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## Revista Brasileira de Medicina do Esporte

*Print version* ISSN 1517-8692

### Rev Bras Med Esporte vol.10 no.2 Niterói Mar./Apr. 2004

#### http://dx.doi.org/10.1590/S1517-86922004000200002

**ORIGINAL ARTICLE **

**Energetic cost estimation
and contribution of different metabolic pathways in speed kayaking**

**Estimativa del costo energético y contribución
de las diferentes vias metabólicas en el canotage de velocidad**

**Fábio Yuzo Nakamura ^{I, III}; Thiago
Oliveira Borges^{I}; Odair Rodrigo Sales^{II}; Edilson Serpeloni
Cyrino^{I}; Eduardo Kokubun^{III}**

^{I}Metabolism, Nutrition and Exercise
Research and Study Group. Sports and Physical Education Center. Londrina State
University

^{II}Environmental Protection and Ecosports Association "Patrulha das
Aguas" Londrina

^{III}Biosciences Institute. Physical Education Department. State of
São Paulo University Rio Claro, SP

**ABSTRACT**

The performance of the speed kayaking depends
on the organism capacity of regenerating ATP in large amounts and high rates
from different metabolic pathways. Thus, the objective of the present study
was to combine two bioenergetic models, the first a generic one, called critical
power, and the other specific for kayaking, proposed by Zamparo *et al*.
(1999), in the attempt of producing estimations of aerobic and anaerobic fitness
for this modality, as well as establishing non-invasive estimations of the contribution
of aerobic and anaerobic systems for different distances performed. In that
purpose, 11 male kayaking athletes (16.0 ± 1.2 years; 174.0 ± 2.4 cm; 65.2 ±
4.4 kg), performed different distances (500, 1,000 and 1,790 m), at the maximal
speed as possible in kayaks type K-1 in a calm water lake. The informations
obtained were initially converted into work generated quantity (kJ) and internal
power (W). The estimated individual values were afterwards applied to three
predictive equations of critical power (PCrit) and anaerobic work capacity (CTAnaer).
Finally, the values produced were transformed into oxygen equivalence units
for the estimation of the aerobic contribution (O_{2 }equivalence for
PCrit x time required to perform the distance) and anaerobic contribution (O_{2
}equivalence for CTAnaer x time required to perform the distance) at the
different distances. The relative anaerobic contribution found for the different
distances analyzed (500, 1,000 and 1,790 m) was of 60.6; 78.6 and 89.4%, respectively.
The results found corroborate the information previously produced by other investigations,
suggesting that the procedures adopted in this study may provide reliable estimations
on the participation of the energetic pathways on the kayaking performance.

**Key words:** Kayaking. Critical power. Metabolic
pathways. Performance.

**RESUMEN**

El desempeño del canotaje de velocidad depende
de la capacidad del organismo de regenerar ATP en grandes cantidades y a altas
tasas, a partir de las diferentes vias metabólicas. Así el objetivo del presente
estudio fué combinar dos modelos bioenergéticos, un genérico denominado de potencia
crítica y otro específico para el canotaje, propuesto por Zamparo *et al*.
(1999), en la tentativa de producir estimaciones de la aptitud aeróbia y anaeróbia
para esa modalidad, así como establecer estimaciones no invasivas de la contribución
de los sistemas aeróbico e anaeróbico para diferentes distancias recorridas.
Por lo tanto, 11 atletas de canotaje (16,0 ± 1,2 años; 174,0 ± 2,4 cm; 65,2
± 4,4 kg), del sexo masculino, correrán diferentes distancias (500, 1.000 e
1.790 m), a máxima velocidad posible, en embarcaciones de tipo K-1, en un lago
con aguas calmas. Las informaciones obtenidas fueran inicialmente convertidas
en cantidades generadas de trabajo (kJ) y potencia interna (W). Posteriormente,
los valores individuales estimados fueron aplicados a las tres ecuaciones predictivas
de la potencia crítica (PCrit) y capacidad de trabajo anaerobio (CTAnaer). Por
fin, los valores producidos fueron transformados en unidades de equivalentes
de oxigeno para la estimación de la contribución aeróbica (equivalente de O_{2}
para a PCrit x tiempo para la distancia) y anaeróbica (equivalente de O_{2}
para a CTAnaer x tiempo para la distancia), a diferentes distancias. La contribución
aeróbica relativa encontrada para las diferentes distancias analizadas (500,
1.000 e 1.790 m) fue de 60,6, 78,6 e 89,4%, respectivamente. Los resultados
encontrados confirmaron las informaciones producidas anteriormente por otras
investigaciones, lo que sugiere que los procedimientos adoptados en este estudio
pueden realizar estimaciones confiables sobre la participación de las vias energéticas
en el desempeño del canotaje.

