stretching a muscle that is contracted. The harder you contract it the more weight it will require to stretch it. Simple as that. How fast you stretch it usually comes naturally to most lifters.</div>
Here's a complete extract of teh FAQ on that:
<div></div><div id="QUOTEHEAD">QUOTE</div><div id="QUOTE">From a physiology point of view, lower a heavy weight too fast and you get golgi-tendon organ interference. The golgi will actually block muscle contraction to prevent tearing, and you aren't really making the muscle engage properly.
Go too slow and the muscle is just fine, but the CNS is, in a manner of speaking, burning through its fuel so fast you can see the gauge moving. It becomes a test of isometric-strength endurance. This will make you better at doing really slow negatives, but it won't necessarily make the muscle bigger at that point.
Methods of primary interest to the serious bodybuilder are negatives, loaded stretching (contrary to popular belief, this method does not require consuming alcoholic beverages prior to stretching) and concentrated loading microcycles. Let us briefly go over these methods and the terms used to describe them.
"Negatives" is a bodybuilding term used to describe the eccentric portion of a movement or exercise. In research you will sometimes see it referred to as "active lengthening".
This means stretching a muscle to increase its length while under voluntary contraction to resist the stretch. The result of this eccentric action is an increase in tissue micro damage and an increase in eccentric strength.
Negatives are known to be responsible for the infamous delayed onset muscle soreness (DOMS) that so many of us sadistically strive to achieve. The increase in eccentric strength is a result of neurological adaptations facilitating motor unit coordination during eccentric contractions. As bodybuilders, all we are interested in is the microtrauma.
As mentioned on numerous occasions, we must have micro trauma in order to allow growth factors to "leak out" into the interstitial space, and thus to activate satellite cells. These satellite cells then donate myo-nuclei which help to produce additional contractile and structural proteins.
Certainly I would not recommend negatives unless there were some evidence indicating there usefulness. Type II fibers are favorably activated by the muscle during eccentric contractions as compared to type I fibers.
Type II fibers are those that contribute the majority of growth produced by bodybuilding type training. The stimuli from eccentric loading and concentric loading are similar except that the proportions of the stimuli from eccentric loading are different in some very important ways.
First, the load that is placed on the muscle during an eccentric movement is not distributed over as many fibers as during a concentric movement (Ebbeling, 1989). When measuring EMG activity, or the electrical activity in the muscle, Ebbeling found that it is lower during negative work at both maximal and sub maximal intensities.
This suggests that relatively few fibers are recruited to produce large forces. Therefore, under comparable workloads, eccentric actions produce greater tension per cross-sectional area of active muscle than concentric contractions. In other words, lowering the weight produces more load per fiber than lifting it!
Does increasing the load per fiber as seen in eccentric contractions lead to increases in fiber diameter or simply put, GROWTH?
Hortobagyi (Hortobagyi, 1996) found dramatic differences between subjects performing isokinetic concentric contractions as compared to isokinetic eccentric contractions. Muscle strength, fiber size, and surface EMG activity of the quadriceps were compared after 36 sessions (12 weeks) of maximal isokinetic concentric or eccentric leg extensions.
Eccentric training increased eccentric strength 3.5 times more (pre/post 46%) than concentric training increased concentric strength (pre/post 13%). Eccentric training increased concentric strength and concentric training increased eccentric strength by about the same magnitude (5 and 10%, respectively).
Eccentric training increased EMG activity seven times more during eccentric testing (pre/post 86%) than concentric training increased EMG activity during concentric testing (pre/post 12%).
Eccentric training increased the EMG activity measured during concentric tests and concentric training increased the EMG activity measured during eccentric tests by about the same magnitude (8 and 11%, respectively).
Type I muscle fiber percentages did not change significantly, but type IIa fibers increased and type IIb fibers decreased significantly in both training groups. Type I fiber areas did not change significantly, but type II fiber area increased approximately 10 times more in the eccentric than in the concentric group.
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