The common perception among many bodybuilders and lifters throughout the years is that muscle damage is necessary to stimulate muscle growth. It is thought that the muscle fibers need to be temporarily broken down through resistance training in order for them to to be repaired and then grow back bigger and stronger. The meathead in me definitely thought this made perfect sense. I liked to scream to my clients, “We stimulate then we annihilate the muscle!!!” Well, my intentions were robust in that I wanted my clients to succeed and push themselves, but my understanding of the mechanisms to get there were a little misguided.
Before we get any further, let’s nerd out in regard to what causes muscle growth. Muscle growth occurs after long-term strength training in that the protein content of individual muscle fibers increases, therefore producing more volume. This can occur because the individual muscle fibers increase in diameter or length. If the diameter increases, this means the number of myofibrils, or rod-like structures found in muscle cells, increase in parallel. Myofibrils are made up of thick and thin myofilaments. Most well-known are the thin actin filaments and thick myosin filaments because they are responsible for forming cross-bridges which result in muscle force. Further, when the length of a muscle fiber increases, it’s myofibrills also get longer due to the number of sarcomeres increasing in series. Sarcomeres are the long, chain-like contractile units that make up myofibrils.
Muscle hypertrophy can occur within these processes without any damage to the myofibrils being done. The idea that a myofibril or its sarcromeres needs to be damaged in order for new ones to be built or added is invalid. Damage to a muscle fiber happens when the outer wrapping layers of its internal structures are harmed. The myofibrils and cytoskeleton can be most easily damaged, therefore potentially creating a scenario where the composition of a muscle fiber seeps out in the sarcoplasm and ultimately, the bloodstream. This then can be validated by noticing an increase in creatine kinase levels.
To validate the claim that muscle hypertrophy can occur without or with very little muscle damage, let’s look at a study where researchers examined the difference between concentric-only and eccentric-only exercises. Franchi et al. took 12 untrained male subjects and divided them into two groups of either concentric or eccentric resistance training for 10 weeks. The subjects did 3 workouts per week in which they performed 4 sets of 8-10 reps on single leg leg press with 80% of eccentric-only 1RM or concentric-only 1RM. Despite the greater loads used by the eccentric-only group, the resulting muscle volume increases were comparative between the eccentric and concentric lifters (+6% and +8%, respectively). This was an unexpected outcome because eccentric training was well known for causing muscle damage and therefore, believed to be a mechanism for attaining greater muscle hypertrophy. Surprisingly, this did not support that commonly accepted belief.
Isometric training is another area where muscle hypertrophy can occur with little or no muscle damage. For example, Balshaw et al. (2016) did a study where they looked at sustained versus explosive isometric contractions. Forty-eight untrained male subjects were told to work out three times per week for 12 weeks. Each training session, they were required to perform 4 sets of 10 repetitions with unilateral isometric leg extensions. The sustained contraction group performed the repetitions by ramping force to 75% of MVT (Maximum Voluntary Torque) for 1 second and then holding it stable for 3 seconds. They would rest 2 seconds before completing another repetition. The explosive contraction strength training group was directed to execute their repetitions up to greater than or equal to 80% of MVT for 1 second and then to rest 5 seconds before continuing with another one. The results showed that sustained isometric contractions have value in regard to hypertrophy as this particular group increased their total quadriceps volume by 8.1%. This outcome demonstrated, once again, that muscle damage is not necessary for hypertrophy. Instead, the primary mechanism for growth is mechanical tension actively produced by the muscle fibers.
Last, muscle damage does not always cause muscle hypertrophy in that muscle can experience contusions but not experience hypertrophy as a result. Chris Beardsley (2021), in his research review on muscle damage, put it this way:
If damaging a muscle fiber is what causes it to grow in size (by building the muscle fiber back bigger and stronger than it was before), then muscle damage must cause hypertrophy regardless of how that muscle damage was caused. In other words, hypertrophy should occur after transverse mechanical loading that leads to contusion injury, as well as after the longitudinal mechanical loading that is involved in producing eccentric contractions. Evidently, this does not happen.
The intriguing part of the muscle damage and contusion injury relationship is that an anabolic signaling response still occurs during this process. The mTOR pathway is activated to regulate muscle protein synthesis However, in the absence of mechanical tension, there is no muscle growth.
Overall, the application related to the aspect of muscle damage and muscle growth is that the goal should never go to the gym looking to absolutely obliterate each muscle group with no rhyme or reason behind it. The thinking of annihilating and damaging muscles to build them back bigger and stronger is ancient and outdated. It is also inefficient and will do more harm than good. There needs to be intentionality about what you are doing and have a purpose behind the organization of your training program. If you want to know which exercises are most effective for each muscle group, you need to look for them to take you through their primary range of motion, particularly to their end range or lengthened position. This criteria, coupled with sufficient stability of the exercise, can be a great foundation for adequate loading to fit your structure and ultimately, help you reach your muscle building goals.
Sources:
Balshaw, T.G., Massey, G.J., Maden-Wilkinson, T.M., Tillin, N.A., & Folland, J.P. (2016).
“Training-specific functional, neural and hypertrophic adaptations to explosive-vs.
sustained-contraction strength training.” Journal of Applied Physiology, 120(11),
1364-1373.
Beardsley, Chris. (2018, October 10). Does muscle damage cause hypertrophy? Medium.
https://sandcresearch.medium.com/does-muscle-damage-cause-hypertrophy-bf99b652694b
Beardsley, Chris. (2021, August 2). Isometrics. Patreon.
https://www.patreon.com/posts/isometrics-53255620
Beardsley, Chris. (2021, December 20). Muscle damage (hypertrophy). Patreon.
https://www.patreon.com/posts/muscle-damage-48445047
Beardsley, Chris. (2018, June 6). What is muscle growth, and how does it happen?
Medium.
https://sandcresearch.medium.com/what-is-muscle-growth-and-how-does-it-happen-b7f7cd68ee34
Franchi, M.V., Atherton, P.J., Reeves, N.D., Flück, M., Williams, J., Mitchell, W.K., & Narici, M.V.
(2014). Architectural, functional and molecular responses to concentric and eccentric
loading in human skeletal muscle. Acta Physiologica, 210(3), 642-654.