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Without a doubt, strength training will improve strength. Resistance training adaptations include increased muscle mass, tendon quality, strength, power, range of motion, and improved voluntary activation (Oranchuk et al., 2019). Dynamic movements that incorporate the stretch-shortening cycle make up the majority of most strength training programs; however, isometric training also has many reported benefits.
Types of Muscle Contractions
Concentric muscle contractions occur when the muscle shortens while generating force to overcome resistance. An example of a concentric contraction would be a bicep curl: as the bicep contracts, the arm bends at the elbow, and the weight moves towards the shoulder.
Eccentric contractions result in the elongation of a muscle while the muscle is still generating force. Eccentric contractions occur when resistance is greater than the force generated by the muscle. Voluntary eccentric contractions include the lowering of a heavy weight raised during the concentric contraction, while an involuntary eccentric contraction may occur when a weight is greater than the force generated by the muscle.
Isometric contractions generate force without changing the length of the muscle. Although there is no net movement, the forces generated during isometric contractions are potentially greater during concentric contractions (Reed and Bowen, 2008). It should be noted that although isometric contractions are characterized by the lack of change in muscle length, the muscle actually slowly shortens, while the tendon lengthens. This muscle shortening coupled with tendon lengthening results in no net movement (Smith).
Types of Isometrics
Yielding isometrics are defined as holding a weight or position and resisting the urge to move. Examples include holding a weight at 90 degrees, causing the biceps to contract isometrically. Bodyweight exercises, such as forearm planks, are also yielding isometrics as the muscles are working to hold the body in place and resist movement. This type of isometric can be done with or without external load and place less stress on the joints because there is no movement. They can also be used to teach proper positioning by incorporating pauses to create bodily awareness and familiarity with the given position. Yielding isometrics also eliminate the use of momentum to “cheat” a rep by bouncing out of the bottom.
Overcoming isometrics involve trying to move an immoveable object. Unlike yielding isometrics in which a position is being maintained, overcoming isometrics actively try to move an external object that will not move. These contractions should be done with maximum intent and are very taxing on the nervous system. However, this type of isometric recruits the maximum amount of muscle fibers and motor units to try to move the object which teaches the nervous system how to engage as quickly and forcefully as possible. An example of an overcoming isometric would be pressing a barbell into pins while bench pressing or squatting.
Benefits of Isometric Training
One benefit of isometric training is the controlled application of force within a pain-free range of motion. This type of contraction has also been shown to be a reliable means of testing and tracking changes in force production (Oranchuk et al., 2019). Isometric training is especially beneficial in rehabilitative settings where joint movement may be limited or painful.
Isometric training provides a force overload because maximal isometric force is greater than that of a concentric contraction (Oranchuk et al., 2019). Additionally, isometric training can be used in a sport-specific capacity by targeting a specific weak point in a range of motion which can positively transfer to performance and injury prevention by strengthening the given joint angle (McArdle et al., 2015). Isometric training is more effective in maximum force development at a specific angle compared to a dynamic movement and can be used to target a biomechanically disadvantaged position of a specific movement (Lum, 2019).
Another benefit of isometric training is the ability to activate nearly all available motor units (Read, 2020). Motor units are recruited during increased voluntary contraction according to the size of the contraction they produce (according to the size principle), so increasing the time of contraction may allow for more motor unit activation (Milner-Brown et al., 1973).
Other potential benefits include improved tendon and joint health, minimal muscle soreness, increased neural drive and efficiency, increased work capacity, and strength through sticking points (Smith). A study conducted in 2001 found that isometric resistance training caused tendon structures to stiffen and found a correlation between the duration of contraction and tendon stiffness (Kubo et al., 2001).
Limitations of Isometric Training
While isometric training has been shown to increase strength, dynamic strength training is more beneficial and transferrable to dynamic movements (Lum, 2019). Therefore, isometric training should be included as part of a training program that also includes dynamic movements.
