Heart Rate Monitoring is State of the Art

from PolarUSA

Heart rate is a useful indicator of physiological adaptation and intensity of effort. Therefore, heart rate monitoring is an important component of cardiovascular fitness assessment and training programmes. The electrocardiogram (ECG) and Holter monitoring devices are accurate, but not feasible for use in field settings due to cost, size and complexity of operation. Light-weight telemetric heart rate monitors equipped with conventional electrodes have been available since 1983 and have proved to be accurate and valid tools for heart rate monitoring and registering in field measurements. Polar Electro Oy has been a leading company in producing ambulatory heart rate monitors for fifteen years. This article reviews the development history of Polar Heart Rate Monitors and their measurement accuracy compared to Holter ECG devices at rest and during exercise both in adults and in children.

Introduction

Accurate heart rate monitoring is essential in fitness training and testing. Manual pulse palpation provides inaccurate results (Clapp and Little 1994). The use of ECG or Holter monitoring is too costly and complex for exercisers to use in the field. The first wireless heart rate monitor was introduced in 1983. It was a portable Polar PE 2000 heart rate monitor which consisted of a transmitter and a receiver. The transmitter could be attached to the chest using either disposable electrodes or an elastic electrode belt. The receiver was a watch like monitor worn on the wrist. The wireless Polar heart rate monitoring method was developed at the University of Oulu, Department of Electronics. In the beginning the heart rate monitors were targeted for coaches and sportsmen to optimize the quality and efficiency of training. Soon exercise scientists started to research the monitors and use them in their work. The first issue of Polar Research Index (1995) includes altogether 200 physiological and medical studies on humans and animals involving Polar heart rate monitors. Today the selection of heart rate monitors includes easy-to-use products for everyone interested in wellness, fitness and health.

Heart rate monitors and their accuracy

Polar Electro Oy introduced it's first retail monitor, Tunturi Pulser, in 1978. This was a heart rate monitor with optional cable-connected chest belt. Five years later, in 1983, the first wireless heart rate monitor using electric field data transfer was introduced. This microcomputer was called Sport Tester PE 2000 (Figure 1). Karvonen et al. (1984) compared heart rates measured by Holter and PE 2000. The results showed that the mean heart rates obtained by ECG and PE 2000 differed from each other at most by 5 beats min-1 and in single measurements by 0-10 beats min-1 at every work load. The differences were caused mainly by the different methods of calculation using either ECG ruler or microcomputer display reading. It was concluded that both methods can be regarded as equally valuable for measuring heart rate during exercise.

In 1984 Polar Electro Oy introduced the world's first heart rate monitor equipped with computer interface and transmission by magnetic field. This was called Sport Tester PE 3000 (Figure 2). Vogelaere et al. (1986) compared the heart rate readings of PE 3000 with Holter ECG reference values on twenty subjects during exercise. The results showed that PE 3000 is a valid alternative for measuring heart rate in the field and for laboratory research purposes compared with the fragile and unwieldy Holter apparatus.

Leger and Thivierge (1988) compared the validity, stability and functionality of thirteen different heart rate monitors. The monitors were divided into three categories according to the correlation of the heart rate readings with those of the Holter. The monitors were regarded as excellent if the correlation coefficient (r) was ­0.93 and standard error of estimate (SEE) less than 6.8%; good if 0.93>r­0.65 (SEE 6.8%-15%); and inadequate with r<0.65 (SEE >15%). Based on this classification the heart rate monitors using conventional chest electrodes to measure electrical activity of the heart namely Exersentry (Respironics Ltd, Hong Kong), PE 3000 (Polar Electro, Finland), Pacer 2000 H (Sportronic AG, Switzerland) and Monark 1 (Monark-Crescent, Sweden) resulted in excellent readings. Seiko 1 (Seiko, Japan) achieved good validity and several others using other types of electrodes or earlobe photocell to measure the opacity of the blood flow, were inadequate. In a study by Seaward et al. (1990) the precision and accuracy of a portable PE 3000 proved to be equal to that of ECG. The 250 data sets obtained at rest and during variable-intensity exercise resulted a correlation coefficient of 0.9979 over the heart rate range of 55 -177 beats min-1.