**Palabras-clave:** Canotaje. Potencia crítica.
Vías metabólicas. Desempeño.

**INTRODUCTION**

The speed kayaking, a sportive modality widely diffused throughout the European continent, is not yet much known in Brazil, despite a large number of river and lakes considered as quite adequate for this sports practice is found in the country, in several regions. However, due to the expressive results recently obtained by Brazilian athletes in international meetings, the speed kayaking has been drawing the media's attention and the sports enthusiasts, in a general manner.

Although the kayaking modality has been disputed since the Berlin Olympic Games (1936), in Germany, few are the available investigations in literature about this modality. This may be explained by the fact that in outdoor modalities such as the kayaking, the behavior of several variables to be investigated may be influenced by weather elements such as the wind, temperature and the air relative humidity.

Thus, the few studies developed on kayaking attempted
to characterize the anthropometric profile of athletes^{(1)}, to evaluate
specific physical fitness indicators for the modality^{(2)}, as well
as to address bioenergetic aspects associated to submaximal and maximal endurance
under controlled laboratory conditions^{(3,4)}.

The competition performance of maximal cyclic
sportive modalities such as the kayaking depends on the organism capacity of
regenerating ATP consumed in the muscular contraction at sufficient rates and
quantities for the performance of the external work. It is presumed that the
capacity of maintaining the intensity of a given maximal exercise is depending
on the anaerobic capacity that, when depleted, the exhaustion is established^{(5)}.

The relationship between power and effort duration
until exhaustion has been objective of many recent studies. Thus, the critical
power model has become one of the most frequently models adopted, once it seems
to describe properly the responses of the aerobic and anaerobic systems to exhaustive
maximal exercise, besides the fact that its physiologic validity has been tested
by several studies^{(6,7)}.

It is worthy emphasizing that both parameters of the hyperbolic model, the critical power and the anaerobic work capacity, respectively describe the maximal power to be aerobically maintained during the physical exercise and the maximal anaerobic capacity, once these parameters are correlated to other aerobic and anaerobic fitness indicators, also being sensible to the effects of specific trainings.

Originally proposed by Monod & Scherrer^{(7)}
for monoarticular exercises, subsequent studies have indicated that the hyperbolic
relationship between power and time until exhaustion may be extended to physical
efforts involving dislocations, and the existence of a linear relationship between
speed and power is admitted. In kayaking, particularly, the internal work that
the organism performs, especially by the upper members, should be used in order
to overcome the resistance the water provides against the boat advance. In such
conditions, the relationship between speed and power does not occur linearly,
especially at higher speeds^{(4)}.

Therefore, with the purpose of estimating the
contribution of the aerobic and anaerobic systems on the kayaking performance,
this study attempted to combine two different models of human bioenergetic performance^{(4,7)}.
For this, the parameters of the critical power model were estimated through
the conversion of the dislocation speed of maximal efforts into power units,
mechanical work and oxygen equivalents.

**METHODOLOGY**

**Subjects**

Eleven male speed-kayaking athletes (16.0 ± 1.2 years; 174.0 ± 2.4 cm; 65.2 ± 4.4 kg), of national level competitions from cadet and junior categories with over one year of practical experience in this modality, voluntarily participated in this investigation. After being informed about the objectives of the present study and procedures they would be submitted to, all participants and their parents signed up an informed consent form.

