Different exercises use different mechanics to induce muscle growth. Most strength training exercises fall into one of two categories - isometric and isotonic exercises. The comparison between isometric vs isotonic exercises is what we're going to discuss in this article.
If you're unsure what either of these terms mean, we'll explain it for you, in plain English (and a little Greek).
We'll look at the benefits of each, a few examples, and give you the answer as to which type of exercise is better for you to focus on.
What is Isometric Exercise?
Isometric exercises are exercises that engage and activate the muscles without movement. The word “isometric” derives from the Greek terms “iso”, which means “same”, and “metric”, which means “length”.
So isometric literally means “same length” - i.e. your muscles remain the same length throughout the exercise.
An example of this is a plank. You're activating a range of muscles with this exercise, however, you're not moving any joints - you're literally staying still. Thus you engage the muscles without contracting and expanding them, which is the basis of an isometric exercise.
What is an Isotonic Exercise?
Isotonic exercises involve contraction of the muscle, moving a joint through a full range of motion while keeping the same resistance on the muscle throughout.
The meaning of the term isotonic is “iso” or “same” (just like with isometric), plus “tonic”, which means “tension”. So, it means “same tension” - the tension on the muscle remains the same.
It's essentially the opposite of isometric exercise. Think about a bicep curl, one example of an isotonic exercise. As you move the elbow joint, your bicep contracts, and the muscle shortens. When you lower it, the muscle gets longer.
Isometric vs. Isotonic: Which is Better for Muscle Development?
When it comes to isometric vs isotonic exercises, isotonic exercises are more effective at building muscle than isometric exercises. The full range of motion and muscle contraction from an isotonic exercise leads to increased muscle activation and better gains in strength and size, as well as bone density.
Isotonic exercises are also best for overall athletic performance, and increasing speed and power.
But that's not to say that isotonic exercises are the best in every situation. There are plenty of benefits to doing isometric exercises as well.
Benefits of Isometric Exercise
Isometric exercises are an excellent choice when you want (or need) to train strength without putting stress on the joints.
Let's say you're recovering from an injury, have joint pain, or you have a health condition that makes it risky to lift weights in the traditional sense. Isometric exercises give you a way to activate and strengthen your muscles while keeping the joints safe and minimizing weight.
Isometric exercise is also convenient, as most isometric exercises need no or little equipment, and minimal space to do.
While you don't get the same level of muscle growth and similar benefits from isometric exercises as you do with isotonic, they're still a good way to increase strength (particularly core strength), muscle definition and muscular endurance, improve bone density, and provide a range of other exercise-related benefits.
Finally, isometric exercise may be good for the heart. A 2014 review of multiple studies found that isometric training lowered systolic blood pressure, both in those with normal and high blood pressure. The effect may be significant enough to prevent heart attacks and other cardiovascular diseases.
Benefits of Isotonic Exercise
Isotonic exercises are primarily beneficial for building muscle and increasing strength.
Most of your traditional strength training exercises are isotonic exercises. While there is a little more risk than with isometric exercises, the potential payoffs tend to be larger.
Isotonic exercises are great for building muscle and improving muscle definition. Yet they're not only beneficial for people trying to build muscle.
A 2017 study found that strength training may improve blood sugar regulation and promote healthy blood pressure, thus decreasing the risk of diabetes and improving cardiovascular health.
Strength training is also widely linked to higher bone mass, and thus a lower risk of osteoporosis, which often afflicts the older population.
Just briefly, there is a third type of exercise related to the two we've been talking about, known as an "isokinetic exercise".
Isokinetic translates to "same motion". It means your muscles travel at a consistent speed and motion throughout the movement, despite changing levels of resistance.
Isokinetic exercises require specialized machines that are able to keep a certain amount of resistance against a person's motion.
These are often rare and expensive machines, only used by professional athletes (generally for rehabilitation), though treadmills and stationary bikes can be considered a form of isokinetic exercise.
3 Most Common Isometric Exercises
Want some ideas for isometric exercises you can add to your workout routine? Here are a few of the most common examples.
Planks, as we mentioned already, are a typical example of isometric exercises. They work with zero joint movement and only your body weight, yet activate a wide range of muscle groups throughout the course of the action.
Wall sits work just the same as planks but target the lower body in particular. If you've ever done wall sits, you'll know that they look easy, but are deceptively painful.
They can help maintain strength and build definition in the legs, and are great for improving stability, but aren't going to provide the same lower body strength gains as an isotonic exercise like a full squat.
The other most common isometric exercise you'll see is a yoga pose. Yoga itself isn't exclusively isometric.
You'll have moments where you shift from one pose to another, which involve movement of the joints and (possibly) contraction of the muscles. But the core of yoga - individual poses - involves holding a static position with the muscles under tension for a length of time, similar to how a plank or wall sit works.
3 Most Common Isotonic Exercises
So how about isotonic exercises?
We could name any number of examples of isotonic exercises, as most things you do in your workout probably come under this category. We mentioned bicep curls already - but how about a few more?
Squats are a great example - and a great exercise. You're putting a few different joints through a full range of motion, while causing a lengthening and shortening of several muscles, primarily in the quads, hamstrings and glutes, all under the common tension of a specific weight. In short, they're a perfect example of an isotonic exercise.
Push ups also fall under this category. Like squats, it doesn't involve just a single joint movement, like with a curl. But they still count as isometric, causing numerous contractions of various muscles all throughout the body.
Running is another example of isotonic exercise, which you might not have considered. But when you think about it, it makes sense, right?
You're putting your joints, such as the ankles and knees, through a range of motion, while contracting several muscles along the legs, under the resistance (or tension) of your bodyweight.
So it's not just resistance training that counts as isotonic exercises - just about anything can fit into this category.
Should I Focus Primarily on Isometric or Isotonic Exercises?
The answer depends largely on your health and fitness goals.
There are more overall benefits to be had from isotonic exercises, than isometric.
Isotonic exercises put more stress on your muscles and work your cardiovascular system more intensely, which leads to bigger gains.
Isotonic exercises are also the winner when it comes to building overall athleticism that translates to other activities, such as sports.
But there is absolutely a place for isometric exercises, too. For a start, many people - if you're recovering from an injury, have a health condition, or are just building up your fitness levels - can benefit more from the safety and relative effectiveness of isometric exercises.
And even if you do focus primarily on isotonic exercises, there's no problem with adding some isometric exercises to your routine, which often have better results for core strength.
The key idea is that any kind of exercise is beneficial for you - whether that's isometric, isotonic, or anything in between. The key is to be active, and you'll live a higher standard of life as a result.