Fatigue in different types of efforts can be characterized and measured in different ways depending on the duration and intensity of the efforts. In this entry we analyze the various factors that cause fatigue according to the duration of the effort.

In this series of articles we deal with some of the most important concepts of strength training, collecting notes from the recently published book Strength, Speed ​​and Physical and Sports Performance written by renowned researchers Juan José González Badillo and Juan Ribas Serna.

SUMMARY

• In short efforts the performance is highly dependent on the oxygen consumption capacity of the subject (VO 2max)
• In efforts of up to 30 minutes, the lactate threshold point (anaerobic) is decisive.
• In efforts that last more than an hour, fatigue is highly associated with the depletion of muscle glycogen stores.
• A good metabolic indicator of stress caused by exertion is the blood lactate concentration.
• The loss of execution speed is a faithful reflection of the fatigue state of the subject.

short duration efforts

From efforts as short as 100 meters of sprint (10-12 s) there are already losses of speed (decrease in performance) involuntarily, which is an indicator that during the test there is a phase in which it manifests itself. fatigue as a loss of capacity to produce force in the unit of time.

The causes of fatigue in this type of effort are multiple, but of all of them the decrease in availability is probably the most important. Considerable increases in the plasmatic concentration of hypoxanthine, ammonia and uric acid have been observed in this type of effort. These results indicate that there have been difficulties in synthesizing ATP via ADP + CP and that energy production has been resorted to through the ADP + ADP = ATP + AMP reaction. This indicates that you there has been significant metabolic stress in the muscle cell, which can be associated with injury to said cell, and the loss of purines that can negatively influence the phosphagen reserves of the muscle, which has repercussions in the reduction of the muscle’s capacity to produce energy quickly in the following days.

Metabolic stress on the muscle cell influences the muscle’s ability to produce energy on successive days.

It does not appear that acidosis is a determining factor in these cases. In addition to what has been indicated, this fatigue is associated with a decrease in the activation of motor units in the excitation-activation process and an increase in Pi and ADP. In other short efforts such as throws, jumps, Olympic lifts and the like, fatigue is related to the same mechanisms, but with less influence from metabolic factors. If the efforts are somewhat longer (15-40 s), the participation of the phosphagen pathway to provide energy is coupled in a very important and decisive way with the ability to rapidly provide energy through the anaerobic glycolytic pathway. For this reason, in this type of effort, all the factors responsible for fatigue in the previous type of effort are present and increased, plus those derived from a drop in pH.

Therefore, it is likely that the concentration of metabolites, the alteration of calcium transport (excessive accumulation of myoplasmic calcium), the accumulation of Pi and the excess of extracellular potassium are also present as responsible for fatigue in this type of effort. The same causes of fatigue occur in efforts that last about a minute, but the fundamental difference is in a greater influence of the pH reduction, which practically reaches its maximum in efforts of this duration. High acidity, in addition to the previously described effects on the cross-bridge cycle, acts on cionide channels (which mainly govern membrane excitability), depolarizing the membrane and leading to the inactivation of sodium channels, essential for the generation of action potentials, at the end of the effort.

In this situation, the hydrogen ions themselves act by priming the working speed of the mitochondria, shifting the burden of maintaining the energy supply to the mitochondrial aerobic pathway. Given the low rate of ATP generation from the mitochondria compared to the anaerobic glycolytic pathway, the rate is clearly reduced at the end of the effort. These same causes could be applied to efforts that last up to three minutes, with a greater dependence on the ability to provide energy aerobically.

long-lasting efforts

When the efforts last between 5 and 10 minutes, performance is highly dependent on the subject’s oxygen consumption capacity (VO 2max), but there is also significant phosphagen depletion and high acidity. Therefore, in this type of effort, fatigue may depend in part on the processes related to phosphagen depletion, and to a large extent on the ability to produce energy aerobically (power and maximum aerobic capacity), but also on the power and anaerobic capacity and problems related to the reduction of pH.

In efforts of up to 30 minutes, the lactate threshold point (anaerobic) is decisive.

