The Polar Fitness Test resulting in OwnIndex (in Polar M-series
heart rate monitors M61 and F92ti) or OwnIndexS (in Polar S-series
heart rate monitors S210, S410, S520, S610i, S625X, S720i, S725 and S810i)
predicts maximal aerobic power (maximal oxygen uptake, VO2max). The
test has been developed using artificial neural network calculation, which is a
widely used method in signal processing.
In the test development
study, 305 laboratory fitness measurements of 15-65- year-old healthy men and
women were performed (Väinämö et al. 1996,
Väinämö et al. 1998). None of the subjects had any medication.
Maximal oxygen uptake was measured with an ergospirometer (Medikro M 909,
Kuopio, Finland)) during graded maximal cycle ergometer (Tunturi EL 400, Turku
Finland) tests. The fact that each subject reached his or her maximal aerobic
power was checked using three criteria: no increase in VO2max
despite load increase, respiratory quotient > 1.1 and blood lactate > 8
mmol/l. Before maximal stress test at least 250 R-R intervals (5 minutes) were
recorded from each subject at complete rest in a laying position using Polar
R-R Recorder™ (Polar Electro Oy, Kempele, Finland). Measurement errors
were removed from R-R intervals using both automatic (Hearts software, Heart
Signals Co, Kempele, Finland) and manual methods (visual inspection).
Development of the VO2max prediction in the neural network was done
in two phases: firstly 25 subjects were randomly selected as testing
(validation) samples. After that the rest of the 305 subjects were used for the
teaching of the network. In addition to heart rate and heart rate variability;
gender, age and height were used as predictive variables in the neural network
analysis. Body weight was used for the calculation of relative
Correlation coefficient between the
laboratory measured VO2max and the artificial neural network
prediction was 0.97 and the mean error in the VO2max prediction was
6.5%. The measured maximal aerobic power values in the data varied between 1-6
l/min (25-60 ml/min/kg). In 95% of the cases in the teaching data and in 60 %
of the cases in the validation data, the error in the VO2max
prediction was less than 0.5 l/min. The mean error of the prediction is good
compared to any other predictive tests of maximal aerobic power. Typically the
mean errors vary between 8-15%. In the laboratory measurements of
VO2max, the test-to-test variation within an individual is 3-5% due
to physiological day-to-day variation and technical parameters (e.g.
calibration of the ergosprirometer).
Further development of the Polar
Fitness Test™ was conducted based on the development study, which was
described above. At this stage 119 fitness measurements of healthy American men
and women, whose maximal aerobic power was measured in a maximal graded
treadmill exercise test, were included in the final development of the neural
network. Thus the number of subjects used in the final stage was 424, 381 of
which were randomly selected for the teaching of the network and 43 for the
validation (Kinnunen et al. 2000). The artificial neural network was modified
into Polar Fitness Test™.
Polar Fitness Test was further
developed to result OwnIndexS, an advanced modification of OwnIndex.
In the test development study, 450 laboratory fitness measurements of
15-65-year-old healthy men and women were performed. Correlation coefficient
between the laboratory measured VO2max and OwnIndexS
prediction in the data was 0.96 and the mean error in the prediction was 8.2%
(3.7 ml/kg/min). In 95% of the cases the error in the prediction was less than
9.4 ml/kg/min. Thus, the accuracy of the OwnIndexS can be considered
good. OwnIndexS was further validated in studies (Peltola et al.
2000, Tschopp et al. 2000) on trained subjects. It was shown that the
VO2max prediction associated reasonably highly with
VO2max measured in the laboratory in both men and women.
Polar Fitness Test
Polar Fitness Test predicts a person's aerobic fitness from the
resting heart rate, heart rate variability, gender, age, height, body weight
and self-assessment of the level of long-term physical activity. To obtain the
measures for heart rate and heart rate variability, 255 heart beats (3 - 5 min)
are measured during the test. In M-series heart rate monitors, physical
activity is assessed using a three-level scale (low/middle/high) and in
S-series heart rate monitors using a four-level scale (low/middle/high/top).
The scale has been modified from NASA/JSC physical activity scale (Ross et al.
1990) used also in a non-exercise test for maximal aerobic power prediction
(Jackson et al. 1990). The physical activity score should remain the same, if a
person's regular exercise habits have not changed during the previous 6 months.
Polar Fitness Test fits best to the follow-up of long-term changes in
aerobic fitness. For obtaining a change in aerobic fitness, regular training
for a longer period of time is required. A healthy adult can achieve a 10-15%
increase in about three months when training 3-4 times weekly for 30-40 min at
The effects of the above mentioned variables in
Polar Fitness Test cannot be totally separated from each other the
variables always act in concert. In general, however, the activity assessment
together with heart rate measurement explain about half of the
OwnIndex/OwnIndexS and the background variables (gender, age, height
and body weight) the other half. The index is raised by a reduction in body
weight and lowered by an increase in it. Because gender and height are very
stable and the changes in age are slow, their effect on the changes of the
index is minor.
