Scientists have argued about the relative merits of concentric, eccentric and static exercise for more than 100 years. In these contractions muscles shorten (concentric), lengthen (eccentric) or remain the same length as they exert tension. Most studies measured strength changes resulting from the various kinds of training, but biochemical and genetic studies hold the key to the effects of each type of contraction on muscle growth.
Muscle physiologists – including Ken Baldwin from the University of California, Irvine – found that eccentric contractions (i.e., negatives) triggered the greatest increases in IGF-1 and mechano-growth factor (MGF) and the greatest decreases in myostatin. IGF-1 and MGF are essential to muscle hypertrophy (muscle growth), while myostatin prevents growth. Growth factors also increased in tendons, which suggest that tendon changes are important in boosting strength.
This study showed that eccentric contractions cause greater chemical changes in muscle and tendon than concentric or static exercise.
HOW TO APPLY IT
There are essentially two types of contractions – fast and slow. Fast contractions would be used in explosive or plyometric exercises, whereas slower contractions would be used in the downward (lengthening) portion of a bicep curl or bench press. Make sure to control the eccentric – or negative – part of your lifts by using a 2-3 second count on most exercises. For time-under-tension training this can increase to as many as 5-7 seconds.
Source: Journal Applied Physiology, 102: 573–581, 2007