 In this video, I will define isotonic contraction and isometric contraction, and we will also discuss two subtypes of isotonic contraction, concentric isotonic contraction, and eccentric isotonic contraction. During isometric contraction, muscle tension increases with contraction, but the muscle length remains constant. This occurs when contraction is unable to produce enough force to overcome the load. The example we see in the illustration here, the biceps brachii muscle contracts stabilizing the position of the elbow or humeral ulnar joint in order to stabilize the load of a dumbbell. There's no movement produced, but biceps brachii is producing muscle tension, and that amount of muscle tension is equal to the load, so maintaining enough muscle tension to prevent movement in this situation, the isometric contraction has to stabilize that load. Another example could be pushing against a wall. As you are increasing the muscle tension, pushing against the wall, you're never able to produce enough force to move the wall unless you are to break the wall and put a hole in it. So if you're pushing against a nice solid wall, like a brick wall, and you're not able to move the wall, you can produce an increase in muscle tension without producing any movement. This is an isometric contraction in contrast to an isotonic contraction that produces movement. Isotonic contraction is when muscle tension remains constant as the muscle length changes. Isotonic contractions produce movement, and there are two major types of isotonic contractions. Here we see an illustration of an isotonic concentric contraction. In a isotonic concentric contraction, muscle tension remains constant, but the muscle tension is greater than the load, and therefore the muscle shortens as it does work. The example shown in the illustration here is the biceps brachii muscle producing the action of flexion of the elbow joint with the added load of a dumbbell. The muscle will produce a greater tension than the weight of the load, and this will then cause the muscle to shorten as the elbow is flexed. Isotonic eccentric contraction is the other major subtype of isotonic contraction. So as an isotonic contraction, muscle tension remains constant during an isotonic eccentric contraction. However, the muscle lengthens during eccentric contraction. You can think of this as muscle breaking as the skeletal muscle is producing tension that is less than the load. Therefore the skeletal muscle is slowing down the movement. The example we can see in the illustration here is biceps brachii performing isotonic eccentric contraction as the elbow joint is extended. The biceps brachii slows down the movement of extension of the elbow. So the biceps brachii is producing less muscle tension than the load, and this enables the movement to be stabilized and slowed down. Another example of an isotonic eccentric contraction would be performing squats. As you're performing a squat, your quadriceps femoris muscles are performing isotonic eccentric contraction in order to slow down the movement of flexion of your knee joints. The load of your body weight is producing the movement, and the quadriceps femoris muscles are producing less tension than your body weight. Therefore the movement occurs as you're performing a squat, but that movement is controlled and slowed down by the isotonic eccentric contractions.