JOURNAL OF SPORTS SCIENCE & MEDICINE
PEAK FAT OXIDATION RATE DURING WALKING IN SEDENTARY OVERWEIGHT MEN AND WOMEN
Gregory C. Bogdanis, Anna Vangelakoudi and Maria Maridaki
Department of Sports Medicine & Biology of Physical Activity, University of Athens, Greece
© Journal of Sports Science and Medicine (2008) 7, 525 - 531
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|The aim of this study was to determine the relative exercise intensity
that elicits maximal fat oxidation during walking in inactive and overweight
men and women and evaluate any possible sex differences. Forty six healthy,
sedentary, overweight men (age: 36.3 ± 1.3 years, body fat: 28.8 ± 0.8%,
n = 28, mean ± SE) and women (age: 36.6 ± 1.8 years, body fat: 37.1 ± 0.8%,
n = 18) participated in the study. Fat oxidation was calculated from expired
air analysis using indirect calorimetry during an incremental treadmill
walking test. Peak fat oxidation rate (PFO) was higher in men compared to
women (0.31 ± 0.02 vs. 0.20 ± 0.02 g.min-1; p < 0.001), but
this difference disappeared when PFO was scaled per kg fat-free mass (4.
36 ± 0.23 vs. 3.99 ± 0.37 mg.kg fat free mass-1.min-1). Also,
the relative exercise intensity at which PFO occurred was similar for men
and women and corresponded to 40.1 ± 1.8 and 39. 5 ± 2.3% of maximal oxygen
uptake (VO2max) and 60.0 ± 1.4 and 57.8 ± 1.4% of maximal heart
rate, respectively. The walking speed corresponding to PFO was 5.5 ± 0.2
and 5.0 ± 0.1 km·h-1 for men and women, respectively. Regression analysis
showed that sex, FFM and VO2max were significant predictors of
PFO expressed in g.min-1 (adjusted R2 = 0.48, p = 0.01). However
when PFO was scaled per kg FFM, only a small part of the variance was explained
by VO2max (adjusted R2 = 0.12, p < 0.05). In conclusion, peak
fat oxidation rate and the corresponding relative exercise intensity were
similar in male and female overweight and sedentary individuals, but lower
compared to those reported for leaner and/or physically active persons.
Walking at a moderate speed (5.0-5.5 km·h-1) may be used as a convenient
way to exercise at an intensity eliciting peak fat oxidation in overweight
Key words: Exercise intensity, calorimetry, substrate utilisation.
activity in the form of regular exercise is often prescribed to facilitate
weight loss and improve health and fitness of overweight individuals (Bensimhon
et al., 2006).
Walking is the most popular activity among adults of all ages because
it is easy to perform and has a low risk of injury (Hardman, 1999).
Several studies have reported that apart from weight management (Hill
and Peters, 1998),
walking may be an effective form of exercise to improve lipoprotein profile
and insulin sensitivity in patients with increased body fat (Dumortier
et al., 2003;
However, the choice of the most appropriate exercise intensity for overweight
individuals is a challenge. Previous studies have shown that training
at a low intensity (40% of maximal oxygen consumption; VO2max)
results in increased fat oxidation during exercise in a group of obese
male subjects, while a higher training intensity (70% VO2max)
had no effect on total fat oxidation during exercise or rest (Van Aggel-Leijssen
et al., 2002).
A recent study in obese individuals (Venables and Jeukendrup, 2008)
has shown that that insulin sensitivity and the contribution of fat to
substrate oxidation during exercise were increased by 27% and 44%, respectively,
following a period of training using continuous exercise at an intensity
that elicited maximal fat oxidation (~44% VO2max). Interestingly,
no changes in these parameters were seen after a eucaloric interval training
protocol at higher exercise intensity (~65% VO2max; Venables
and Jeukendrup, 2008).
Thus, exercising at an intensity that elicits peak fat oxidation rate
(PFO) may be preferable in obese persons. However, there is large variation
of the relative exercise intensity at PFO and there is evidence to suggest
that this may be affected by body composition, exercise mode and sex (Achten
et al., 2003;
Perez-Martin et al., 2001;
Recent studies have shown that in young and healthy trained individuals
maximal rates of fat oxidation are reached at intensities between 59%
and 64% VO2max (Achten and Jeukendrup, 2004),
while these values were lower (48%VO2max) in a large sample
of the general population (Venables et al., 2005).
