The concept of "threshold" has little more than 40 years. In 1959 at the Third Pan-American Congress of Sports Physican, held in Chicago, the German physiologist Wildor Hollmann, commenting on the performance of some physiological parameters in an effort led to increasing loads to the cycle ergometer, introduced the idea that above certain exercise intensity, the energy demand could be covered by anaerobic metabolism, in addition to aerobic exercise.
As we know, aerobic metabolism is the metabolic pathway through which the body burns food made by combining con l’ossigeno respirato, producendo in questo modo energia utile alla contrazione muscolare. A riposo, consumiamo poco ossigeno, perché ci serve poca energia e, dunque, bruciamo pochi alimenti. Man mano che l’intensità della nostra attività fisica cresce, aumenta la quantità di energia necessaria per sostenerla e con essa la velocità con la quale gli alimenti (che sono la nostra benzina) vengono bruciati con l’ossigeno inspirato (ciò, di conseguenza, fa sì che aumenti anche la quantità d’aria respirata ogni minuto). L’intensità massima dello sforzo che possiamo compiere avvalendoci prevalentemente dell’energia fornita da questo sistema – che, essendo basato sull’utilizzazione oxygen in the air, it is rightly called aerobic - is roughly equal to that which we can develop for no more than 5 minutes: maximal efforts in this period, oxygen consumption may reach 100 percent capabilities of the subject, namely the so-called maximum oxygen uptake (VO2max usually indicated by the initials): around 3 liters per minute in a sedentary, about twice in a cycling champion. Running or cycling, from a mild strain in a progressively more intense, an almost proportional increase in the need for energy, so that oxygen and, with it, the heart rate, expression of the growing work made from the heart to pump more blood enriched with oxygen from the lungs to our muscles. It happens, however, that the increase in these variables is not linear (ie not constant) until the maximal oxygen consumption: over 2 / 3 around this maximum intensity, in an effort to increasing loads, there is a more abrupt acceleration of ventilation and also the accumulation of lactic acid in the blood.
When we produce a lot of energy in a few seconds - like a sprint in athletics or cycling, or as a result of a rapid switch from mild to more intense - our body is not able to cope with the sudden increase in demand for energy only accelerates the process of burning food with the inspired oxygen (acceleration time-order of tens of seconds, and that may still not be enough to completely cover the increased energy requirements). So this energy surplus is largely produced by degrading the sugar without burning it with oxygen through a metabolic pathway that is therefore called "anaerobic" without oxygen, and that leads to the formation of the so-called lactic acid (the one that makes sense burning muscle after a flight of stairs without running, for instance). The formation of the
lactic acid, therefore, is an expression of the activation of anaerobic metabolism, just that he Hollmann noted that Congress in 1959, introducing the idea that above a certain intensity of exercise to cover energy needs would be guaranteed not only by aerobic metabolism (It burned with oxygen), but also from the anaerobic (without oxygen consumption sugars degraded with formation of lactic acid). This is, in essence, what the concept of anaerobic threshold means today, after more than forty years: the intensity at which metabolic energy to fully aerobic metabolism becomes partly anaerobic.
The term itself of "anaerobic threshold" was introduced in 1964 by Wasserman and Mciloy to define - in tests conducted at progressively higher loads - the intensity with which a "surge" of ventilation and other parameters reflecting the transition between the mentioned two conditions: that the partially complete aerobic and anaerobic. Circulation being based on the analysis of ventilatory parameters, the threshold determined with the methods subsequently coded by Wasserman is just called "ventilation". The research that followed tended to relate the intensity of effort at which the surge in the ventilation Concomitant with the accelerating accumulation of lactic acid in blood. But they were always conducted experiments on incremental test, ie protocols where the power is increased by a few tens of watts every 30-60 seconds (increasing the inertia of the stationary bike ride on which the athlete) to reach values \u200b\u200bso high exhausted the subject, namely, its inability to continue the operation (which, in similar situations, occurs after 10-15 minutes of work in increasing intensity). Basically, then, we went to investigate - how do you continue with this kind of protocols - what happens in conditions described as "transient" from a physiological point of view, in which, ie, the adaptations are in place (increased heart rate, ventilation, etc.) that in the few tens of seconds interval between each load and the next does not allow the body to "get in balance "(and then settle down) compared to the level of energy demand means that the load reached. The body, in practice, did not have time to fully adapt to the new situation, which already is required to support a more demanding.
Taking this fact into account, it remains to see what happens instead in a "balance", ie those that can be obtained after you are lavorando per alcuni minuti (non meno di una decina) a una stessa intensità. Uno dei primi gruppi di ricerca a effettuare questo tipo di verifica fu, nel 1981, quello di Liegi, composto da Scheen, Juchems e Cession-Fossion, che esaminarono l’andamento dell’acido lattico e di altri parametri durante prove di carico costante, ciascuna della durata di 20 minuti. Osservarono che a intensità di lavoro pari al 40-50 per cento circa del VO2max la concentrazione ematica dell’acido lattico si elevava nei primi minuti di esercizio, per poi iniziare a calare molto lentamente nel prosieguo dello stesso, pur continuando a rimanere al di sopra dei livelli basali anche al ventesimo minuto (la maggior elevazione transitoria iniziale è dovuta all’inerzia di regolazione del metabolismo aerobico, che, come già detto, richiede diverse decine di secondi prima di raggiungere una condizione di equilibrio, ciò comporta, nella fase iniziale dello sforzo, un’attivazione di un certo rilievo del metabolismo anerobico, evidenziata dal conseguente accumulo di acido lattico nel sangue, che poi viene in parte progressivamente rimosso). Per carichi di intensità superiore al 60 per cento circa del VO2max notarono invece che l’aumento della concentrazione di acido lattico nel sangue era costante, fino al momento della cessazione della prova. Per carichi intermedi – tra il 50 e il 60 per cento circa del VO2max – il lattato ematico aumentava nei primi 10 minuti dello sforzo, per poi attestarsi a constant value until the end of the (twentieth minute). The three scholars call this "steady-state lactate threshold", or "lactate threshold constant" and, not insignificant, showed that during constant load (as opposed to incremental ones) this anaerobic threshold "lactic acid" is not the same as intensive work with the "ventilation" in accordance with the deduction of detectable Wasserman.
