Compound movements occur at more than one joint and work more than one muscle group. Isolation exercises occur at only one joint and target only one muscle group. For example, the squat exercise involves movement at your knee joint and hip joint. This compound leg exercise works your hamstrings, quadriceps, glutes and lower back. The leg extension exercise occurs only at the knee joint and works only your quadriceps muscles.
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Compound exercises save you time because one exercise works several muscle groups. If you want to work your thighs, you can do both leg extensions and hamstring curls, or you can do squats. Compound exercises stimulate more muscle tissue, meaning you don't have to do as many exercises to hit all your muscles. You can target all the major muscles in your body with a handful of compound exercises: chest presses for the chest and triceps, bent-over rows for the back and biceps, squats for the legs and overhead presses for the shoulders.
How You Move
Compound exercises are more functional than isolation exercises; they more closely mimic everyday movements. Think about the squat and overhead press. You squat down to pick up a box; you press an object overhead to set it on a high shelf. The increased strength, coordination and muscular endurance you reap from doing compound exercises transfers to these daily situations. Isolation exercises, although important, do not mimic real-life movements as well.
Where's Your Focus?
Isolation exercises, such as biceps curls, triceps extensions and leg extensions, still have their place in a workout routine. They allow you to zero in on one specific muscle, which you can't do with a compound exercise. For example, you would use isolation exercises to focus on a single muscle that lacks strength. Compound exercises take more energy to perform, so place these movements at the beginning of your workout and save the isolation exercises for the end.
One of the biggest differences between isolation and compound exercises is their fat-burning potential. You need a calorie deficit to lose weight and that can only occur with compound exercises. You're performing big movements that involve a lot of different muscle groups and the potential to burn more calories increases significantly. An added benefit is that fat-burning continues for an hour or more after your compound exercise workout.