7 Bioenergetics Applied to Swimming : An Ecological Method to Monitor and Prescribe Training

Systematic assessments of athletes’ physiological conditions are central to monitor and prescribe swimming training according to the needs and goals. Thus, it is possible to understand the current physiological state and follow its development in order to assess the effects of training, to identify the swimmer's skills profile and to predict athletic performance (Vilas-Boas & Lamares 1997). Specifically regarding swimmers and their skills, aerobic capacity is a major determinant of these athletes performance, and it is defined as the ability to maintain a high percentage of maximal oxygen uptake (VO2max) for a long period of time (DI PRAMPERO et al., 2011). Furthermore, the endurance is influenced by VO2max, swimming economy (or energy cost, defined as the total energy expenditure required to move the body to a certain distance in a determined velocity) and anaerobic capacity (Dekerle & Pelayo 2011). In a group of swimmers with similar values of swimming economy and anaerobic capacity, those with greater aerobic potential (VO2max and aerobic capacity) will be faster at distances of 400 m and longer. Four hundred meters, when swimming in front crawl, is usually suggested as a trial in which VO2max is reached (Dekerle & Pelayo 2011). Thus, the longer events (800 m, 1500 m and open water marathon), which are covered primarily with energy from aerobic metabolism, are covered in a fraction of the VO2max. The intensity will be lower the longer is the distance, reaching 60-65% of VO2max on the 25 km open water marathon (Zamparo et al. 2005). In this sense, one of the objectives of the swimming training is to increase the aerobic capacity. Thus, a valid and reliable measure of the swimmer aerobic profile is essential to verify the benefits that the training program is or is not providing, and, also, to set training intensities according to the physiological profile of the athlete. Dekerle & Pelayo (2011) emphasize that the methodology used for this purpose cannot be considered valid unless it is reliable. Whenever possible, the degree of reliability should be assessed. The origin of the variability measurement (human error, equipment error, biological variation, or motivational factors when performing the test) needs to be taken into account. Thus, the aim of this chapter is to present a careful review of the bioenergetics contribution on the physiological assessment of the swimmer, especially related to aerobic profile.


Introduction
Systematic assessments of athletes' physiological conditions are central to monitor and prescribe swimming training according to the needs and goals.Thus, it is possible to understand the current physiological state and follow its development in order to assess the effects of training, to identify the swimmer's skills profile and to predict athletic performance (Vilas-Boas & Lamares 1997).Specifically regarding swimmers and their skills, aerobic capacity is a major determinant of these athletes performance, and it is defined as the ability to maintain a high percentage of maximal oxygen uptake (VO 2max ) for a long period of time (DI PRAMPERO et al., 2011).Furthermore, the endurance is influenced by VO 2max , swimming economy (or energy cost, defined as the total energy expenditure required to move the body to a certain distance in a determined velocity) and anaerobic capacity (Dekerle & Pelayo 2011).In a group of swimmers with similar values of swimming economy and anaerobic capacity, those with greater aerobic potential (VO 2max and aerobic capacity) will be faster at distances of 400 m and longer.Four hundred meters, when swimming in front crawl, is usually suggested as a trial in which VO 2max is reached (Dekerle & Pelayo 2011).Thus, the longer events (800 m, 1500 m and open water marathon), which are covered primarily with energy from aerobic metabolism, are covered in a fraction of the VO 2max .The intensity will be lower the longer is the distance, reaching 60-65% of VO 2max on the 25 km open water marathon (Zamparo et al. 2005).In this sense, one of the objectives of the swimming training is to increase the aerobic capacity.Thus, a valid and reliable measure of the swimmer aerobic profile is essential to verify the benefits that the training program is or is not providing, and, also, to set training intensities according to the physiological profile of the athlete.Dekerle & Pelayo (2011) emphasize that the methodology used for this purpose cannot be considered valid unless it is reliable.Whenever possible, the degree of reliability should be assessed.The origin of the variability measurement (human error, equipment error, biological variation, or motivational factors when performing the test) needs to be taken into account.Thus, the aim of this chapter is to present a careful review of the bioenergetics contribution on the physiological assessment of the swimmer, especially related to aerobic profile.

