Curtin University of Technology
Skip to content
School of Physiotherapy

Monitoring exercise heart rate during training is not worth the bother!

Topic for Summary and Critique - by Jay Chau

Contents

Statement of the Topic

Monitoring exercise heart rate during training is not worth the bother!

Introduction

Athletes in many sports disciplines monitor their heart rate (HR) during exercise sessions. This enables them to train at the required exercise intensity in order to achieve the desired training effect. The American College of Sports Medicine (ACSM 1995) has set guidelines for appropriate training intensities to achieve physiological change, depending on the objectives of the activity. Regular training at appropriate intensities can lead to an increase in cardiovascular fitness, an increase in muscle strength and endurance as well as an improvement in body composition (decreased fat mass and increased lean body mass)(King and Senn 1996, Meyer 1999). This is partly achieved by a significant change in the respiratory capacity of the muscles, an increase in myocardial function leading to increased stroke volume and cardiac output, and an increase in fat utilisation (Hills et al 1998, King and Senn 1996).

The training-induced physiological changes in the body are determined by the intensity of the exercise performed. To achieve an increase in aerobic capacity, an athlete must exercise at 70 percent HRmax (McArdle et al 1996). When performing leg exercise such as cycling and walking, this corresponds to approximately 55 percent of VO2max (McArdle et al 1996). The intensity of exercise can be measured in several ways: percentage of maximal oxygen uptake (%VO2max); percentage of oxygen uptake researve (%VO2R; percentage of maximal HR (%HRmax); blood lactate concentration, multiples of resting MET and rating of perceived exertion (RPE) (Hills et al 1998, Lear et al 1999, McArdle et al 1996).

A linear relationship exists between exercise HR and VO2. Assuming that HR increases proportionally to VO2, HR monitored during exercise is able to give the athlete an indication of the intensity at which the exercise is being performed (Arts and Kuipers 1994, McArdle et al 1996). The lactate threshold is defined as the work rate at which the blood lactate concentration begins to rise above the resting level (Hills et al 1998). This lactate concentration can also be used to determine the exercise intensity at which an athlete is exercising. The rating of perceived exertion scale (RPE) of Bor (1962) is a psychophysical measure of the athlete's perception of the intensity of training. The athlete completes the subjective RPE scale that indicates the amount of perceived effort (Eston and Williams 1988, McArdle et al 1996).

As the body performs exercise, there is an increased demand for oxygen to be delivered to the exercising muscles, and tif this demand can be met there is an increase in the uptake of oxygen. The amount of oxygen consumption is dependent on the intensity of exercise (Lear et al 1999). Age, gender, exercise history or habits, hereditary factors and current health status influence the maximal oxygen uptake (VO2max). The HR of an individual is also influenced by age, state of health or conditioning, as well as some cardiac medications, body position, mode of exercise, environmental conditions, the autonomic nervous system and hormonal status.

The cardiac output (CO) is the capacity to circulate oxygenated blood to active tissues, and will effect the aerobic capacity of an individual (McArdle et al 1996). CO increases linearly with increasing exercise. It can increase from 4.5 L/min. at rest to as much as 20-30L/min. during maximal exercise. The stroke volume (SV) increases until approximately 50percent of VO2max is reached. Further increases in CO are achieved primarily by an increase in HR (Lear et al 1999). The increase in HR is dependent on exercise intensity, body posture and the type of exercise. In upright exercise the SV increases by 50-100 percent, while in a supine position, where the SV is already high at rest, there is only a slight increase. At the onset of exercise an increase in cardiac sympathetic nerve activity and a decrease in vagal activity results in the increase in HR and SV (Levick 1996).

Exercise prescription involves the determination of mode, intensity, frequency and duration of activity. It is dependent on the individuals current health status as well as the goals and objectives of the training program (King and Senn 1996). Heart rate can be used to indicate the intensity of exercise to assist exercise prescription. Heart rate monitors were originally designed for coaches and athletes to improve the quality and efficiency of training sessions. The first wireless heart rate (HR) monitor was developed in 1983 (Laukkanen and Virtanen 1988).

Affirmative Argument

Monitoring HR during training is not worth the bother as there are a number of factors, physiological and environmental that may have an effect on HR. This may provide an inaccurate reflection of the metabolic stress on the body.

The monitoring of HR during exercise to give an indication of the intensity of exercise is not appropriate in all populations. For example those people who are required to take medications such as beta-blockers (to treat hypertension or following myocardial infarction), or athletes wishing to slow their HR. Beta-blockers act to decrease the HR. Therefore HR would not be an accurate representation of exercise intensity (Knopp et al 1997, Lear et al 1999). There would not be a corresponding increase in HR for an increase in work rate.

