Welcome to part 2 of Understanding Strength. In part 1 we explored the definition of strength, the structure of our muscles and the factors involved in increasing strength. We used this article to highlight the huge potential to increase strength without the need to increase muscle size (hypertrophy).
In this article we will discuss the benefits of increasing muscular size, what conditions and training stimulus can lead to building muscle and how training for hypertrophy differs from training for strength.
What is Hypertrophy?
Hypertrophy is the growth in size of muscle fibres . Referring to part 1 and our muscular physiology, we need to look a little deeper. Each muscle fibre can be further broken down into filaments called myofibrils which are in turn made up of the contractile elements of the cells called Sarcomeres. Each Sarcomere consists of protein strains that pull against one another to produce force. The more protein strains you have in parallel to each other the more force you can produce.
The majority of muscle growth from resistance training come from an increase of sarcomeres and myofibrils added in parallel, within each muscle fibre rather than the actual number of muscle fibres. [1,2,3]
What are the benefits of Hypertrophy?
As we mentioned in part one, muscle size does have a direct correlation to strength, power and sports performance [1,4]. The bigger your muscles the more potential strength you possess, for the reasons mentioned above. However adequate levels of muscle mass are also an important issue from a health standpoint. Low levels are associated with increased risks of several diseases such as: cardiovascular disease , cardio-metabolic risk in adolescents  and type II diabetes in middle aged and older adults .
From an aesthetic approach, muscles are what shape our bodies, providing curves, shape and definition. Most people may still think of big biceps and shoulders when discussing lifting weights, however building your booty follows the same the rules. In all seriousness, if you want to change the shape of your body (or your bum) you must either burn fat or build muscle.
Burning fat will help you look thinner but will not add shape as building muscle in certain places will. The cells within our muscles are the engines that burn the energy that we eat, therefore the more of these cells we have the greater our energy requirement and potential to burn energy through exercise…therefore losing more fat.
Protein Synthesis vs Protein Break down.
For muscle hypertrophy to occur muscle protein synthesis (building) must exceed muscle protein breakdown over a cumulative period .
This is an article focusing on the training factors that induce protein synthesis, so we will not dwell on protein breakdown (recovery or dietary requirements) beyond what I cover here.
Building things requires materials and fuel, be it brick and mortar or proteins, fats and carbohydrates.
Whilst proteins are the building blocks for most of our body’s cells, they are also a source of energy. Therefore, if we can not source enough energy (Kcals) elsewhere, then our bodies can start to break down proteins in the muscles to source energy.
You can only significantly build muscle if you have sufficient calories from various energy sources throughout your day to support your training or activity demands.
Energy sources include those stored within our bodies (i.e. fat stores) and those that we consume through our diet.
Whether you are training for strength or hypertrophy goals you must maintain an energy balance and consume enough protein to support muscle repair and growth.
If you are eating in a calorie deficit for fat loss purposes and do not have sufficient internal energy stores you will find it very difficult to increase muscle mass, and this is an article within itself.
If you have any further questions please do get in touch and book in to speak to our registered dietitian Alejandra about how to best support your training routine.
It does not matter what or how heavy you lift in the gym you will not gain muscle unless your diet is conducive of this.
Training for Hypertrophy
Training to stimulate muscle growth means we must convince the body that what we currently possess is insufficient to perform the task at hand.
There has been a lot of research  into what conditions are needed for hypertrophy to occur. Keeping it simple we can categorise these into two areas:
Mechanical Tension and Metabolic Stress.
Mechanical tension of a muscle (specifically its fibres) created through force generation, a stretch or both is considered essential to muscle growth . More specifically, loading the muscle fibres more than they are used to, increases muscle mass .
Importantly, from a health standpoint, the opposite is also true. Inactivity (a lack of loading) results in muscular shrinkage or atrophy .
To stimulate hypertrophy, we must place individual muscle fibres under maximal mechanical tension. When we place enough tension on the muscle fibres, sensory receptors will signal to GET HELP, starting the process to adapt and create more tissue to resist this tension.
One approach to doing this is lifting an extremely heavy weight that requires close to 100% of our muscle fibres to fire. This means that all our muscle fibres are working under extreme tension and will provide the stimulus that hypertrophy may be needed. In actual terms this would mean selecting a weight that we could only lift for 1-3 repetitions (>85% of 1RM)
Our bodies are smart and building muscle is difficult. Therefore, before trying to build muscle mass our bodies will make what it has more efficient first.
As discussed in Part 1, if we lift a heavier weight than we are used to, our body will get stronger through neuromuscular improvements, increased muscle fibre recruitment, co-ordination and inhibitory responses.
Only once we have exhausted this route of improvement and we are using 100% of what we have, will our bodies build new tissue to allow for further neural adaptation.
Lifting at this intensity could produce hypertrophy in individuals with a lot of strength training experience, who had exhausted neuromuscular improvements. A lesser trained person would get stronger through this sort of training but not any bigger muscles.
How then do we see less trained individuals increase muscle mass or even people who never touch weights?
Many studies [13-15] have shown that lifting maximal weights does not lead to optimal hypertrophy. In fact, lifting weights as low as 30% of your maximum still induce similar levels of Hypertrophy providing you maintain the overall loading . This means you can lift less (apply less force) if you do it more times. By making the muscle work for an extended period of time or reps, we can still apply maximal tension to the individual muscle fibres.