In efforts that last up to approximately 30 minutes, the aerobic power of the subject is still very important, but the speed at the lactate threshold point (called anaerobic) seems to be more decisive. Therefore, fatigue may be closely related to the ability to capture, transport, and use oxygen for the oxidation of glucose by the aerobic route, but especially to speed or power in conditions of suprathreshold lactatemia. In the final sprint of some tests, the depletion of muscle CP reserves or excessive muscle acidity may influence. Another factor that may be related to fatigue is high body temperature, although this would be more relevant after one hour of effort.

In efforts that last more than an hour, fatigue is highly associated with the depletion of muscle glycogen stores., and, therefore, although all the factors indicated for the previous efforts are present to some extent, the availability of glycogen stores could be a factor causing the fatigue of this exercise. In addition, glycogen depletion is associated with fatigue as it may cause decreased calcium release from the sarcoplasmic reticulum and consequent effect on muscle activation, although the link to low glycogen is uncertain. with failure of calcium release (Allen et al., 2008).

In efforts that last more than an hour, fatigue is related to the depletion of glycogen stores.

Other factors such as an excess of ammonium, an increase in muscle Mg concentration, an excessive increase in body temperature or an insufficient capacity to use lipids to produce energy could also be the cause of fatigue in this type of effort.

Efforts to overcome external loads

As we have indicated when discussing the concept of fatigue, in addition to a decrease in force production, another aspect of muscle performance such as speed of shortening is also an indicator of fatigue (Allen et al., 2008; Edman, 1992). If we take into account that the loss of speed before the same load is a direct consequence of the reduction of the force applied to said load, we must admit that the loss of speed is a faithful reflection of the state of fatigue of the subject.

It is evident that when a subject is visually perceived to be “tired” (fatigued), we detect it by the loss of execution speed, whatever the activity the subject performs: displacing an external load or displacing his own body. Speed ​​also has an advantage over force as an indicator and quantifier of fatigue, and that is that it can be measured more easily and accurately than force, and also in competition and training gestures or actions.

The loss of speed in efforts to overcome external loads is a faithful reflection of the state of fatigue.

Therefore, when a gesture has to be performed at the maximum speed possible, knowledge of the loss of speed may be the best procedure to determine the degree of fatigue in which the subject is found during and after the effort. These reasonings lead us to propose that when training is carried out through the displacement of external loads, the loss of speed in the series is an accurate indicator of the fatigue (and the load) that carrying out the exercise supposes for the subject.

Given this premise, the validation of the loss of speed in the series as an indicator of fatigue is achieved if there is a high relationship between this loss of speed during and at the end of the effort, and the reduction in contractile capacity, which could be quantified. also through the loss of speed with respect to the speed reached when displacing the same load prior to the fatiguing effort. Specifically, as mechanical indicators we can use two exercises:

1) the loss of speed before the same load, which in our case is the maximum load that can be moved approximately 1 m*s-1, and

2) the loss of jump height (which is really also a loss of speed) after the effort.

To this main validation, the relationship with indicators of the degree of stress caused by the effort could be added, which could contribute to a better knowledge of the type of effort made and the possibility of replacing the measure of certain metabolites by the loss of speed (concurrent validity ). As metabolic indicators we consider the changes in the concentration of lactate and ammonium. Indeed, a good metabolic indicator of stress caused by exertion is the concentration of lactate in the blood.

Lactate production is related to the difference between the motor command of the central nervous system and the actual mechanical execution of the muscle. The greater the difference between what is commanded by the central nervous system and what is executed by the muscle, the greater the lactate production will be. In addition, lactate production, far from being detrimental to the functioning of muscle fibers, is actually an essential component to improve muscle fiber excitability by blocking chloride channels (Ribas, 2010; González-Badillo and Ribas, 2002). As shown later, the relationship between the lactate concentration and the loss of speed of movements executed at maximum speed is excellent, such that the greater the loss of speed, the greater the production of lactate by the muscle fibers (Sánchez -Medina and González-Badillo, 2011; Rodríguez-Rosell et al., 2018).

Fatigue is a complex and multifactorial process that affects performance. Neither the way fatigue occurs nor the hierarchy of factors that cause it in any of the production modalities is still not completely known.

