Improve Your Performance: Understanding Muscle Fatigue

Muscle Fatigue? As many of you will know, recently I published a questionnaire related to diet and training in people who performed Crossfit. Where almost 1000 people gave their opinion. One of the data that caught my attention is that 2 out of 3 people commented that they did not recover or that they tired during training. This confirmed one of my beliefs: People do not recover well.

Understanding Muscle FatigueUnderstanding Muscle Fatigue

In my opinion, many people try to base their performance on a day-to-day basis. They do not focus on the long-term plans that are what will really allow you to achieve a record or improve your brands. If you try to go 100% every day, you will sooner or later get a bill (ailments, joints, injuries, pinching, muscle overload … etc).

Actually, there is not much information about muscle fatigue in strength athletes. Most of the existing studies talk about muscle fatigue in athletes who train resistance, such as marathons or cycling. However, the muscular fatigue of these people is somewhat difficult to achieve compared to strength sports. In endurance sports, muscle contraction is intermittent, in addition to having a lower load than a person. He performs weights or who does powerlifting training, where the muscle load is much higher.

When Muscle Fatigue Occurs

Leaving aside this factor, we have to take into account that muscle fatigue varies throughout the training, I explain:

The fatigue that occurs in the first series of a workout will be different from the one that occurs in the 4th series of the second or third exercise of a muscle group. This is a point of vital importance, since a person with a bad diet / supplementation, can have the same result to a series in squat than a person with good diet / supplementation.

However, as the number of series (and therefore repetitions) progresses, the yield threshold varies by a large amount.  In other words, where we will truly see if a diet or supplementation works, is with a high training load. .

An example of this is observed when we compare the effects by making a series at 80% of arm curl, compared to 3 series. Observing the following 1 :

Contraction Muscular Fatigue

What we see here are the lactate levels produced during the test. As we can see, the group that made 3 sets of biceps curls (green lines), reached to multiply by 30 the levels of lactate produced. For those who do not know, lactate is produced during training at high intensity, which produces an acidification of the cell environment. A worse release of calcium and therefore prevents muscle contraction, stopping our training.

Substrate During High IntensiUnderstanding Muscle Fatiguety Training

Knowing that the rest between sets is not enough for the muscle to recover from a series of weights (it can be biceps curls that squat or press bench). knowing which substrate the muscle uses during contraction becomes vital importance if we want to improve our training, as this will translate as greater muscle gain.

During a high intensity exercise, we observed that more than 80% of the energy used is produced through glycolysis 4.  In other words, 80% of the energy used arises from glucose ( carbohydrates). In this way, as the body’s need for energy increases, the use of fat as a source of energy is less.

Now many will ask: If at high intensity we basically use carbohydrates. How is it that there are people who train at high intensity on an empty stomach?

There are many reasons. The main one is that the carbohydrates that we eat are stored mainly at the muscular level and in the liver (liver). During the night, or even a 16h fast, the body degrades glycogen to keep our blood glucose levels stable. However, the enzyme responsible for this happening is only found in the liver, not in the muscle. In this way, our reserves are reduced in the liver, but at the muscular level we have them intact. This fact allows the person to do a brief but very intense training, even if they are fasting.

Obviously, people who are sedentary or have little experience in this type of training have a lower metabolic flexibility when compared to a habituated athlete. Which translates into a much faster use of glucose and therefore the feeling of a person.

Hence, I recommend only doing high-intensity training fasting to people who have been training for a long time, or who in their planning put in enough days of HIIT / lactic workouts

How to fight muscle fatigue

To avoid muscle fatigue, we can focus on two routes:

On the one hand, improve the contribution of substrate to the cell. Which will translate as a greater facility to produce energy, improving directly our performance.

On the other, improving the cellular environment, or in other words, eliminating waste products that are produced with training.  That obviously will have a negative influence on our training.

In the first case, the answer is simple. If 80% of the energy we use during high intensity comes from glycogen. Providing carbohydrates during training will facilitate the use of this as an energy source. When there is an intense muscle contraction, the entry of glucose into the cell is much higher (hence a weight routine is always recommended for a diabetic or obese person).

In people with a very low carbohydrate diet, the glucose intake is reduced and the entry of fatty acids is favored. However, this occurs when the training intensity is mild or moderate. When we talk about intense workouts, fatty acids are not enough, so the body secretes more adrenaline and cortisol to increase the release of glucose and therefore maintain performance. In a short training, the body is able to maintain performance without the presence of glucose, but when we talk about a training session of 23-32 series, the thing changes completely.

