Eccentric muscle contractions happen when the muscle lengthens under tension. By contrast, concentric contractions happen when the muscle shortens under tension. Eccentric contractions perform negative work through ‘braking’ and elastic storage of energy 1. During walking, active muscles shorten via their contractile proteins, myosin and actin, but ‘just as often, resist lengthening’ 2. Eccentric work through decelerating, i.e. ‘braking’ is equally important as concentric muscle work 3. During walking, eccentrically contracting muscles are able to convert kinetic energy into elastic strain energy of tendons and aponeuroses which is ‘regained during limb support in locomotion’. 2,4 Two interesting properties of eccentric contractions or ‘active lengthening’, is that the energy requirement for force production is less, compared to active shortening during concentric contractions. This is known as the ‘negative Fenn effect’ 5,6. Furthermore, energy efficiency is increased because maximum muscle force is greater in eccentric compared to concentric contractions 3,7. During an active stretch, human muscle fibers produce 1.4 to 2.1 times more tension (force per cross-sectional area) 8 depending on the type of fiber. Eccentric exercises (EEX) have been well known in resistance training (RT) and have also found their way into injury prevention and rehabilitation and are starting to find their place in (chronic) disease management.
Eccentric exercises for hypertrophy and strength
It has been a long-held belief that high load (heavy) exercises are more effective in increasing strength and muscle size 9. Indeed, superior strength gains are achieved with heavy-load training, but substantial strength increases can also be attained with low-load training 10. However, the key driver for muscle growth is the level of effort with ‘both heavy and light loads .. equally effective in promoting muscle growth.’11. Superior hypertrophic changes – in both untrained and resistance-trained individuals – occur when RT is carried out with a (very) high level of effort 10,12. Contrary to popular belief, it is not necessary to achieve muscle (or repetition) failure 13. The level of effort determines the degree of motor unit recruitment and thus the amount of force produced by single muscle fibers. These fibers undergo mechanical tension and metabolic stress, both important factors for muscle growth and strength gains.
The eccentric one-repetition-max (1-RM) is around 30% higher compared with a concentric 1-RM as (human) muscle tissue is 20-35% more strong during the eccentric phase compared to the concentric phase 14,15. The load or resistance in conventional RT is typically the same during the concentric and eccentric phase and usually based on a percentage of the concentric 1-RM. Therefore, in conventional RT, level of effort and concomitant degree of motor unit recruitment is lower in the eccentric phase of an exercise movement compared with the concentric phase. Fibers from high-threshold motor units which are not being recruited (due to lower degree of motor unit recruitment) will not undergo potentially hypertrophic changes as these fibers do not experience mechanical tension and metabolic stress. Therefore, it has been reasoned that eccentric-only training – compared to concentric-only training – and accentuated eccentric loading (AEL) can induce larger hypertrophic (and strength) changes. A review and meta-analysis reported a (nonstatistical) small benefit on changes in muscle size in eccentric-only versus concentric-only RT 16. Research demonstrated that AEL, i.e. higher loads during the eccentric phase of the movement, e.g. 30-50% of the concentric 1-RM load added to the eccentric phase, did not result in larger muscle volume in RT-trained young men 17,18, but did increase ‘fatigue resistance (number of repetitions to failure) compared to conventional RT. The subjects also had greater voluntary muscle activation as measured by EMG activity. Also, AEL training resulted in larger gains in both eccentric and isometric strength compared to conventional RT 18. In untrained young men researchers came to similar results19. These results suggest no difference in muscle growth between 8-10 weeks of conventional RT or AEL or eccentric-only training. Interestingly, according to a review on AEL and in contrast to these acute AEL responses (duration AEL of less than 12 weeks), research in chronic AEL, i.e. AEL lasting longer than 12 weeks, seems to suggest that AEL increases muscle cross-sectional area (CSA) at the distal portion of the muscle (as well as fascicle length and hypertrophy of the distal portions of muscles in eccentric-only training) whereas concentric exercise increases muscle belly CSA (as well as pennation angle and larger hypertrophy mid-muscle in concentriconly training). Results in several studies indicate that chronic AEL and/or eccentric-only training may enhance contraction velocity, strength and hypertrophy to a greater extent than conventional RT 20.
- Strength is best achieved with heavy-load training (>60%)
- Hypertrophy is best achieved when sets are performed to volitional fatigue, independent of load (i.e. >60% or <60% of 1-RM)
- No greater benefits for eccentric-only or AEL for lessthan 10 weeks of RT
- Research suggests that chronic (> 10 weeks training) AEL, eccentric- or concentric-only training induce specific adaptations in muscle tissue
- Chronic AEL and eccentric-only may result in superior hypertrophy, strength and speed
Authors and Affiliations:
By Michiel R.M. Twiss, @physiotwiss
Michiel R.M. Twiss is a Dutch physiotherapist in Buchs SG, Switzerland. He has a keen interest in systematic reviews and meta-analyses in gerontology research and specifically strength and conditioning training in old age. He holds a private practice in Buchs, Sankt Gallen, Switzerland.
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- Eccentric Exercise: Physiology and application in sport and rehabilitation, 1st Edition (Hardback) – Routledge. Routledge.com https://www.routledge.com/Eccentric-Exercise-Physiology-and-application-in-sport-and-rehabilitation/Hoppeler/p/book/9780415690508.
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