The energy expenditure assessment in Polar heart rate monitors is
called the OwnCal (in M-series heart rate monitors) or OwnCalS (in
S-series heart rate monitors) and it is based on prediction equations developed
and evaluated in a series of research projects. Polar Electro Oy started this
research co-operation with the UKK Institute, Tampere, Finland in 1995. Later
the Department of Human Biology at the University of Maastricht, The
Netherlands, joined the project. The first project was a comparative study
about energy expenditure assessment methods (Fogelholm et al. 1998). In this
study doubly labeled water measurements were done in obese women and compared
with Caltrac accelerometer, Fitty3 pedometer, heart rate monitoring (Polar
PE-3000), physical activity log and food diary. Heart rate, with individual
HR-EE (energy expenditure) equations, gave an unbiased estimation of daily EE
in obese females despite large individual errors in some cases. It was
concluded that the critical points in using HR as a measure of total daily EE
are (1) the choice of FLEX-point (HR discriminating sedentary and activity EE)
and (2) the discrimination of activity vs. emotion related HR above the
FLEX-point.
After the study described above, it was considered that
the association between exercise energy expenditure and heart rate should be
solved. A total of 86 women and men was measured on a bicycle ergometer and
during walking in a graded exercise protocol to define the heart rate/energy
expenditure -relation. As a result, generalizable gender specific regression
equations including age, body weight and heart rate were developed for the
energy expenditure assessment during exercise for adults (Hiilloskorpi et al.
1997,1999b). The reference measure for the EE in the laboratory was
gas-analysis based on the Weir equation (1949). The prediction yielded
r2 of 0.70 in walking. The mean deviation between the predicted and
measured EE during walking was 0.4 kcal/min and the limits of agreement
(mean±2SD) were between -4 and 3 kcal/min. In a validation study the
measured EE was underestimated by 2.7% in women and overestimated by 6.5% in
men on an average during walking. In cycling the corresponding values were
overestimations by 5.4% and 18%, respectively. Despite the rather high
overestimation in men in cycling, the obtained EE estimation accuracy was
considered satisfactory. The accuracy was more than any other commercially
available assessment method for field settings (activity recorders,
accelerometers, pedometers) could report, and Polar adopted this for the
technical development of the OwnCal feature.
After this basic study
the regression equations developed have been cross-validated in a sample of 135
adults at the Cooper Institute for Aerobics Research (unpublished). In this
data the mean differences between the predicted and measured EE were 2% in
women and 10% in men during incremental walking-jogging.
Further, the
SmartEdge heart rate monitor prototype developed was used to study the accuracy
of the energy expenditure equations on 50 adults in the field setting during
walking-jogging and cycling protocols (Hiilloskorpi et al. 1998). The results
showed that the mean difference between the energy expenditure predicted by
Polar SmartEdge equations and the measured (Cosmed K4) energy expenditure was
in females during cycling and walking -2.5 kcal/min and in males in cycling
-1.2 kcal/min and in walking -1.1 kcal/min. In two thirds of the subjects the
predicted energy expenditure differed from the measured value by less than 15%
in women and in men by less than 14 % in cycling and 12% in walking. The
difference between the gas analyzers (Medikro in the laboratory, Cosmed in the
field measurements) confused the interpretation of these results and partly
explained the underestimation in both genders in this study (Hiilloskorpi et
al. 1999a). However, based on the results it was concluded that despite this
underestimation, the EE equations built in SmartEdge provide an estimate of
exercise EE that is satisfactorily accurate in healthy adults.
The
OwnCal equations have been further validated in two studies. Altogether 40
healthy adults were measured on treadmill and on cycle ergometer at the Paavo
Nurmi Centre, Turku, Finland (Kapanen et al. 2000). The equations were
validated on heart rate levels 120-165 bpm. In men the mean difference between
the measured and estimated EE was about 2 kcal/min in cycling and about 1
kcal/min in walking-running. In women the corresponding values were less than
0.5 kcal/min both in cycling and in walking-running. In all other cases except
for in women during walking-jogging, the SmartEdge™ prediction values
were slight overestimations.
