| buzzer -> RE: negatives ??? (May 9 2008 8:44:42) |
this might interest you
"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 submaximal 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.
It was concluded by these authors that adaptations to training with maximal eccentric contractions are specific to eccentric muscle actions that are associated with greater neural adaptation and muscle hypertrophy than concentric exercise. It is the specificity of this type of exercise that gives it questionable value to performance athletes.
There has been a lot of controversy surrounding the optimal amount to weight that should be used during eccentric work. Rather than argue who is right and who is wrong, just remember that if a movement is too fast, say 1 second or less, not enough fibers will be participating to get good growth. If the movement is too slow, you begin to do quasi-isometric movements that fail to induce sufficient micro trauma. You may be asking, "how much weight should I use?". That question is answered by the amount of time it should take you to perform the eccentric rep. If it is too heavy you wont be able to slow the weight down sufficiently, if the weight is too light you will find yourself "lowering" the weight even though you could stop the weight from falling.
Eccentric movements should be performed with the help of a spotter whenever possible. I make no claim that eccentric reps should only be performed sparingly. There is no evidence that I have seen that would contraindicate the frequent use of negatives in a "bodybuilding" routine. If you are a performance athlete you should focus on muscle movements that most closely represent those used in your sport. There are not many sports that require heavy eccentric contractions more than skilled concentric contractions so excessive eccentric work would thus be contraindicated. |
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