Although it is widely believed that a linear relationship exists between HR and oxygen uptake, this is only true for light to moderate work loads. At heavier workloads, there is a larger than expected increase in the VO2 per unit increase in HR. That is the VO2 increase is larger than would be predicted when extrapolating the line on the HR-VO2 graph (Gilman 1996, McArdle et al 1996). It has been suggested that when using percentage HRmax to estimate VO2max, an error of up to eight percent may occur (McArdle et al 1996).

The prediction of VO2max using submaximal exercise HR assumes that there is a constant HR for given age. This is not the case as there are many factors affecting HR response to exercise (Hills et al 1998). State of health, conditioning and heredity are just a few. A prediction of VO2max using HR may result in an error. The ACSM (1995) have reported variability of HRmax of up to 10-12 beats per minute in normal subjects when using the popular formula: HRmax = (220-age). This suggests that HR may not be a valid measure of exercise intensity.

Heart rate is commonly used to monitor exercise intensity during training and competition, as it is easy and convenient to measure. There are many factors that can effect HR other than the exercise intensity. Intrinsic variation in HR exists in athletes. This day to day variation, of one to six beats per minute, must be considered when using HR response to submaximal exercise as a marker for exercise intensity. Extrinsic factors such as exercise duration, exercise mode, environmental conditions, time of day and competitive exercise will all effect HR response to exercise (Lambert et al 1998). Hot and humid environments, windy conditions causing increased air resistance, hilly terrain and body position on the bike can all increase exercise HR (Creagh and Reilly 1997, Gilman 1996, Jeukendrup and Van Diemen 1998).

Cardiac drift refers to the slow rise in HR, as much as 20 beats per minute, as exercise duration exceeds 20-60 minutes (Boulay et al 1997, Gilman 1996). Boulay et al (1997) examined the effect on work rate if the heart rate was kept constant. The results showed that in order to maintain a stable HR (176-180bpm), the work rate had to be decreased significantly (17%). The %VO2max decreased from 80% to 73% during 20 to 80 minutes of exercise, suggesting that during endurance exercise (for example long distance running) at a constant work load, the HR will overestimate the training effect.

Gnehm et al (1997) examined the effect of the cyclists body position on heart rate. The use of aerobars, which lowers the body at the front in order to reduce the drag coefficient, appeared to increase the HR disproportionately to the oxygen consumption. They showed an average increase of 5 beats per minute in the aerodynamic position when compared to the upright position. The authors suggest that this may be due to increased use of the shoulder musculature and a decreased efficiency of the hip angle.

Altitude has been shown to affect exercise HR. The hypoxic conditions at higher altitudes increase the athlete's heart rate for the same workload (Jeukendrup and van Diemen 1998). Training at a percentage HRmax that has been determined at another altitude will not produce the expected physiological response to exercise.

Sutherland et al (1999) examined the HR response to a specific step aerobic exercise called "Uni-step". It involves a group session where aerobic exercise is performed on steps of varied heights, specific maneuvers for 30 minutes duration. It also included five minutes each of muscle conditioning and flexibility. The results showed an elevated HR response, which if used to predict the intensity of exercise; the aerobic fitness achieved would be less than expected.

The authors suggest that this response may be due to the inclusion of large arm movements at or above shoulder height, or to the unique test modality used in the study.

Endurance sports, which exhibit a steady state work rate, utilise HR as a measure of the exercise intensity. However, some sports such as field or court games, and orienteering, demonstrate inconsistent exercise intensities (Creagh and Reilly 1997). This variability in the intensity of exercise will be reflected in the HR response to some degree, but will be influenced by the energy systems being utilised. There is variability in the physiological response when performing submaximal exercise (Meyer 1999). This may be due in part to the relative contributions of the aerobic and anaerobic energy systems. If athletes relied on percentage HR or percentage VO2max to monitor the intensity of exercise, it is likely that there will be a wide range of exercise intensities performed.

Athletes may also use the RPE scale as an indicator of exercise intensity. The RPE response to graded exercise shows a high correlation with physiological responses such as HR, ventilation and blood lactate concentration (ACSM 1995). The scale is noninvasive, simple and does not require sophisticated equipment (Hills et al 1998). Eston and Williams (1988) reported that the RPE scale was more accurate than any other single psychophysical or physiological indicator of exercise intensity.

