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December 09, 2021 3 min read

There are two types of muscle actions when you lift weights, and both of them involve muscle contraction.

They are:

  • Eccentric action: Muscle lengthens while contracting
  • Concentric action: Muscle shortens while contracting   

Although it intuitively feels like and eccentric movement is just lengthening the muscle, it is actually involved contraction or shortening of the fibers. There is some speculation that the mode of contraction (concentric vs. eccentric) may influence the degree of muscle growth.  

We can handle higher forces during eccentric compared to concentric contractions.

Therefore, the concentric strength will determine the absolute loading conditions during conventional weight training that utilizes both types of muscle actions (e.g. barbell or dumbbell exercises). 

For example, the amount of weight used to lower the bar when performing a bench press (an eccentric action of our triceps muscle) is greater than what we can handle to press the bar on a bench press (which is a concentric action of our triceps muscle). 

Therefore, the amount of weight you can press off your chest determines the load used during that particular exercise because you incorporate both concentric and eccentric actions.  

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 during a prolonged training program.  

What about tendons?

It’s clear from research that tendons also respond to intense weight training [3].

However, the influences of contraction mode (concentric vs eccentric) on tendon growth haven’t been directly investigated.  In addition, no research has ever examined if timed nutrient timing with whey protein combined with intense resistance exercise can enhance tendon size.

What does the evidence tell us?

In order to answer these questions, a recent study investigated whether whey protein combined with prolonged eccentric only intense resistance training is more effective at promoting skeletal muscle and tendon size compared to a concentric only and a placebo intervention. 

This study investigated the effect of 12 weeks of either maximal eccentric or concentric resistance exercise combined with either a high-leucine whey protein hydrolysate + carbohydrate supplement or isoenergetic (same # of calories) carbohydrate only placebo, on quadriceps muscle and patellar tendon size [4].       

Main findings

  • The training-induced hypertrophy of both tendon and muscle were further enhanced with a high-leucine whey protein hydrolysate supplement.  A novel finding was that patellar tendon size can be increased with intense resistance exercise combined with whey protein hydrolysate supplementation. There was no further enhancement in muscle or tendon size from the placebo (carbohydrate only) condition. 
  • These effects were observed to be independent of contraction (eccentric vs concentric) modality. This indicates that there is no benefit in utilizing eccentric only contractions when trying to enhance muscle size. This means that you wouldn’t get bigger biceps by just lowering the bar and not raising it while doing biceps curls during your training cycle.


Implications of this research

In support of previous research, nutrient timing with high-leucine whey protein hydrolysate enhances muscle hypertrophy. The synergistic effect of combining high-leucine whey protein hydrolysate and intense weight training on tendon hypertrophy could have important clinical implications since enhancing tendon size and strength may lower the mechanical stress on the tendon during exercise and potentially assist in tendon rehabilitation following injury.   


Observations from this research suggest that intense resistance exercise enhanced tendon and muscle size following 12 weeks of training. Muscle and tendon size was further enhanced by high-leucine whey protein hydrolysate supplementation compared to a placebo (carbohydrate only) supplement with the same number of calories. There was no advantage of performing a certain contraction mode (concentric vs eccentric) when trying to enhance muscle and tendon size.

It’s clear that muscle size can be enhanced no matter if you perform eccentric only or concentric only actions, and it appears that timed protein ingestion is a strong determinant for inducing muscle hypertrophy.



1. Atherton, P.J. and K. Smith, Muscle protein synthesis in response to nutrition and exercise. J Physiol, 2012. 590(Pt 5): p. 1049-57.

2. Hulmi, J.J., C.M. Lockwood, and J.R. Stout, Effect of protein/essential amino acids and resistance training on skeletal muscle hypertrophy: A case for whey protein. Nutr Metab (Lond), 2010. 7: p. 51.

3. Seynnes, O.R., et al., Training-induced changes in structural and mechanical properties of the patellar tendon are related to muscle hypertrophy but not to strength gains. J Appl Physiol (1985), 2009. 107(2): p. 523-30.

4. 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.


Dr. Paul Henning

About Dr. Paul

I'm currently an Army officer on active duty with over 15 years of experience and also run my own health and wellness business. The majority of my career in the military has focused on enhancing Warfighter health and performance. I am passionate about helping people enhance all aspects of their lives through health and wellness. Learn more about me