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## Revista Brasileira de Medicina do Esporte

##
*Print version* ISSN 1517-8692

*On-line version* ISSN 1806-9940

### Rev Bras Med Esporte vol.11 no.2 Niterói Mar./Apr. 2005

#### http://dx.doi.org/10.1590/S1517-86922005000200006

**ORIGINAL ARTICLE**

**Use of the y-intercept in
the evaluation of the anaerobic fitness and performance prediction of trained
swimmers **

**El uso del intercepto-y en la evaluación
de adaptacion anaeróbica en la predicción de la performance de
nadadores especializados**

**Marcelo Papoti ^{I, III}; Alessandro
Moura Zagatto^{II, III}; Paulo Barbosa de Freitas Júnior^{V};
Sergio Augusto Cunha^{III}; Luiz Eduardo Barreto Martins^{IV};
Claudio Alexandre Gobatto^{III} **

^{I}Bauru Integrated College
Cepaf, Bauru, SP

^{II}Mato Grosso do Sul Federal University UFMS, Campo Grande,
MS

^{III}Biodynamics Laboratory, IB, Unesp, Rio Claro, SP

^{IV}Laboratory for Instrumentation in Exercise Physiology, Unicamp,
Campinas, SP

^{V}Laboratory for Movement Studies, IB, Unesp, Rio Claro, SP

**ABSTRACT**

The objective of this study was to verify the use of y-intercept from the critical velocity model in the evaluation of the anaerobic fitness and prediction of maximal performance in trained swimmers in crawl style. Fourteen swimmers with ages ranging from 15 to 18 years participated in this study. The athletes performed the tied swimming test, maximal performances tests and critical velocity (CV) for the determination of anaerobic swimming capacity (AWC). 1) The tied swimming test was applied through maximal effort during 30 seconds fixed to the equipment with load cells for the measurement of the peak force, anaerobic fitness and peak lactate. 2) The subjects also performed maximal performances at distances of 100, 200, 300, 400 and 600 meters with two hours interval between each swim. 3) AWC at CV model was determined utilizing all possible combinations by maximal performances applying the distance-time linear regression model. The AWC value obtained was of 25.07 ± 4.22 m, with linear regression coefficient between 0.99 and 1.00, and linear coefficient error of 19.30 ± 5.9%. AWC was not correlated with all maximal performances, peak force (227.81 ± 63.02 N), anaerobic fitness (85.55 ± 13.05 N), and peak lactate (6.80 ± 1.08 mM). However, the anaerobic fitness was correlated with all maximal performances. Thus, it was concluded that the AWC obtained by y-intercept of the distance/time of swim relation does not seem to be a good parameter for the anaerobic fitness evaluation neither to predict the maximal performances between 100 and 600 meters in crawl style.

**Key words:** Swimming anaerobic capacity.
Anaerobic fitness. Tied swimming. Critical velocity. Performance. Lactate.

**RESUMEN**

El objetivo de ese estudio fue verificar el
uso del intercepto-y en la evaluación anaeróbica de la aptitud
y predicción de la performance de los nadadores especializados. Los participantes
del estudio fueron 14 nadadores con edad entre 15 y 18 años. Los atletas
realizaron la prueba de nado atado, máxima performance y velocidad crítica
(VC) para la determinación de la capacidad de nado anaeróbico
(CTA), todos en estilo crawl por un periodo de tres días. 1) La prueba
de nado atado consistió en lograr el máximo esfuerzo durante 30
segundos atado a un aparato de medición con células de carga para
la medida del pico de fuerza (F_{pic}), de la aptitud anaeróbica
(AP_{ANA}) y la concentración de pico del lactato ([la^{-}]_{pic})
según Papoti et al.^{(11)}. 2) Los participantes también
lograron actuaciones al máximo en las distancias de 100, 200, 300, 400
y 600 m, con el intervalo mínimo de dos horas entre cada nado. 3) La
prueba de VC se aplicó para la determinación de CTA que usa todas
las posibles combinaciones de los resultados de las máximas actuaciones,
a través del modelo de regresión lineal entre la distancia vs.
tiempo. Se encontró un promedio de 25,07 ± 4,22 m en las 16 combinaciones
de CTAs y se halló un coeficiente de regresión lineal que varía
entre 0,99 y 1,00 con un error de coeficiente lineal de 19,30 ± 5,9%.
No se encontraron en ellos correlaciones significantes entre CTAs y máximas
performances, F_{pic} (227,81 ± 63,02 N), AP_{ANA} (86,55
± 13,05 N) y [la^{-}]_{pic} (6,80 ± 1,03
mm). Sin embargo, si se encontraron en ellos correlaciones significantes entre
AP_{ANA} y las máximas performances. De este modo, es posible
concluir que la CTA representada por el intercepto-y de la distancia de la relación
vs. tiempo de nado, parece no ser un parámetro bueno en la evaluación
de la aptitud anaeróbica y la predicción de las actuaciones entre
100 m y 600 m del nado crawl.

