Critical Velocity and Anaerobic Capacity of Running Rats
40
Journal of Exercise Physiologyonline
(JEPonline)
Volume 13 Number 4 August 2010
Managing Editor
Tommy Boone, PhD, MPH
Editor-in-Chief
Jon K. Linderman, PhD
Review Board
Todd Astorino, PhD
Julien Baker, PhD
Tommy Boone, PhD
Eric Goulet, PhD
Robert Gotshall, PhD
Alexander Hutchison, PhD
M. Knight-Maloney, PhD
Len Kravitz, PhD
James Laskin, PhD
Derek Marks, PhD
Cristine Mermier, PhD
Chantal Vella, PhD
Ben Zhou, PhD
Official
Research Journal of
the American Society of
Exercise Physiologists
(ASEP)
ISSN 1097-975
Metabolic Responses to Exercise
Determination of Critical Velocity and Anaerobic Capacity of
Running Rats
FÚLVIA DE BARROS MANCHADO-GOBATTO1, CLAUDIO
ALEXANDRE GOBATTO2, RICARDO VINÍCIUS LEDESMA
CONTARTEZE3, MARCELO PAPOTI4, GUSTAVO GOMES DE
ARAUJO3, MARIA ALICE ROSTOM DE MELLO3
1Health
Science College, Methodist University of Piracicaba - UNIMEP,
Piracicaba, Brazil, 2State University of Campinas - Department of Sport
Sciences - UNICAMP, Campinas, Brazil, 3Sao Paulo State University UNESP. Department of Physical Education, Rio Claro, Brazil, 4Sao
Paulo State University-UNESP. FCT, Presidente Prudente, Brazil
ABSTRACT
Manchado-Gobatto FB, Gobatto CA, Contarteze RL, Papoti M,
Araujo GG, Mello MAR. Determination of Critical Velocity and
Anaerobic Capacity of Running Rats. JEPonline 2010; 13(4):40-49. The
aim of this study was to validate a non-invasive protocol to determine
aerobic and anaerobic capacity of treadmill running rats. Thirteen male
Wistar rats (90 days old) were submitted to 4 exercise tests, consisting
of running at 25, 30, 35 and 40 m∙min-1, continuously until exhaustion.
For the critical velocity (CV) and anaerobic running capacity (ARC)
estimations, the hyperbolic curve (velocity versus time to exhaustion
(tlim)) was linearized to V= CV+ARC/tlim, where the CV and ARC were
linear and slope coefficients, respectively. In order to verify if the CV was
the maximal aerobic intensity, the rats were submitted to the maximal
lactate steady state test (MLSS) composed of three 25-minute tests of
continuous running trials at 15, 20 and 25 m∙min-1, with blood collection
every 5 minutes. The CV was obtained at 22.80.7 m∙min-1 and the
ARC, at 26.802.77 m. The MLSS was observed at 20m∙min-1, with
blood lactate 3.84  0.31 mmol∙L-1. There was a progressive increase in
lactate concentration at 25 m∙min-1. The CV and MLSS were different,
but presented a high and significant correlation (r=0.81). These results
indicate that the non-invasive protocol can be used for physical
evaluation of aerobic running rats, but the ARC should still be further
investigated.
Key Words: Non-invasive Protocol, Treadmill Running, Wistar Rats,
Blood Lactate.
Critical Velocity and Anaerobic Capacity of Running Rats
41
INTRODUCTION
The determination of the transition intensity between the predominance of the aerobic and anaerobic
metabolisms in the energy supply for exercise is of extreme importance, both in sport performance
evaluation and in physical training prescription, as well as in the prevention and treatment of
diseases. Therefore, numerous studies have been conducted to establish protocols to identify this
metabolic transition (9,27,36-38,42). The most popular protocols are the ventilatory threshold (VT)
(42); the anaerobic threshold proposed by Kinderman et al. (27), the anaerobic threshold obtained by
the 4.0 mmol∙L-1 blood lactate concentration (OBLA) (36), and the lactate minimum test (38). These
protocols include invasive procedures and/or are expensive.