The effect of long-term physical activity on the Index
is essential: the greater the activity, the better the fitness. In general,
OwnIndex/OwnIndexS is raised by a decrease in the resting heart rate
and an increase in heart rate variability, and lowered by an increase in the
resting heart rate and a decrease in heart rate variability. To achieve
long-term changes in the resting heart rate and heart rate variability, regular
physical activity of at least 6 weeks is needed.
Resting heart rate
and heart rate variability are sensitive measures and reflect the status of the
body. Short-term changes in these variables explain the changes in consecutive
Polar Fitness Test™ measurements. There is normal daily variation in the
resting heart rate and heart rate variability, and breathing and momentary
changes in blood pressure cause normal momentary variation. There can also be
undesired, transient changes in the measured heart rate values due to coughing,
speaking, body movement, excitement or other disturbances. It is therefore
important to minimize the disturbing effects and standardize the testing
conditions in order to achieve accurate and reliable results (always perform
the test in a similar way at the same time of the day). However, there is no
need to control the effects of breathing to the normal variation of heart rate
and heart rate variability during the test.
Validity and reliability of the test
Polar Fitness Test has been validated in a study, where 52
healthy 20-60-year-old men were measured before and after an 8-week exercise
training. Fifteen men were in the control group. Before the training period the
mean error in VO2max prediction by Polar Fitness Test was 2.2% and
after the training -0.7% compared to the laboratory measurement of maximal
aerobic power. The mean deviation in the prediction before and after the
training was 4-5 ml/min/kg in all groups. Because this is less than standard
deviation of the mean VO2max values within an age group (5-7
ml/min/kg), the validity of Polar Fitness Test can be considered good. In this
study Polar Fitness Test was also validated as a measure of fitness change. The
effect of the exercise training was on the average 4.1 ml/min/kg (10 %) when
measured in the laboratory. Polar Fitness Test predicted this change to be 2.4
ml/min/kg (6 %) on an average. The test thus detected the direction of the
change correctly but slightly underestimated the change. The mean deviation in
the estimated change of aerobic power was 4.5 ml/min/kg.
reliability of Polar Fitness Test in consecutive tests for the same individual
is good. When 11 subjects repeated the test in the morning, in the middle of
the day and in the evening during 8 days, in both sitting and laying positions,
the average individual standard deviation of the consecutive test results was
less than 8 % from the individual mean value. The standard deviations
calculated separately for each time of the day were smaller than the standard
deviation of all results. This indicates that the test can be conducted at any
time of the day but it should always be repeated at about the same time.
Practical Conduction of Polar Fitness Test
The background variables, gender, age, height and body weight as
well as physical activity level, are given to the heart rate monitor. Height
must be given to the nearest centimetre (or feet and inches) and weight within
the nearest kilogram (or pounds).
Activity assessment is done by
selecting the alternative that best describes your general long-term activity
In M-series heart rate monitors the activity levels are:
1.Low: You do not participate regularly in programmed recreation
sport or heavy physical activity. E.g. you walk only for pleasure or
occasionally exercise sufficiently to cause heavy breathing or perspiration.
2.Middle: You participate regularly in recreation sports. E.g. you
run 5 miles a week or spend 30-60 minutes a week in comparable physical
activity or, your work requires modest physical activity
You participate regularly, at least 3 times a week, in heavy physical exercise.
E.g.you run regularly more than 5 miles a week or spend more than 1.5-2 hours
in comparable physical activity.
In S-series heart rate monitors the
activity levels are:
1. Low: You do not participate regularly in
programmed recreation sport or heavy physical activity. E.g. you walk only for
pleasure or occasionally exercise sufficiently to cause heavy breathing or
2. Middle: You participate regularly in recreation
sports. E.g. you run 3-6 miles per week or spend 0.5-2 hours per week in
comparable physical activity or, your work requires modest physical activity
3. High: You participate regularly, at least 3 times a week, in
heavy physical exercise. E.g.you run 6-12 miles per week or spend 2-3 hours per
week in comparable physical activity.
4. Top: You participate
regularly in heavy physical exercise at least 5 times a week. E.g. you exercise
to improve performance for competitive purposes.
heart rate and heart rate variability measurement the test should be conducted
in well-standardised conditions. It is recommended to be performed in a
peaceful environment, since talking (even a cough), noisy music and telephone
ringing disturb the testing. Eating a heavy meal or smoking 2-3 hours prior to
the testing should be avoided. Unusually heavy physical effort as well as
alcoholic beverages or pharmacological stimulants should be avoided on the test
day and the day before.
How to interpret Polar OwnIndex/OwnIndexS
OwnIndex/OwnIndexS is equivalent to the maximal
aerobic power, VO2max, in ml/min/kg. This indicates how many
milliliters of oxygen your body is able to transport and use per each kilogram
of your body weight in one minute. The maximal aerobic power, as any other
fitness test result, is most meaningful when used in comparing individual
values and changes. Norms, rather national, can be used to compare the fitness
results to the average values of those with the same age and gender. Below an
example of normal values presented as a mean(standard deviation) according to
the age group (Fletcher et al. 1995).