**Palabras-clave:** Capacidad de nado anaeróbico.
Aptitud anaeróbica. Nado atado. Velocidad crítica. Natación.
Performance lactato.

**INTRODUCTION**

In swimming, the methods used to measure anaerobic
variables are not quite well developed such as those that evaluate the aerobic
qualities, although these variables are important aspects for the swimmer evolution^{(1)}.
Maglischo^{(2)} suggested the determination of the blood lactate concentration
after maximal efforts as a way to evaluate the anaerobic capacity, where low
lactate values along with unsatisfactory performances could indicate deterioration
of this capacity. Although the use of the lactacidemia is a tool sensible to
small adaptations in the swimmers training^{(3)}, its reduction after
maximal efforts may also be a result of an overtraining state^{(4-7)}.
Methodologies that evaluate the strength of swimmers out of the water through
the use of the swim bench^{(8)} and in the water through semi tied swim^{(9)}
and tied swim^{(10-12)} situations are also frequent. The latter, besides
presenting higher specificity when compared with the swim bench, is a reproducible
ergometer^{(11,13)}, highly correlated with the swim velocity at distances
between 25 and 400 m in crawl style^{(10,11)}, and sensible to variations
on the training volume and intensity^{(12,14)}.

Unfortunately, not all swimming teams count on the financial support required for the acquisition of specific equipment for strength and power measurement or for the performance of constant evaluations using lactacidemia.

The critical power test, initially proposed by
Monod and Scherrer^{(15)} and validated by Moritani *et al*.^{(16)},
has as concept the maximal exercise intensity that can theoretically be maintained
for a long period of time with no fatigue. This evaluation method has been objective
of many studies, not only for being a low-cost non invasive test, but also for
providing indicatives of aerobic and anaerobic capacities.

Wakayoshi *et al*.^{(17)} linearized
the hyperbolic equation applied in the prediction of the critical power and
verified whether the critical velocity (CV) may be used to estimate the performance
of high-level swimmers. In this study for the CV and the anaerobic swimming
capacity (AWC) determination, the swimmers were submitted to six efforts until
exhaustion in the swimming flume. The six points obtained from the relation
between the limit time (Tlim) and the swim distance (SD) were submitted to linear
regression procedure, where the angular coefficient represented the CV and the
linear coefficient (y-intercept) represented the AWC. The authors observed high
correlation of CV with lactate threshold for concentration of 4 mM (r = 0.95)
with the oxygen uptake at the anaerobic threshold intensity (r = 0.82) and with
maximal velocity of 400 m (r = 0.86). Later, these authors made available and
popular the use of the CV by determining this parameter in conventional swimming
pool using the linear relation between prefixed distance (200 m and 400 m) and
swim time^{(18)}.

As previously mentioned, the AWC, represented
by the linear coefficient (y-intercept), when determined with stimuli in which
the participants perform efforts until exhaustion, seems to correspond to the
anaerobic variable of the CV model. It has been demonstrated that this parameter
is sensible to eight high-intensity training weeks with intervals^{(19)}
and to six endurance training weeks^{(20)}. Furthermore, the AWC was
significantly correlated with the Wingate test^{(21)}, anaerobic production
of muscular ATP (r = 0.70), anaerobic capacity determined through the ATP change
and phosphocreatine (r = 0.73) in well-trained cyclists^{(22)}, and
with the maximal accumulated oxygen deficit (MAOD), demonstrating that the y-intercept
may be a valid index to represent the anaerobic work capacity^{(22,23)}.

