Isotonic Vs. Isometric Contraction

Whether a muscle's job is to push or pull, bend or stand, lift or lower, muscle activity isn't rocket science. They contract according to the demands on your body and the request you have made of the muscle at that time. Understanding contractions is where understanding muscle activity can get tricky. Muscle contractions are classified as isotonic, isometric and isokinetic. The two most common are isotonic and isometric.

Contractions

Contractions happen as a result of muscle fibers gathering together to generate tension to perform an activity. Muscle contractions are voluntary and involuntary. Involuntary contractions occur in the smooth muscle tissue and keep your heart pumping, your lungs breathing and your stomach operating without any reminders from you. Voluntary contractions happen as a result of a request, sent from your brain to the muscle, to perform an activity, whether it's walking, lifting weights or sitting on your bum.

Types of Voluntary Contractions

Isokinetic contractions generally occur in a controlled setting such as for research or assessment purposes. Isotonic and isometric contractions occur in our daily lives and can be seen in exercise and sports activities. With isometric contractions, constant tension is placed on a muscle but the length of the muscle does not change. Examples include wall sits, plank exercises and many yoga and martial arts activities when the poses are held in the same position for a period of time. Isotonic contractions are dynamic, occurring when we exert force on a muscle while changing the joint angle or moving the muscle.

Isotonic Contractions

Isotonic contractions are the common movements we think of when lifting weights. With an arm curl, for example, we are creating an isotonic contraction with the lifting and lowering of a handheld weight. As we lift the weight, the joint angle in the elbow decreases and the biceps muscle shortens. As we lower the weight, the joint angle at the elbow increases and the biceps muscle lengthens. These two phases are known as concentric and eccentric.

Concentric and Eccentric Contractions

During an arm curl, we shorten the muscle as we lift a weight. This is the concentric part of the contraction. As the weight is lowered, its force is still exerted and creates tension on the muscle, and this is known as the eccentric phase. When determining how to incorporate this into your fitness plan, first determine the goal. This will help determine what type of exercise best suits you, be it isotonic or isometric movements.