A MATHEMATICAL MODEL FOR ACCURATE DE

1
A MATHEMATICAL MODEL FOR ACCURATE DE- SCRIPTION
OF LIPID OXIDATION KINETICS DURING GRADED
EXERCISES Chenevière Xavier, Malatesta Davide,
Borrani Fabio (Institut des Sciences du Sport et
de lEducation Physique, University of Lausanne,
Switzerland) Introduction During a graded
exercise, absolute fat oxidation rates in-crease
from low to moderate exercise intensities and
then decline at higher intensities. Thus, there
is an intensity (Fatmax) at which the rate of fat
oxidation is maximal (MFO). It is known that fat
oxidation kinetics, MFO or Fat-max could be
influenced by factors such as training level,
gender, or body composition. At the same time,
Venables et al. 3 have shown that these factors
could only account for 34 of the variance of
MFO, which means there is still a large degree of
inter-individual variability in substrate
uti-lization which stays unclear. Therefore, the
aim of this study was to develop a mathe-matical
model, including different independent factors
di-latation (d), symmetry (s) and translation
(t) corresponding to expected shifts of the
basic theoretical pattern of fat ox-idation
curve, in order to model accurately all specific
fat kinetics and to determine Fatmax, MFO and the
exercise intensity (Fatmin) where the fat
oxidation rate reached zero. Methods 32 healthy
volunteers (17 women and 15 men), sedentary to
moderately trained, performed a graded exercise
test to exhaustion on a cycle ergometer, with
3-min stages and 20-W increments. Fat and
carbohydrate oxidation were de-termined by
indirect calorimetry and plotted as a function of
exercise intensity. The data over a wide range of
intensi-ties were used to develop the
mathematical model MFO sinPi(1/s)/(Pi2d)(K
(VO2max)dts,withPi 3.14andKPi/100. Results
Fitting curves constructed with this
mathematical model were as accurate as those
obtained with other methods currently used (i.e.,
polynomial curve 2 or non-protein res-piratory
quotient technique 1), and Fatmax (4410
VO2max) and MFO (0.370.16 g/min) were not
different from measured values. No strong
correlations (i.e., r lt 0.5) have been found
be-tween subjects anthropometric characteristics
and the dif-ferent factors of the model.
Nevertheless, dilatation (d) is connected with
Fatmax and MFO (r 0.79 and 0.6, P lt 0.001), and
Fatmin is significantly correlated with factors
of dilatation (d) and translation (t) (r 0.67
and r -0.76, P lt 0.001). Discussion The
sinusoidal model could accurately describe all
fat ox-idation kinetics obtained during graded
exercises, and de-termine with efficiency
important exercise parameters such as Fatmax,
Fatmin and MFO. The lack of correlations be-tween
factors and physical characteristics confirms the
idea that fat oxidation kinetics is individual
and main fac-tors such as training level or
gender explained only a little
part of the variance. Therefore, the sinusoidal
model with its independent factors could be of
great interest when in-vestigating differences
between individuals, or the impact of a specific
factor (e.g., training program) on fat oxidation.
1. Perez-Martin et al., Diabetes Metab, 2001.
2. Stisen et al., Eur J Appl Physiol, 2006. 3.
Venables et al., J Appl Physiol, 2005. Keywords
Lipid Metabolism, Modeling
12thAnnual Congress of the ECSS, 1114 July 2007,
Jyväskylä, Finland I