When a muscle contracts the length can either change or stay the same. If the muscle length remains the same it is known as an isometric contraction, an example exercise is holding the plank. Whereas if the muscle length changes it is known as an isotonic contraction, an example exercise is performing a bicep curl. An isotonic contraction involves two phases; the shortening phase (i.e. the up phase of a bicep curl) which is called a concentric contraction and the second phase is the lengthening phase which is known as an eccentric contraction (i.e. the lowering phase of a bicep curl).
Research has shown that eccentric training, where the muscle lengthens, can be more beneficial for optimal performance training. With eccentric training, muscles are able to create more for less work. This means that eccentric contractions use less energy and actually absorb energy that will be used as heat or elastic recoil for the next movement.
While energy costs remain low, the degree of force is very high. This leads to muscles that respond with significant increases in muscle strength, size and power. Research has shown that increases in both strength and muscle fiber are higher in eccentric training than in traditional concentric training. In old age, loss of strength and muscle mass is commonplace. Eccentric training enables the elderly, and those with the same problems, the ability to train muscle groups and increase strength and resiliency with low-energy exercise.
Performing eccentric dominant contractions have been shown to also assist in injury prevention. This is particularly true for hamstring injuries. By conditioning the muscle eccentrically they will become stronger at longer lengths and therefore decrease the risk of hamstring injuries. Some great example exercises are deadlifts and back extensions.
In conclusion eccentric contractions use less energy, even though they create more force than concentric actions. Performing these types of muscle contractions can have significant benefits in decreasing the risk of injuries. Furthermore due to significant increases in strength and power seen in eccentric contractions it is optimal for improvements in training.
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