In this series of articles we deal with some of the most important concepts of strength training, collecting notes from the recently published book Strength, Speed ​​and Physical and Sports Performance written by renowned researchers Juan José González Badillo and Juan Ribas Serna.

Summary

• Fatigue can be defined as any situation in which the value of muscle activation is inevitably and involuntarily decreased.
• The feeling of fatigue increases faster than the amount of work done in the unit of time to protect the body from possible injury.
• Without fatigue there would be no possibility of improving performance, because the adaptation processes would not take place. The challenge is to reach the degree of fatigue with which to obtain the best results.

Observations related to fatigue range from the will to perform specific acts to changes in the behavior of intracellular proteins. In general, it could be conceptualized as the inability to continue a task at a stipulated level (usually stipulated by the central nervous system).

The difficulty in understanding the production of fatigue derives from numerous factors: places where it can originate, the different methods that must be used to measure the effects of fatigue, the difficulty in extrapolating in vitro results to situations in normal or physiological conditions or difficulty in integrating all the results.

The feeling of fatigue increases faster than the amount of work done in the unit of time (Mosso, 1904), thus protecting our body from possible injuries of lesser or greater severity.

Thus, fatigue is largely an emotion, part of a complex regulatory system that keeps us from taking risks. In extreme conditions, in which the will ignores this emotional indicator, tissue damage occurs and, in very extreme cases, death.

We have examples of this every day in endurance competitions such as the marathon, which precisely commemorates the death of a soldier (Philipides) who, ignoring his fatigue, insisted on continuing to run until he exceeded the limits of the regulation systems and died after deliver important news.

The feeling of fatigue increases faster than the amount of work done in the unit of time

Our brain uses fatigue symptoms as a key regulator to ensure that exercise is stopped before bodily harm is done. However, among the symptoms of fatigue, the “sense of effort” stands out.

This feeling of exertion increases as more repetitions of a task are performed, until just one more repetition is an extreme effort. This sensation of effort is proportional to the difference between the task commanded by the nervous system and the real difficulty in carrying it out.

For its part, the difficulty in carrying out a task will depend on many mechanical, physiological and biochemical variables at different levels from muscle cells to the organs in charge of general homeostasis. This sensation of effort is modulated to a certain degree by the will of the athlete.

For individuals with the same level of training and performance, the differences between winners and losers sometimes only includes the mental decision, the will, different in the winners.

Fatigue is synonymous with a wide range of physiological conditions, from pathology and general health to sport and exercise (Wilkinson et. al., 2010). Fatigue in sport and physical activity in humans has usually been described in subjective terms and has been measured by the acute reduction in physical performance during and after exertion.

The consequence of exercise-induced fatigue is the inability to maintain a certain value of applied force, which results in loss of speed and power of execution in dynamic actions. It is considered that there are three factors through which fatigue is expressed in mammalian muscle:

1) reduction in the number of active cross bridges, which affects the loss of isometric strength,

2) reduction of the maximum speed of muscular shortening in activations without opposition to the shortening (absolute speed) and,

3) increase in the curvature of the force-velocity curve that affects the reduction of maximum power (Jones, 2019).

For individuals with the same level of training and performance, the differences between winners and losers sometimes only includes the mental decision, the will, different in the winners.

Therefore, fatigue is quantified by the loss of strength, muscle shortening velocity, and force production in unit time (RFD). Loss of static or isometric strength depends on reducing the number of active cross bridges (pc) and the force exerted by each pc.

The loss of speed and RFD depends on the decrease in the rate of formation and activation of pc. As a consequence of the loss of strength and speed, power will decrease. A phenomenon associated with the above that affects them is the deactivation rate of the pc, which is a determining factor in the relaxation time and in the rate of formation of the pc themselves.

However, the physiological mechanisms prior to the final consequences that we have just indicated, and that underlie fatigue, give rise to different proposals and are still the objective of numerous investigations.

