Contraction refers to the active process of generating a force in a muscle.
The force exerted by a contracting muscle on an object is referred to as the muscle tension, whereas the force exerted on a muscle by the weight of an object is referred to as the load. Muscle tension and load are thus opposing forces, and to lift a load, the muscle tension must exceed the load. From isotonic measurements one obtains the velocity of shortening with various loads, a property of the contractile apparatus of the muscle. Isometric measurements indicate the degree of tension developed in elastic elements of a muscle at a fixed length. You will determine the properties of isotonic and isometric muscle contractions.