Information about Polar OwnCal calorie counting feature

R&D/Research/Polar Electro Oy
Updated 02/2002


Body’s energy expenditure

Total energy expenditure is an important determinant of one’s physical fitness and health. It is also important for reducing and managing weight. The main factors in total energy expenditure are basal metabolism, accounting for appr. 50-70%, and the energy used for physical activity (muscular work), amounting to some 20-40%. In addition, some 10% is expended in the digestion of food.

The amount of energy expended by physical activity depends on exercise intensity and duration. Energy expenditure is also dependent on body weight, so that a heavier person consumes more energy than a lighter one when performing the same exercise because the mass that the person needs to move is greater. For example, persons weighing 60 kg and 100 kg expend 5 kcal and 8 kcal per minute in brisk walking, respectively. Also, the larger the muscle mass used in the exercise the larger the energy expended. Thus, very high energy expenditures can be reached in e.g. cross-country skiing and rowing. Types of exercise where the person must support his/her body weight typically expend more calories than types where the exercise equipment supports the weight.

OwnCal and OwnCalS

Polar M-series heart rate monitors measure the amount of calories consumed during exercise with OwnCal feature and Polar S-series heart rate monitors with OwnCalS feature. The M-series heart rate monitors are designed to motivate people to get fit, stay in shape or lose weight and S-series models are designed for those with more ambitious exercise targets and for competitive athletes. This is why OwnCal and OwnCalS differ in some aspects. The heart rate monitors of both series show the cumulative energy expenditure of an individual on the display during exercise and total kilocalories of current exercise session after exercise as well as save accumulated kilokalories. In OwnCal the energy expenditure assessment is based on gender, heart rate and body weight and in OwnCalS on individual VO2max and HRmax along with heart rate and body weight. In OwnCal the calorie counting starts from the heart rate 100 bpm and in OwnCalS from 90 bpm. The limit is set because the OwnCal/ OwnCalS -feature has been created to calculate only total calories consumed during exercise and heart rate values below 100 bpm do not correspond to such a situation in most individuals. In OwnCalS the counting starts at 90 bpm because athletes have lower heart rates than people with lower fitness level at the same exercise intensity.

Setting exercise goals using OwnCal/OwnCalS feature

Exercise dose can be determined using kilocalories. Daily and weekly exercise goals can conveniently and easily be set in terms of kilocalories. Because the heart rate monitor tracks both the energy expenditure in one session and the accumulated kilocalories, it helps in achieving both short term and long term goals.

Fat consumption in M-series

Reducing the amount of extra fat tissue in the body is an important target for those exercising for weight loss and weight management purposes. M-series heart rate monitors M21/22/31/32 and M51/52/61/62 calculate an estimation of fat consumption from total kilocalories expended during an exercise session. Fat consumption is expressed in percentages of the total energy expenditure with 5% accuracy. The fat consumption calculation is based on the physiological interaction between exercise intensity and utilization of the energy sources during exercise. In this interaction the use of fat as an energy source is optimal (highest possible percentage) at the exercise intensity of about 50% maximal aerobic power, VO2max , and decreases thereafter. This "optimal point" corresponds close to the heart rate variability (HRV) plateau during exercise, which is a base for the OwnZone (the lower limit of OwnZone basic or the lower limit of the "light zone" of OwnZone advanced). Figure1 below illustrates fat consumption of total energy expenditure and exercise intensity.

Figure 1. Energy sources during exercise .

In the Physical Activity and Health, a report of the Surgeon General (USA,1996) it is stated that activity leading to an increase in the daily expenditure of approximately 150 kcal/day, equivalent to about 1000 kcal/week, is associated with substantial health benefits. It is also stated that the activity for health benefits needs not to be vigorous.

For weight loss purposes the recommended energy expenditure can be set to 300 kcal/ session. Conducted on most days of the week this will result 2000 kcal/week on a 70 kg person, approximately the kilocalorie content of a 1 kg (or 2 pounds) fat (7000 kcal) in a month. The higher the exercise intensity, the higher the heart rate, and the faster the calorie expenditure. However, at high exercise intensities the percentage of fat consumption of the total energy expenditure is less than at lower intensities. Figure 2 presents comparison between the distribution of energy sources in jogging and walking sessions.

Figure 2. Comparison between the distribution of energy sources in jogging and walking

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.

Additional reading:
Kukkonen-Harjula K, Laukkanen R. Precision Weight Management. Polar Electro Oy. Fourth Edition in English, 2001.

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