The Science Behind Isometric Exercise

As humans, we are always looking for ways to improve our physical performance and build strength. One way to do this is through isometric exercise. Isometric exercise involves holding a static position, such as a plank or wall sit, for an extended period of time. In this article, we will explore the science behind isometric exercise and why it is an effective method for building strength.

The Mechanism of Isometric Exercise

To understand why isometric exercise is effective for building strength, we first need to understand how muscles work. Our muscles are made up of fibers that contract and relax to create movement. During isometric exercise, the muscle fibers contract but do not change length. This creates tension in the muscle, and the body responds by recruiting more muscle fibers to generate greater force.

Over time, as you continue to perform isometric exercises, your body adapts to this increased demand by increasing the number and size of muscle fibers. This is known as muscle hypertrophy (see the appropriate scientific study here).

In addition, isometric exercise can also lead to neural adaptations, which means that your nervous system becomes better at coordinating the recruitment of muscle fibers to generate force. This can improve your ability to generate force during other types of exercise and daily activities, leading to improved overall strength.

There are different types of isometric exercises, including wall sits, planks, and static holds. These exercises can be performed with bodyweight or with equipment such as resistance bands or weights. The benefits of isometric exercise include increased strength, improved balance, and reduced risk of injury.

Muscle Fiber Recruitment during Isometric Exercise

Muscle fiber recruitment refers to the number of muscle fibers that are activated during exercise. The more muscle fibers that are recruited, the more strength gains can be achieved. During isometric exercise, the muscle fibers are recruited in a specific pattern that leads to increased strength.

There are two types of muscle fibers: slow-twitch and fast-twitch. Slow-twitch fibers are used for endurance activities such as long-distance running, while fast-twitch fibers are used for explosive movements such as sprinting or weightlifting. Isometric exercise recruits both types of muscle fibers, leading to overall strength gains.

One study gave the following advice:

“To increase muscle hypertrophy, IST (isometric strength training) should be performed at 70-75% of maximum voluntary contraction (MVC) with sustained contraction of 3-30 s per repetition, and total contraction duration of>80-150 s per session for>36 sessions. To increase maximum strength, IST should be performed at 80-100% MVC with sustained contraction of 1-5 s, and total contraction time of 30-90 s per session, while adopting multiple joint angles or targeted joint angle.” 

So, this would be longer contractions at lower intensity for hypertrophy and shorter contractions at higher intensity for a focus on strength gains.

Progressive Overload and Isometric Exercise

Progressive overload is the concept of gradually increasing the demands placed on the body in order to continue making progress. In the context of isometric exercise, this means gradually increasing the time held in a static position or increasing the resistance used.

By applying progressive overload to isometric exercise, the muscles are constantly challenged and forced to adapt, leading to increased strength gains. This is why it is important to vary the intensity of isometric exercises and avoid plateauing.

Isometric Exercise and Neural Adaptations

Neural adaptations refer to the changes that occur in the nervous system as a result of exercise. Isometric exercise can lead to neural adaptations, such as increased firing rate of motor units and improved synchronization of motor units.

These adaptations lead to more efficient muscle recruitment and ultimately increased strength gains. This is why isometric exercise is an effective method for building strength in a shorter period of time compared to traditional strength training.

The Effect of Joint Angles on Isometric Exercise

Joint angle refers to the angle at which a joint is positioned during exercise. The angle of the joint can affect the amount of muscle activation and ultimately the strength gains achieved.

It’s important to note that while isometric exercise can lead to strength gains, those gains will primarily be specific to the joint angle at which the exercise is performed, as confirmed in this study. This is because the muscle fibers that are recruited during an isometric exercise are only activated at that specific joint angle.

For example, if you perform an isometric exercise to target your biceps at a 90-degree elbow angle, you will primarily strengthen the muscle fibers that are active at that angle. If you want to improve your strength throughout the full range of motion of your bicep curl, you will need to perform isometric exercises at different joint angles to target the muscle fibers specific to each angle.

This is why it’s important to vary the joint angles at which you perform isometric exercises to ensure that you are strengthening your muscles throughout their full range of motion. By doing so, you can improve your overall strength and performance in other exercises and activities.

Varying the joint angle during isometric exercise can lead to more balanced strength gains and prevent muscle imbalances. 

Additionally, joint angle can determine the degree of hypertrophy.  This study  showed that  isometric training at longer muscle lengths produced greater muscular hypertrophy when compared to equal volumes of shorter muscle length training.   Additionally, long muscle length training results in greater transference to athletic performance.   For example, training the bicep with the arm outstretched would result in greater hypertrophy than when the arm is in the fully bent or flexed position.


Isometric exercise is an effective method for building strength due to the mechanism of muscle fiber recruitment, progressive overload, and neural adaptations. By applying these principles and varying the intensity and joint angle, isometric exercise can lead to increased strength gains and improved eccentric strength. Additionally, isometric exercise can help prevent injuries by strengthening the muscles and improving joint stability.

If you are looking to incorporate isometric exercise into your fitness routine, it is important to start with proper form and gradually increase the intensity over time. As with any exercise program, it is also important to listen to your body and rest when necessary.


Q: How long should I hold an isometric exercise?

A: The amount of time you hold an isometric exercise depends on your current fitness level and the specific exercise.  It also depends on your goals:  strength or hypertrophy.   As a general guideline, aim for 10-30 seconds for each exercise.

Q: Can I do isometric exercise every day?

A: It is generally safe to do isometric exercise every day, but it is important to listen to your body and rest when necessary.

Q: Do I need equipment to do isometric exercise?

A: Isometric exercises can be performed with bodyweight or with equipment such as resistance bands or weights.

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