**Kayaking tests**

The athletes performed different distances (500, 1,000 and 1,790 m), at maximal speed as possible in kayaks type K-1 (maximal length of 5.2 m and minimal mass of 12 kg) in a calm water lake. Each one of the three tests was preceded by a quick warm-up, where the athletes were to run for 1,000 m at a self-selected rhythm.

At the end of the warm-up exercise, the subjects were positioned at a preestablished point for the start of the distance to be performed at that day. At the sound sign emitted by one of the investigators, the athletes were encouraged to perform at the shortest time as possible the distance proposed, which was recorded with the aid of a digital watch calibrated in seconds. The same procedure was repeated in the three testing occasions.

All three tests were applied along a seven-day period with a 24-hour minimal interval between each. In the attempt of reducing the possible impact of the wind speed, the tests were rather performed in sunny days, with winds both favorable to and against the kayaks' linear movement direction. It is worthy emphasizing that it rained only one out of the seven days. Tests programmed for that day were postponed until weather conditions were reestablished.

**Calculations**

The individual time data for the different distances
(500, 1,000 and 1,790 m) and the respective average speeds were recorded to
be analyzed by means of equations proposed in literature^{(4,6)}.

Based on these information, the internal work
required to perform the fixed distance of one meter was estimated through equation
1, proposed by Zamparo *et al*.^{(4)} for the different average
speeds of water dislocation, recorded at distances of 500, 1,000 and 1,790 meters.

where C_{k} represents the dislocation
energetic cost in kayaking (kJ.m^{-1}), whereas v is the dislocation
speed (m.s^{-1}). Therefore, according to equation 1, the energetic
cost per distance unit is related to the dislocation speed through a power function.

From the conversion of measure units promoted
by the equation 1, it was possible to estimate the internal mechanical work
required for the distances of 500, 1,000 and 1,790 m to be achieved, as well
as the internal mechanical power. In this purpose, the total internal work was
calculated through the simple multiplication of C_{k} by the distance
performed, while the power was obtained through the division of the internal
mechanical work by the effort time, in seconds.

Following, the individual data regarding effort
time, work and power were applied into three models mathematically equivalent^{(6)},
according to the critical power model^{(7)}, which are presented as
follows:

The estimations of critical power (PCrit) in
watts (W) and the anaerobic work capacity (CTAnaer) in joules (J) were then
converted into O_{2} equivalents through the known relationship between
the metabolized O_{2} volume and the mechanical work (20.9 kJ. lO_{2}^{-1}).
Thus, one could obtain the respective estimations of the O_{2} equivalent
for the critical power (EqO_{2PCrit}), which represents the average
oxygen cost for exercises performed at PCrit and the maximal accumulated oxygen
deficit (MAOD), that would be a fixed quantity of anaerobic energetic reserve
available for the supramaximal effort (above PCrit).

The aerobic and anaerobic energetic contributions
were estimated taking into consideration that the MAOD was reached in all distances,
once the distances have been performed at maximal speed. Thus, the MAOD value
establishes the absolute anaerobic energetic contribution in the exercise. The
aerobic contribution was estimated multiplying EqO_{2PCrit} by the effort
time in each distance.

**Statistical treatment**

The data were initially treated through descriptive
procedures. For the estimations of the critical power parameters (PCrit and
CTAnaer), the determination correlation coefficient (r^{2}) and the
estimation standard errors (EPE) were calculated for each parameter. The analysis
of variance (ANOVA) for repeated measures was employed for the comparison between
the results obtained from the three tests adopted (500, 1,000 and 1,790 m) as
well as for the comparisons between the different equations (1, 2 and 3), according
to the critical power model. The Scheffé *post hoc* test for multiple comparisons
was used for the identification of differences between averages. The preestablished
significance level was of *P* < 0.05.