When placing muscle under a maximal load, all of the fibres have to work together to produce a maximal force. This leads to all the individual fibres being under maximal tension at the same time.
Muscle fibres require energy to contract their protein strains and contain a limited supply of their own energy source. This means they are susceptible to fatigue.
When our muscles work repeatedly or over an extended period of time, some muscle fibres' energy stores will deplete, and they will start to fatigue. If the muscles are still required to produce force beyond this point the remaining non-fatigued fibres are placed under a higher relative tension as they have to maintain the same workload split across less fibres.
Now our body has no choice but to increase the fibres' ability to produce force and resist fatigue by building more contractile strains, to produce increased force and to store a larger amount of energy.
Through this process we can still apply maximal mechanical tension to individual muscle fibres without lifting a maximal weight, therefore signalling to the body that more muscle mass may be required.
Although this method may not recruit all of our fibres to the same level, it does provide a very effective stimulus for our second factor in hypertrophy, Metabolic Stress.
2. Metabolic Stress.
If Mechanical tension is the flashing beacon for help on the front line, then metabolic stress is the General who decides what help to send.
Metabolism is a term that is used to describe all chemical reactions involved in maintaining the living state of the cells in the body . This relates to energy production, use and storage as well as cell synthesis and breakdown also known as Anabolism (Synthesis) and Catabolism (breakdown). These processes are controlled by various chemical messenger’s aka hormones.
To build muscle we need to stimulate the release of anabolic hormones to synthesize muscle proteins.
Different hormones are released under different conditions when lifting weights. Testosterone for example releases at higher weights  and repeated sets but does not seem to depend on metabolic stress and fatigue.
Anabolic hormones such as growth hormone have been shown to release at a higher rate  when the muscles are forced to produce energy without oxygen (anaerobically). This occurs when the muscle fibres fatigue, having depleted their own energy stores, faster than we can get oxygen into our system to replenish them.
This can happen when the muscle fibres are placed under tension for an extended period of time, a larger number of repetitions or are not allowed sufficient rest to take in sufficient oxygen.
The more metabolic stress we place our muscles under the more hormones are released into our system to stimulate hypertrophy.
The downside to this is, when we work at an such intensity, and in the absence of oxygen our muscle start to produce lactic acid and hydrogen ions. This is what causes the burning and somewhat painful effect as our muscle start to fatigue (any 400m runners out there will get this).
Putting it all together:
Mechanical tension and metabolic stress work together to produce hypertrophy. Mechanical tension is the signal for help, while the level of metabolic stress dictates the type and quantity of help to send.
A thought to take away:
As every human movement creates some sort of muscular tension, any form of activity could in theory produce some level of hypertrophy, provided there is also sufficient metabolic stress.
Relating all of the above back to exercise, specifically in the gym, Table 1 below summarizes the key differences between setting up sessions for strength goals and for hypertrophy goals.
In short, when we train for Strength we need to focus on producing the maximum force we can each and every repetition. This means minimising fatigue so that we can recruit as many muscle fibres as possible each and every rep.
We should focus on 1-4 big compound movements per session, not isolating any particular muscle group for fear of fatigue.
A simple guide to the weight you should lift is to always leave one repetition in the tank to save fatiguing.
When training for Hypertrophy we want to recruit and fatigue as many muscle fibres as we can by cumulating mechanical tension throughout the session. Depending on your training experience and levels of strength this can be done across a wide spectrum of intensities.
Unlike training for strength we want to induce a level of metabolic response. Targeting single body parts each session, larger sets of repetitions, longer controlled contractions and shorter rest periods can all contribute to increasing over all muscular tension as well as metabolic stress.
It is possible to work across all the different spectrums of intensity when developing hypertrophy. I would always recommend starting your session with sets of a compound movement at a higher % of 1RM (something you can do sets of 4-6 reps with), to promote some neuromuscular strength gains as well as recruiting all available muscle fibres. Then you can work into a more specific session, consisting of higher reps, lower weights and less rest.
There is a reason that relatively heavy repetition ranges between 6-12 are popular for hypertophy. This is because while you can attain the same results from more lighter repetitions (20+), the discomfort that comes with the metabolic fall out of these sets is normally only tolerated by extremely dedicated individuals.
Also note that if training for hypertrophy remember you are focusing on placing tension on the muscle and aiming to fatigue it. Therefore, don't stick rigidly to repetition ranges if they feel easy, make sure you are feeling the effects by the last rep of each set.
How heavy the weight you lift is not key to muscle growth.
Building muscle is a complicated process. While we can create optimal conditions for hypertrophy, all movement can stimulate some sort of muscle growth provided there is a sufficant combination of mechanical tension and metabolic stress.
Creating optimal conditions for muscle growth is very hard work and uncomfortable
Lifting a few weights will not make anyone bigger.
Diet must be carefully planned to support an training at a high enough intensity to promote muscle growth.
Well done for making it this far, hopefully that was not too heavy and was an informative read.
The next article will be a lighter read on a few caveats, considerations and side notes on training to build muscle.
If you have any questions, please comment below.
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