Training under fatigue is an actual trend among elite level athletes. Experts suggest that by simulating real match conditions, athletes will be more prepared to fatigue exposition, resulting in reduced injury risk. But is it the best strategy?

This article has concluded that training under fatigue reduce risk of fatigue-related injuries during the late stage of a match, and that “training under a fatigue state may improve performance in a fatigue state”.

First of all, in order to understand what fatigue is, we should understand some basic bioenergetics.

1. Why does fatigue occur?

The human body needs energy to function. The conversion of macronutrients – carbohydrates, proteins and fats – into biologically usable forms of energy is what allow us to maintain basic function and to be able to exercise.

ATP is an intermediate molecule which drives energy production. Without ATP, muscle function would not be possible. Thus, it is vital to understand how exercise affects ATP hydrolysis and resynthesis.

Due to economy, muscle cells store limited amounts of ATP, and since activity requires a constant ATP supply to provide energy to muscle activity to occur, ATP-producing processes must occur within the cell.

There are two main mechanisms: aerobic, which requires the presence of oxygen, and anaerobic, which can occur without any oxygen supply. Regarding energy systems, three basic systems can be highlighted: phosphagen system, glycolysis and oxidative system.

The phosphagen system provides ATP primarily for short-term, high intensity activities (dependant on PCr stores, especially 0-6 seconds, but can reach 30 seconds – it depends on creatine supplementation, for example) such as sprinting, strength/power training and other single effort activities. When trying to improve the capacity of the phosphagen system, the recommended work to rest ratio is 1:12 to 1:20.

The glycolysis can be divided in lactic (also known as fast glycolysis – anaerobic) and alactic (also known as slow glycolysis – partially aerobic) processes. It is the breakdown of carbohydrates – the reason why carbohydrates are so important for athletes – in muscle glycogen or blood glucose, to resynthesize ATP. Since glycolysis involves a more complex process, the rate of ATP resynthesis is slower than phosphagen system, but the total capacity is superior due to a higher supply of glycogen and glucose when compared to PCr (until 2-3 minutes duration). To improve its capacity, the recommended work to rest ratio Is 1:3 to 1:5.

The oxidative system, which is an aerobic system, is the primary source of ATP when at rest and during low intensity activities, depending primarily on carbohydrates and fats as substrates (protein can also be metabolized during long-term starvation and long bouts of exercise). To improve its capacity, the recommended work to rest ratio is 1:1 to 1:3.

Despite most authors divide energy systems by duration and intensity of exercise, it is vital to acknowledge that, at any given moment, all energy systems are active. The only difference, related to exercise duration and intensity, is their percentage of usage. For example, even for a 100m sprint, aerobic mechanism accounts for approximately 13% of total. So, it is not possible to classify an activity as anaerobic-only, for example. Energy systems are more of a continuum, without gaps in between.

Fatigue can be the result of inefficient ATP resynthesis, H+ ions accumulation, autonomic nervous system state, etc. So it is a multifactorial event. Fatigue is sort of an alarm, alerting that our capacities are likely to be compromised.

2. Adaptations to Strength/Power training

There are three main adaptations related to weight training: neural, structural and metabolic adaptations.

It is well known that strength and power output gains are primarily related due to neural adaptations, and it is consistent with strength gains observed during the first weeks of a weight training program, since there is not enough time to structural adaptations to occur. Structural adaptations are related to muscle hypertrophy, bone, tendon and connective tissue adaptations. Myofibrillar hypertrophy occur due muscle fiber enlargement, resulting in an increase of cross-sectional area of the muscle, and not really due to hyperplasia, since it was still not proved among humans. Metabolic adaptations are primarily related to local muscle endurance.

The most important neural adaptations include intramuscular coordination (the rate at which a motor unit fires and the number of motor units that are recruited) and intermuscular coordination (optimal recruitment of agonist, antagonist and synergist muscles in a movement).

While fatigue must be induced as an important part of the program in order to achieve optimal muscle hypertrophy and local muscle endurance, the same does not happen with strength and power development, regarding neural adaptations.

In order to optimize these neural adaptations, one needs to avoid fatigue at all cost. That’s why when training to develop maximum strength, reactive strength, low-load power and high-load power, the ratio work:rest is so high, being rest time way superior than work time. A similar thing happens with low-load power training, where one works, for example with 30% RM loads up to 5 repetitions, despite theoretically that percentage is not equivalent to 5 repetitions. It is also recommended to use power and other core exercises (multijoint movements which have the spine axially loaded) in the beginning of the session. This is justified to avoid central and peripheral fatigue, and to maximize power output.

3. Motor Learning

When learning a new motor skill, or trying to improve the quality of any movement, fatigue is a drawback. Everything that involves improving quality should not provoke fatigue, otherwise it will become an energy systems development method, and it will not be beneficial to improve quality. That is simply because fatigue has also a central component, and it affects learning capacities. All exercises dedicated to improve motor skills should have low duration, high work to rest ratios, should not alter breathing patterns and should emphasize movement quality.

4. Putting All Together

After analyzing energy systems, adaptations to strength/power training and motor learning, we should notice that the presence of fatigue assumes a negative role in their efficacy and efficiency. 

Transfering it to the field, all the literature related to motor learning, sports physiology and training methodology do not support the training of these components under fatigue, otherwise one will not experiment positive adaptations.

I believe that those articles which have found positive adaptations by working under fatigue are related to energy systems development, and not really due to enhancement of other characteristics such has strength, power or improved motor skills.

Plyometrics, maximum strength (such as eccentric overload), sprinting, single or multiple effort power exercises or other high intensity low duration activities are largely dependent on PCr stores. If already in a fatigue state, those stores will be minimal, affecting negatively exercise quality. These kind of activities should be evoked to promote neural adaptations, not energy systems development. So they should be used in a non-fatigue state. Besides, training these characteristics under fatigue will increase risk of injury substantially.

Fatigue could be an interesting variable within practice (sports specific/field – different from training) in order to increase the challenge of open skills. But we should realize that we will not induce adaptation, but only to increase difficulty.

To minimize the risk of injury during late stages of a match due to fatigue, one should increase his motor skills  abilities and strength/power output when in a non-fatigue state, and to develop energy systems in order to avoid fatigue so soon. Regarding sport-specific practice, fatigue could be an important variable to challenge decision making. When fatigued, recovery strategies, such as sleep and nutrition, load monitoring, hot/cold therapy, active recovery, etc should be employed in order to reach supercompensation and avoid exhaustion.

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Luís Mesquita

REFERENCES

1. Baechle, T.R., Earle, R.W. and Wathan, D. (2008). Essentials of Strength Training and Conditioning. Ed: Baechle, T. R., Earle, R. W 3rd edition. Champaign, IL: Human Kinetics.

2. Cardinale, M., Newton, R. & Nosaka, K. (Eds.) (2011). Strength and Conditioning: Biological Principles and Practical Applications. Chichester: Wiley-Blackwell.

3. Rippetoe, Mark, & Kilgore, Lon. (2010). Practical Programming for Strength Training. (Second Edition). Wichita Falls, TX: The Aasgaard Company.