**RESULTS**

The time required for the kayakists to accomplish
the distances of 500, 1,000 and 1,790 m and the respective dislocation average
speeds are presented on table 1. The average speed values
decreased significantly with the increase of the distances performed (*P*
< 0.05). The decrease found was on the order of ~4% when the distance was
doubled (500 versus 1,000 m) and of ~8% when compared to the distances of 500
and 1,790 m. It is also worthy emphasizing that, although the decrease on the
average speed has been proportionally larger when compared to the distances
of 500 versus 1,000 m than when compared to the distances of 1,000 versus 1,790
m, statistically significant differences were verified in all comparisons, following
the modifications observed in the tests execution time (*P* < 0.05).

The estimations of the C_{k}, the internal
mechanical work and the internal mechanical power from the equation proposed
by Zamparo *et al*.^{(4)} are found in table 2.
Statistically significant differences were verified in the C_{k} (*P*
< 0.05), in the internal work (*P* < 0.05) and in the internal mechanical
power (*P* < 0.05) between the different distances. A reduction on C_{k
}(9% and 18%), when analyzed relatively to the distance performed in meters
and at the absolute internal mechanical power (13% and 25%), followed by an
increase on the absolute internal work (81% and 193%), was verified in the comparisons
between 500 and 1,000 m and between 500 and 1,790 m, respectively (*P*
< 0.05).

The figure 1 illustrates
the values of the internal mechanical work, the internal mechanical power and
the effort time of an investigated athlete, applied to the equations 2, 3 and
4, according to the critical power model. Through visual inspection, the performance
data seem to be suitable for the equations used. This fact could be also confirmed
through the high determination coefficient values (r^{2}) presented
on table 3.

The table 3 contains information
about PCrit and CTAnaer estimated through equations 2, 3 and 4, followed by
the respective estimation standard errors (EPE) and by the determination coefficient
(r^{2}). Significant differences were verified in both, the estimations
of PCrit provided by the different equations (*P* < 0.05), with the
largest values found through equation 4 (*P* < 0.05) and the estimations
of CTAnaer (*P* < 0.05) with the largest values found through equation
2 (*P* < 0.05). The average EPE of PCrit provided by the equation 2
was smaller (*P* < 0.05) than those verified in equations 3 and 4, whereas
the average EPE of CTAnaer provided by equation 3 was smaller (*P* <
0.05) than those verified in equations 2 and 4. With regard to the values of
r^{2}, associations significantly higher in equations 2 and 3 when compared
to the equation 4 (*P* < 0.05) were verified.

The conversion of the PCrit and CTAnaer values
into O_{2} equivalents produced estimated values of EqO_{2PCrit}
and MAOD (table 4). Significant differences were verified
in the comparisons between the equations both for the EqO_{2PCrit} (*P*
< 0.05) and for the MAOD (*P* < 0.05). The highest value of EqO_{2PCrit}
was found through the equation 4 (*P* < 0.05), approximately 7% and
4% higher than the values generated through equations 2 and 3, respectively.
On the other hand, the MAOD found through equation 2 was significantly higher
(*P* < 0.05) than the value estimated through equations 3 (14%) and
4 (34%).

Table 5 presents the estimations
of the distance total O_{2} cost (the sum of the absolute contributions
of the aerobic and anaerobic systems of energetic transference) as well as the
aerobic and anaerobic contributions estimated for the distances of 500, 1,000
and 1,790 m, from the presupposed application of the critical power model^{(7)},
combined with the equation proposed by Zamparo *et al*.^{(4)},
for the calculation of C_{k}. Statistically significant differences
were verified both in the O_{2} (*P* < 0.05) cost and in the
contribution percentage of the aerobic and anaerobic systems (*P* <
0.05). The O_{2} cost for the distance of 500 m was 39% and 64% lower
than the cost observed for the distances of 1,000 m and 1,790 m, respectively.
Thus, the results indicated a smaller contribution of the aerobic system for
the distance of 500 m and, as result, a larger contribution of the anaerobic
system (23% and 32%, when compared to the distances of 1,000 m and 1,790 m,
respectively).