Some coaches have been wary of including plyometrics in their resistance training programs citing decreases in coordination and speed of movement or decreased muscle elasticity (Kubo et al., 2017). In 2001, Kubo et al. found that isometrics resulted in increased tendon stiffness, but their study in 2017 found plyometrics to be a superior means of improving performance in stretch-shortening cycle exercises (Kubo et al., 2017).
Another concern of coaches is that isometrics will only be beneficial at the specific joint angle. Verkhoshansky and Siff found that isometric training could produce strength gains in a range of 15 degrees on either side of the training angle, however given the specificity of adaptation at the trained joint angle, improving strength through the entire range of motion may require training at multiple angles which may be impractical and time-consuming (McArdle et al., 2015).
Although isometric training may not result in soreness, it is taxing on the central nervous system (CNS) and will take the nervous system longer to recover than the muscular system (Read, 2020). This fatigue may not be as obvious as muscle fatigue or soreness but may impact performance if followed by other CNS-demanding activities.
Incorporating Isometrics into Training
While isometrics should not make up the majority of a training program, they can be beneficial in motor unit recruitment and improve strength without causing much stress on the joints. While they are very useful in rehabilitative settings to control force production at a given joint angle, isometrics are not as transferrable to dynamic performance as dynamic movements (Lum, 2019). If using isometrics, the current literature suggests performing a contraction of 1-5 seconds at 80-100% maximum voluntary contraction (MVC) for a total of 30-90 seconds per session to increase maximum strength. To increase hypertrophy, the contraction should be performed at 70-75% of MVC for 3-30 seconds for greater than 80-150 seconds per session (Lum, 2019).
- Isometric muscle contractions result in no movement; however, during the contraction the muscle shortens while the tendon lengthens
- Isometric training is effective in increasing strength, but may not be as beneficial to dynamic movement as a dynamic resistance training
- Isometric training is more effective in improving maximum force at a specific angle compared to dynamic training
- Isometric training is effective in rehabilitative settings as force can be controlled in a pain-free range of motion
- Kubo, K., Ishigaki, T., & Ikebukuro, T. (2017). Effects of plyometric and isometric training on muscle and tendon stiffness in vivo. Physiological reports, 5(15), e13374. https://doi.org/10.14814/phy2.13374
- Kubo, K., Kanehisa, H., & Fukunaga, T. (2001). Effects of different duration isometric contractions on tendon elasticity in human quadriceps muscles. The Journal of physiology, 536(Pt 2), 649–655. https://doi.org/10.1111/j.1469-7793.2001.0649c.xd
- Lum D, Barbosa TM. Brief Review: Effects of Isometric Strength Training on Strength and Dynamic Performance. Int J Sports Med. 2019 May;40(6):363-375. doi: 10.1055/a-0863-4539. Epub 2019 Apr 3. PMID: 30943568.
- McArdle, W. D., Katch, F. I., & Katch, V. L. (2015). Chapter 22 Muscular Strength: Training Muscles to Become Stronger. In Exercise physiology: Nutrition, energy, and human performance (pp. 512-513). Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams & Wilkins.
- Milner-Brown, H. S., Stein, R. B., & Yemm, R. (1973). The orderly recruitment of human motor units during voluntary isometric contractions. The Journal of physiology, 230(2), 359–370. https://doi.org/10.1113/jphysiol.1973.sp010192
- North, D. (2020, January 09). 2 Types of Isometrics for Maximal Strength and Muscle. Retrieved September 25, 2020, from https://www.fortitudetraining.ca/articles/2-types-of-isometrics-for-maximal-strength-and-muscle
- Read, A. (2020, June 03). Isometric Training: What It Is and How to Do It Correctly. Retrieved September 25, 2020, from https://breakingmuscle.com/fitness/isometric-training-what-it-is-and-how-to-do-it-correctly
- Smith, J. (n.d.). Isometric Exercises for Athletes: The Complete Guide. Retrieved September 25, 2020, from https://www.just-fly-sports.com/isometric-exercises-for-athletes-the-complete-guide/
- Verkhoshansky, Y., & Siff, M. C. (2009). Isometrics. In Supertraining. Rome, Italy: Verkhoshansky