(i) Isotonic contractions: The force exerted on a muscle by lift and load. The muscle contraction is said to be isotonic (in a constant tension) since the load remains constant throughout the period of shortening of muscle.
(ii) Isometric contraction: Shortening is prevented by maintaining the muscle at a fixed length. The development of tension occurs at the constant muscle length. This type of contraction is said to be in isometric contraction (constant length).