For many years if you wanted to build your body you had to establish what worked via trial and error or rely on hearsay passed down from one generation of meathead to the next.
In recent times, however, there has been a lot of scientific research on the mechanisms and training principles of hypertrophy. This increased level of investigation makes planning training for hypertrophy, based on science, a lot easier than it was just a few years go.
Admittedly, much of it is just telling us what we already know, but it is still of value. To quote Professor John Hawley…
“We often just confirm in the lab, under controlled conditions, what athletes have been doing in training for years.”
This isn’t a criticism of the scientific community. Just the reality. It is still useful though because it takes us from knowing something works to knowing why something works. This is far more powerful!
If you understand why something works you can establish different methods and protocols, based on the underlying scientific principles, to suit your specific goals, training schedule, and equipment availability, to continually create effective training programs.
One key example of the expanding scientific knowledge on hypertrophy is the work of Brad Schoenfeld. He identified the following three mechanisms of hypertrophy in his pioneering research.
- Mechanical tension – external forces put on the muscles by the weights, resulting in muscle contraction – AKA lifting heavy
- Metabolic stress – the accumulation of metabolic by-products, referred to as metabolites (e.g., lactate, hydrogen ions, and inorganic phosphate) during and following resistance exercise, which indirectly mediate cell and muscle swelling – AKA the pump
- Muscle damage – induces a hypertrophic response to repair damage to micro tears accrued from deliberately lifting weights. There is a migration of inflammatory immune cells to help build a bigger muscle. Often felt as muscle soreness – AKA DOMS
If you’ve been looking into training for size then, you are likely well aware of these three mechanisms and how to train to maximize them. We know that we need to train for mechanical tension, metabolic stress and muscle damage.
Or do we?
Recently, there is increasing evidence that training for muscle damage may not be required.
To investigate whether you should be deliberately training for muscle damage a brief discussion of each mechanism and how they apply to hypertrophy is required.
Mechanical tension can be defined as external forces (the weights) acting on the body to produce a joint moment. To resist this the muscles contract which generates tensile force.
Schoenfeld states that…
“The importance of mechanical tension in promoting muscle growth is indisputable.”
Mechanical tension appears to be the most important training related factor in muscle hypertrophy. If you mechanically load the body and then supply your body with the appropriate nutrients and sufficient recovery, muscle growth will occur. In my opinion, 75-80% of your muscle building results will come from mechanical tension. If you focus on progressively lifting more in the big lifts over time then, a lot of your muscle gains will be taken care of.
Practical Tip: The most effective way to create mechanical tension in a muscle is to lift a heavy load in the 4-8 rep range. To create high levels of mechanical tension, use big compound exercises (squats, chins, rows, bench presses etc.) and create a significant muscular stretch. Aim to lower the weight under control through a full range of motion to maximize this. Loads at, or above 80% of 1 rep-max achieve full muscle activation and high levels of muscular tension.
There is overwhelming evidence that metabolic stress significantly contributes to hypertrophy. In gym speak, metabolic stress is better known as the “pump”. It turns out that all the old school bodybuilders were right. Getting a pump does help you to build muscle.
Training with sets of 15-20 reps (perhaps as high as 30 or even 50 with certain exercises) can create a huge amount of metabolic stress. Doing training in these rep ranges will enhance your ability to buffer lactic acid. As a result, your lactate threshold will improve. This results in you being able to tolerate longer times under tension and do a higher volume of work. All great for helping to maximize hypertrophy.
Keeping rest periods short also appears important to maximize the accumulation of metabolic stress. To quote Brad Schoenfeld…
…” metabolic stress diminishes with longer rest periods, and this conceivably could negatively affect anabolic signaling”
The mechanism by which metabolic stress causes increased muscle size is not exactly clear. It appears that it is probably, a consequence of one, or a combination of, the hypoxic state created, increased muscle activation, or cell swelling.
Research shows that metabolic stress increases recruitment of higher-threshold motor units even when lifting light loads. Extremely light loads (e.g., 20-30% 1RM) can cause high activation of fast-twitch fibers provided the set is taken to failure.
Cell swelling via metabolic stress is one explanation of muscle gain. Cell swelling is thought to serve as physiological regulator of cell function. Cell swelling has been shown to positively regulate anabolic and anticatabolic processes. An increase in the hydration status of a cell increases protein synthesis and decreases protein breakdown. It is thought that an increase in cellular hydration causes pressure against the cytoskeleton and cell membrane. This pressure is perceived as a threat to the cell’s integrity. Consequently, anabolic signaling is upregulated. As a result, of this the cells structure increases in size.
The emerging evidence that the slow twitch, type I fibers can substantially contribute to overall muscle size provides further support for the impact of metabolic stress on hypertrophy. It has been shown that low load training maximizes type I hypertrophy. In fact, recent research by Brad Schoenfeld found that low load, high rep sets preferentially hypertrophied the type 1 fibers. This research also concluded that low load training can illicit the same gains in muscle size as more traditional training.
Practical Tip: High rep sets, taken to failure, with relatively short rest periods cause high levels of metabolic stress and cause significant hypertrophy, especially in the slow twitch muscle fibers. Using machine based exercises for this type of training is sensible as it allows you to push to the point of failure safely and without the necessity for a spotter. High rep deadlifts, however, are a recipe for disaster!