However, other studies did not demonstrate association
between AWC with MAOD^{(24)}, and the Wingate test average power^{(25)}.
In addition, in swimming, the vast majority of studies found no association
between AWC and performance^{(26-28)}, thus emphasizing the necessity
of researches aimed at investigating the meaning of the AWC as performance predictor
in swimming. Thus, the objective of the present study was to verify the use
of the y-intercept in the evaluation of the anaerobic fitness and in the performance
prediction of trained swimmers.

**METHODOLOGY**

**Participants**

Fourteen state and national level swimmers (three
female and 11 male) from the city of Bauru-SP with ages ranging from 15 to 18
years and minimum swimming competition time of two years, who trained approximately
5000 m.d^{-1} with frequency of six days.week^{1} were evaluated.
The participants were only confirmed after authorization through the consent
form, approved by the Unesp Ethics Committee, campus of Rio Claro, signed by
parents and team coaches.

**Tests**

The swimmers were evaluated during three days, when the anaerobic fitness and maximal performances tests were conducted.

No exercises of any type were performed during the 24 hours preceding the tests. This caution was taken so that no acute effect as result of training sessions could influence the results.

Before the beginning of tests, a warm-up period with duration of ten minutes at moderate intensity subjectively determined by swimmers in crawl style was performed.

**Determination of anaerobic fitness (FIT _{ANA}),
peak force (F_{peak}) and lactate peak concentration ([la^{-}]_{peak})
in tied swim**

For the anaerobic fitness determination (FIT_{ANA}),
a tied swim protocol standardized by Papoti *et al*.^{(11)} was
used due to the high stability and reproducibility of measurements (r = 0.93).
This system contains load cells (strain gages) as primary sensor element, being
suspended on two wooden beams fixed to the ground at a distance of one meter
parallel to the border of the swimming pool. A steel wire of 4.08 m length was
connected to the center of the dynamometer with a nylon belt at its opposite
extremity around the swimmer's waist at a distance of three meters in relation
to the border of the swimming pool and four meters in relation to the equipment
(figure 1).

The test itself consisted of the application
of a maximum effort in crawl style with duration of 30 s with swimmers tied
to the measurement apparatus. During the entire test, the participants were
verbally encouraged to perform maximum efforts. The beginning and end of the
test were determined by a sound signal (whistle). The deformation detected by
the load cells (strain gages) due to the tension generated by the swimmer's
effort was amplified through a portable extensometry source (*Sodmex ME-01D*).
The values obtained during efforts were sent to a computer by an interface and
stored in the *Lab View* data acquisition at 400 Hz. The values were submitted
to the residual analysis process and soothed using the fourth order "butterworth"
filter with frequency of three hertz (Hz). The 400 initial points were disregarded
so that the peak force values (F_{peak}) were not overestimated in function
of the transition from moderate swim to intense swim^{(11,29)}.

With the use of the calibration straight line
(obtained through the superposition of known weights), the values obtained were
converted into force units (N) through the *Matlab 5.3* program, thus enabling
the determination of peak force (F_{peak}) and average force (AF_{NA}).
F_{peak} was determined as the average of the five highest values during
the test. AF_{NA} was considered as indicative of anaerobic fitness
(FIT_{ANA})^{(11)}. One, three and five minutes after FIT_{ANA
}test, blood samples were collected from the ear lobe (25 µL), diluted
into 50 µL of NaF 1% and analyzed in electrochemical lactimeter (*YSI*
model *Sport 1500*, Yellow Spring Co., USA) for lactate peak concentration
determination ([la^{-}]_{peak}).

**Determination of anaerobic swimming capacity
(AWC) and maximal performances (P _{MAX})**

For the determination of the maximal performance
(P_{MAX}), five maximal efforts randomly established at distances of
100 m, 200 m, 300 m, 400 m and 600 m in crawl style were performed in 25 m swimming
pools at temperature of 27 ± 1ºC with a minimum rest period of two hours.

The distance and time values were submitted to linear regression procedure for the estimation of AWCs (distance-time model), where the linear coefficient (y-intercept) of each individual regression represented the anaerobic swimming capacities (AWCs) (figure 2).

