Increasing muscle mass is an important aspect of training for many sports, especially early in an athlete’s development. Some recent studies, however, have cast some doubt on the legitimacy of earlier research about the importance of hypertrophy, suggesting we might need to examine some of our long-held beliefs in this area.
There’s a very real possibility that increases in muscle size are not particularly well correlated with increases in muscle strength. If true, this could mean that the standard hypertrophy phase of training is less important and may not even need to be programmed in sports where hypertrophy itself is not crucial.
In the early stages of athlete development, a coach typically looks for general training-based improvements, the majority of which are often a function of muscle hypertrophy. As such, there is a natural focus on the best type of training required to drive hypertrophy optimally in athletes.
Over the years, it’s become clear that there are a plethora of ways by which we can stimulate skeletal muscle hypertrophy. We can lift heavy loads (>75% 1RM). We can lift light loads (~30% 1RM), provided we get close to muscle failure. We can lift loads in the middle of this range. We can restrict the blood flow to the muscle, allowing us to promote hypertrophy with lower loads, which is crucial during rehabilitation from an injury where higher loads come with an increased risk of re-injury. We can use different contraction types: isometric, eccentric, and concentric. We can lift quickly or slowly. We can alter the frequency, volume, and intensity of training sessions. Provided that the load is sufficient, we can promote muscle hypertrophy.
To Infinity and Beyond: Hypertrophy Timelines and Plateaus
Typically, we think of muscle hypertrophy as a slow process, which is why we believe that the majority of early improvements in strength and hypertrophy programs are due to neural adaptations. But is this actually the case? This is where a recent review—with the Toy Story-inspired title “Muscle Growth: To Infinity and Beyond?”—comes in. It’s yet another paper born from collaborations with various researchers, including Jeremy Loenneke from the University of Mississippi.
These recent papers have been really interesting because they question the underlying assumptions on which training theory is formed—such as Selye’s General Adaptation Syndrome—and bear similarities to the work of my Prof Doc supervisor, John Kiely. “To Infinity” is a review of studies of adult humans using at least three muscle size measurements over time.
Upper Arm and Chest Muscles. The researchers found eight papers that measured changes in the biceps muscle size at multiple time points. Taken together, it appears that muscle size increases after about four weeks of training. In older females or untrained subjects, though, this may take longer. For the triceps, the amount of time appears to be longer, about six weeks. For the chest, muscle size increases after three to six weeks of training.
Leg Muscles. For the quadriceps, muscle growth is often seen after one to three weeks of training. For the older adults, though, some studies show no increases in muscle size after three months; fortunately this is not a common finding in the research and may be related to the methodology used in those particular studies. The same is true for the hamstrings, with significant increases in size reported by the first week of training.
Plateaus. Plateaus—the point where further improvements in muscle size are not seen—varied between the upper and the lower body. For the upper body, a set point in time could not be determined, in part due to studies’ shorter time periods. For the lower body, further increases in muscle size do not occur after 12 weeks of training. Again, there is a dearth of studies that explore longer-term adaptations in muscle size because it’s hard to get participants to adhere to the exercise guidelines for long periods of time.Increases in muscle size are likely to slow down after twelve weeks, says @craig100m. Click To Tweet
The main findings, then, are that muscle growth plateaus tend to occur after about 12 weeks (although this could be due to methodology) and that skeletal muscle hypertrophy can occur sooner than commonly thought. Both challenge current beliefs and, as such, make this review potentially very important.
Key Variables to Consider
Obviously, we need to examine variations in methodology among the studies here, as the authors point out. As mentioned, many studies simply don’t last for long periods of time, making it difficult to fully understand how muscle hypertrophy may vary over time. There is the possibility—although I’m purely speculating here—that a second, slower, more sustained period of muscle hypertrophy may occur following the initial, rapid, and acute skeletal muscle hypertrophy in reported in shorter studies.
Gender and Age. Additionally, the people participating in the study impact the results. From the research cited in this review, apparently muscle size increases more rapidly in males, potentially due to the greater amount of anabolic hormones. But they also plateau more rapidly when compared to females. It seems age also is a significant modifying factor, with older adults tending to exhibit slower and, in some cases, no improvements in muscle size compared to younger people.
Diet and Emotional State. We also need to consider inter-individual variation, which is a drum I continually like to bang. The diet of the people participating in these studies may limit how much muscle they can grow and how long the process will occur. Are they consuming sufficient protein and calories? Their psycho-emotional state will also impact their adaptations. It’s now well established that non-training stress, such as university exams, can negatively impact adaptations following resistance training. Might these factors come into play here?
Genetics. Genetics is another variable to bear in mind. There are many genes (more precisely, single nucleotide polymorphisms, or SNPs) that can impact both the time course and magnitude of increases in muscle size. It’s a fairly safe assumption that SNPs associated with greater levels of muscle mass may be more prevalent in athletes who are successful in sports and events where increased muscle mass is important. As such, can elite athletes undergo faster levels of muscle growth or extend their muscle growth for longer periods of time without plateauing?
It seems logical that they can. Professional bodybuilders are huge, and it seems unlikely that all this hypertrophy occurred within the first three months of their training. Ok, they’re possibly doped up to their eyeballs, but “natural” bodybuilders (note the quotation marks) are still highly muscular. On a purely anecdotal level, I gained about 7kgs of mass when I transitioned from track to bobsleigh, despite being a well-trained, genetically gifted athlete with a 9-year resistance training background. While I have no doubt this was not all muscle, I know at least some of it was.
So where does this leave us? “To Infinity” is certainly an interesting and very important review. The main take-home is that, despite popular beliefs, skeletal muscle hypertrophy can occur pretty quickly during the first three weeks following the start of a resistance training program. A second consideration is that these increases in muscle size tend to plateau after about twelve weeks. Given the points I made above, we can take this with a pinch of salt.
Nevertheless, it’s certainly true that increases in muscle size are likely to slow down after twelve weeks while increases in strength do not. Anecdotally again, I added 90kgs to my power clean personal best after my first three months of training—although it did take seven years to achieve this. Also, given that the power clean is a highly technical lift, many of these increases in “strength” may have been technical.As athletes develop, we may want to deemphasize or omit muscular #hypertrophy-based training, says @craig100m. Click To Tweet
Given this new information, as an athlete develops, we might wish to place less—or indeed no—emphasis on specific muscular hypertrophy-based training. Instead we could focus on aspects that are more likely to lead to performance enhancements, including exercises with increased transfer to the competitive movement and special strength exercises. By selecting these exercises, coaches may be able to drive further improvements in well-trained athletes that would not occur when following traditional hypertrophy-centered training.