Eccentric Versus Concentric
It has been well proven that the eccentric (lowering) portion of an exercise when compared to the concentric (lifting) phase, gives greater strength values, and increases in strength over time results in greater muscle cross-sectional area. Therefore if your goal is to increase muscle it would be wise to go slower or alternatively use more weight on the eccentric part of the exercise than the concentric part. For example when performing the EZ-bar biceps curl, you should curl the bar up in 1 second and return the bar down in 3 seconds. Another example would be at a Preacher Curl machine, take the bar up with both hands and then return to the start position using one hand.
Back to Articles
http://www.getfitco.com/Articles_EcentricVsConcentric.html