In 1965, Monod and Scherrer observed that the mechanical power generated at different effort
intensities and their respective durations until exhaustion presented a hyperbolic relationship. These
authors postulated the existence of a critical power (CP), equivalent to the maximal power that the
individual can maintain indefinitely, theoretically, for an infinite time period, proposing then, the
“Critical power model”. Moritani et al. (1981) extended the critical power concept to cycling exercise,
and provided evidence of the anaerobic nature of the intercept of the work-time relationship, referred
to as AWC or anaerobic work capacity.
The relation power vs. time of exercise until exhaustion (tlim) represents a hyperbolic response.
Therefore, the non-invasive CP determination technique consists of using one of the parameters from
the hyperbolic function that correlates exercise intensity with maximum time until exhaustion. Some
mathematical models have been employed in order to describe the relation between work limit and
time limit (7,22,23), calculating their variables (CP and AWC). It is possible to calculate the
mathematical linearization of the curve by using the exercise power and the inverse value of the time
to exhaustion during exercise or time limit (1/tlim) (20). Based on this linearization, the Y-intercept
and the slope of linear regression are obtained, where the first one corresponds to the CP and the
second to the AWC.
This mathematical model, originally purposed by Monod and Scherrer (1965), has become commonly
used. According to Hill (1993), Jenkins and Quigley (1990), and Jenkins et al. (1998), the CP and
AWC determination provides advantages such as non-invasiveness, easy application and the
requirement of low-cost materials or equipment. With the aid of an ergometer and a chronometer, it is
possible to estimate both aerobic (CP) and anaerobic (AWC) capacities. Thus, the application of this
method has been utilized across sports among them running, swimming, soccer and others,
corroborating its usefulness in the prediction of parameters related to the traditional determinations of
anaerobic and aerobic capacities. The use of this method is not only attractive for its non-invasive
characteristic, but also for allowing specific evaluations in sports (6,16,19,33,41).
In addition to the simplicity of its determination, CP has proven to be highly related to the aerobic
capacity parameters in humans, such as ventilatory threshold, lactate threshold, maximal oxygen
uptake (21,24), fatigue threshold (14) and maximal lactate steady state (35), being the latter
considered gold standard for the quantification of aerobic conditioning.
Numerous studies have been conducted with experimental models using animals, mainly rats, with
the aim of verifying physiological responses to exercise and after physical training interventions. Due
to the scarce number of animal evaluation protocols, there are few studies involving the evaluation
and control of exercise intensity.
Critical Velocity and Anaerobic Capacity of Running Rats
42
In the last decade, our research group adapted and developed new methods for the evaluation of
swimming and running rats. These protocols include an incremental test for swimming rats (17), a
maximal lactate steady state for aerobic evaluation in sedentary and trained swimming rats (18), a
lactate minimum test performed in water (26), and a maximal lactate steady state in running rats (29).
In 2002, Marangon et al. (28) tested the adaptation of non-invasive critical power model, initially
suggested for human evaluation (31) to swimming rats. The results were satisfactory, demonstrating
the adequacy of this model for the evaluation of the aerobic capacity in animals.
Billat et al. (2005) also evaluated the mouse critical running speed using a non-invasive but
exhaustive procedure. In this study, the possibility to determine critical velocity in the mouse model
was examined taking into account strain (CD1, C57BL/6J, FVB/N) and sex. The critical velocity was
not significantly different from lactate threshold velocity. For this reason, the authors conclude that
CV, which reflects the aerobic capacity, can be determined in mice, as well as in human beings and
horses.
Since the critical power model presents simplicity in its determination and proved to be correlated to
the maximal lactate steady state, considered the gold standard for the aerobic capacity evaluation
(1,5), the present study was designed to validate the critical power model to the evaluation of aerobic
(critical velocity) and anaerobic (anaerobic running capacity) parameters in running rats.