Unfortunately, the majority of studies have been performed on relatively
young individuals with moderate or high maximal oxygen uptake (VO2max)
and normal body composition, while there is little information regarding
fat oxidation in obese individuals (Perez- Martin et al., 2001).
Furthermore, most studies used cycling (e.g. Achten and Jeukendrup, 2003;
Perez-Martin et al., 2001),
that is a mode of exercise where fat oxidation is ~30% lower compared
to walking at an equivalent intensity, possibly due to the relatively
smaller muscle mass recruited (Achten et al., 2003).
characteristics and the predicted VO2max of the participants
are shown in Table 1. The calculated
maximal heart rate was similar for men and women (182 ± 1 b·min-1).
As expected, men were heavier and had greater FFM and VO2max
in absolute units (l.min-1) and per kg body mass compared to
women. However, VO2max was not different between men and women
when it was expressed per kg FFM (Table
The results of the bivariate correlations between PFO in absolute terms and relative terms and their possible predictor variables are shown in Table 3. When PFO in absolute terms was the dependent variable in the regression analysis, the following predictor variables were included: sex, FFM, percent body fat, and VO2max per kg body mass. When PFO relative to FFM was the dependent variable, the predictor variables entered into the model were: VO2max per kg body mass and VO2max per kg FFM. Regression analysis showed that sex, FFM and VO2max were significant predictors of PFO in g.min-1 (adjusted R2 = 0.48, p = 0.01), while only a small part of the variance in PFO per Kg FFM was explained by VO2max per kg FFM (adjusted R2 = 0.12, p < 0.05).
main finding of the present study was that PFO in overweight and sedentary
men and women was observed at a low exercise intensity (~40 % VO2max).
Furthermore, although absolute PFO rate (g.min-1) was 50% higher
in men compared to women this difference disappeared when PFO rate was
expressed relative to FFM (Figure 1).
The present study is one of the few that used walking, instead of cycling,
at a range of speeds commonly used for exercise in this type of locomotion
(Rotstein et al., 2005).
An important practical information from the results is the treadmill speed
corresponding to PFO (5.0-5.5 km·h-1) was similar to the self-selected
speed of walking (Browning and Kram, 2005;
Minetti et al., 2003).
Thus the present study has shown that this speed is not only convenient
for walking for overweight individuals (Browning and Kram, 2005),
but also maximizes the contribution of fat metabolism to energy expenditure.
It is interesting to note that walking may be preferable compared to cycling
because it enables to attain the target energy expenditure at lower heart
rate, blood lactate concentration and subjective perception of effort
Miles et al., 1980).
|PFO rate and the corresponding relative exercise intensity in male and female overweight and sedentary individuals were lower compared to those reported for leaner and/or physically active persons. Although the absolute values of PFO rate were 50% greater in men than women, the differences disappeared when PFO rate was expressed per kg FFM. The low fat oxidation rate and the early turn of metabolism to carbohydrate as energy substrate may suggest that overweight persons may have an impaired fat metabolism due to decreased physical activity and/or metabolic disturbances due to excess fat accumulation. The fact that PFO is attained at a moderate walking speed, that is similar to the reported preferred speed of walking for obese individuals, suggests that it may be prescribed as a convenient way to improve health in this population.|
Gregory C. BOGDANIS
Employment: Department of Sports Medicine & Biology of Physical Activity, Faculty of Physical Education and Sports Science, University of Athens, Greece.
Degree: MS, PhD.
Research interests: Muscle metabolism, anaerobic exercise, muscle damage, eccentric exercise.
Employment: PhD student, Department of Sports Medicine & Biology of Physical Activity, Faculty of Physical Education and Sports Science, University of Athens, Greece.
Degree: MS, PhD student.
Research interests: Sailing physiology, genetic factors influencing performance, training adaptations.
Employment: Assoc. Prof., Director of Exercise Physiology laboratory, Department of Sports Medicine & Biology of Physical Activity, Faculty of Physical Education and Sports Science, University of Athens, Greece.
Research interests: Pediatric exercise physiology, genetic factors influencing performance.