As I wait anxiously for the birth of my good friend's baby, I can't help but think about contractions. Though I know nothing about muscle contractions as they relate to giving birth, I can tell you how they influence your performance at the gym. You see, our muscles can experience three different contractions when we strength train.
Let's start with isometric contractions, as shown above. When our muscles contract isometrically, we're not actually moving them. The muscle is simply maintaining a contracted state in order to hold a weight. Sitting against a wall is another example of this, as are planks. The nice thing about isometric training is that it doesn't put much pressure on the joints surrounding the muscle, which is why a number of physical therapists will employ this method to rehab injuries. And in all actuality, an isometric contraction is the best representation of muscle strength. For example, I may be holding a 15-pound dumbbell in the photo above, but ask me to perform bicep curls and I will tire out quickly. Though I have the strength to hold it as shown, I can do more bicep curls with a 12-pound weight. That, however, can be explained by concentric contractions.
Concentric contractions cause the muscle to shorten, and internal muscle friction weakens it slightly. This, of course, is the result of it acting against an outside force. In the case of a bicep curl, the outside force is the weight itself and the concentric contraction occurs as the dumbbell is lifted. And that's why I can't necessarily curl 15 pounds—because of the weight itself in combination with movement. But the act of curling 12 pounds repeatedly still challenges me, and the more I lift it, the more tolerant my muscles will get which means, of course, that I'm building strength. And as the bicep muscle contracts concentrically during the up phase of a curl, it starts to contract eccentrically during the down phase. Meaning, it lengthens—or relaxes
Next time you strength train, I challenge you to really feel your muscles as they work. It's not about the act of lifting and lowering, or pushing and pulling, but it is about contractions. Decipher when your muscle is contracting concentrically or eccentrically, maybe even isometrically, and you'll connect to the essence of the exercise itself. And that, hopefully, will grow your understanding of and appreciation for all your hard work.