Individual OwnIndex/OwnIndexS can be compared to the
population norms as follows: One standard deviation around the mean (half SD up
and half down) represents "average fitness". E.g. for a 33-year-old woman any
index between 31-37 (34-3 and 34+3) represents "average fitness" compared to
other women of the same age. Values less than 31 are below the average and
those higher than 37 are above the average.
For international use the
fitness classification by Shvartz & Reibold (1990) presented in Table 1 is
Table 1. Classification of maximal oxygen uptake (Shvartz
& Reinbold 1990). Data from adults in USA, Canada and 7 European countries.
MEN / MAXIMAL OXYGEN UPTAKE (VO2max, [ml x
kg-1 x min-1])
WOMEN / MAXIMAL OXYGEN UPTAKE (VO2max, [ml x
kg-1 x min-1])
In this classification, class 1 corresponds to "very poor", class
2 "poor", class 3 "fair", class 4 "average", class 5 "good", class 6 "very
good" and class 7 "excellent" cardiovascular fitness compared to individuals of
the same gender and age. In a population, 11 % of the people belong to classes
1-2 and 6-7, 22% in classes 3 and 5 and 34% in class 4. This corresponds to
"gaussian distribution", because the classification has been developed in
representative samples of individuals from different countries.
Fitness class is a useful reference when interpreting the individual test
results. Because cardiovascular health is related to aerobic fitness, the
people in classes 1-3 would most probably obtain lots of heath benefits and
improve their fitness by starting regular exercise. Those in class 4 should at
least maintain their exercise habits to ensure better health. However, increase
in exercise is recommended for fitness improvement. The people in classes 5-7
most probably already have good health, and their exercise increase targets to
improve their performance. Top athletes in endurance sports typically score
VO2max values (ml/kg/min) above 70 (men) and 60 (women). The values
differ to some extent according to the sport but there are no reliable
reference values in the literature for the different sports. Regular exercisers
participating occasionally in competition events score 60-70 (men) and 50-60
(women). Individuals exercising regularly, but not in competitive level, have
values between 40-60 (men) and 30-50 (women) and sedentary adults most probably
below 40 (men) and 30 (women). General guidelines to help the interpretations
are illustrated in Picture 1.
Picture 1. How to interpret the result of Polar Fitness Test?
Maximum heart rate prediction in Polar S-series
Maximum heart rate prediction(HRmax-p) is carried out
simultaneously with Polar Fitness Test in S-series heart rate monitors.
HRmax-p is based on resting heart rate, heart rate variability at
rest, age, gender, height, body weight and maximal oxygen uptake,
VO2max (measured or predicted). HRmax-p has been
developed on 431 15-65-year old men and women (Hannula et al. 2000). Of the
subjects 175 were used in the development of the HRmax prediction
formula and the rest 256 in a validation study. The study showed that
HRmax-p predicted the individual HRmax more accurately
than the age-based formula (220-age). The mean absolute error in
HRmax-p was 6.5 bpm (3.5%) compared to 7.6 bpm (4.1%) in the
age-based formula. The standard deviation (SD) of the prediction error was 7.9
bpm with the HRmax-p method and 9.4 bpm with the age-based formula.
Fletcher, Balady, Froelicher, Hartley, Haskell, Pollock. Exercise
Standards. A statement for healthcare professionals from the American Heart
Association. Circulation 91,2,580-615,1995.
Jackson, Blair, Mahar,
Ross and Stuteville. Prediction of functional aerobic capacity without exercise
testing. Med Sci Sports Exerc 22,6,863-870,1990.
Nissilä, Kinnunen, Virtanen. Development of a new HRmax
prediction model. Proc 5th Annual Congress of the ECSS, Jyväskylä,
Finland, 19-23 July 2000, p 306.
Kinnunen, Hautala, Mäkikallio,
Tulppo, Nissilä. Artificial neural network in predicting maximal aerobic
power. Med Sci Sports Exerc 32,5,1535,2000.
Peltola, Hannula, Held,
Kinnunen, Nissilä, Laukkanen, Marti. Validity of Polar Fitness Test based
on heart rate variability in assessing VO2max in trained
individuals. Proceedings of 5th Annual Congress of ECSS, Jyväskylä,
Finland, 19-23 July 2000, p 565.
Ross, Jackson. Exercise concepts,
calculations, and computer applications. Carmel, IN, Benchmark Press, 1990, pp
Shvartz, Reibold. Aerobic fitness norms for males and
females aged 6 to 75 years: a review. Aviat Space Environ Med 61,3-11,1990.
Tshopp, Peltola, Held, Kinnunen, Hannula, Laukkanen, Marti.
Traditionelle und neue Ansätze zür Schätzung der maximalen
Sauerstoffaufnahme in Ruhe. Schweizerische Zeitschrift für Sportmedizin
und Sporttraumatologie 48(2),58-63,2000.
Tulppo, Mäkikallio, Röning. An atrificial neural network for human
aerobic fitness approximation. Proceedings of International Conference on
Neural Networks (ICNN), Washington DC, June 3-6, 1996, pp 1939-1949.
Väinämö, Tulppo, Mäkikallio, Röning. A neuro-fuzzy
approach to aerobic fitness classification: a multistucture solution to the
context-sentive feature selection problem. Proceedings of ICNN, Anchorage,