Critical velocity (CV)
The performance achieved in competitions is an important setting information from training sessions in swimmers (Sweetenham & Atkinson, 2003).However, constant evaluations are necessaries during the cycles and training sessions in order to verify the effectiveness of training and ensure the best performance in the competition (Sweetenham & Atkinson, 2003).Physiological and biomechanical swimmers conditions' knowledge is crucial to implement and/or to control the training processes that surround them (Pyne et al. 2001).These assessments can be applied in the field of competitive and / or recreational swimming.Tests used to evaluate and determine swimming speeds (SS) for the development of aerobic endurance training can be divided into invasive and noninvasive (Pyne et al. 2001), based on the relationship between oxygen consumption (VO 2 ), blood lactate concentration ([La]), heart rate (HR) and SS (Vilas-Boas & Lamares 1997).Although the precision provided by some of these tests, which require invasive sampling, such as those using the [La], ethical conflicts may arise (Heck et al. 1985), especially when applied to children.Moreover, it is common a high number of athletes to be evaluated in a training session by only one coach, so that they may require a longer period for implementation.Another limiting factor is the high cost for each testing session (Heck et al. 1985).Considering these difficulties, the tests that verify the SS in durations of 30 (T 30 ) and 60 (T 60 ) minutes (Olbrecht et al. 1985;Madsen 1982) or even over distances of 2000 m (T 2000 ) (Touretski 1993) and 3000 m (T 3000 ) (Madsen 1982), the perceived exertion (PE) (Lima et al. 2006), the critical velocity (CV) (Ettema 1966) and 400 m testing (T 400 ) (Wakayoshi et al. 1993a;Dekerle et al. 2006;Alberty et al. 2006;Pelayo et al. 2007) have been widely disseminated in swimming.However, T 30 , T 60 , T 2000 and T 3000 can provide very subjective information to determine training intensities in young and/or low level of experience swimmers.These protocols require the maintenance e of a given SS for a long time require psychological and physiological capacity compatible with the demands of the test (Zacca & Castro 2008, 2009).Regarding the PE, the athlete needs good training base to swim extensive sets with minimal adjustments in intensity between each repetition (Zacca & Castro 2008, 2009).In this sense, determination of SS for swimming training through the CV (Dekerle et al. 2006;Greco et al. 2008;Leclair et al. 2008;Vandewalle et al. 2008) seems to correspond to these swimmers profiles.CV's use is also justified due to the low cost and facility to apply in various populations.Another advantage is tha t C V i s a b l e t o b e g o t t e n e v e n d u r i n g competitions (Vilas-Boas & Lamares 1997).Since Hill (1927), it is accepted that the relationship between power output and time to exhaustion is a hyperbole.The asymptote of this relationship of power (critical power or PC) is equivalent to the slope of the regression line related to the work and time to exhaustion (time limit or tlim) (Monod & Scherrer 1965).Since then, CP represents, at least theoretically, the largest power that could be sustained, whose energy would be derived preferably by the aerobic metabolism without fatigue, and is suggested as a good performance index in events of long duration (Vandewalle et al. 1997).Ettema (1966) applied the CP concept in cyclists, swimmers, speed skaters and runners.Instead of power and work, the author used speed (S) and distance limit (dlim), respectively.The hyperbolic relationship between S and tlim (Hill 1927) and the linear relationship between dlim and tlim (Equation 1), usually called critical velocity (CV), have the same physiological meaning of CP (Pepper et al. 1992;Housh et al. 2001).
In Equation 1, the slope of the regression line corresponds to CV (obtained through a twoparameter model, CV 2par ), the y-intercept (second parameter) is mathematically defined as a finite stock of reserve power available pre-exercise (Ettema 1966;Wakayoshi et al. 1992), usually referred as "anaerobic distance capacity" (ADC 2par ).The non-linear SS-time limit to exhaustion ("SS-tlim"), the linear relationship between distance limit and time limit (dlim-tlim) and the linear relationship between SS and the inverse of tlim (Equation 2) are two-parameter models commonly used to estimate the VC (Billat et al. 1999;Housh et al. 2001;Whipp et al. 1982).
Equation 2 shows that the CV can be obtained by expressing SS as a function of tlim (Ettema 1966).In order to revise the statement that in the hyperbolic model SS is infinite when time approaches zero, Morton (1996) proposed a mathematical model including an additional parameter representing the maximum instantaneous velocity (V max obtained from a threeparameter model, V max3par ).V max3par allows a time asymptote (tlim) which is below the x-axis where tlim is zero, thus providing a V max in the y-intercept (Morton 1996).Equation 3expresses SS as a function of tlim (Zacca et al. 2010;adapted from Morton 1996).
Where SS is the swimming speed, tlim is the time limit and ADC 3par , V max3par and CV 3par are the parameters.The fact that two-parameter model assumes that there is no upper limit for power output or SS (Morton et al. 1996;Dekerle et al. 2006) leads some authors choose threeparameter models (Gaesser et al. 1995;Bull et al. 2000;Hill et al. 2003).However, both (two and three parameters) models have an important limitation: they do not take into account the "aerobic inertia" (τ) (Wilkie 1980;Vandewalle et al. 1989) (4) Zacca et al. (2010) proposed to plot tlim and SS values using a four-parameter model (Equation 4).The CV was corrected on this model by an exponential factor, proposed by Wilkie (1980).This exponential factor represents the time constant of the increased aerobic involvement, called "aerobic inertia" (τ), understood as a temporary delay in the response of VO 2 , caused by dissociation of O 2 absorbed in lungs and used especially by skeletal muscle.The use of CV in swimming training is suggested since 1966 (Ettema 1966).Studies by researchers about its use continue to be published (Dekerle & Pelayo 2011).

Intensity domains (training zones)
Some authors (Gaesser et al. 1996;Greco et al. 2008) suggest a range of intensities of three domains (sometimes referred as training zones) and others (Dekerle & Pelayo 2011) a scale of five domains and their physiological effects.According to Table 1, exercise can be conducted in three different intensity domains, resulting in very distinctive physiological effects in each of these domains (Gaesser et al. 1996;Greco et al. 2008).The individual can maintain this intensity for hours without exhaustion.

