Quote (Synonym @ Jan 14 2011 11:33am)

Going down is the eccentric contraction, which should take 4 seconds. Going up with a spotter while performing an eccentric exercise should take 2 seconds just to put the bar up again, without you even helping to raise it (0% involvement while the concentric movement is being made via outside party / helpers).

Your entire involvement is the eccentric movement, a.k.a Going down at BB Flat. Nothing else.

Quote (Synonym @ Jan 14 2011 01:24am)

Table of Contents
Contraction Types & Definition
What is Contraction?
Speed-Tension Curve
Eccentric Contraction- Benefits
Why So Slow?

Contraction Types & Definition

Eccentric- The part of the exercise in which the outside weight or resistance factor (Body weight in relative exercises) is overpowering the muscle newton strength.
The muscle lengthens as it contracts by having the weight drop the ligament or body part in a controlled timing period.

Concentric- The part of the exercise in which the muscle newton strength is overpowering the outside weight or resistance factor.
The muscle shortens as it contracts while lifting the weight.

Isometric- The part of the exercise in which both the muscle newton strength and the resistance factor are equal.
The muscle neither shortens nor lengthens, rather contracts in a static manner. This is why these type of exercises may be referred to as "Static exercises".

What is Contraction?

Every muscle fiber (Myofibril) hones a great deal of fiber filaments (Myofilaments), which are divided into two groups:

• Actin Filaments- These are also termed "The Thin Filaments". These filaments are coiled with nebulin filaments.
  
• Myosin Filaments- These are also termed "The Thick Filaments". These filaments are coiled with titin filaments.

The two groups converge into a complex composition, which is also known as "Actomyosin". A perfect view of that phenomenon can be seen here (0:54-1:11):

http://www.youtube.com/watch?v=CepeYFvqmk4

Speed-Tension Curve

The elements which affect the muscle's ability to produce strength state:

• Maximal power can be achieved via Eccentric contraction.
  
• One cannot develop maximal power by performing fast contractions
  
• The abilities to develop maximal power and maximal speed in the same action are different abilities

Remember:
Concentric-wise, as long as your speed is greater, the muscle will develop less power.
Eccentric-wise, as long as your speed is greater, the muscle will develop more power.

These two statements are true, to an extent. Why? Because we need to remember the 2nd element, which tells us that fast contractions simply don't work efficiently. Having your concentric contraction last more than 10 seconds would be too slow, and having your eccentric contraction last less than 1 second would be too fast.

Eccentric Contraction- Benefits

Applying Motor Units
A motor unit is the smallest operable functional unit for contracting muscles. Its structure is formed of a motoric neuron and all the muscle fibers it is attached to.
Not all motor units are the same. Motor units differentiate in number of muscle fibers. Knowing that, we must remember the following rule: "All or nothing". A motor unit will either operate at 100% muscle fiber contraction, or not at all. A motor unit consisting of 10 muscle fibers will apply 10 muscle fibers when operating, or not at all.
Therefore, the smaller the motor unit, the less power it produces, the more delicate the action is. One could see the difference when looking at an eye and a leg. The leg has motor units that measure in thousands of myofibrils per neuron, whilst the eye has but a few hundreds, or a few dozens in some cases. Hence eye movement is extremely delicate and slow in comparison to leg movements.

Fact: While Concentric contractions use X muscle fibers to apply muscle strength, Eccentric contractions use only 40% of those muscle fibers to apply the same muscle strength. Isometric contractions use 60%, and even those are more efficient than Concentric contractions.

Therefore, it stands to reason that comparing the developing power in these different contractions shows that during Eccentric contraction, the muscle is able to develop the same power using a smaller amount of motor units and by doing that, becoming more effective, more economic in terms of ATP/CrP usage, and should we load extra weight during the eccentric part of the exercise, we could be able to apply all of the motor units and eventually develop greater strength.

One of the most effective training methods is the 'Super Maximal Eccentric Workout'.
In this method, the trainee will operate against weight which is 30% larger than his RM1. The concentric contraction, which is obviously unable to be performed due to 130% of maximal strength being applied, is performed by a 2nd party (Another trainee or a trainer), while the eccentric contractions will be performed solely by the trainee, in a slow and controlled manner. This method is designated to the power development of strong and proficient athletes.

DOMS
Delayed Onset Muscle Soreness, the phenomenon which the trainee receives a day or two days after the workout. The muscles are damaged, torn, constantly in repairs during that period, and are extremely sensitive to further contractions due to their periodic weakness.

Fact: Eccentric contractions hurt more than Concentric or Isometric contractions. Meaning, they cause even greater DOMS and provide with an overall greater and more efficient workout outcome.

Why So Slow?

As we've learned, muscle contraction works best when during Concentric contraction, the movement needs to be slow and fast when during Eccentric contraction.
What are the recommended time periods?

In every possible exercise or routine, the most recommended time period of concentric contraction is 2 seconds. The recommended time period of Eccentric contraction is 4 seconds. Indeed, 4 seconds - 200% the time of Concentric contraction.

Quote (White_Light @ Jan 16 2011 04:45pm)

isometric contractions did shit for me. 60% or not I lost muscle mass by doing those exercises. Eccentric ones I lost muscle mass as well but that's because I made something wrong. I had a break and started with eccentric ones so just over trained myself.
I actually had some benefit with eccentric ones when I used those for a short term, not more then 2 weeks and when my progress during normal training came to an halt.

Anyways your claim is isometric ones could be more beneficial then concentric ones if I understand you right.
Have you ever tried to train isometric ones for a longer period of time? I doubt you'll be making progress. Thing is, imagine a biceps curl. When you curl up first a lot of strain for a short time is on the lower part of the biceps and then goes further up the biceps as we curl it up. SO there is a lot of strain for a short time on individual parts. With isometric exercise there there is not such an intense strain on individual parts for a short time. Its for a longer time. I could imagine the results you get from isometric exercise similar to those you would get from concentric exercise ding a high amount of repetitions.

Concentric exercise gives when mentioning the biceps curl again intense strain on small individual parts of it for a short time and that's what's great for strength and bodybuilding. Also usually you get good in what you train and do not get as good in what you do not train. Hence if you train concentric exercises you will be better in performing concentric exercises as if you train isometric exercises. I doubt that training concentric exercises gives you any edge in competitions based on concentric exercises.

Sports are widely researched, there is good knowledge out there but despite what the benefits of isometric or eccentric exercise are I rarely see them being used by the best bodybuilders of the world. If they were that great I guess they would be using it being twice as big, which sounds just logically if it is true that iso and ecc put much more strian on your muscle fibers. But to be honest I am pretty sure they don't become twice as big by altering there routine to iso and ecc. exercises. Its just one of those things that work out through logical argumentation but when put into practice fails.

Anyways as I said I am not totally against it and eccentric ones could be useful as an augmentation to your routine as long as they are not used as the main form of training.