Isotonic Vs. Isometric Muscle Exercises

When it comes to getting fit, there are countless exercise options. Learning about different types of exercise and identifying your goals can help you design an exercise program that meets your individual needs.

Learning about different types of exercise and identifying your goals can help you design an exercise program that meets your individual needs. (Image: yoh4nn/E+/GettyImages)

Combining isometric and isotonic exercises is one approach for optimal functional fitness.

Muscle Actions and Joint Movement

During exercise, muscles can develop tension while shortening, lengthening or staying the same length. Muscle shortening, known as concentric contraction, forces a joint angle to decrease. Muscle lengthening, known as eccentric contraction, causes a joint angle to increase.

When tension develops in a muscle but the length does not change, the joint does not move, and the contraction is said to be isometric. When comparing isotonic to isometric exercise, you are comparing exercises that respectively initiate joint movement to exercises that are static, causing no movement.

Isotonic Exercise Benefits

Isotonic exercise, also know as dynamic constant external resistance, or DCER for short, encompasses exercises where muscle tendons pull against bone to cause joint movement. Any moving exercise, from weight training to rowing or running, falls into this category.

Isotonic exercise is further broken down into two types of contractions: concentric and eccentric. Concentric exercise occurs when a muscle shortens as it contracts — such as the biceps muscle shortening during a curl. Eccentric exercise causes the muscle to lengthen even though it is contracting — such as the biceps muscle as you lower the weight back down to the curl starting position.

In fitness, isotonic contraction exercises most commonly refers to exercises that isolate a particular muscle or muscle group to increase strength or improve performance. Because most human activity and athletic performance involves movement, isotonic exercise is foundational to most training protocols.

The Centers for Disease Control and Prevention recommends strength training exercises be performed for all major muscle groups, at least two days per week.

Benefit of Isometric Exercise

Isometric exercises are static, meaning no joint movement is involved. The training effect of isometric exercise is specific to the joint angle at which it is performed. For example, performing a "wall sit" exercise with your back against the wall and your knees and hips fixed at 90 degrees will result in increased strength at that angle, but the benefits will not carry over to joint actions that go far beyond that range. Planks are another isometric exercise example.

Strength adaptations from isometric exercise are a function of the length of time the body is held in position. To increase strength, hold the position for as long as possible until muscle failure.

Isometric vs Isotonic Exercise Choices

There are several factors to consider when choosing isometric vs. isotonic exercise. For the average exerciser, isotonic exercise provides the most useful improvements for daily function, but isometric exercise may nonetheless have a place in your workout regimen.

Because muscles of the core perform the important function of stabilizing the spine throughout the day, isometric exercises like the yoga plank can be useful for strengthening those muscles. Isometric exercise can dramatically increase blood pressure and thus may be inappropriate for hypertensive individuals.

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