Moderate intensity domain
[La] stabilizes quickly and can be maintained almost similar to resting levels.Similarly, VO 2 shows a quick set (1-3 min) before stabilization, and the individual can maintain the intensity for hours without exhaustion.The main explanation for the "end" of the exercise refers to substrate depletion (muscle and liver glycogen), changes related to hydration and electrolytes or problems related to the process of thermoregulation (Greco et al. 2008).

Heavy intensity domain
Production and removal rates of lactate levels are high due to a high metabolic demand.
Consequently, [La] tends to stabilize at higher concentrations when compared to exercise at moderate intensity.Moreover, the efficiency of the specific motor gesture seems to be smaller, generating higher VO 2 values than the linear relationship between VO 2 and exercise intensity that characterizes the Moderate intensity domain (development of a slow www.intechopen.comcomponent of VO 2 ).Although the metabolic stress is high, it is possible to maintain a state of physiological balance and to perform the exercise for a long period (Greco et al. 2008).However, Baron et al. (2008) found exercise performed at maximum intensity possible to maintain the stabilization of the [La], i.e., in the maximal lactate steady state (MLSS), depletion occurred while physiological reserve capacity still existed, but in association with an increase in PE assessments, as predicted by the central regulator model (Noakes & St Clair Gibson 2004;Noakes et al. 2005).The end of the exercise could then be induced by an integrative homeostatic control of peripheral physiological system to ensure specifically the maintenance of homeostasis.

Severe intensity domain
There is no stabilization in metabolic variables.Specifically, the rate of lactate production is greater than the rate of removal, with a consequent increase in the accumulation and the relationship between lactate and pyruvate and the concentration of protons ([H + ]) (Greco et al. 2008).At the same time, VO 2 increases towards to its maximum (VO 2max ) and the amplitude of the slow component is much higher than those that characterize the heavy intensity exercise (Xu & Rhodes 1999).This reduces exercise tolerance, with tlim related to the cellular level of disturbance (metabolites production and removal rates), caused by high demand of muscle adenosine 3-phosphate (ATP) (Greco et al. 2008).

Scale of five intensity domains proposed by Dekerle & Pelayo (2011)
Dekerle & Pelayo ( 2011) propose a scale of five domains and their physiological effects.On this scale, lactate threshold (LT), MLSS and CV 2par can be understood as boundaries that demarcate some intensity domains.Figure 1 shows the five intensity domains proposed by Dekerle & Pelayo (2011), in which the behavior of [La] and VO 2 is illustrated in each domain.Each of the five intensity domains (Dekerle & Pelayo, 2011) is characterized by acute specific physiological responses.Dekerle & Pelayo (2011) establish the lactate threshold (LT) as the boundary between moderate and heavy domain.The LT is defined as the first increase in lactate response to an incremental test (Wasserman et al. 1990).

Heavy intensity domain
The exercise is performed in intensity very close to the LT, but a little higher, which causes a small increase in [La] (no more than 1 mmol•l -1 ) in the first minutes, with subsequent stabilization close to resting levels (≈ 2.1 mmol•l -1 ).The maximum exercise intensity at which [La] stabilization occurs is defined as maximal lactate steady state (MLSS, ≈ 3-5 mmol•l -1 ) (Beneke, 1995).The MLSS is the heavy intensity domain upper limit (Barstow 1994).The intensity corresponding to LT can be maintained for a very long period (e.g.aquatic marathons) and occurs at a slower speed when compared to MLSS (tlim ≈ 60 min).MLSS is located in the smaller SS than CV 2par (tlim ≈ 14.3 to 39.4 min).Importantly, for being difficult to detect the MLSS through the curve obtained in [La] and SS, and also to avoid any misinterpretation, the term "anaerobic threshold" should not be associated to the MLSS.Swimming in a very low SS is a difficult task (<0.4 to 0.5 m•s -1 or 50-60% of V 400 -average speed of 400 m front crawl in maximal effort).Thus, the lowest speed that can be adopted by swimmers using a good technique, it is almost equal to LT (Dekerle & Pelayo 2011).

Severe intensity domain
In SS above the MLSS (heavy intensity domain upper limit) there is an increase in [La], HR and VO 2 (occurrence of the slow component).Initially, it was suggested that the increase in VO 2 in these intensities reach the maximum (VO 2max ) before exhaustion, which characterizes the severe intensity domain).This statement is controversial and difficult to investigate because of the low reliability of time to exhaustion obtained in constant intensity tests (variability of tlim) (Hinckson & Hopkins, 2005).The SS equivalent to the Severe intensity domain includes performances of approximately 2 to 60 minutes (VO 2max reaching the end of the exercise) with the performance of 400 m in front crawl, the maximum aerobic speed (MAS) and CV 2par lying within that domain (Lavoie & Montpetit et al 1981;Lavoie et al. 1983;Lavoie & Leone 1988;Rodrigues 2000;Pelayo et al. 2007;Billat et al. 2000;Dekerle et al. 2010).

Extreme intensity domain
This domain includes performances of very short duration (< 2 min).Due to the limited response of VO 2 , VO 2max is not reached during exercise, although the task is performed to exhaustion.Dekerle & Pelayo (2011) suggest the subdivision of Heavy intensity domain.According to these authors, the range of effort associated to this area is wide (performances of ≈ 2 to 60 min) and associated with many chronic responses to training, i.e., the physiological adaptations of a training period in SS near the MLSS are different from the training adaptations induced by a training period in MAS or above.