Thivierge and Leger (1989) also published a review about the operation principles, validity, stability and functional characteristics of heart rate monitors. In this paper the results were consistent with their previous work (Leger and Thivierge 1988); the heart rate monitors with conventional electrodes gave more valid results and the use was more feasible compared with those using non-conventional electrodes or photo-electric sensors placed either on finger or ear.

Treiber et al. (1989) studied heart rate monitoring with children in the laboratory and in field settings during six different exercise activities and recovery. They reported correlation coefficients of at least 0.93 (SEE 1.1-4.3 beats min-1) between the Sport Tester PE 3000 and ECG derived heart rates. The interface and software package (Sport Tester Training System) proved to be an efficient tool for heart rate analysis. This was the first computerized training system for measuring, registering and printing heart rate information.

Polar Sport Tester, also known as Polar Vantage XLâ , came out in 1989 (Figure 3). This was a water resistant heart rate monitor with contactless (magnetic field) computer interfacing and a large memory in watch size. The accuracy of this monitor was studied by Godsen et al. (1991). They compared 2633 heart rate readings during treadmill running, rowing, arm-leg cycle ergometry and weight training. As a result, the Sport Tester yielded heart rate values within ± 6 beats min-1 from ECG values about 95% of the time. Their conclusion stated that arrhythmias, anticipatory heart rate rises and rapid adaptation to or recovery from exercise explained most of the errors. Wajciechowski et al. (1991) published a study about the accuracy of two Polar heart rate monitors (most probably Polar Vantage XLâ) compared with ECG readings during walking, jogging and aerobic dance in women. When the monitor values were averaged for 10-s readings (400 cases), the correlation coefficient between the monitor and ECG values was 0.99. Ninety percent of all measured errors were within ± 8 beats min-1.

During 1990-1993 Polar Electro introduced many new innovations. Polar CycloVantage was the world's first cycle-computer with a computer interface measuring speed, time, distance and pedalling rate. Polar Accurex IITM heart rate monitor had sport watch functions and an average heart rate, Windowsâ based analysis software and an integrated, lightweight, water resistant one-piece transmitter (T40, Figure 4). Easy-to-use consumer-friendly products including buttonless FavorTM and BeatTM heart rate monitors were introduced during 1991-93.

Lewis (1992) compared Polar Favor and Edge heart rate monitors in his work on 24 subjects during light to maximal intensity endurance activities. The correlation coefficient and standard deviation (S.D.) of the heart rates registered by the monitors were 0.97 (± 3-4 beats min-1) when compared to ECG measurements.

In 1995 Polar introduced the Vantage NVTM heart rate monitor (Figure 5) including for the first time coded transmission (one signal from each transmitter to receiver) and R-R recording (beat to beat) and analysis system (Polar Advantage Interface SystemTM and Precision Performance SoftwareTM for Windowsâ). This innovative monitor was used in the study of Kaikkonen et al. (1997) for the detection of recovery and overtraining in male orienteers. They reported that the measurements were easy to perform and analyse by the sportsmen at home and during a training camp with the Vantage NVTM and a Precision Performance SoftwareTM. Kinnunen and Heikkilä (1997; also see abstract in this journal) evaluated the timing accuracy of the Polar Vantage NVTM heart rate monitor in the measurement of R-R intervals. Their results showed that in 99.9% of the R-R intervals the difference between Polar Vantage NVTM and Polar R-R RecorderTM (Ruha et al., 1997) was within ± 5 ms.

In 1997 Polar launched the Xtrainer PlusTM, which is a heart rate monitor and a cycle-computer in one unit. This device is able to measure heart rate, distance, time, speed, cadence and altitude during performance.

The very latest innovation, Polar SmartEdgeTM (Figure 6), is a heart rate monitor with an automatic intensity guidance feature (called the "OwnZone"), and is also capable of estimating energy expenditure during exercise (the "OwnCal"). Both features are based on R-R recording and equations derived from extensive physiological research conducted in several research units.