Using all possible combinations with number
of points ranging from three to five, besides the AWC originated from protocol
proposed by Wakayoshi *et al*.^{(18)}, which only uses distances
of 200 m and 400 m, 16 AWCs were obtained (AWC_{12346}, AWC_{1234},
AWC_{1246}, AWC_{1346}, AWC_{123}, AWC_{124},
AWC_{126}, AWC_{134}, AWC_{136}, AWC_{146},
AWC_{234}, AWC_{236}, AWC_{2346}, AWC_{246},
AWC_{346} and AWC_{24}).

**Statistical treatment**

Values are presented as average + standard deviation.
The one-way analysis of variance (ANOVA) was used with *post hoc* Newman
Keuls test if necessary for all AWC obtained in this study. The relations between
AWCs with F_{peak}, Fit_{ANA}, [la^{-}]_{peak}
and performances (P_{100}, P_{200}, P_{300}, P_{400}
and P_{600}), as well as the crossing between F_{peak}, Fit_{ANA},
[la^{-}]_{peak} and performances were obtained from the Pearson
correlation analysis. In all cases, the significance level adopted was of 5%.

With the use of the *Origin 6.0* program,
the linear coefficient errors (LCE) for the AWCs obtained from three to six
velocities, called by Hill *et al*.^{(32)} as estimation standard
error.

**RESULTS**

Figure 3 presents the performance
values (m.s^{-1}) used for the determination of the anaerobic swimming
capacities, while table 1 presents the values of F_{peak},
Fit_{ANA}, [la^{-}]_{peak}, respectively.

The relation between distance and swimming time
seems to be highly linear with determination coefficient (r^{2}) ranging
from 0.99 to 1.00. Average AWC and LCE values of 25.07 ± 4.22 m and 19.30
± 5.9%, respectively, were observed, so that only AWC_{236} presented
error below 10% (8.86%). Significant differences between AWCs (P < 0.05)
were observed. However, these values were highly correlated (r @
0.80).

No significant correlations were observed between
AWCs and maximal performances or between AWCs and F_{peak}, Fit_{ANA}
and [la^{-}]_{peak} (table 2).
F_{peak} and [la^{-}]_{peak} did not present
significant correlation with P_{MAX} either. However, Fit_{ANA}
was significantly correlated with all P_{MAX} (table
3).

**DISCUSSION**

The main finding of the present study was that
the AWC presented no significant correlation with anaerobic fitness and swimmers
performance. Experimental and literature review studies have demonstrated significant
associations between AWC and the Wingate test^{(16,21,23)}, the total
accumulated intermittent work^{(19)} and the muscular ATP production^{(22)},
besides demonstrating the significant AWC contribution to the performance in
running above eight km^{(31)}. It was yet demonstrated that the AWC
is a reproducible and sensible parameter^{(23)} to the effects of enduring^{(20)},
intense^{(19)} training, and to the creatine supplementation^{(32)},
emphasizing the possibility of this parameter being used as indirect measurement
in the evaluation and prediction of anaerobic performances^{(22,30,33)}.

It is interesting to observe that the AWC values in the present study, unlike most investigations previously mentioned, presented no significant correlations with any of the maximal performances and anaerobic fitness test that used the same duration time as the Wingate test.

Guglielmo and Denadai^{(34)} found no
correlations between AWC of swimmers with the average power determined during
30-second maximal efforts in isokinetic arm ergometer. Papoti *et al*.^{(27)}
used a tied swim system and verified significant correlation between average
force (FNA) during 30-second maximal efforts and performances of 100 m and 200
m in crawl style, but not between FNA and AWC obtained through the y-intercept
of the distance x time linear relation using distances of 200 m and 400 m, proposed
by Wakayoshi *et al*.^{(18)}. In the present investigation, the
FNA, assumed by Papoti *et al*.^{(11)} as Fit_{ANA} indicative,
was also significantly correlated with performances between 100 m and 600 m
in crawl style.

Soares *et al*.^{(35)} found no
significant correlations between AWC (determined through the relation obtained
between the prefixed distance and the swimming time) and the average power in
swim bench during 45-second maximal effort in children and adult swimmers. Those
authors concluded that the AWC provides no consistent information on the anaerobic
capacity of swimmers, regardless the age range considered.