The causes of fatigue may be related both to the oxygen transport capacity and the available metabolic substrates, as well as to the cerebral causes of the contractile fibers of skeletal muscle and the muscle activation mechanisms themselves. Therefore, the decrease in force / speed associated with fatigue can originate in any process at different levels, from the brain order to the formation of actin-myosin cross-bridges (Debold, 2012).

But in practice, to study fatigue it is necessary to specify the task and the production mechanism. Otherwise it would be, if not impossible, if not very complex, to study all the elements that can intervene in the generation of fatigue simultaneously. For example, the speed and extent with which fatigue occurs depends largely on the type and intensity of the physical activity performed (Fitts, 1994).

But the main purpose is not to discuss the different opinions regarding the causes of fatigue or the methodologies used to detect and measure them, but to expose the most accepted ideas, although also discussed, and that have a practical application for physical and sports performance. .

fatigue concept

Fatigue can be defined as any situation in which the value of muscle activation is inevitably and involuntarily decreased. (loss of force, production of force in the unit of time or RFD, speed, power,) with respect to another value reached in a time immediately prior to the effort. In this sense, Macintosh and Rassier (2002) define it as a contractile response that is less than what is expected for a given stimulation. It can also be expressed as the inability to maintain a certain intensity (speed or power) over time.

And it can also be defined and differentiated by the recovery time after the effort. Fatigue can begin in the first moments after the muscle activation command is initiated or from the first effort in a series of repeated efforts, without the need for muscle failure or the inability to maintain a certain intensity.

Therefore, the most relevant and appropriate way to define fatigue is to consider it as the magnitude and time of loss of performance in whatever the situation may be in relation to what is programmed or intended by the will or the CNS. From these definitions the need to know the value of contraction or performance prior to the measurement of fatigue can be deduced. Therefore, the conditions that must be met for us to be in a position to quantify fatigue are that there is loss of performance, that this loss does not occur voluntarily, and that there is a previous value that is taken as a reference.

In the Essential Dictionary of Sciences, fatigue is defined as the deterioration of the performance of a living being… over time. It is associated with a feeling of tiredness, lack of concentration, slowness and the appearance of simple errors. But a muscular activation, in addition to fatigue, can also produce potentiation, which is an opposite response to fatigue, whereby an increase in muscular performance is produced as a consequence of an immediately previous activation. Therefore, fatigue and potentiation can coexist.

The possible existence of two opposite effects in the same muscle activation makes it difficult to determine the degree of fatigue. In this situation, great care must be taken in the interpretation of the data referring to a “before” and an “after”: the result can be a mixture of fatigue and potentiation.

However, potentiation has a limited duration while fatigue may persist until functional incapacity. Even when the post-effort performance is greater than the initial response, there is no guarantee that the mechanisms associated with fatigue are not present (Macintosh and Rassier, 2002).

a muscular activation, in addition to fatigue, can also produce potentiation, which is an opposite response to fatigue, whereby an increase in muscular performance is produced as a consequence of an immediately previous activation.

In this way, we can find situations in which the response is greater than that which occurs in the resting state (potentiation), but probably less than what could be expected if there were no fatigue. In fact, In training practice, it is observed that when the efforts are not made until exhaustion, the response after the effort (for example, measured through the vertical jump) in some cases is superior to that offered before it., even having previously warmed up to reach maximum initial performance.

That is, the effort has meant a “better warm-up” than the one previously made. But there are also situations in which the contractile response is less than before the effort. If this is the case, it can be concluded that fatigue exists with certainty, but its quantification is not easy, because there are also potentiation mechanisms simultaneously. This means that if the potentiation mechanisms were not present, the magnitude of the fatigue measured would be greater.

The term fatigue should not be identified with situations in which one becomes exhausted, with a forced interruption of the activity. Muscle fatigue begins immediately after starting physical activity and includes changes in physiological processes that reduce muscle strength (Enoka, 2002).

fatigue and training

Fatigue must be considered as a component of training, and therefore, it must also be considered as an essential character of the stimulus necessary to ignite the adaptation processes of training. The degree of fatigue (subjective, observed by the coach, or measured through the relevant means) is the reference point to determine and assess the training load. Without fatigue there would be no possibility of improving performance, because the adaptation processes would not take place. The problem that arises is the degree of allowable fatigue to achieve the best result, or how training makes us more resistant to fatigue.