Very heavy intensity domain
In addition, the physiological responses to swimming at intensities equal to or above the MLSS are still unclear, since it is not certain that VO 2max is reached.Thus, it is justifiable to establish at least one domain between the MLSS and CV 2par : the "very heavy intensity domain".Thus, exercise performed in this domain (very heavy) suggests an increase in [La] and the occurrence of the VO 2 slow component, but without reaching VO 2max in the end of the exercise (Dekerle et al. 2010).VO 2max would only be achieved if the exercise was conducted in intensity above CV 2par and continued until exhaustion (featuring the severe domain).Thus, CV 2par represents the boundary between very heavy and severe intensity domain.However, Dekerle & Pelayo (2011) suggest that more experiments are needed in these models of training zones.As a result, coaches and swimmers will be able to use them with a greater degree of reliability.
Based on the information presented, it is believed that the model of five intensity domains proposed by Dekerle & Pelayo (2011) best describes the physiological responses to exercise in different intensities.

Physiological meaning of each parameter
4.1 Two-parameter model 4.1.1Critical Speed (CV 2par ) PC was used initially to determine exercise intensity that could be theoretically maintained for a long period of time without exhaustion (Monod & Scherrer 1965).CP (or CV in running or swimming) proved to be valid for aerobic capacity prediction (Dekerle et al. 2005a) and sensitive to physiological changes from aerobic training programs (Jenkins & Quigley, 1991).CP or CV determined by two-parameter model (CP 2par or CV 2par ) represents the lower boundary t of the severe intensity domain (Poole et al. 1990;Hill & Ferguson 1999).Poole et al. (1990) found that when subjects performed exercise intensity on CP 2par , VO 2 stabilized around 75%VO 2max .In addition, studies have investigated the hyperbolic relationship between power and time to achieve VO 2max .The results also suggest that this relationship is the lower boundary of the severe intensity domain, or CP 2par (or CV 2par ) (Hill & Smith 1999;Hill & Ferguson 1999).Thus, CV 2par can determine the exercise intensity equivalent to the lower boundary of the severe intensity domain.

Anaerobic distance capacity (ADC 2par )
The physiological meaning of ADC 2par is still subject of many studies (Moritani et al. 1981;Green et al. 1994;Miura et al. 2000;Heubert et al. 2005).Evidence trying to suggest the ADC 2par anaerobic nature was observed in cyclists (Green et al. 1994).Also in cyclists, Heubert et al. (2005) found a decrease of 60 to 70% in ADC 2par values as a result of a 7 s maximal effort performed before a protocol of four exercises at constant intensity (95, 100, 110 and 115%VO 2max ) and to determine the ADC 2par and CP 2par .CP 2par values did not change.Moritani et al. (1981) also found no differences in ADC 2par values in response to ischemia, hypoxia and hyperoxia.In relation to prior depletion of glycogen, Miura et al. (2000) found a decrease in ADC 2par values (in cycle ergometer).Jenkins & Quigley (1993) found an increase in ADC 2par values in response to high-intensity training in untrained individuals, but the CP 2par values did not change.ADC 2par values also showed increases in response to creatine supplementation (Miura et al. 1999) and demonstrated good correlation with predominantly anaerobic exercises (Vandewalle et al. 1989;Jenkins & Quigley 1991;Hill 1993;Dekerle et al. 2005b). www.intechopen.com

Three-parameter model 4.2.1 Critical Velocity (VC 3par )
The oxygen supply spends a period of time to reach a steady state or maximum.This has led some researchers (Vandewalle et al. 1989;Morton 1996) questioned the "immediate" availability of CV in two-parameter models (CV 2par ).As a result of this lapse of time, probably CV 2par was being overestimated.In addition, studies found that CV 2par could be sustained only by 14.3 to 39.4 min by swimmers (Dekerle et al. 2010).These results suggest that the concept of CV 2par as a speed that could be sustained infinitely would not be appropriate.
There is little information on CV and the type of mathematical model used to obtain it in sports.Morton (1996) suggests that CV 2par values may be overestimated.Gaesser et al. (1996) also found that three-parameter model generated CP values (CP 3par ) significantly lower, and the subjects were able to resist in a continuous work for a long period.Thus, CV 3par seems not to be at the lower boundary of the severe intensity domain, requiring further investigation.Probably CV 3par is below the lower boundary of the severe intensity domain.

Anaerobic distance capacity (ADC 3par
) Vandewalle et al. (1989) question the assumption that at exhaustion all ADC 2par is used, as theoretically is suggested by two-parameter models.Thus, ADC 2par may be underestimated (Vandewalle et al. 1989;Morton 1996).

Maximum instantaneous velocity (V max3par )
As a result of the lapse of time ("immediate" availability of CV 2par ), Morton (1996) proposed a three-parameter model (Equation 3) which the "maximum instantaneous speed" (V max3par ) was included (third parameter).With the addition of the parameter V max3par , the threeparameter model is more accurate in estimating the CV (and therefore ADC) surpassing the initial concept of the relationship velocity-tlim, that when tlim approaches zero, velocity is infinite (Morton 1996).V max3par allows a time asymptote below the x-axis, where time = zero, and provides a Vmax3par value in the intercept-x (MORTON 1996).