At the same time, with publications in 1981 and 1982, the German group of Stegmann and Kindermann examines the concept of anaerobic threshold, identifying it with the so-called "maximum lactate steady state" (abbreviated in the initial MLSS), which represents the maximum work intensity at which the individual a state of constant lactate, ie the highest intensity at which there is a balance between lactate (produced by the muscles) that enters the bloodstream and is removed from the blood lactate ( the latter gives way to other organs such as heart and liver, are able to use it).
trying to simplify and summarize, the concept of anaerobic threshold and physiological phenomenon due to the following: a mild intensity of work, the muscles produce lactic acid that goes slowly in the blood, but at the same time ejecting the blood to other organs and removes tissues (muscles intensely involved in the exercise). This occurs at a rate as to keep pace with production, so as not to significantly increase the absolute level of the presence of blood lactate. Increasing the intensity of effort, the rate of production and revenue increases of lactic acid in the bloodstream, and it also increases the removal rate, that maintains a state of relative balance between the two phases. But further increasing the intensity of effort, reached a certain limit, the removal efficiency reaches its maximum, that is a roof. The highest level of physical exertion to which the capacity of removal of lactate is still capable of counteracting the production of lactate that corresponds to the MLSS, ie the true anaerobic threshold. Going further, the rate of production exceeds the cost of moving inexorably, leading to a progressive accumulation of lactic acid in the blood. This last condition is that an athlete refers when he says: "I'm out of range" or "are on acid," suggesting that a little later that continuous growth of lactic acid in the blood - an expression of intense muscle production - the "intossicherà" legs, disturbing the muscle contraction itself (as a result of hydrogen ions that make it up) and, consequently, forced to reduce l’intensità dello sforzo.
Questa, dunque, è la concezione più diffusa del concetto di soglia anaerobica intesa come massimo lattato in steady-state, ma è una concezione del fenomeno abbastanza grossolana e imprecisa. Un tempo si era portati a ritenere che in uno sforzo prolungato a carico costante la concentrazione di acido lattico nel sangue riflettesse quella presente nei muscoli, arrivando progressivamente a un equilibrio tra questi due comparti: si considerava infatti che il lattato passasse dalla cellula muscolare al sangue quasi esclusivamente per semplice diffusione. Oggi, grazie al lavoro di numerosi autori – tra i quali vale la pena citare Brooks e Gladden – sappiamo che mentre alcuni muscoli producono acido lactic acid, there are others that use it, and that the balance of lactate between blood cell and are regulated by very complex mechanisms, resulting from the interaction of active transport systems - the protein transposed monossilate, called MCT - with dissemination mechanisms ; that the operation of the latter is influenced by different concentration of hydrogen ions (H +) which is to determine between the inside and outside the cell, and that - in fact, quite important - when the lactic acid can not be regarded as a mere product terminal, a gap, a simple refusal resulting from anaerobic degradation of sugars, but must be taken into account in its most complex biochemical role of regulator and mediator of energy processes in their entirety.
The above said can be nebulous if you do not have a minimum of familiarity with these topics, but basically the message is this: the lactic acid is not considered only as a poison to our muscles, as many cyclists have taken thinking.
To return to the evolution of the concept of anaerobic threshold, we can say then that the MLSS has become the "gold standard" of that threshold, that is, the criterion is provided for reference, both from a theoretical point of view (maximum possible balance between production and removal of lactate), both in terms of the measure; so much so that today the easiest direct way to determine the anaerobic threshold is based on the execution of a protocol similar to that of the cited work Scheen and colleagues: I make a subject so many tests at constant load, each lasting 20 -30 minutes on different days to ensure that the fatigue of a test does not affect the outcome of the next.
is clear that this method requires many test sessions to get through several attempts to locate the MLSS: a protocol in fact impossible for a cyclist who wants to perform routine assessments. For this reason, indirect methods - such as the Conconi test, or method of ventilatory Wasserman, or others - have had far more widespread among sportsmen.
the late seventies, some German authors, including Mader and Heck, they had noticed that the anaerobic threshold corresponds to an average concentration of 4 mmol / l (millimoles per liter) of blood lactate. This value has taken on symbolic importance with time, as to be used in practical terms - often with excessive ease science - to identify the anaerobic threshold not only in the incremental test but also in exercises at constant load and in any sport genre (from the bicycle race at the football game ...), which has led to some confusion and often gross errors interpretation.
There are three points to keep in mind in this respect: the first is that the value of 4 mmol / l identifies the average concentration of lactate anaerobic threshold, but the variation between a subject and one may even be a mmol / l in more or less (approximately one third of the athletes have less than 3.3 mmol / l or more than 4.7 mmol / l!). The second is that the concentration of lactate (for example, 2 or 4 mmol / l) corresponding to a given work intensity, and detect when in an incremental test does not match that found then - at the same intensity - in a constant effort extended for tens of minutes. The third is that the concentration of 4 mmol / l is an expression of physical effort and internal equilibrium is very different when seen in a game of tennis or football rather than the cycle ergometer, and therefore one must be careful not to fall into wrong interpretations of its meaning, similar to what takes in exercises at constant load or incremental.
From the book - the side of cycling. Sports ethics, new training techniques and the fight against doping - Sperling & Kupfer Editori
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