The requirements and situational needs of athletes typically require a blending of certain muscle actions: isometric, concentric, eccentric, or a coupling of an eccentric-concentric muscle action termed a stretch-shortening cycle.
Most human movement involves this eccentric-concentric coupling or stretch-shortening cycle muscle action, and successful coaches & trainers understand these muscle actions and how to program them into a resistance training program to optimize performance.
In this article we will look specifically at eccentric training i.e. muscle lengthens as it contracts and examine relevant and recent research that explains the applications and benefits of it.
Humans are able to recruit fewer motor units during an eccentric muscle action than a concentric contraction at an absolute load. This demonstrates that the neural efficiency of eccentrics is greater.
Therefore, it has been suggested to maximize neural activation and subsequent strength adaptation during eccentric muscle actions, greater loads are required(1,2).
Some research suggests that participants may be as much as 20-60% stronger with eccentric contractions compared to concentric contractions(3).
Therefore, the eccentric portion of a traditional resistance exercise is underloaded even when the concentric portion is at maximum.
Most of the research demonstrates similar improvements in strength when utilizing supramaximal eccentric muscle actions and standard resistance training utilizing both concentric and eccentric muscle actions. The issue with some of the current research is that despite using supramaximal eccentric training, eccentric strength is rarely assessed(4).
It’s important to note that supramaximal eccentric training has no advantage over standard resistance training with regard to muscle growth.
However, there is some speculation that the mode of contraction (concentric vs. eccentric) may influence the degree of muscle growth. Greater loads can be handled during eccentric compared to concentric contractions; consequently, the concentric strength will determine the absolute loading conditions during conventional resistance exercise that utilizes both types of muscle actions.
For example, the amount of weight used to lower the bar on a biceps curl (an eccentric action of our biceps muscle) is greater than what we can handle to raise the bar on a biceps curl (a concentric action of our biceps muscle).
Therefore, the amount of weight we can use to raise the bar on a biceps curl determines the load used during resistance exercise utilizing both concentric and eccentric contractions.
Although there is speculation of one type of muscle action being preferred over the other, there is no research that shows eccentric only contractions enhance muscle growth with a prolonged training program.
When a muscle needs to overcome resistance, or contract concentrically, its ability to do so may be determined by whether that concentric contraction was preceded by an eccentric muscle action.
Concentric force production in isolation is relatively low compared with concentric contractions that are coupled with an initial eccentric muscle action(5). This pairing is termed the stretch-shortening cycle as defined previously in this article.
Eccentric training is known to enhance this stretch-shortening cycle and cause a more powerful concentric contraction.
An example of this is in jumping where an athlete performs a small initial eccentric contraction by squatting down a little prior to jumping up on a platform or to rebound a ball.
Recent research investigated whether whey protein combined with prolonged eccentric only resistance training demonstrated a superior means in promoting skeletal muscle and tendon size compared to a concentric only and placebo intervention.
This study investigated the effect of 12 weeks of either maximal eccentric or concentric resistance training combined with either a high-leucine whey protein hydrolysate + carbohydrate supplement or carbohydrate only placebo containing the same number of calories, on quadriceps muscle and patellar tendon size(6).
Here is what they found:
These effects were observed to be independent of contraction (eccentric vs concentric) modality indicating no benefit in utilizing eccentric only contractions when trying to enhance muscle size.
Skeletal muscle has an optimum length for producing peak tension. As muscle lengthens beyond its optimal length, tension levels decrease. This descending portion of length/tension is thought to be the region of vulnerability in which muscle strain injuries typically occur.
Data also indicates that athletes who produce peak tension at shorter than normal muscle lengths are more likely to suffer acute muscle strains(7-9).
Research indicates that muscle strain injuries could be reduced if the optimum length is shifted to a longer length.
This can be accomplished by loading the muscle as it stretches and pausing at the end of the movement, like you would do on the lowering portion of a leg curl, a good morning, or at the bottom of a bench press.
Eccentric contractions is the only form of muscle actions that have consistently shown to increase the optimum length of tension development(7,10,11).
The magnitude of the change in length depends on three variables:
Research indicates the greatest improvements utilized protocols with either high volume or high load at long muscle lengths(12).
Achilles tendinosis is a degenerative process due to overuse where there are no inflammatory cells, but changes in the structure of collagen fibers result in an inability of the tendon to adapt to alterations in loading patterns(7,13).
Eccentric strength training has gained popularity in the rehabilitation of Achilles tendinosis.
