Well not that kind of eccentric. I'm talking about the muscle-building type of eccentric. The kind of eccentric that allows you to do exercises that you normally don't have the strength to do. Ok ok lets go back to the beginning in case you didn't get your degree in gym, like me.
In every excercise there is an concentric and eccentric component. Concentric contraction is the part where the muscle is producing force and shortening in length. Eccentric contraction is the opposite, the muscle is producing force but is lengthening. Confused? Let's look at an example. Imagine, or do, a bicep curl. When you lift the weight up from the starting position and you see that lil knot of muscle get smaller ( no sight of one? do more curls, just don't do too many) that is the concentric phase. When you lower the weight back to the starting position you muscle is contracting eccentrically.
So why do you need to know this? Working the eccentric phase of an exercise allows you to perform an exercise you might not otherwise be able to do. This is particulary useful for those just getting back into the swing of things fitness-wise or those who are building up to a more difficult strength skill. For example, like many people, particularly woman, I am unable to perform a full set of unassisted pull-ups. So instead of struggling for one and being done, I break the pull-ups into two components. The first part, I pull myself up to the bar assisted by a chair, focusing on full range of motion. Once up I hang unassisted and slowly lower myself down for a count of 5 to the starting position. Make sure that you lower yourself in a controlled manner, don't just drop.
So what other excercises can I do this with? Well......anything. If you are at a stand still in progression with a particular exercise try working on the eccentric component, especially with the more difficult exercises (e.g. pistol squats). One warning: You will be sore. For reasons not fully undersood (although there are many theories) eccentric exercises will make you more sore and stiff. However, the next time you perform the exercise soreness and stiffness will decrease. But in my personal opinion the gains made trumps the annoying soreness that makes you feel like an old lady/man hobbling around. And you can also tell everyone how sore you are from the killer workout you just did, which in turn causes them to think your a superstar of fitness.
With knowledge comes change (or at least it should), so use this knowledge to expedite your fitness goals and create the functional strength you require ( from squatting while planting your herb garden to jumping a fence while evading the long arm of the law) to live the life you desire.
I would lift my arm to wave good bye, but I'm too sore...