**DISCUSSION**

The speed kayaking is a sport modality performed in calm waters in kayaks for one (K-1), two (K-2) or four (K-4) athletes, while the competition official distances are 200, 500 and 1,000 m. In this study, only athletes using kayaks type K-1 were investigated.

In the present study, the contribution of the energetic systems was estimated from the different distances performed by competition kayakists. Furthermore, the combination between two mathematical models: a generic bioenergetic model called critical power model and a specific model for the kayaking energetic cost estimation was tested in the attempt of producing parameters of aerobic and anaerobic fitness specific for speed kayaking.

The first model, known as the critical power
model^{(7)}, presupposes the existence of two energetic parameters (PCrit
and CTAnaer) related to the performance at different types of physical exercises.
The PCrit represents the maximal power that could be maintained for a long period
at the expense of the aerobic metabolism^{(7,8)}, while the CTAnaer
represents the maximal quantity of work generated from the intramuscular reserve
of high energy phosphagen and from the anaerobic glycolisis^{(7)}. Thus,
the PCrit is coincident with the maximal steady-state of O_{2}
and lactate^{(9)}, being used as an indicator of the aerobic capacity^{(10)}.

On the other hand, the CTAnaer may be quantitatively
compared to the MAOD, also showing a good correlation with this index^{(11)},
thus being considered as a valid measure of the anaerobic capacity^{(12)}.

The second model was developed specifically for
speed kayaking^{(4)}. Through the direct measures of O_{2}
and blood lactate, and through the estimation of the muscular phosphagen concentrations,
the model's authors proposed an equation for the forecast of the energetic cost
of human dislocation in kayaks at different speeds.

Therefore, the approach proposed in the present study may be considered as original, once it seeks to combine two different mathematical models of mechanical and bioenergetic performances.

The equation of Zamparo *et al*.^{(4)}
for the determination of the kayaking energetic cost was employed for the forecasting
of the internal work and power produced in each distance performed by kayakists.
These data, in addition to the respective tests duration, were used for solving
equations 2, 3 and 4, which provided estimations of PCrit and CTAnaer. The estimations
produced are non-conventional, once they reflect internal parameters rather
than parameters externally measured, as proposed by Monod & Scherrer^{(7)}.

One of the criterions for the estimations provided
by equations 2, 3 and 4 to be reliable is that the differences between the values
of PCrit and CTAnaer produced by such equations are not significant^{(6)}.
Thus, it would be desirable that the variability between the equations was below
10%, above all for the CTAnaer could be considered as an accurate measure of
the anaerobic capacity^{(11)}, which valid measure is provided by the
MAOD.

In the present study, the presence of significant
differences between the estimations of CTAnaer and consequently of MAOD between
the three equivalent equations reflects the presence of probable systematic
errors in the empiric data regarding the tests. This may indicate that the equation
proposed by Zamparo *et al*.^{(4)} or the critical power model
are not adequate for the conditions of this study.

The variability between the estimations of CTAnaer
from the three equations in this study was higher than the variability proposed
by Hill & Smith^{(11)}, reaching 25% when the lowest and the highest
average values are compared (equations 4 and 2, respectively). On the other
hand, the values of PCrit varied only 7%. As the difference between the parameters
provided by the different equations was significant, the random utilization
of any of them in the subsequent analyses could influence the results interpretation.
Thus, the equation 2 was adopted as referential of analysis in this study, once
it places mathematically right the dependent (time) and the independent (power)
variables, fact that does not occur to the other equations, thus being considered
by some researchers^{(13)}, as the most adequate equation among all
equations employed.