Our research group has evaluated Polar SmartEdgeTM "OwnZone" and "OwnCal" features (unpublished observations). The lower heart rate limits determined by the Polar SmartEdgeTM heart rate monitor correspond to 62 ± 4% and 65 ± 3% and the upper limits to 80 ± 5 and 84 ± 3% of the maximum heart rate in men and women, respectively. The energy expenditure predicted by SmartEdgeTM was compared with that measured by Cosmed (K4, Italy). In two thirds of the subjects, the difference between the values of the two pieces of apparatus was less than 15% during cycling and walking, which was considered satisfactory.

Summary

Polar Heart Rate Monitors have for fifteen years been recognized as the most accurate tools for heart rate monitoring and registering in the field. Extensive research and development work has also resulted in top quality devices for the analysis of heart rate data. Table 1 summarizes the most notable innovations of Polar Electro Oy since 1977. In the future the heart rate monitors and analysis tools will increasingly develop in the direction of interpretation of heart rate information.

Table 1. "Firsts" in heart rate monitoring (HRM) by Polar Electro Oy

References

Clapp III, J. and Little, K. (1994). The physiological response of instructors and participants to three aerobics regimens. Medicine and Science in Sports and Exercise, 26(8), 1041-1046.

Godsen, R., Carroll, T. and Stone, S. (1991). How well does Polar Vantage XL Heart Rate Monitor estimate actual heart rate? Medicine and Science in Sports and Exercise, 23(4), Suppl., S14.

Kaikkonen, H., Karppinen, T. and Laukkanen, R. (1997). Recovery and overtraining detection in male orienteers before, during and after intensive training period. Abstract in 6th International Scientific Symposium on Orienteering, Oslo, Norway, 18-19 August.

Karvonen, J., Chwalbinska-Moneta, J. and Säynäjäkangas, S. (1984). Comparison of heart rates measured by ECG and Microcomputer. The Physician and Sportsmedicine, 12(6), 65-69.

Kinnunen, H. and Heikkilä, I. (1997). The timing accuracy of Polar Vantage NV heart rate monitor. Journal of Sports Sciences (present issue).

Leger, L. and Thivierge, M. (1988). Heart rate monitors: validity, stability and functionality. The Physician and Sportsmedicine, 16(5), 143-151.

Lewis, D. (1992). An investigation into the accuracy of the Polar Favor and the Polar Edge heart rate monitors compared with direct ECG measurements. Newcastle Polytechnic, Newcastle, UK, Masters Thesis.

Polar Research Index (1998). Polar Electro Oy, Kempele, Finland.

Ruha, A., Sallinen, S. and Nissilä, S. (1997). A real-time microprocessor QRS detector system with a 1 ms timing accuracy for the measurement of ambulatory HRV, IEEE Transactions on Biomedical Engineering, 44(3),159-167.

Seaward, B., Sleamaker, R., McAuliffe, T. and Clapp, J. (1990). The Precision and Accuracy of a portable heart rate monitor. Biomedical Instrumentation & Technology, 24(1), 37-41.

Thivierge, M. and Leger, L. (1989). Critical review of heart rate monitors. Canadian Association for Health, Physical Education and Recreation Journal, 55(3), 26-31.

Treiber, F., Musante, L., Hartdagan, S., Davis, H., Levy, M. and Strong, W. (1989). Validation of a heart rate monitor with children in laboratory and field settings. Medicine and Science in Sports and Exercise, 21(3), 338-342.

Vogelaere, P., De Meyer, F., Duquet, W. and Vandevelde, P. (1986). Vergleich zwischen "Sport Tester PE 3000" und Holter-EKG zur Messung der Herzfrequenz (Sport Tester PE 3000 vs Holter ECG for the measurement of heart frequency). Science and Sports, 1(4), 321-329.

Wajciechowski, J., Gayle, R., Andrews, R. and Dintiman, G. (1991). The accuracy of radio telemetry heart rate monitor during exercise. Clinical Kinesiology, 45, 9-12.

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