Concentric, Eccentric, and Isometric Muscle Contractions

Isometric muscle contraction is a type of static contraction in which muscle length remains constant as tension is increased (“iso” meaning “stable” and “metric” referring to length; Hartmann & Tünnemann, 1995). Muscle fibers shorten, while elastic components of the muscle lengthen by the same amount, resulting in an unchanged muscle length (Hartmann & Tünnemann, 1995). The force of this muscle tension is less than or equal to the load it is exerted against, such that the load does not move, and neither does the individual’s joint angle. Energy is expended, but no work is completed, technically (W = F*d and d = 0; Hartmann & Tünnemann, 1995). So, what matters for isometric contractions is not how much work is performed (e.g., how much weight an individual can lift or how far they can throw an object, etc.), but rather how much muscle tension is produced and how long that tension remains. 

Some examples of exercises based on isometric contraction include planks, Palloff holds, spring ankle holds, and wall sits. Isometric contraction is especially useful for establishing postural control, which is essential for everyone, from elite athletes to the elderly (Mill). Since many isometrics do not require heavy loads or simply use bodyweight, such exercises are suitable for most people, regardless of fitness level. While isometric contraction in resistance training has many benefits, maximal isometric or static strength is not usually applied in most sports or daily motions, making these exercises less useful to some individuals, depending on their fitness needs and goals (Hartmann & Tünnemann, 1995).

Relatedly, you would likely not want to build a training plan entirely composed of isometric exercises. Isometric contraction with high or long-lasting tension may produce an unsafe amount of pressure in the body, especially for individuals with cardiovascular issues. 

In contrast to isometric contractions, in which muscle length does not change as tension does, there are isotonic contractions, during which muscle length changes while tension remains constant (again, “iso” meaning “stable” and “tonic” referring to tension; Hill, 1925, as cited in Padulo et al., 2013). Isotonic muscle contractions are dynamic contractions, meaning that movement occurs–and work is completed, unlike in isometrics–and can be categorized in one of two types: concentric or eccentric (there can also be isometric or static concentric and eccentric contractions, but those are less commonly considered in resistance training). These types of dynamic contractions are distinguished by change in muscle length.

Concentric contractions, or positive work, involve the shortening of muscle due to muscle tension exceeding the load, while eccentric contractions, or negative work, involve the lengthening of muscle to slow down the joint movement while resisting the load (and gravity).

During dynamic concentric contraction, resistance is overcome, meaning that the internal forces are greater than the external forces. Concentric contraction is involved in any lifting movements, such as lifting your glasses to your face or picking up a glass. In terms of resistance training, concentric contraction is a critical component of many exercises, such as the upward phases of bench pressing, squatting, and leg pressing. Some exercises can isolate concentric movements completely, such as barbell deadlifts, cleans, and high pulls in which the bar is dropped at the highest part of the movement.

One advantage of exercises that primarily involve concentric contraction is that they typically result in less muscle soreness than lengthening movements. With concentric-focused exercises, the training load can be increased without needing excessive recovery. In fact, concentric movements, such as cycling and swimming, can be especially beneficial elements of an individual’s recovery.

On the other hand, predominantly concentric exercises tend to seem more difficult than eccentric ones (e.g. walking uphill versus walking downhill), which may deter some individuals from maintaining a training plan. Evidence also suggests that eccentric movements are more effective at building strength than concentric ones. 

During dynamic eccentric contraction, movement still occurs as with concentrics, but this is due to the external forces exceeding the internal forces of muscle tension. Rather than overcoming, eccentric movements resist.

Eccentric contractions are common in many daily movements, such as placing a glass down, sitting down, and walking downhill. Exercises that focus on eccentric contraction include negative pull-ups and the lowering phase of squats, push-ups, and bicep curls. One of the greatest advantages of eccentric contraction is that the muscle stretching has been shown to be an effective way to develop strength and muscle mass, as compared to concentric contraction (Hartmann & Tünnemann, 1995). Almost always, more load can be handled eccentrically versus concentrically. Eccentric contractions also require less metabolic energy than isometric contractions of the same force (Hody et al., 2019). Due to their ability to improve strength and power with a lower energy requirement, eccentric contraction can be especially useful for individuals with reduced aerobic capacity and/or muscular dystrophy related to a medical condition (Hody et al., 2019).

One concern about the use of eccentric contraction in resistance training is its cause of relatively great muscle damage as compared to other exercises (Hody et al., 2019). This increase in muscle damage can cause a range of uncomfortable symptoms, such as delayed-onset muscle soreness (DOMS). Continuing to exercise while still experiencing DOMS may increase the risk of injury, potentially making it difficult for an individual to train with eccentric exercises regularly. 

-Hanna Reuter

References

Hartmann, J., & Tünnemann, H. (1995). Fitness and strength training for all sports: Theory, methods, programs (P. Klavora, Ed.). Sport Books Publisher.

Hill A. V. (1925). Length of muscle, and the heat and tension developed in an isometric contraction. The Journal of physiology, 60(4), 237–263. https://doi.org/10.1113/jphysiol.1925.sp002242

Hody, S., Croisier, J. L., Bury, T., Rogister, B., & Leprince, P. (2019). Eccentric Muscle Contractions: Risks and Benefits. Frontiers in Physiology, 10, 536. https://doi.org/10.3389/fphys.2019.00536

Mills, A. Isometric exercises: Examples, benefits, and applications. National Academy of Sports Medicine. https://blog.nasm.org/isometric-exercises

Padulo, J., Laffaye, G., Chamari, K., & Concu, A. (2013). Concentric and eccentric: muscle contraction or exercise?. Sports health, 5(4), 306. https://doi.org/10.1177/1941738113491386

Roig, M., O'Brien, K., Kirk, G., Murray, R., McKinnon, P., Shadgan, B., & Reid, W. D. (2009). The effects of eccentric versus concentric resistance training on muscle strength and mass in healthy adults: a systematic review with meta-analysis. British Journal of Sports Medicine, 43(8), 556–568. https://doi.org/10.1136/bjsm.2008.051417

Siff, M. What is muscle action? Concentric, eccentric, and isometric muscles. National Academy of Sports Medicine. https://blog.nasm.org/what-is-muscle-action