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.
How Your Muscles Contract
Your muscles contain fibers called myosin. Depending on how you need to use your muscles, the myosin fibers either tighten up and shorten or loosen up and stretch out. Myosin is also responsible for muscle contractions like your heartbeat that happens at regular intervals.
Understanding Muscle Contractions
Concentric Contractions. This type of contraction happens when your muscle is actively shortened. Your muscle tightens when you activate it to lift something heavier than normal, which generates tension.
Keep in mind that this type of muscle contraction happens when the load is less than your muscle’s maximum capacity. Your muscle cannot move the load without shortening the fibers to physically move the object.
An example of a concentric muscle contraction is picking up a heavy box. If you squat down to lift a box, your arm muscles may contract to hold the weight, but your leg muscles tighten as you stand up with the additional weight.
Eccentric Contractions. This type of contraction happens when your muscle is actively lengthened during normal activity. An example of this is walking because your quadriceps muscles are active when your heel touches the ground and your knee is bending or straightening out in stride.
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.
Passive Stretch. This type of muscle contraction happens when your muscle is passively lengthened. For example, you lean down to touch your toes. There’s no additional weight that your hamstring muscle needs to hold or lift by applying force, but it still stretches from the movement.
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 muscle for that single, specific movement. An isometric muscle contraction is good for practicing the use of a muscle in a particular way following an injury.
Concentric and eccentric muscle contractions. These two types of contraction 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.
Passive stretching. This type of muscle contraction is helpful for gently lengthening your muscles. You can contract your muscles passively by stretching them as far as they can physically go. This lengthens your muscles in a way that activates them without using force.