Without fatigue there would be no possibility of improving performance, because the adaptation processes would not take place. The problem that arises is the degree of fatigue that is acceptable to achieve the best result, or how training makes us more resistant to fatigue.

degree of fatigue

Overload is a situation in which the subject is subjected to a stimulus (load) higher than usual. In order to produce fatigue, it is not necessary for overload in this sense, but other minor stimuli than the usual ones can also cause fatigue. Depending on this degree of fatigue and its duration, we find ourselves in three different situations:

i) acute or immediate fatigue of short duration (from a few minutes to a few hours or 2-3 days)

ii) fatigue of medium duration (from several days to 2-3 weeks) and,

iii) long-term (chronic) fatigue (several weeks to several months)

Acute fatigue corresponds to the fatigue produced by an exercise (a series or repetition) or a training session. Recovery should occur before the next set or repetition (in full or in part) or before the next session (in full).

Medium duration fatigue is the fatigue produced intentionally by several training sessions. It is made up of several units of acute fatigue without sufficient recovery between sessions. After several training units, a special, broader recovery occurs. It is expected that from this sustained load phase a higher supercompensation phase will emerge, which corresponds to the English term “overreaching”, for which there is no equivalent term in Spanish. but if the consequence is that optimal supercompensation is not reached, the subject is considered to be in an “overloaded” situation, or with excessive fatigue.

Chronic or long-term fatigue does not occur on purpose. It is the consequence of an error in training programming, although it can sometimes be associated with other circumstances such as certain diseases. It is caused by carrying out an excessive number of fatigue phases of medium duration. Sometimes it is difficult to distinguish between the phase of medium and long duration fatigue. Recovery from this state of fatigue may take several months. It corresponds to the English term “overtraining”, which in Spanish would be equivalent to the term “sobretraining”.

When we talk about leading a healthy lifestyle, we are all thinking about eating right and exercising regularly. However, a healthy lifestyle also includes aspects such as good hygiene, in this case maintaining good oral health.

If you don’t already know Fitenium is a free, mobile and video-based social network for users who train strength and/or body weight exercises. At Fitenium users can find free personalized routines, follow their performance, compete and get discounts at nutrition stores and sports equipment. Download it here.

Impact of oral health on performance

Since the 1968 Olympics, there has been a link between elite athletes and the oral health of the poor.

According to a systematic review, 28% to 40% of athletes say that their oral health affects their quality of life and 5% to 18% of their performance. Oral health is also one of the factors that determine the quality of life.

There is little evidence on how diseases such as caries, periodontal disease, and periodontitis negatively affect quality of life. And the impact in this area can make a big difference in the performance of that sporting elite.

Published on Unplash by John Fornander

Pain, systemic inflammation or the impact of an athlete on the social environment may be part of the cause of poor performance due to poor physiological adaptation to training or its poor quality.

Why is the athlete’s oral hygiene deficient?

With very few studies available, it is difficult to establish one or more strong causes. Still, it is almost impossible to design a good study that can answer this question.

High carbohydrate intake, especially from gels and sports drinks, is speculated to be one of the nutritional causes of diseases such as dental caries in elite athletes. It is also said that eating disorders can cause vomiting and damage enamel, especially in light weight sports such as gymnastics, boxing and horse riding.

Another cause that can contribute to the appearance of these diseases is oral dehydration during sports. Saliva has a moisturizing and remineralizing effect, deficient in the aforementioned carbohydrate drinks and below, which increases the diffuse effect on teeth.

What can you do to keep your teeth healthy?

For the nutritional habits of elite athletes, it is difficult to make a difference because training performance depends on these habits, but regular visits to the dental office prophylactically are good oral hygiene.

For amateur practitioners, it is important to maintain oral hygiene habits, as an overdose of sugar and acidic drinks and poor oral hygiene can cause a variety of diseases.

After all, the best medicine is prevention. This is because many drug models are treatment-based and treatment-based, but not prevention-based, which is detrimental to both patient health and societal health costs.