Three-parameter model 4.3.1 Critical velocity (CV 4par )
Both models (two and three-parameter models) have an important limitation: do not predict the "aerobic inertia" (τ) (Wilkie 1980;Vandewalle et al. 1989), related to cardio respiratory adjustments so that the VO 2 reach steady state or maximum.Thus, a four-parameter model (CV 4par , ADC 4par , V max4par and τ) proposed by Zacca et al. (2010) could provide more information on bioenergetics in cyclic sports.The four-parameter model proposed by Zacca et al. (2010) was based on the three-parameter model, and CV 4par was corrected by an exponential factor, first proposed by Wilkie (1980).This exponential factor is theoretically defined as the time constant that describes the increased aerobic involvement, the "aerobic inertia" (τ).Zacca et al. (2010) suggest that CV is sensitive to additional parameters in young swimmers (93% of the variation was explained by the mathematical model used).The effect of the models showed that CV 2par was higher than CV 3par and CV 4par .CV 3par and CV 4par were similar (and therefore the physiological meanings of both models are also similar).Thus, future studies are necessary to understand the physiological meaning of CV 3par and CV 4par in young swimmers and probably in other sports.Figure 2 shows the plot of the data using two, three and four-parameter models with speed and tlim data of 50,100,200,300,400,800 and 1500 m from swimmers (adapted from Zacca et al. 2010).It is easy to see that the data fits more appropriately in three and four-parameter models.Thus, CV 2par was higher than CV 3par and CV 4par , as previously described.

Anaerobic distance capacity (ADC 4par )
ADC 2par was originally defined as the maximum distance (m) that could be covered anaerobically (Ettema 1966).However, Costill (1994) conceptualized ADC 2par as the total work that can be performed by a set of limited power of the human body (phosphagen, anaerobic glycolysis and oxygen reserves) suggesting that the anaerobic energy system is predominant but not exclusive (Gastin 2001).Zacca et al. ( 2010) compared ADC 2par , ADC 3par and ADC 4par values.The results showed that ADC 2par (13.77 ± 2.34 m) was lower than ADC 3par and ADC 4par (30.89 ± 1.70 and 27.64 ± 0.03 m respectively).Moreover, ADC 3par and ADC4 par values were similar.These results are consistent with others that also observed an overestimation of the parameter ADC in two-parameter model (Billat et al. 2000).Dekerle et al. (2002) evaluated ten well-trained swimmers, when the objective was to verify the possibility of determining ADC 2par .They concluded that ADC 2par is not perfectly linear and is very sensitive to variations in performance.Thus, according to the authors, it is impossible to estimate the anaerobic capacity by two-parameter models.Toussaint et al.
(1998) also suggest that the anaerobic capacity in swimming obtained by two-parameter model does not provide an accurate estimate of the real anaerobic capacity.It seems clear that three and four-parameter models seem more suitable to predict ADC.

Maximum instantaneous velocity
There are gaps in the literature regarding the prediction of V max by mathematical models.Billat et al. (2000) found that V max3par was not different from the maximum speed obtained in 20 m at maximal effort.However, Bosquet et al. (2006) suggest that V max3par is smaller than the real V max (obtained by the average speed of the last 10 m of a maximal 40 m effort).Zacca et al. (2010) found that V max was higher in sprint than endurance swimmers (2.53 ± 0.15 m•s -1 and 2.07 ± 0.19 m•s -1 respectively) independent of the mathematical model used (three or four parameters).In addition, V max4par was greater than V max3par (2.42 ± 0.29 m•s -1 and 2.18 ± 0.34m•s -1 respectively), suggesting future studies to compare V max and real V max .

Aerobic inertia
The two-parameter model given by the relation "SS-tlim" (or "Dlim-tlim") and three-parameter model given by the relation "SS-tlim" have an important limitation: they do not take into account the "aerobic inertia" (τ) (Wilkie 1980; Vandewalle et al. 1989) ARMSTRONG 2003).Invernizzi et al. (2008) suggest that the time to reach steady state in VO 2 after the beginning of the exercise depends on the characteristics of the subject: endurance swimmers reach this balance sooner than sprint swimmers, and children reach earlier than adults.Thus, "τ" could be a good tool for evaluating cardiovascular and pulmonary performance in athletes (Kilding et al. 2006;Duffield et al. 2007).

