metabolic stress

Metabolic Stress and Hypertrophy Training [Free Gym Routine]

Many people nowadays work hard in the gym to try build some muscle, but the majority don't really know what they are doing. Metabolic stress is one of the main mechanisms driving muscle building. Understanding how it works and how to optimize it will bring you more muscle gains.

In this 5min read that we have prepared for you, you'll be able to learn how to apply different strategies to optimize metabolic stress and muscle hypertrophy


Muscle hypertrophy is mainly caused by three mechanisms: mechanical tension, metabolic stress and muscle damage. Going to the gym and programming your training to follow the specific requirements to induce these mechanisms is what will make you able to optimize your gains and looked jacked next summer.

We have seen before in THIS POST (if you haven't read it I highly recommend it) what was muscle hypertrophy and mechanical tension. But metabolic stress is the other side of the coin. It's also requried to induce and potentiate muscle hypertrophy, and our training program should take this into consideration.

Knowing how metabolic stress works and how to optimize will be crucial for maximizing your gains and progress in the gym.

Mechanisms for muscle hypertrophy


First of all, let's go through the definition. Taken from Conrado et al, 2017, metablic stress is defined as the physiological process that occurs during exercise in response to low energy that leads to metabolite accumulation in muscle cells. These metabolites are mainly lactate , phosphate inorganic, and ions of hydrogen.

The metabolite accumulation induced by resistance training leads to hormonal release, hypoxia, reactive oxygen species production and cell swelling. These phenomena is what will cause the acute oxidative and inflammatory response to training, and future adaptations and muscle hypertrophy.

It is believed that most of their effects come from the hypoxic conditions. Under the absence of oxygen, lactate production is triggered and the accumulation in the cellular matrix is captured by our nervous system to induce hypertrophy.


Protocols inducing metabolic stress are widely used by bodybuilders. In fact, you may have seen many times a huge guy lifting 'low' load (compared to his dimensions), and he still builds muscle mass overtime. Although this may be confused by the use of steroids or other anabolic substances, it opens a gate to ask why low loads are able to induce muscle hypertrophy.

Increased muscle fiber activation

We have different types of fibers depending on the ability of contraction (source). Fast-twitch fibres were believed to be succesfully contrated only under high intensities and loads. But that's not how it is. In fact, low loads and higher reps showed an activation of these fibres (study).

The enhanced activation of muscle fibres happens because of the accumulation of metabolites, mainly ionic hydrogen, inhibiting muscle activation and calling for the recruitment of more muscle fibres.

In other words, what the accumulation of H+ is telling our body is to activate more fibres because the already activated are not able to function at their best to carry out the task required (source).

But there are other causes that may be able to induce these adaptations, these being reactive oxygen species and hypoxia conditions (study). As it usually happens in physiology, enhanced muscle fibre activation is most likely to be caused by a combination of these three factors.

Metabolic Stress Mechanisms

Hormone production

Hormones play an important role in the anabolism and building of new muscle fibres. The buildup of metabolites from an induced metabolic stress may increase the hormonal production post-exercise and induce a greater anabolic response (study). In this study, the group that followed a training method to induce greater metabolic stress showed higher production of growth hormone, epinephrine and norepinephrine.

The hormones that seem to induce the greater anabolic response are growth hormone (GH), insulin-like growth factor 1 (IGF-1) and testosterone. These three hormones are able to activate and potentiate anabolic pathways and inhibit or slow other catabolic pathways, therefore showing a greater anabolic response (study)(study)(study).

Myokine production

Myokines are cytokines produced and released by muscle cells during muscle contraction. They are implicated in the paracrine regulation of muscle mass (source)

There is uncountable different myokines interplaying and inducing muscle hypertrophy. The main myokine associated with regulation of muscle mass is interleukin-6 (IL-6). It potentiates accretion of myonucleus to muscle cells, increasing the number of sarcomeres and consequent muscle mass. (study).

Not only increases anabolic myokines, but metabolic stress may also decrease action of catabolic factors such as myostatin (study). This myokine is widely known for its down-regulation of muscle hypertrophy (study)

Cell swelling

Cell swelling, also known as intracellular hydration. This phenomenon may positively induce muscle hypertrophy by an increase in cell satellite proliferation.

Cell satellites are stem-cells with no metabolic activity. In simple words, they are waiting to be activated to join existent muscle cells and become a metabolically active cell.

If there is a higher intracellular hydration and satellite cell proliferation, it is believed that muscle hypertrophy and anabolic response post-exercise may be greater (study)

However, there is still not enough evidence backing up this novel mechanism, and we are still waiting for more studies and evidence to conclude that this mechanism actually takes place as described.

Influence of Myokines and ROS in metabolic stress

Reactive Oxygen Species Production

These biocompounds, also referred as ROS, are an unstable molecule that contains oxygen and that easily reacts with other molecules in a cell (source). When prolonged over time it's associated with excess aging, inflammation and chronic deterioration. But when induced from exercise, it acts as a signal for potentiating the anabolic response (study).

ROS may induce muscle hypertrophy via different metabolic pathways, such as MAPK (study). Metablic stress, once more, has been shown to increase acute ROS production post-exercise, potentiating anabolic signalling (study)


  • Metabolic stress is the accumulation of metabolites in the muscle cells

  • Metabolites accumulating are mainly lactate, hydrogen ions and phosphate inorganic

  • The consequences of metabolite accumulation is an increased muscle fibre activation and increased production of anabolic hormones, myokines and ROS.