METHODS
Animals
All experiments involving animals were conducted according to the American College of Sports
Medicine politics. Thirteen male sedentary Wistar rats (90 days old) weighting 438±27g were used.
During the experiment, the animals received water and commercial chow for rodents (Labina-Purina,
Pet Care Company, Paulínia - SP) ad libitum. The rats were housed in collective cages (5 animals
per cage), in a room with a light cycle from 06:00am to 6:00pm, at 25C. All animal procedures
complied with the European Convention for the Protection of Vertebrate Animals used for
Experimental and other Scientific Purposes of the Council of Europe, n 123, Strasbourg, 1985.
Selection of the running rats and adaptation to the treadmill exercise
The selection of running rats occurred for 10 consecutive days with animals running for 5 minutes at
velocity of 15 m∙min-1. The sedentary animals that were able to run for 9 or 10 days were selected for
the experiment. Later, the selected animals were adapted to the treadmill exercise. This adaptation
consisted of daily runs performed 5 days/week during 3 weeks, with duration of 1-5 min and velocity
5-10 m∙min-1. The adaptation was aimed at reducing ergometer-induced stress without promoting
physiological alterations in relation to physical training.
Experimental Protocol
Determination of the Critical Velocity and Anaerobic Running Capacity
The animals were initially submitted to a protocol composed of four exhaustive running tests at for
distinct velocities equivalent to 25,30,35 and 40 m∙min-1. The velocities were alternated in intervals of
48 hrs and randomly distributed among rats. For each velocity (V expressed as m∙min-1), the
individual tlim in seconds was recorded. The velocities were selected expecting the exhaustion to
occur between 1 and 15 min of exercise (7,25).The exhaustion criterion adopted was when the
animal showed exhaustion being paralyzed for 5 seconds due to the intensity imposed by the
treadmill. Electrical stimulus was not used in this experiment.
Critical Velocity and Anaerobic Capacity of Running Rats
43
As for human beings, the CV and the AWC were determined by the relationship between the V and
the tlim through the hyperbolic function (tlim=ARC/V-CV) (Figure 1). For the determination of the CV
and ARC parameters, the linear fit of the hyperbole was used (V=CV+ARC/tlim), in which plotting the
linear regression, the CV corresponds to the Y-intercept and the ARC the slope of regression line (13)
Determination of the Maximal Lactate
Steady State
In order to verify the possible stabilization of
the blood lactate at the CV intensity
estimated through the non-invasive model,
the rats were submitted to 25 min of
continuous exercise in intensities equivalent
to 15, 20 and 25 m∙min-1 velocities
(10,11,29) Each velocity test was separated
by 48 hours. The sequence of velocities
was distributed at random, and the same
velocity was never used twice by the same
rat. Each test consisted of continuous
running for 25 min until exhaustion with a
Figure 1. Example of linear regression (velocity x
-1
single velocity. Blood samples for lactate
1∙tlim ) for one rat. The value of the slope of
determination were collected six times:
regression line is equivalent to the ARC and the
before the beginning and every five min of
Y-intercept corresponds to the CV of this animal.
exercise during the test. The highest
intensity in which the increase on blood lactate concentration was equal to or below 1 mmol∙L-1 from
the 10th to the 25th minutes was considered the maximal lactate steady state (MLSS) (1,18,29).
Blood Samples and Analysis
During the tests, blood samples (25 l) were collected from the tail of animals in periods already
described then placed in Eppendorf tubes (1.5 ml capacity) containing 50 l of sodium fluoride (1%).
Blood lactate concentrations were determined in a lactate analyzer (YSI 1500 Sport, Yellow Springs,
USA).
Statistical Analysis
The regression coefficient of the individual curves linear adjustment V versus 1/tlim was initially
analyzed with the objective of testing the model for our exercise protocol. The normality test was
applied. A One-Way ANOVA and Newman-Keuls test were used for the comparison of the tlim for the
four exercise velocities. For the comparison of the CV and MLSS, the paired t-Student test was used.
