The fitness world is fraught with ill-defined terms. Is it possible that “strength training” is the most egregious offender in this realm? Ask ten fitness professionals and you will get ten variations of weight training. Ask a yogi and you’ll get a different answer. Most unfortunate is the public, and to a certain extent the medical community, equating strength training with traditional weight lifting and bodybuilding. The deeper this mindset penetrates a community, the less understanding and appreciation of subtle strength training techniques are likely.
The physiology and kinesiology community recognize three main modes/types of muscular contraction:
Concentric Muscle Contraction: When a muscle becomes shorter in length and increases in girth as a result of neural stimulation (ie. upward phase of an arm curl)
Eccentric Muscle Contraction: When a muscle increases in length and decreases in girth despite being activated by neural stimulation (ie. controlled downward phase of an arm curl)
Isometric Contraction: When a muscle experiences no change in length where the neural stimulation is insufficient to overcome a given resistance (ie. halting and holding an arm curl in the middle range of motion or attempting to arm curl the bumper of a big truck)
This seems pretty simple right? If not I will provide clarification by categorizing the movements presented in the exercise catalog by these terms so that as you progress through the material you will develop a better understanding.
To optimize the gains in functional strength, emphasizing all three of these types of contractions is necessary as specifically training only one of them provides only minimal cross-over to another. To illustrate this, we turn to the arm curl once again.
If you were to do arm curls in a manner where you eliminated the downward or eccentric phase of the movement, say by having a partner take the weight from at the top of the movement after completing the concentric phase of the movement (from thigh to chest) and hand it back to you at the thigh, where you complete the next concentric repetition. In this instance you would, over time, enhance your capacity in the upward, concentric phase of the movement, likewise your partner will gain in eccentric strength required in the lowering phase.
After 3 months of training to a maximal one repetition capacity of 100 lbs, you and this partner are faced with a 98 lb. object while moving boxes from a shelf. The shelf is at chest height and a chair at thigh height. You would easily be able to lift this package up to the shelf; your partners likely would not. When removing this object from the shelf, your partner would be able to easily lower it to the chair, whereas you would likely pull the object off the shelf and drop it. This is an example of specificity of training and a real world effect.
It is also important to note that the eccentric phase partner would experience much more muscle soreness after each training session.