Muscle ContractionUnderstanding Muscle Fatigue

Muscle contraction facilitates the entry of glucose, where one of the mechanisms is free radicals (ROS), therefore, prevents the intake of antioxidants around the training

The point is that nobody trains with empty glycogen reserves. With a low carbohydrate intake (about 2-3g of carbohydrate / kg body) our glycogen stores can maintain that glucose requirement during a high intensity workout. Only with a ketogenic diet (0.5g of carbohydrate / kg body) is it observed when the body is unable to supply these needs during training.

At this point, we will agree that the ideal would be to look for a tool for those days in which we want to train with low glycogen reserves. The solution is very simple (and cheap): CREATINA

Creatine as a fundamental aid in performance

Any athlete, who wants to train at high intensity or subject the muscle to a large contraction, will benefit from this supplement. I will not go into details of what creatine is, since it is a topic that I have touched in a multitude of articles. What we should know, is that this substance helps provide energy in situations where the requirements soar, allowing training with greater intensity.


Increase your athletic ability. Creatine Monohydrate micronized.


Some studies 6, show how creatine supplementation increases our record in bench press by 6%. Even allows us to increase the number of repetitions by more than 30%.

Another detail to take into account is the water retention produced by creatine. Many athletes reject this supplement in definition since they argue that “tapa”. This is totally false, creatine as such, helps retain intracellular water, which will translate as a greater protection against muscle loss, thus, creatine in “definition” is not counterproductive, if not even beneficial.

As I commented above, the other way by which we can avoid muscle fatigue is by eliminating the waste products that appear during training. In this way, we can use supplements, such as citrulline malate, or through our diet.


Performance enhancer, Great precursor of Nitric Oxide, Dampens the action of lactate, Restrains the threshold of fatigue and Contributes to muscle recovery.


It is in this last point where more has been investigated, since it has been observed that during a high intensity training the medium is acidified (thanks in measure to the lactate). Our body has a series of “buffers” that help regulate the physiological PH through our organs (hence the alkaline diets have no evidence), however. Many researchers have wanted to see the impact of alkalizing substances during the training.

An example of this is observed in athletes of high intensity 7 where the administration of sodium bicarbonate before training delayed the onset of fatigue by 42%.

In my opinion, this protocol with bicarbonate, would make sense if we want to make long-term training and with a very high requirement. In situations in which the duration is very short, the body can “clean” the medium without problems, preventing a slight acidification. Even so, the evidence on the consumption of bicarbonate in this type of training is not very conclusive, since it has been observed that there is no improvement in the performance of those who perform a weight routine 8.


In summary, we can see how not to adjust carbohydrates as we increase the intensity or duration of exercise, can reduce performance both in the short term (fatigue) and in the long term (recovery). In any case, the introduction of creatine in our supplementation can have a very interesting role, having a synergistic effect to di-peptides in the case of people who perform strength routines.

However, this does not mean that we shoot our carbohydrate intake on a daily basis, since training with low reserves in short-term training, can have a beneficial role on glycogen maintenance. In other words, do training with high days in fat, makes our body more efficient when using the little glycogen available, so alternating high fat days with high carbohydrate days (as I describe in my protocol) may be one of the best ways to maintain our performance

  1. Muscle substrate utilization and lactate production. MacDougall JD1, Ray S, Sale DG, McCartney N, Lee P, Garner S.
  2. Fitts RHCellular, molecular, and metabolic basis of muscle fatigue
  3. Lactate inhibits Ca2 + -activated Ca2 + -channel activity from skeletal muscle sarcoplasmic reticulum. Favero TG, Zable AC, Colter D., Abramson
  4. Anaerobic energy release in working muscle during 30 s to 3 min of exhausting bicycling. Medbo JI, Tabata I.
  5. Critical Review Skeletal Muscle Glucose Uptake During Exercise: A Focus on Reactive Oxygen Species and Nitric Oxide Signaling.Troy L. Merry and Glenn K. McConnell
  6. The effect of creatine monohydrate ingestion on anaerobic power indices, muscular strength and body composition. Earnest CP, Snell PG, Rodriguez R, et al.

7.Acid-base balance during repeated bouts of exercise: influence of HCO3. Costill DL, Verstappen F, Kuipers H, et al.

  1. Effect of sodium bicarbonate ingestion on exhaustive resistance exercise performance.WebsterMJ, WebsterMN, Crawford RE, et al.

Hasibul Hasan Jini

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