Dekerle *et al*.^{(26) }also verified
no significant correlation between AWC and the maximal anaerobic distance in
swimmers, which was considered as the distance in which the swimming maximal
velocity may be maintained, and suggested the non utilization of this parameter
to control anaerobic variables.

A possible explanation for the contradiction
observed in literature with regard to the use of AWC as parameter for the prediction
of anaerobic performances^{(19-21,32)} may be that the relation used
for the linear regression procedure considers the limit time (Tlim). The fixed-distance
model proposed by Wakayoshi *et al*.^{(18) }considers in theory
that the swimmer would not be able to support the swimming velocity imposed
during efforts at any distance above the prefixed distance (200 m and 400 m).
This hypothesis seems to limit the use of this model, considering the anaerobic
aspect only, once some swimmers are capable to support the swimming velocity
obtained at distances of 200 m and 400 m for a few more meters, probably due
to the lactate tolerance capacity.

Green^{(33)} verified that the higher
accuracy on the AWC determination of well-trained cyclists was obtained when
the exhaustion criterion for the attainment of limit times was extended until
the intensity corresponding to the O_{2}
peak rather than the impossibility of maintaining a prefixed rhythm (90 rpm).
The author believes that this criterion enables maximizing the use of substrates
generally used in the performance of anaerobic exercises and, hence, the attainment
of more accurate AWC values.

Toussaint *et al*.^{(28) }investigated
whether the concepts of critical power and AWC could be used to evaluate the
aerobic and anaerobic capacities of swimmers. To do so, the authors developed
a mathematical model related to the mechanics and energetics involved in the
crawl style, based on previous studies and evaluations performed in the swimming
flume. The authors also modeled the release of aerobic and anaerobic energy
in relation to the swimming time. The authors concluded that, although the critical
velocity is an indicative of the aerobic system, the AWC is influenced by variations
of energy from both the aerobic and anaerobic systems, thus providing no actual
estimation of the anaerobic capacity. Furthermore, the results found in literature
on its reproducibility range from r = 0.62^{(36)} to r = 0.87^{(23)}.

Other hypothesis to explain the non representativeness
of AWC as performance predictive parameter of swimmers is the great fluctuation
on the y-intercept values to small variations on the swimming velocity. In addition,
Bishop and Jenkins^{(20)} found high negative correlation (r = -0.94)
between alterations on the critical power (CP) and on AWC after six weeks of
endurance training. These authors believe that a great change on CP or AWC may
influence both variables due to the rotative effect of the mathematical model
emphasizing a limitation to the linear model to determine the critical power
and AWC.

Hill *et al*.^{(32)} reported that
the AWC is a parameter sensible to measure the anaerobic capacity only when
this one presents a linear coefficient standard error below 10%. In the present
study, the average of the linear coefficient errors remained between 9% and
29%. Only the AWC determined with distances of 200 m, 300 m and 600 m presented
error below 10% (9%). However, this AWC presented no correlation with Fit_{ANA}
and performance. Bullbulian *et al*.^{(25)} found no associations
and significant relation between AWC and the anaerobic capacity in the Wingate
test (r = 0.07), and very low when corrected by the body weight (r = 0.41),
and suggested that AWC could not be an indicative of the glycolytic anaerobic
via. Although more researches comparing AWC with validated anaerobic evaluation
methods are required as, for instance, the oxygen maximal deficit accumulated,
one may conclude that the AWC represented by the y-intercept of the distance
x swimming time relation does not seem a good parameter in the evaluation of
the anaerobic fitness and in the performance prediction between 100 m and 600
m in crawl style.

**ACKNOWLEDGMENTS**

The authors would like to thank technicians André Barbosa and Oscar Fleury from the Bauru Lusitanian-Brazilian Association for the important aid in the performance of this study.

Fapesp (process-01/08295-2) and CNPq (process-130841/2003-0).

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**
Correspondence to**

Claudio Alexandre Gobatto

Universidade Estadual Paulista (Unesp), Instituto de Biociências, Departamento
de Educação Física

Av. 24ª, 1.515, Bela Vista

13500-230 - Rio Claro, SP

E-mail: mpapoti@yahoo.com.br

Received in 15/10/04. 2^{nd} version
received in 27/12/04. Approved in 11/2/05.

All the authors declared there is not any potential conflict of interests regarding this article.