The muscle damage hypothesis
Ask anyone with a rudimentary understanding of muscle growth if muscle damage plays an integral role in building muscle and they will probably answer with a resounding yes.
Unfortunately, that notion is not as concrete as many assume. Research has shown that muscle damage often decreases as you become more trained, due to something called the “repeated bout effect.”
Exercise is a stressor that drives the body to adapt. When first beginning exercise this stress can often be too much for body to handle, resulting in many different responses, one of which is damage to muscle fibers.
Over time, the body adapts to this stress in one-way or another, resulting in less actual damage to the muscle itself. (Exercise variation may cause damage, but not necessarily growth – more on that later).
Researchers out of the University of Sao Paolo in Brazil wanted to increase the knowledge base of how muscle damage relates to muscle growth while attempting to gain a better understanding of how resistance training itself leads to growth.
The Study - Methods
Researchers used 10 individuals whom had experience with lower body resistance training in the past but where “untrained” for at least 6 months prior to the study.
Subjects were exposed to both leg press and leg extension exercises, for 3 sets of 9-12 repetitions until failure. Weight was adjusted each set to ensure adequate reps.
Subjects performed these exercises, twice per week for a total of 10 weeks (19 sessions).
Muscle biopsies were taken on 3 separate occasions:
Also, blood samples were taken to assess creatine kinase levels before and 48 hours after sessions; a marker of muscle damage.
Cross Sectional Area
When viewing the data, it was clear that at the beginning of the study, protein synthetic responses to training was significantly higher than when compared to later in the study. However, muscle growth was only seen at the end of the study.
That seems to be in stark contrast to the theory that protein synthesis is a main driver of how muscle actually grows.
To better explain, let me show you how this could happen.
When an un-experienced person begins training, muscle damage can be very high. One of the ways that muscle damage actually occurs is something called “z-line streaming.”
In the muscle you have something called sarcomeres. These contain filaments that actually allow the muscle to contract. There are many sarcomeres in the muscle that are separated by these z-lines. Think of them as a wall or divider.
For un-experienced trainees, these Z-lines can become destroyed due to these sarcomeres being “stretched” resulting in something called Z line streaming. You can see in the image below, the difference between undamaged and damage muscle (left).
The muscle damage / protein synthesis relationship
As it turns out, over time this Z-Streaming begins to reduce. This is the repeated bout effect. Over time of repeating exercises in similar rep and weight ranges, this amount of Z-line streaming begins to no longer occur.
The interesting thing is that we are beginning to believe that the initial increase in muscle protein synthesis that is seen with un-experienced trainees (like in this study) is actually to help repair this muscle damage, and not necessarily to grow muscle.
So where does this leave us?
Based on the findings, we can begin to understand a couple things:
Why this should matter to you
Many people like to train very hard in the hopes that they will get sore or that damaging the muscle is 100% necessary to grow.
Based on this research, muscle damage probably gets less and less over time with similar exercises. Further, when you do insight muscle damage, much of your protein synthetic response is being used for repair, not growth.
While progressive overload is essential, that doesn’t mean that you need to train to the point of damaging your muscle. In fact, doing so is probably ill advised for a number of different reasons such as extra fatigue, inability to train due to debilitating soreness and a reduction in force output.
Training to the point of stimulating an adaptation, while not doing so much as to cause damage, is probably essential in order to stimulate protein synthesis for growth specifically rather than simply repair.
Lastly, due to the repeated bout effect, using similar rep ranges, exercise and weight can reduce the growth response in addition to muscle damage. As such, varying exercises, weight, reps or all three can help keep your training fresh, while also stimulating growth responses. Initially you may have some muscle damage and additional soreness, but this will be reduced with time.
Damas, F., Phillips, S. M., Libardi, C. A., Vechin, F. C., Lixandrão, M. E., Jannig, P. R., ... & Tricoli, V. (2016). Resistance training‐induced changes in integrated myofibrillar protein synthesis are related to hypertrophy only after attenuation of muscle damage. The Journal of physiology, 594(18), 5209-5222.