There are 3 types of muscle fiber contraction during exercise. 1) CONCENTRIC or “positive” contraction - shortening of the muscle fibers during contraction. The joint angle decreases between the proximal and distal attachments. 2) ISOMETRIC or “neutral” contraction - No change in the length of the muscle fibers during contraction. The joint angle does not change. 3) ECCENTRIC or “negative” contraction - lengthening of the muscle fibers during contraction. The joint angle increases between the pr