In another study of over 100 adults at
the Sports Science Institute of South-Africa, Cape Town (unpublished), the
SmartEdge EE equations were shown to predict EE at lower exercise intensities
(<10 kcal/min) with a reasonable accuracy (the mean deviation 1.6 kcal/min).
Because the OwnCal development was focused on less fit to moderately
fit individuals, the next step was to update the EE estimation calculation to
be more accurate in highly fit individuals/athletes. This resulted in the
development of OwnCalS. OwnCalS estimates EE from
exercise heart rate and individual HRmax and VO2max
(measured or predicted values). The development group consisted of 105 20-59
year old men and women (data collected in collaboration with the Cooper
Institute, Dallas, Texas). The developed model was further validated on 101 men
and women (data collected in collaboration with the UKK Institute, Tampere,
Finland). All subjects went through a maximal treadmill test with continuous
heart rate measurement and respiratory gas analysis. In the validation data,
the error of estimate (mean+/-SD) for OwnCalS was -0.7+/-1.3 and
-0.3+/-0.8 kcal/min and standard error of estimate 1.4 and 0.9 kcal/min in men
and women, respectively (Kinnunen et al. 2000). Thus, good accuracy for EE
estimation was obtained in OwnCalS.
In Physical Activity
and Health: a Report of the Surgeon General (U.S. Department of Health and
Human Services 1996) it is stated that activity leading to an increase in daily
energy expenditure of approximately 150 kcal/day, equivalent to about 1000
kcal/week, is associated with substantial health benefits.
OwnCal/OwnCalS provides a useful alternative for assessing exercise
dose in kilocalories.
References
Fogelholm M, Hiilloskorpi H, Laukkanen R, Oja P, Van Marken
Lichtenbelt W, Westerterp K. Assessment of physical activity and energy
expenditure in overweight women. Med Sci Sports Exerc 30(8), 1191-1197, 1998.
Hiilloskorpi H, Fogelholm M, Laukkanen R, Oja P, Natri A,
Mänttäri A. Factors affecting the relation between heart rate and
energy expenditure. International Congress of Movement and Sport in the
Life-Cycle of Woman, Lahti, Finland. Book of Abstracts, nr 31, 1997.
Hiilloskorpi H, Fogelholm M, Laukkanen R, Pasanen M, Oja P. Validation of
gender spesific equations for predicting energy expenditure during exercise.
Med Sci Sports Exerc 30(5), 330, 1998.
Hiilloskorpi H,
Mänttäri A, Fogelholm M, Pasanen M, Laukkanen R. The comparison
between three different gas-analysers. Med Sci Sports Exerc 31(5), nr 1787,
1999a.
Hiilloskorpi H, Fogelholm M, Laukkanen R, Pasanen M, Oja P,
Mänttäri A, Natri A. Factors affecting the relation between heart
rate and energy expenditure during exercise. Int J Sports Med, 20, 438-443,
1999b.
Kapanen J, Laukkanen R, Hiilloskorpi H, Fogelholm M, Heinonen
O. Estimation of EE during exercise by equation based on heart rate. Med Sci
Sports Exerc 32(5), nr 984, 2000.
Kinnunen H, Nissilä S.
Estimation of exercise energy expenditure from heart rate and aerobic capacity.
Proceedings of 5th Annual Congress of the ECSS, Jyväskylä, Finland,
19-23 July 2000, p 395.
U.S. Department of Health and Human Services.
Physical Activity and Health: A Report of the Surgeon General. Atlanta, GA:
U.S. Department of Health and Human Services, Centers for Disease Control and
Prevention, National Center for Chronic Disease Prevention and Health
Promotion, 1996, p 147.
Weir J. New methods for calculating metabolic
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