Swimming speeds prescription through a 400 m front crawl maximum effort (T 400 )
Although many distances used in swimming competition does not exceed 2 min (50, 100 and 200 m), the zone related to VO 2 , commonly referred as aerobic power, is relevant in swimming (Di Prampero 2003), perhaps because T 400 is performed in similar SS reach VO 2max (Rodrigues 2000).The concept of aerobic power refers to the rate of oxidative energy synthesis (i.e., the maximum power at which the oxidative system can operate, also known as maximum aerobic speed, MAS), available to the muscle work, which can be measured by VO 2max .Measuring VO 2max in swimming is always a great challenge (PELAYO et al. 2007).This is due to the fact that conventional techniques interfere in swimming biomechanics (Keskinen et al. 2003;Barbosa et al. 2010), which performs the side breathing impossible, changes can occur in hydrodynamics, and most of the times the turns are not performed (Montpetit et al. 1981).Training programs, in order to develop aerobic power in swimmers, are related to the increase in VO 2max and the ability to use a high percentage of VO 2max for a long time.Maximal aerobic power is widely used to assess aerobic fitness and training intensities prescription (Lavoie & Montpetit 1986).
In an attempt to find alternatives and make the evaluation of athletes swimming closer to reality applied in swimming pools, several studies have been conducted in order to verify the possibility to prescribe training intensities through a single test, but not so extensive such as T 30 (Lavoie et al. 1981;Lavoie et al. 1983;Lavoie & Montpetit 1986;Rodrigues 2000;Takahashi et al. 2002;Takahashi et al. 2003Takahashi et al. , 2009;;).The attainment of VO 2max values from the recovery curve of VO 2 (the back extrapolation method proposed by Di Prampero et al. 1976) was first tested on swimmers by Lavoie et al. back in 1983. Lavoie et al. (1983) found a high correlation between VO 2max and tlim of T 400 .The possibility to prescribe training intensities using a single test has renewed expectations of swimming coaches and researchers.The attainment of VO 2max values trough the back extrapolation involves obtaining VO 2 after swimming and applying a simple regression curve between the time and the values of consumption in order to predict the value of VO 2 in time zero (Lavoie & Montpetit 1986).
It is believed that the high correlation between VO 2max and tlim T 400 m found by Lavoie et al. (1983) is probably the first indication of the T 400 as a non-invasive alternative.Since then, T 400 a reference to verify the MAS and prescribe swimming training intensities (Montpetit et al. 1981;Lavoie et al. 1983;Rodrigues 2000;Pelayo et al. 2007).However, despite many studies reporting the use of T 400 by swimming coaches (Wakayoshi et al. 1993b;Dekerle et al. 2005a;Alberty et al. 2006;Dekerle et al. 2006;Pelayo et al. 2007), we did not find a reliable protocol for prescribe more than one swimming training zone through the T 400 , i.e., a protocol not only able to predict aerobic power, but also another training zone.By questioning some brazilian coaches, we find that some of them use a protocol (of unknown origin) based on the T 400 to monitor and to prescribe three different SS for swimmers and triathletes.Table 2 presents a summary of the equations used to calculate the SS for "aerobic threshold", "anaerobic threshold" and "VO 2max ".Table 2. Equations used to calculate the SS for "aerobic threshold", "anaerobic threshold" and "VO 2max ".K is a constant: K = 0.94 if tlim is between 3 min 50 s to 4 min 40 s, K = 0.95 if tlim is between 4 min 41 s to 5 min 40 s, K = 0.96 the tlim is between 5 min 41 s to 6 min 40 s, K = 0.97 if tlim is above 6 min 41 s, t = time prescribed for a given distance; I VO2 = intensity prescribed to increase VO 2max , I LA = intensity for anaerobic threshold and I LAe = intensity prescribed for aerobic threshold.
In this protocol, the coach just needs that your athletes swim 400 m in front crawl under maximum intensity (in training situation, but preferably in competitive situation).
According to the protocol, the T 400 is able to prescribe SS in three different intensities for training in swimming called (1) "aerobic threshold" (I LAE ) (2) "anaerobic threshold" (I LA ) and ( 3) "increased VO 2max " (I VO2 ) (Olbrecht 2000;Maglischo 1999).For each intensity, the protocol suggests the time prescription for distances of 50, 100, 200, 400 and 800 m.SS prescribed by T 400 for I VO2 is between 94 and 97% from the SS of 400 m (V 400 ).SS prescribed for I LA is proposed as approximately 90% of the V 400 .SS prescribed for I LAe stands at approximately 84% of the V 400 .
It can be seen throughout this review that the literature presents a wide naming to explain the [La] response to exercise.However, despite being related to the same phenomenon, the physiological responses are often different, such as LT and MLSS mentioned above, and I LAE and I LA used in this protocol.This means that it cannot be used interchangeably.
As Maglischo (1999) and Olbrecht (2000) suggest, sets on L AE are swum in SS ranging from an intensity which is observed in the first rise in [La] above the resting level to the SS that sits comfortably below the I LA of the swimmer.The total distance can vary between 2,000 and 10,000 m for adult swimmers or 20 to 120 min for young swimmers.Any distance can be used in the interval sets.Regarding the rest intervals between each repetition, it is suggested 5 to 30 s (Olbrecht 2000).Still, in I LA sets, the total distance of the set can range from 2,000 to 4,000 m for adults, or approximately 30 min for younger athletes (Maglischo 1999;Olbrecht 2000).Distances between 25 and 4,000 m be used in the interval sets (Maglischo 1999;Olbrecht 2000), with rest intervals between 10 to 30 s (Olbrecht 2000).
Series aimed to increase VO 2max , Maglischo (1999) suggests SS slightly above the I LA until 95% of best performance (Maglischo 1999) (Severe intensity domain).It is suggested distances between 25 to 2.000 m, with intervals of rest of 30 s to 120 s between each repetition (Maglischo 1999).However, the SS percentage suggested for training zones prescription have not been observed in constant speed tests until exhaustion.However, similarities were observed in tlim and percentage of training zones prescription between the T 400 and the 1 mile running applied by Daniels (2005).Daniels's concepts (Daniels 2005) were based on "velocity at VO 2max " (vVO 2max ).

