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.