Eccentric and concentric are terms used when you are stretching or shortening your muscles.
When you complete an exercise like running, throwing, jumping etc. These use both types of actions as your muscles are stretched and then shortened very quickly.
This is known as the stretch-shortening cycle (SSC.)
It is important for us to know this as it is a far more efficient way for us to complete our exercise and a lot of us are even using it without even knowing.
For example; A football player needs to bring back the kicking leg first before they can kick the ball or it is not going to go very far!
Try it for yourself, place a ball on the floor and from a standing stance bring your leg straight forward and kick the ball. It doesn’t move all that far!
However, if you first bring back your leg (eccentric) and then quickly shorten the stretched muscles (concentric) by bringing your leg forward you are going to get a much bigger energy release and able to kick the ball a lot further.
You can also take the example of a vertical jump.
If you try and jump straight up in the air from a standing position you won’t get very high up. But if you bend down and then jump up you are going to get a lot higher.
In order to get the best efficiency out of the transfer of energy is to make sure that the stretching to shortening of the muscle is immediate as if it’s not, the stored energy will be absorbed by the stretched muscle.
For example, if you bring one leg back as if you were going to kick a ball.
Instead of instantly moving your leg forward, keep it stretched back for a couple of seconds and then move it forward. You will see exactly how much of the forward power had reduced.
Weight training is an example of a measured loss as when you are at the bottom of the bench press just for that 1 second you will get a 55% loss of force than if your weight was straight away pushed back up.
If you are completing an exercise routine than employs the SSC concept (also known as plyometric,) always start with a warm-up and finish with a cool-down.
Ensure you should have between a 24-48 hour recovery times in between your sessions.