When you want to build muscle, take some time to learn which exercises are going to pack the punch you need. In your regular workout routine, it's likely you've done both isometric and isotonic exercises, maybe without even knowing the difference. While both can have their place, it's important to know one from the other to help you achieve the specific fitness goals you may have in mind.
When you move your muscle from point A to B and then back again, such as when you're doing a bicep curl holding a dumbbell, you're performing an isotonic exercise -- essentially, putting your muscle through a wide range of motion and either shortening or lengthening it in the process. If instead you pulled upward on a fixed chain, holding and flexing your bicep muscle without moving it up or down, you'd be performing an isometric exercise that doesn't lengthen or shorten the muscle or force you to move the joints.
Isometric exercises are good for people who want to maintain muscle strength, but they won't help build it, according to MayoClinic.com. As such, isometric exercises can be a good choice for people who are recovering from an injury, or who may have conditions in which a lot of movement is painful. If you're looking for exercises to help build muscle, get faster or improve your performance in a sport, isotonic exercises are probably more appropriate.
To train your gluteal muscles, quadriceps and other muscles of the legs, one option is to do squats -- traditionally an isotonic exercise. In the standard squat, you'll stand with your feet about shoulder-width apart and then bend your knees until your quads are level with the floor. You'll then stand back up, repeating the motion about 10 to 12 times. For an isometric variation, you'll hold the squat position without continually moving up and down. Some people choose to hold this stationary squat while their backs are resting against a wall. If you can hold that position for 10 to 20 seconds, your leg muscles will definitely let you know they're there.
You'll also find variations for isotonic or isometric exercises that work the abdominals. Take a look at the traditional isotonic situp. In the standard version, you'll work to touch your elbows or chest to your legs, doing anywhere from 10 to 100 repetitions. In the isometric version, you'll move to the "up" position in which your elbows are nearly touching your legs -- or your arms are at your sides and pointed forward, and you'll hold the pose for 10 to 20 seconds.
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