The eccentric training theory promoted the importance of structural adaptation of the symptomatic tendon, so it could deal with the increased repetitive load and prevent injury(14).
Rehab programs involving eccentric training using loads greater than bodyweight have provided positive outcomes in treating Achilles tendinosis. Results show a decrease in pain along with a higher percentage of patients returning to pre-injury levels of physical activity(15-17).
A minimum of 12 weeks is recommended for eccentric strengthening programs due to the time course of tendon remodeling and regeneration. Three sets of 15 repetitions with a moderate increase in resistance over time appears the most common loading progression(12).
Observations from this research suggest that resistance training enhanced tendon and muscle size following 12 weeks of resistance training. Muscle and tendon size was further enhanced by high-leucine whey protein hydrolysate supplementation compared to supplementation with a carbohydrate only placebo containing and equal amount of calories.
There was no advantage of performing a certain contraction mode (concentric vs eccentric) when trying to enhance muscle and tendon size, so it’s best to utilize both modes (concentric and eccentric) during a structured resistance training program to maximize your strength and muscle building results.
References:
1. Kaneko M, K.P.V., and Aura O., Mechanical efficiency of concentric and eccentric exercises performed with medium to fast contraction rates. Scand J Sports Sci, 1984. 6: p. 15-20.
2. Rodgers, K.L. and R.A. Berger, Motor-unit involvement and tension during maximum, voluntary concentric, eccentric, and isometric contractions of the elbow flexors. Medicine and science in sports, 1974. 6(4): p. 253-9.
3. Hollander, D.B., et al., Maximal eccentric and concentric strength discrepancies between young men and women for dynamic resistance exercise. Journal of strength and conditioning research / National Strength & Conditioning Association, 2007. 21(1): p. 34-40.
4. A., S.J.a.T., Effects of eccentric versus concentric training on thigh muscle strenght and EMG. Int J Sports Med, 2005. 26: p. 45-52.
5. Komi, P., The stretch-shortening cycle in athletic activites. 1985, Schomdorf, Germany: Hofmann.
6. Farup, J., et al., Whey protein hydrolysate augments tendon and muscle hypertrophy independent of resistance exercise contraction mode. Scand J Med Sci Sports, 2014. 24(5): p. 788-98.
7. Brockett, C.L., D.L. Morgan, and U. Proske, Predicting hamstring strain injury in elite athletes. Medicine and science in sports and exercise, 2004. 36(3): p. 379-87.
8. Brooks, J.H., et al., Incidence, risk, and prevention of hamstring muscle injuries in professional rugby union. The American journal of sports medicine, 2006. 34(8): p. 1297-306.
9. Lindstedt, S.L., et al., Do muscles function as adaptable locomotor springs? The Journal of experimental biology, 2002. 205(Pt 15): p. 2211-6.
10. Gabbe, B.J., R. Branson, and K.L. Bennell, A pilot randomised controlled trial of eccentric exercise to prevent hamstring injuries in community-level Australian Football. Journal of science and medicine in sport / Sports Medicine Australia, 2006. 9(1-2): p. 103-9.
11. Proske, U., et al., Identifying athletes at risk of hamstring strains and how to protect them. Clinical and experimental pharmacology & physiology, 2004. 31(8): p. 546-50.
12. Cowell, J.F., Cronin, J. Brughelli M., Eccentric muscle actions and how the strength and conditioning specialist might use them for a variety of purposes. Strength and Conditioning Journal, 2012. 34(3): p. 33-48.
13. Brooks, J.H., et al., Epidemiology of injuries in English professional rugby union: part 1 match injuries. British journal of sports medicine, 2005. 39(10): p. 757-66.
14. Crosier J, F.B., Foidart-Desalle M, Godon B, and Crielaard J-M. , Treatment of recurrent tendinitis by isokinetic eccentric exercises. Isokinet Exerc Sci, 2001. 9: p. 133-141.
15. Arnason, A., et al., Risk factors for injuries in football. The American journal of sports medicine, 2004. 32(1 Suppl): p. 5S-16S.
16. Bowers, E.J., D.L. Morgan, and U. Proske, Damage to the human quadriceps muscle from eccentric exercise and the training effect. Journal of sports sciences, 2004. 22(11-12): p. 1005-14.
17. Brockett, C.L., D.L. Morgan, and U. Proske, Human hamstring muscles adapt to eccentric exercise by changing optimum length. Medicine and science in sports and exercise, 2001. 33(5): p. 783-90.