The EPE produced by the three equations employed
should also be below 10% so that the CTAnaer would reflect the MAOD precisely,
keeping in mind that a high EPE leads to considerable random errors in the results
modeling of exhaustion tests, according to the equations of the critical power
model^{(11)}. In the present study, the EPE of the CTAnaer found ranged
from 15% to 25%, whereas the EPE variation of the PCrit ranged from 2% to 6%.

The results indicate that the CTAnaer is more
susceptible to the variation due to systematic and random errors of tests treated
from the equation of Zamparo et al.^{(4)}. These results corroborate
with findings of Moysés *et al*.^{(14)} that, when investigating
the critical power model in 20 m bidirectional running, reported high values
of the systematic and random errors for CTAnaer, when compared to those associated
to the PCrit.

The PCrit and CTAnaer estimations generated through
equation 2 were used for the calculation of EqO_{2PCrit} and MAOD. The
MAOD confidence interval estimated in the present study includes the averages
found by Faina *et al*.^{(15)} (3,2 l and 3 l, respectively), for
elite kayakists submitted to high-intensity arm cycle ergometer exercise, adapted
to simulate the paddling movement and frequency, typical of the modality. It
is worthy emphasizing that in this study, the researchers have determined the
MAOD according to the recommendations originally proposed by Medbo *et al*.^{(12)},
through the use of indirect calorimetry procedures for the attainment of the
O_{2}.

On the other hand, the EqO_{2Pcrit} found
in this study (1.96 l.min^{-1}) could not be compared to results from
other studies available in literature by being considered as an unusual measure.
It is also worthy emphasizing that the EqO_{2PCrit} is an estimation
of the average aerobic contribution per time unit along the complete exercise,
not taking into consideration the O_{2}
inertia. Therefore, the EqO_{2PCrit} measure overestimates the actual
O_{2}
value at the beginning of the exercise and underestimates it at the end of it.

At the final phase of this study, the EqO_{2Pcrit}
and the MAOD were employed for the estimations of the aerobic and anaerobic
systems percentile contribution during the different distances performed at
maximal speed by kayakists. According to the presupposition of the critical
power model in which the EqO_{2Pcrit} and the MAOD are fixed in exhaustive
activities, the aerobic system percentile contribution increased with the increased
distance performed. Consequently, the anaerobic system percentile contribution
was higher in shorter distances.

The estimations found for the distance of 500
m were similar to estimations reported by Zamparo *et al*.^{(4)}
(60% and 40% of aerobic and anaerobic contributions, respectively). On the other
hand, for the distance of 1,000 m, Zamparo *et al*.^{(4)} found
an aerobic contribution slightly higher than the contribution found in this
study (83% versus 79%), although within the confidence interval established
in our study for this variable.

On figure 2, the data obtained
in the present study were superposed to a data compilation from the literature
performed by Gastin^{(16)}, with regard to the aerobic system relative
contribution at different maximal exercises. It is observed that the confidence
interval of the present study is within the compiled data. These results indicate
that energetic contribution estimations according to procedures used in this
study result in values comparable to those reported in literature for other
types of exercise.

**CONCLUSIONS**

The informations produced in the present study
suggest that the association between the critical power model and the equation
proposed by Zamparo *et al*.^{(4) }for the determination of the
kayaking energetic cost provide interesting estimations about the aerobic and
anaerobic fitness, represented by EqO_{2PCrit} and MAOD, respectively.
Furthermore, the presuppositions adopted in this study also seem to enable the
forecasting of the aerobic and anaerobic energetic systems relative contributions
at different distances in the speed kayaking, with no need of invasive procedures
or procedures of direct determination of physiological variables.

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

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**
Correspondence to**

Fábio Yuzo Nakamura

Grupo de Estudo e Pesquisa em Metabolismo, Nutrição e Exercício

Centro de Educação Física e Desportos

Universidade Estadual de Londrina

Rod. Celso Garcia Cid, km 380, Campus Universitário

86051-990 Londrina, PR Brasil

E-mail: fabioy_nakamura@yahoo.com.br

Received in 13/11/03

2^{nd} version received in 11/1/04

Approved in 21/1/04