Velocity at VO 2max (vVO 2max )
Although VO 2max is accepted as the physiological variable that best describes cardiovascular and respiratory capacities (Hill & Lupton 1923;Billat & Koralsztein 1996), vVO 2max was measured only five decades later in order to provide a practical method to measure aerobic fitness in runners (Billat & Koralsztein 1996).In the 80's there was a growth interest in the physiological assessments in order to monitor athletic training (Billat & Koralsztein 1996).However, it is known that protocols for VO 2max measurement, for example, require trained professionals, special equipment and need to be conducted in a controlled environment.
The first field test used to measure vVO 2max was intended to replace the 12 min test Cooper (Cooper 1968) as an alternative to predict VO 2max in a unique effort to simplify procedures and reduce costs.Cooper (1968) reported a correlation of 0.9 between VO 2max and the distance covered in a 12 min test running or walking.However, the motivation and rhythm was mentioned as critical to achieve good reliability in a 12 min test (Cooper 1968).Importantly, when prescribing training intensities based on the performance test, is also considered the psychological characteristic of the race, because instead of applying laboratory tests to monitor training status of the athlete, we use the performance obtained in competitive events, which is directly affected by the willingness to deal as discomfort.Tests www.intechopen.combased on test performances reflect everything that an athlete recruited to travel any distance in a competitive situation (Daniels, 2005).The Cooper test (1968) was based on the linear relationship between running speed and VO 2 when, while driving the subject until exhaustion, it was possible to determine VO 2max .Billat & Koralsztein (1996) suggest that the accuracy of prediction of VO 2max , or also its inaccuracy, depends on the energy cost inter-individual variation, i.e., the total energy expenditure required to move the body to a certain distance.Daniels et al. (1984) introduced the term "velocity at VO 2max " (vVO 2max ) suggesting that it is a useful variable that combines VO 2max and movement economy (Conley & Krähenbühl 1980) on a single factor that identifies aerobic differences among various runners or group of runners.According to Daniels (2005), vVO 2max explains individual differences in performance that VO 2max or running economy alone could not identify, i.e. individuals with the same VO 2max for example, may have different performance times.Daniels et al. (1984) found in female runners who had various combinations of VO 2max and running economy (submaximal VO 2 ), that vVO 2max was similar to the average speed required to run 3,000 m (maintained approximately for 9 min).In a study with sub-elite distance runners, Billat et al. (1994a) measured a dlim at vVO 2max of 2,008.7 ± 496 m.However the authors suggest that there is a need to distinguish total run at vVO 2max and time run at VO 2max race only.Daniels et al. (1984) calculated vVO 2max extrapolating through a regression curve relating running speed and VO 2 .When VO 2max was reached, the running speed corresponding to VO 2max was identified.Sub-maximal VO 2 was calculated from efforts of 6 min at speeds of 230, 248 and 268 m.min -1 at intervals of 4 to 7 min between each effort.VO 2max was measured separately in a test based on the incremental pace of 5,000 m, adding 1% for the treadmill speed every minute until the test is terminated, where subjects reported that they would not be able to run more than 30 s.The highest VO 2 achieved during the maximal test was considered as VO 2max .

