Skeletal muscle contractions can occur with or without changes in length. If its length changes, the contraction is termed isotonic. When a muscle is contracting and shortening the contraction is isotonic concentric, while if the resistance exceeds the tension generated and the muscle lengthens while contracting, then the contraction is isotonic eccentric. Conversely, if a muscle contracts, but the load does not move and the muscle length remains the same, the contraction is called isometric (same length).