I hope you now know and understand the mechanisms underlying metabolic stress. But how meaningless is the theory if we don't know how to apply it in real life?! That's what we are going to do now. Quick tips to take to the gym and boost your crazy workouts.

Use low loads

This doesn't have to be all the time. In fact, you can also benefit from lifitng high loads to induce mechanical tension. But for metabolic stress, the best you can do is to drop out some weight and go for higher reps, looking for that 'muscle-burning' feeling.

Go at around 40-50% RM, or the load that allows you to perform 12-15 reps to a high intensity degree. You can go beyond 15 reps if you want, but in terms of fatigue is a bit unefficient when doing it all the time.

Separate it from mechanical tension

Both mechanisms act in synergy, but they have different requirements and mechanisms behind. If you want to focus on one, it should separated from the other. For this, I usually follow two protocol:

  1. Do one training focused on metabolic stress and another one on mechanical tension
  2. Do the first part of the session with high loads (mechanical tension) and later start going for higher reps and lower loads (metabolic stres)

Leave it for the end of the session

As I said before, mechanical tension and metabolic stress should go separated if we want to optimize both. Metabolic stress induces fatigue, which could compromise our neuromuscular connections and efficiency of muscle fibre activation. If we boost the accumulation of metabolites before lifting high loads to induce mechanical tension, it is most likely we won't be able to lift as much as we could if we were fresh.

Because of this fact, I highly recommend leaving lower loads and higher reps for the second part of the session. But this is my honest opinion, and of course the main determining factor will always be your adherence to the program.

Lower rest between sets

Lower rest time between sets have been associated with higher metabolite accumulation and hormone production (study)(study).

However, it's important that you feel totally recovered in each set to give your best and build up greater adaptations. Being this said, resting 30s between sets may not be the best protocol when trying to induce muscle hypertrophy and metabolic stress. Mainly because you'll be still so fatigated that intensity during the next set will be far down under your limits. What I recommend here is to take around 1'-1'30" of rest between sets.

Use of isolation exercises

For mechanical tension and general muscle hypertrophy we are highly interested in compound exercise. But for metabolic stress, we should be focusing on isolation exercise with easy techniques.

We are looking for metabolite accumulation and the 'burning' feeling. Just compare a leg press with a squat. Have you ever felt that burning doing a squat? And doing a leg press?

Compound exercises involve many different muscle, and local muscle hypertrophy is not likely to happen. On the other hand, isolation exercise are focused on training one solely muscle. This means that all the stimulus will go where we want it, achieving higher degrees of metabolic stress and local muscle hypertrophy.

Use of advanced techniques

Advanced techniques (dropsets, myoreps, rest pause) are a great tool in some specific cases. However, if you are a beginner, I don't reall recommend you doing them. Better to focus on doing a proper technique and feeling how your muscle is being contracted along the set. Once you have learned the technique and you can really take your sets to failure, then you are ready to do them.

Advanced training techniques may induce higher metabolic stress by removing rest time between sets or/and combining different stimulus. But be careful if you do too many per day. They induce high levels of fatigue, compromising later exercises on the day. So if you are going to do them, put them at the end of your session.

Blood Flow Restriction

This specific protocol has been widely researched for its increased metabolic stress. It's performed by using oclusion bands in your limbs, usually biceps and quads. By doing this, you are basically limiting the pass of oxygen and inducing hypoxia conditions (we said that was on the main causes of metabolic stress). If there's no oxygen available, there will be more metabolites being accumulated, and therefore more metabolic stress.

The 'advantatge' of blood flow restriction training is that it has shown muscle adaptations even when using very low loads (20%RM)(study). Also, with the COVID pandemic, you probably had to train at home during some time. This protocol is a great tool when we don't have high loads available, being able to keep building muscle without needing 100kg for your bench press.

Metabolic Stress


Before getting in the routine itself, I want to say clearly that your training should always be individualized and adapted to your needs, lifestyle and goals. This being said, I created a training routine focused on metabolic stress for you to get an idea on how you could start your next gym routine.

In this excel sheet you'll find four examples of different routines, depending on how many days you are availabel to train.


You simply have to go to the button below, click and you have it!!

Can it get any easier? I really don't think so...


Besides mechanical tension, metabolic stress is the other main mechanism by which we can induce and potentiate muscle hypertrophy. The science behind enabled us to understant why it could do such thing and build more muscle mass. Summaryzing, mechanisms behind metabolic stress are mainly metabolite accumulation, increased fibre activation, hormone and myokine production, and ROS acute response.

In future posts we'll discuss how to optimize and set a training program for both mechanical tension and metabolic stress. Time is gold and we don't like wasting time in the gym, so if we can take one session to focus on both mechanisms, why not?

If you have any doubts leave your comment below in the comments section.

4 thoughts on “Metabolic Stress and Hypertrophy Training [Free Gym Routine]”

  1. Pingback: Guide and Uses of Blood Flow Restriction Training - TrainingbyScience

  2. Pingback: Mechanical Tension and Muscle Hypertrophy [2021] - TrainingbyScience

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  4. Pingback: Home Workout With No Equipment - How to Build Muscle at Home - TBS

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