Isolation exercise

An isolation exercise involves movement at only one joint. In a seated leg extension, you straighten only your knee, moving just the knee joint to focus on the quadriceps femoris at the front of your thigh. Biceps curls, which involve bending only the elbow, target the biceps brachii, while lateral raises, which involve lifting your arms out to the sides, target the shoulder's deltoid muscle. Leg curls, in which you bend your knees while lying down or lying on your stomach, work the hamstrings at the back of your thighs.

By contrast, exercises such as squats, in which several joints and muscles move at once, are called compound exercises. In Korean gyms, isolation exercises are also called "body-part exercises." As the name suggests, they are often used when training is divided by body part, such as arms or shoulders, on particular days.

Isolation exercises involve simple movements and a defined position, making it easier to feel which muscle is working. They are therefore often used in the following situations.

• When you want to train a weak muscle separately — Stronger muscles take on much of the work in compound exercises, whereas isolation exercises place a load directly on relatively weaker muscles.
• During rehabilitation after an injury — They are used to slowly reactivate an individual muscle that has weakened after a knee or shoulder injury, using light weights.
• When you want to improve balance between sides of your body — If one arm or leg feels weaker, isolation exercises performed one side at a time are used to work toward balance.
• When you have little exercise experience and are learning how to engage your muscles — Many are machine exercises that hold your body in place, making it easier to get into position.

Even with the same leg extension, how the muscles feel changes depending on whether you straighten your knees fully, how slowly you lower the weight, and how long you rest between sets. The stimulus from the same exercise can vary with the range of movement, speed, rest time, and how familiar you are with it.

People structure resistance training in many different ways, and a systematic review and meta-analysis of exercise order (11 studies) reported an interesting finding. When overall strength gains were pooled, there was no difference by exercise order. However, doing compound exercises first led to greater strength gains in compound exercises, while doing isolation exercises first led to greater strength gains in isolation exercises. This is because you can exert the most force in exercises placed earlier in a session. Exercise order had no clear effect on muscle hypertrophy.

Here is a useful way to think about it.

• Put the exercise you most want to improve first. If your goal is to build the front of your thighs, one option is to do leg extensions first and squats afterward.
• It is also common to start with bigger exercises and finish with isolation exercises. This means working your lower body with squats, then directing your remaining effort into leg curls and leg extensions.
• Change your exercise selection occasionally. A systematic review examining the effects of varying exercise selection (8 studies, 241 participants) concluded that some systematic variation helped regional muscle hypertrophy and dynamic strength. Switching too frequently between exercises that target the same area may instead disrupt adaptation, so changing them every few weeks is a suitable approach.

• Technique comes before weight. Start with a weight that lets you feel the target muscle working without using momentum.
• Resist slowly as you lower the weight, too. Your muscles are working on the way down just as they are on the way up.
• Do not hold your breath. You may find it comfortable to breathe out during the exertion phase and breathe in as you return.
• If a joint hurts, stop and try changing the angle or weight. A pulling sensation in a muscle is different from a sharp, tingling sensation in a joint.
• You can do them without equipment. Lateral raises using a resistance band or water bottles, and single-leg knee extensions using a chair, are also isolation exercises.