Concentric Contraction 

From the earlier mnemonics we can see that:

Concentric - Shorten and up movement. 

Concentric - Tension. 

From this we understand that:

Concentric contraction is shortening of the muscle in tension, or:

Concentric contraction = Shortening of the muscles 

Concentric contractions occur when you:

1. Move a dumbbell in a bicep curl upwards towards your body.

2. When you stand up from a squat position. 

Note: Your quadriceps (quads) are made up of four muscles hence quad. 

3. Doing a press up from the position of your nose being close to the floor to pushing away from the floor.