Muscle contraction is the tightening, shortening, or lengthening of muscles when you do some activity. It can happen when you hold or pick up something, or when you stretch or exercise with weights. Muscle contraction is often followed by muscle relaxation when contracted muscles return to their normal state.
Why Do Muscles Contract?
Muscles serve several purposes in your body. Your muscles contract for any number of reasons, but they primarily do the following:
- Offer stability to your joints and connective tissues – Your muscles lengthen and shorten, sometimes involuntarily, as your body needs them.
- Produce heat to maintain your body temperature – Around 40% of your body’s temperature converts into muscle work. Shivering is your body’s response to feeling cold, and your skeletal muscles activate to warm your body.
- Maintain posture – Muscles help you maintain a position, like sitting or standing.
- Most importantly is movement. To live, we have to move, and muscles are the means to do so.
How Your Muscles Contract
Your muscles, at the deepest level, are made of proteins called myosin and actin. Depending on how you need to use your muscles, the myosin fibers either tighten up by pulling on the actin and shorten or loosen up and stretch out. Myosin and actin are also responsible for the muscle contractions of your heart and other organs that contract and expand.
Understanding Muscle Contractions
Concentric Contractions. This type of contraction happens when your muscle actively shortens. Your muscle tightens when you activate it to lift something, which generates tension, such as bringing a glass of water to your mouth.
Keep in mind that this type of muscle contraction happens when the load is less than your muscle’s maximum capacity. If too heavy, your muscle’s available proteins cannot shorten to move the load.
Eccentric Contractions. This type of contraction happens when your muscle is actively lengthened during normal activity. An example of this is when you control the glass of water from your mouth back to the counter. In both activities, you are using the same muscles, but in a concentric contraction, the muscle is shortening, and in an eccentric contraction, the muscle is lengthening.
Eccentric muscle contractions also happen when you lower something heavy. Your muscle has to remain tight to manage the weight, but it lengthens to shift the weight into a different position.
Isometric Contraction. This type of muscle contraction happens when your muscle is actively held at a set length. Instead of lengthening and shortening as it would during some activities, you hold it in a position that requires a specific length once activated. An example of this type of contraction is carrying something in your arms in front of you. You aren’t trying to raise or lower the object, but keep it at a steady position.
How You Use Muscle Contractions
Isometric muscle contractions. This type of contraction is used when your muscle stays in a single position, and the attached joint doesn’t move. It doesn’t provide overall strengthening to the muscle group. Instead, it strengthens your muscles for that single, specific movement. An isometric muscle contraction is good for activating a muscle in a particular way following an injury and protecting a joint that may be injured.
Concentric and eccentric muscle contractions. These two types of contractions often go together. A concentric muscle contraction helps you lift something heavy. It is often referred to as positive work.
An eccentric muscle contraction is called negative work. Your muscle reacts eccentrically to help you lower something heavy. An example of these two contractions is lifting a dumbbell while working out.
When you pick the dumbbell up, your bicep muscle tightens and contracts to lift the weight. When you lower the weight down, your bicep muscle remains contracted, but it lengthens instead.