Brutally hard weight training will cause damage to a muscle. This damage is referred to as exercise induced muscle damage (EIMD). You have probably felt this damage manifested as DOMS (Delayed Onset Muscle Soreness).
Skeletal muscle tissue has an extraordinary ability for self-regeneration following damage. Muscle damage is associated with increased hypertrophy. Despite this there is very little research directly investigating the causal relationship between EIMD and muscle growth. Because of the association of muscle damage to hypertrophy it has been believed that muscle damage causes hypertrophy.
Researchers have hypothesized that muscle damage strengthens and increases the size of muscles to reduce the risk of injury because of its influence on gene expression. Muscle damage alone has been shown to increase satellite cell proliferation and potentiate the anabolic hormone IGF-1, cause cell swelling, and anabolic signaling via inflammatory factors. Considering these findings, it has been suggested that muscle damage is a direct contributor to muscle hypertrophy.
Consequently, many lifters have dedicated large quantities of training time to trying to maximize muscle damage with very slow and/or heavy eccentric training. This type of training, while effective at causing high levels of damage, is extremely taxing and takes a lot of recovery time. Training in this manner is likely a false economy when your return (muscle gain) on investment (effort, soreness, longer recovery times) is considered. Even worse, it might be completely unnecessary and be robbing you of training time which could have been better spent on mechanical loading or metabolic stress training protocols.
Correlation Does Not Equal Causation
There is no doubt that muscle damage correlates with markers of hypertrophy. However, just because muscle damage and hypertrophy are correlated it does not mean that the muscle damage is causing the increased hypertrophy.
Recent research is starting to question the theory that muscle damage is a driver of hypertrophy. It is possible that muscle damage is more a symptom of the sort of training which causes hypertrophy than a direct driver of hypertrophy. It is best described as a secondary rather than primary mechanism of hypertrophy because it requires mechanical loading to occur. This has led several researchers to suggest that muscle damage acts as an intermediary step between the primary mechanisms of hypertrophy (mechanical loading and metabolic stress) and other secondary mechanisms.
To provide a crude analogy, it might be better to describe muscle damage as a passenger on the hypertrophy ride rather than the driver.
In recent times, an increasing body of evidence has emerged indicating that hypertrophy can occur in the relative absence of muscle damage. Admittedly, much of the research to date has been conducted on relatively untrained individuals so further investigation is required. The evidence is starting to pile up though and calls into question what we thought we knew. The conflicting findings of the existing research caused Brad Schoenfeld to state that…
“Considering that a ceiling effect slows the rate of muscle growth as one gains training experience, it is possible that muscle damage may become an increasingly important factor in promoting hypertrophy in highly trained individuals.”
Those that support the role of muscle damage admit that muscle damage is not a primary mechanism of hypertrophy and it is possible to build muscle in its absence. They argue, however, that the available literature provides a solid theoretical rationale supporting its role in the hypertrophic response. Only time will tell if this theory manifests in practice.
Practical Tip: Specifically training for muscle damage is probably unnecessary to cause hypertrophy. Based on current evidence, it seems that rather than specifically training to cause muscle damage you would be best served training in a manner which emphasizes mechanical tension and metabolic stress. This will inherently cause some muscle damage and likely facilitate the potential benefits of this pathway for growth. As you become more advanced it may be appropriate to place a greater emphasis on training to cause muscle damage. If you are an advanced trainee who has hit a plateau then peridoizing phases specifically targeting muscle damage might be effective. In this case, methods such as heavy eccentrics are a viable option.
So, to conclude, perhaps there are only two real mechanisms for hypertrophy (mechanical tension and metabolic stress). Muscle damage is just be a by-product of these (a very important by-product nonetheless). But significantly, muscle damage occurs, because of, mechanical tension and metabolic stress. Thus, to maximize your training efficiency you should only focus on trying to stimulate these two pathways. It appears that doing so might be all you need to cause hypertrophy and even if muscle damage is more important than the current research indicates, doing so will cause sufficient muscle damage to stimulate growth via this pathway anyway.
This isn’t to say you shouldn’t or will not get sore. If you train hard you will get DOMS occasionally. If you don’t then I would question the effectiveness of your training and/or the amount of effort you’re putting in. It is simply to say that rather than driving hypertrophy, muscle damage might just be a consequence of you doing what is effective – overloading the body via mechanical tension and getting a pump.
The following guidelines will take care of the bulk of your needs by maximizing mechanical tension and metabolic stress:
- Lift loads heavier than 65% 1RM most of the time
- Two-thirds to three-quarters of your training should be in the 6-12 rep range (this provides the most efficient combo of mechanical loading and metabolic stress)
- Most of those should be for sets of 8-10 close to, or to failure
- Occasionally do sets for <5 reps at 80+% of 1RM and high reps sets at lighter than 60% of 1RM
- Go to failure on all sets performed using lighter than 60% 1RM
- Lift with a moderate tempo (about a 2 second eccentric and 1 second concentric)
- Only focus on muscle damage style training if very advanced and you have hit a plateau