The Pearson Correlation test identifies the correlation between MLSS and CV. Statistical effect size
(d) and statistical power (p) were also determined. In all statistical procedures the significance level of
P<0.05 was adopted (12). The statistical package used was STATISTICA 7.0 (StatSoft, Inc., Tulsa,
OK)
RESULTS
Results are expressed in mean ± SEM. Figure 2 presents the tlim for animals at different velocities.
The obtained tlim were in range of time suggested by Bishop et al. (1998) and Jenkins et al. (1998).
The One-Way ANOVA identified that the tlim for the four exercise velocities were different (Figure 2).
Critical Velocity and Anaerobic Capacity of Running Rats
44
Table 1 presented the individual CV and
ARC values for the rats estimated by noninvasive model proposed and the linear
coefficients for linear adjustment (R2). The
CV (m∙min-1) and AWC (m) obtained were
respectively 22.8±0.7 and 26.80±2.77,
with
significant
linear
adjustment
2
(R =0.88±0.30) (Table 1).
The animals presented MLSS at
3.840.31mmol∙L-1 of blood lactate, at the
velocity of 20 m*min-1. At 15 m∙min-1,
there was also stabilization of blood
lactate, but in lower concentration
(3.170.36 mmol∙L-1). There was a
progressive increase in blood lactate
concentration at 25 m∙min-1 and some
animals (approximately 10%) reached
exhaustion between the 10th and 25th
minute of exercise (Figure 3).
Figure 2. Time to exhaustion (tlim) obtained for
animals at four different velocities. Results are
expressed as mean ± sem. *Significant difference
between all values (P≤0.05).
The CV and MLSS presented a high and significant correlation (r=0.81), but the non-invasive model
overestimated the MLSS intensity by approximately 10%. The effect size for CV and MLSS was d>3
and the statistical power was p>0.93.
DISCUSSION
The critical power model purposed
by Monod and Scherrer (1965)
provides a simplified methodology
for the aerobic and anaerobic
evaluation in human beings, which
is the reason why this model has
been target of a large number of
laboratory and specific studies in
several sport modalities (19,33,35).
Figure 3. Maximal Lactate Steady State (n=13). The results
expressed the blood lactate concentrations during running
continuous exercise tests at 15 m∙min1, 20 m∙min-1 and 25
m∙min-1 (mean ± SEM).
Laboratory animals are often used
in studies involving exercise.
However,
few
studies
have
determined the actual effort
intensity
for
animals
during
swimming and running exercises.
Due to its simplicity and reduced
risks, the non-invasive methods to evaluate the physiological responses to exercise seems to be
adequate for the determination of the aerobic and anaerobic condition in humans and animals. In the
present study, we have selected treadmill running exercise and adapted the non-invasive critical
power model for aerobic and anaerobic evaluation of sedentary rats.
Critical Velocity and Anaerobic Capacity of Running Rats
45
According to Monod and Scherrer (1965), the mechanical power produced at different effort
intensities and their respective time to exhaustion presents a hyperbolic relationship in humans. In
Figure 2 it is possible to observe that the animals tlim at the 4 different running velocities presented
similar relationship as the ones described in humans. Also at the higher velocities, the time to
exhaustion was reduced. Further, it is possible to observe that time to exhaustion in all velocities
occurs between 1 and 15 min, as suggested by Bishop et al. (1998) and Jenkins et al. (1998).
As proposed by Marangon et al. (2002), using
swimming rats, and Billat et al. (2005) in their
study using running mice, our findings also
demonstrated that the adaptation of the noninvasive protocol initially suggested for humans
(5,33) may represent a way to evaluate the effort
intensity in animals. Table 1 shows results that
corroborates with this statement. In agreement
with results obtained by Marangon et al. (2002),
for all cases, the linear fit obtained with results of
time to exhaustion was satisfactory and
statistically significant (R2=0.880.03), using the
linearization of the hyperbole method purposed
by Hill (1993). Billat et al. (2005) reported similar
results using running mice.
