Most people know that to build strength or prevent any form of muscle wasting, they need to exercise and load their muscles. The question that follows is then: what sort of loading is ideal? Well, there are so many different kinds of exercises for different individuals of different needs, hence, it is important to first point out the various kinds of muscle contraction and how they affect muscle fibres.
A) Isometric contraction
This form of muscle contraction does not involve the change in length of muscle fibres. This is when muscles generate force without the joint needing to move. For example, when pushing a wall or when holding a bottle of water. Isometric contractions are also usually used in maintaining posture and stability. When starting to load a muscle after an injury, strengthening exercises are usually in the form of isometric contraction with lighter resistance as muscles can build strength without moving. It is important that this type of contraction does not involve holding your breath (valsalva maneuver) to avoid a sudden increase in blood pressure which can be dangerous.
B) Isotonic contraction
Isotonic contraction is a general term that involves muscles maintaining constant tension while changes in muscle length occur. Isotonic contraction can be either concentric or eccentric in nature.
C) Concentric contraction
Muscles shorten in length to overcome resistance during concentric contraction. For example, when lifting your leg up to step over a curb, your hip flexor muscles undergo concentric contraction to perform that action. In most movements, muscles that serve as the main movers usually contract concentrically to move the joint. This usually requires higher energy levels as only active elements are producing the force. As compared to eccentric contraction that will be mentioned later, this becomes less efficient.
D) Eccentric contraction
An eccentric contraction results in elongation of muscles when generating force. This can be voluntary or involuntary. A voluntary eccentric contraction would include controlled lowering of the load whereas if it occurs involuntarily, it is most likely that the load is too heavy for the muscle and starts lowering on its own. Eccentric contraction usually involves high force output with low energy cost and tend to be able to manage heavier loads compared to concentric contraction. This is a result of the actions of both active and passive elements. In eccentric contraction, muscle fibres are being deformed by increasing in length and decreasing in diameter. This process requires lower energy levels and causes minimal metabolite accumulation as the fibre fatigues. While eccentric contraction allows greater loading, the risk of damage in the tissues also increases.
While both contractions differ greatly, they tend to work simultaneously in terms of co-contraction. For example, when lifting a heavy load with your arm, if your biceps are your main movers and are contracting concentrically, your triceps would also be working during the movement but in a lengthened state eccentrically. Research has shown that both forms of contractions contribute to hypertrophy which includes an increase in muscle fibre volume. However, eccentric-only strength training causes greater gains in muscle fibre length, while concentric-only strength training leads to greater increases in muscle fibre diameter. Also, single muscle fibres can produce approximately 50% more force while they are lengthening, than when they are shortening, hence, we are usually 25–30% stronger when lowering a weight, than when lifting a weight in the same exercise.
Isometriccontraction (static / holding)
Concentric Contraction ( shortening)
Eccentric contraction(lengthening)
In a nutshell, different ways of performing an exercise affects muscles differently. Regardless of your method of loading, remember to load gradually to prevent any form of injuries.
Reference:
1. Beardsley, C. (2018, October 04). Do eccentric and concentric training produce different types of muscle growth? Retrieved October 02, 2020, from https://medium.com/@SandCResearch/do-eccentric-and-concentric-training-produce-different-types-of-muscle-growth-ec66197b0f5c
2. Ryschon, T. W., Fowler, M. D., Wysong, R. E., Anthony, A., & Balaban, R. S. (1997). Efficiency of human skeletal muscle in vivo: Comparison of isometric, concentric, and eccentric muscle action. Journal of Applied Physiology, 83(3), 867-874. doi:10.1152/jappl.1997.83.3.867
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