Today has been a bad bad day. I was feeling damn upset after school. It makes me angry not being to able to understand the concept between concentric movement and eccentric movement. The rest of the class are able to grasps it.

Eccentric movement. Assisted by gravity. Lengthening of muscles.
Concentric movement. Against gravity. Shortening of muscle.

Sitting down, contract of hams extent of quads
Standing up, contract of quads extent of ham.