The critical velocity (CV) of sedentary rats
obtained
by
non-invasive
model
was
22.8±0.7m∙min-1. Billat et al. (2005) adapted the
critical power model for running mice evaluation
and obtained the critical velocity at 15 m∙min-1
intensity. These differences among studies using
Wistar rats and mice demonstrate that the critical
model parameters are dependent to animal
species differences.
Table 1. Results of the individual locity (CV)
To test the CV determined by the non-invasive
and anaerobic running capacity (ARC) of the
model, the Wistar rats were submitted to the
rats, estimated by non-invasive model and
maximal lactate steady state method, considered
linear coefficients for linear fit (R2).
the “gold standard” protocol for aerobic
evaluation of humans (1,2,3,5) and rats (18,29). Figure 3 shows the results of blood lactate kinetics
in three different velocities. The highest intensity in which the increase on the blood lactate
concentration was equal to or below 1 mmol∙L-1 from the 10th to the 25th min was considered the
MLSS (6,29). In the present study, the MLSS was obtained at 20 m∙min-1, with blood lactate
concentration of 3.84 ± 0.31 mmol∙L-1. These results corroborate with our previous study in which we
observed MLSS of sedentary running rats at similar intensity (29). According to Pillis et al. (1992) and
Langfort at al. (1996), the anaerobic threshold obtained by incremental protocol with rats in treadmill
running occurs in same blood lactate concentration (4 mmol∙L-1).
When the effort intensities as estimated by the non-invasive procedure and MLSS were compared,
we observed that CV overestimated the MLSS by 10%. In other studies accomplished in humans,
similar results were obtained. Pringle and Jones (2002) evaluated a group of cyclists and calculated
Critical Velocity and Anaerobic Capacity of Running Rats
46
the power equivalent to fatigue threshold, critical power and maximal lactate steady state. The
authors also observed that the critical power was 10% higher than MLSS.
Despite of the overestimation observed in the present study, the critical power model seems to be
appropriated for aerobic evaluation of rats since there was a high and significant correlation between
CV and MLSS intensity (r=0.81). However, small adjustments at critical velocity, in a range of 10%,
should be considered.
The anaerobic running capacity also was estimated using the non-invasive model adapted to rats.
This possibility is another relevant aspect for the critical power model. In the present study, the
anaerobic running capacity was 26.80±2.77 m. Unlike the CV, already well established and
considered as an aerobic capacity (14,41), the physiological response associated with the anaerobic
parameter is still questionable and of difficult understanding. Some studies have shown correlation
between anaerobic work capacity and other anaerobic indexes, such as oxygen deficit and maximal
accumulated oxygen deficit (22) and Wingate test (19). On the other hand, Bulbulian et al. (1996) did
not observe a positive correlation between AWC and Wingate test in male and female subjects. In the
same way, Dekerle et al. (2002) also did not verify a significant correlation between AWC and
maximal anaerobic distance performed by swimmers. Other studies also failed in finding this
correlation and questioned the AWC physiological relevance (13,39). Further investigation on the
anaerobic parameter determined by critical power model is necessary, especially using laboratory
animals.
We consider that the non-invasive protocol purposed in the present study may be useful as a tool for
the evaluation of running rats, especially for animal models of diseases such as diabetes and obesity.
CONCLUSIONS
In summary, the results of the present study indicate that critical power model adapted to treadmill
running was adequate for the aerobic evaluation of running rats, but the anaerobic running capacity
requires further investigations.
ACKNOWLEDGEMENTS
We would like to thank the FAPESP (Proc. 07070-5/2004), CAPES and CNPq for the financial
support.
Address for correspondence: Fúlvia de Barros Manchado-Gobatto, PhD, Health Science College,
Methodist University of Piracicaba - UNIMEP, Piracicaba, Sao Paulo, Brazil. Phone: +55 (19)
31241558; Fax: +55 (19) 31241659 ; E-mail: fbmanchado@yahoo.com.br, fbgobatt@unimep.br
13400-911
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