tlim that swimmers are able to keep at vVO 2max (tlim-vVO 2max )
For several years, many studies have remained focusing on measuring vVO 2max during swimming.However, few investigations in order to determine the tlim-vVO 2max were carried out.This training tool which requires the swimmer to keep the exercise intensity corresponding to its vVO 2max has been studied mainly by the Billat et al research group.
Based on the pioneering work of Hill and Lupton (1923), Billat & Koralsztein (1996) defined this parameter as the maximum time that the vVO 2max is maintained until exhaustion (tlim-vVO 2max ).The difficulties of measuring VO 2 in the aquatic environment hindered the swimming research and related modalities.The first studies were conducted in "swimming flume" (Faina et al. 1997;Demarie et al. 2001).To our knowledge, the first study in the pool, i.e., under normal swimming conditions, was performed by Renoux (2001).However, Renoux (2001) did not present results for cardio respiratory parameters such as VO 2 and ventilation.The main results obtained in studies with "swimming flume" suggested that: a) the tlim-vVO 2max has low inter-individual variability in swimming, unlike other sports such as running (Billat et al. 1994b), and the values are between 4 min 45 s and 6 min 15 s; b) There is an inverse relationship between tlim-vVO 2max and vVO 2max , similar to running (Billat et al. 1994c); c) There was an inverse relationship between tlim-vVO 2max and anaerobic threshold.
The method for obtaining vVO 2max of swimmers in swimming pool proved to be valid by Fernandes et al. (2003a).First, each subject performed an intermittent and individualized protocol, with increments of 0.05 m.s -1 at each stage of 200 m and with 30 s intervals between each stage, until exhaustion.The VO 2 was measured directly with a ergospirometer (K4b 2 , Cosmed, Rome, Italy) connected to the swimmer through a snorkel and a valve system (Keskinen et al. 2003) If a plateau lower than 2.1ml•min -1 •kg -1 could not be observed, the vVO 2max was then calculated by the equation proposed by Kuipers et al. (1985): where SS is the speed corresponding to the last completed stage, ∆S is the increment of speed, n indicates the number of seconds that the subjects were able to swim during the last stage, and N is the preset time (in seconds) to that stage.After determining the vVO 2max of each swimmer, followed by an adequate recovery period, applies the test of tlim-vVO 2max w h e n e a c h s w i m m e r t r y i n g t o s t a y i n y o u r s w i m m i n g v V O 2max (speed control) to exhaustion.
The main studies in swimming suggest that tlim-vVO 2max : a. Correlates inversely with the energy cost, ie, it has a direct relationship with swimming economy (Fernandes et al. 2005); b.Correlates inversely with the speed of the individual anaerobic threshold (Fernandes et al. 2006a); c.Presents negative correlation values with the delta lactate (Δ[La]), ie, the difference found between [La] at the end and [La] at the beginning of exercise (Δ[La]) (Fernandes et al. 2008); d.Presents negative correlation with maximum values of [La].(Fernandes et al. 2008); e. Shows no significant correlation with VO 2max (Fernandes et al. 2003a;2003b;2005;2006a;2006b;2006c); f.Depends on the biomechanical parameters, correlating inversely with the strokes frequency and directly with the distance traveled per stroke cycle and the swimming index (product of the average SS and average distance traveled per stroke cycle) (Fernandes et al. 2006b); g.During the protocol to obtaining tlim-vVO 2max there is a significant increase in stroke frequency and a great decline in the distance per stroke cycle (Marinho et al. 2004(Marinho et al. , 2006)).Studies in runners and cyclists (Billat & Koralsztein 1996) found that the tlim-vVO 2max is less than 12 minutes, and the average is about 6 minutes.Despite these results, is not only the complexity of measuring vVO 2max that affect the application of this concept by coaches.Because it is an abstract goal, the use of vVO 2max and tlim-vVO 2max in swimming training would be more attractive if a "dlim" was associated with tlim-vVO 2max .The studies presented in Table 3 suggest that efforts related to aerobic power (vVO 2max ) have very similar dlim of 400 m front crawl, ranging from 4min01s (3min17s to 5min21s, elite swimmers) and 5min25s (4min8s to 6min41s, recreational swimmers).Fastest swimmers endure less time vVO 2max likely for two reasons: a. Higher SS imply higher energy cost (Fernandes et al. 2008); b.Higher vVO 2max in best swimmers require more strenuous levels of exercise, more anaerobic system request (Fernandes et al. 2008).

Conclusion
Is well justified that CV 2par seems to be higher than CV 3par and CV 4par .CV 3par and CV 4par better represent the relationship between "SS-tlim" due to its better fit.CV 3par and CV 4par are similar and probably are located below the lower boundary of the severe intensity domain.However, its applicability to swimming training is questioned because of the need to conduct many maximum efforts to obtain the CV.
In this sense, obtaining vVO 2max through the T 400 seems to be an interesting ecological noninvasive protocol.tlim-vVO 2max relationship should be considered during swimming training, specifically in the evaluation sessions of the training status.This parameter, together with other indicators, such as LT, MLSS, PE and general biomechanical parameters allow improving the assessment and intensity prescription of training programs.In this sense, assuming some limitations that bring non-invasive tests, vVO 2max can be obtained through a single effort of 400 m front crawl at maximum intensity (T 400 ), with the advantage of being easy to use, low cost, and have great ecological validity (i.e., reflect the real swimming condition, as it is applied in the training environment.Thus, evaluations and prescriptions for training swimmers would be more practical and accessible, not only for the shortest time spent (i.e, collected even in a competitive situation) but also because do not impact cost.The ability to prescribe more than one training zone through T 400 still deserves further studies.

Fig. 1 .
Fig. 1.Intensity domains (adapted from Dekerle & Pelayo 2011) and the response of each to [La] and VO 2 kinetics during exercise in different SS.
. The "τ" is a temporary delay in VO 2 response because of dissociation between O 2 absorbed in the lungs and the mainly used by skeletal muscle, lasting approximately 15 to 20 s. "τ" is associated to vasodilatation, i.e, the time it takes for the body to increase heart rate and redirect blood flow.
Studies regarding oxygen kinetics during exercise with children and adolescents is limited to few articles and until recently was based on d a t a c o l l e c t e d w i t h a d u l t s ( F A W K N E R & (HOWLEY et al. 1995) of expired gases were measured breath-bybreath.A speed controller (visual pacer, TAR.1.1,GBK-electronics,Aveiro, Portugal) with lights in the pool, was used to help the swimmers to keep their pre-determined SS.VO 2max was considered to be reached according to primary and secondary physiological criteria:(HOWLEY et al. 1995): a. Occurrence of a VO 2 plateau independent of the increase in SS; b. [La] level ( ≥ 8mmol•l -1 ); c. High respiratory exchange ratio (r ≥1,0); d.High HR (≥90% of [220-age]; e. High value of PE (visually controlled).Thus, vVO 2max is equal to the SS corresponding to the first stage at which VO 2max is reached.