Affirmative Conclusions

Athletes use heart rate monitors during exercise to ensure that they are working at the required exercise intensity to achieve the goal of training. There are several physiological and environmental factors that can affect the HR during exercise, as well as the mode of exercise (Londeree et al 1995), and these must all be taken into account when interpreting exercise HR data. Heart rate is an indicator of cardiac stress or overall exercise-induced stress on the body (Jeukendrup and van Diemen 1998), and not simply a measure of the work rate or intensity. In order to compare meaningful results on several occasions of HR monitoring during exercise, the exact conditions must be reproduced.

Negative Argument

Heart rate monitoring during exercise is recognised as a practical, non-invasive means by which coaches and athletes can measure the intensity of a training session. It can also be used to show improvements due to training and to prevent injury, overtraining or illness (Gilman 1996, Hills et al 1998, Laukkanen and Virtanen 1998, McArdle et al 1996). This is critical to the performance of endurance athletes such as cross country skiers, triathletes and long distance runners, who use exercise intensity to set race pace or prevent overtraining (Gilman 1996, Lambert et al 1998). In the sport of cycling, power output is considered to be the best indicator of exercise intensity. However, it is easier and more practical in most situations to monitor HR during exercise (Jeukendrup and van Diemen 1998).

An athletes HR can be used as a marker of the intensity of training as there is a linear relationship between work rate, HR and VO2, for intensities of 60-90% VO2max (Arts and Kuipers 1994, Gilman 1996). HR monitoring during exercise is useful to determine the exercise intensity or to predict VO2max, regardless of gender, age or level of fitness (McArdle et al 1996).

Telemetric HR monitors developed in the past decade provides the athlete with a valuable tool to monitor HR response to training. The HR monitor is a means of providing immediate feedback to the athlete and motivation to train at high intensities. The data can be stored for later analysis of the training session or competition and can be used to develop individual training programs to coincide with the competitive calendar (Gilman 1996, Hills et al 1998). HR monitors with conventional electrodes have been shown to be more valid measures of exercise HR than the photoelectric sensors worn on the finger or earlobe (Leger and Thivierge 1988).

Overtraining can be detrimental to the athlete's performance. Fatigue, irritability, sleep problems and lack of motivation are signs of overtraining, and can lead to overtraining syndrome (Jeukendrup and van Diemen 1998). Monitoring of the athletes HR during training can provide warning signs. If an athlete is overtrained, performance will decrease, as will the exercise HR, but there is no corresponding change in the RPE (Jeukendrup and Van Diemen 1998). Therefore, a decrease in exercise HR for the same amount of perceived effort may suggest overtraining. Resting HR may become elevated during sleep and in the mornings, with a change in HR pattern.

In certain populations the risks involved when performing a maximal exercise test outweigh the benefits (Hills et al 1998). Such populations include people with hypertension, obesity or cardiovascular disease. In order to assess the oxygen consumption or to design an appropriate training program for these people, it is feasible to perform a submaximal test and use HR as a guideline, as previously discussed. Submaximal tests have low risk, are safe and practical, and can be administered by qualified personal in a non-medical setting.

Negative Conclusions

Monitoring exercise HR is arguably the best method of estimating exercise intensity during competition or training sessions, in order to exercise at the required intensity level to achieve the desired physiological goals (Hills et al 1998). It can also provide valuable information regarding the health status of the athlete.

Conclusion

The use of HR monitors to estimate the exercise intensity during a training session can be a valuable tool for the athlete and coach. Monitoring HR can prevent injury of overtraining, and if used within the limitations of the equipment, can ensure that training occurs at the desired level of intensity. There are many factors effecting exercise HR or VO2. These must be considered carefully when interpreting data from HR monitoring, and determining the required exercise intensity. If not, the athlete is in danger of overtraining, or underachieving their goals.

Athletes who have been prescribed cardiac medication, for example beta-blockers, must be aware that their HR will not increase proportionately to the increase in wok load. Conversely, and athlete exercising in hot, humid or windy conditions will experience an increase in HR out of proportion to work load.

When using exercise HR to determine the intensity of exercise, it is important to consider the large number of factors that can effect the physiological response of the body. This will enable the athlete to exercise at the intensity to achieve the desired physiological change. The conditions under which testing of exercising is performed must also be recorded and reproduced if meaningful results are to be compared.

References

American College of Sports Medicine (1995)
Guidelines for exercise testing and prescription. (5th ed.) Baltimore: Williams and Wilkins.
Arts FJP and Kuipers H (1994)
The relationship between power output, oxygen uptake and heart rate in male athletes. International Journal of Sports Medicine 15:228-231.
Boulay MR, Simoneau J-A, Lortie G and Bouchard C (1997)
Monitoring high-intensity endurance exercise with heart rate and thresholds. Medicine and Science in Sports and Exercise 29:125-132.
Creagh U and Reilly T (1997)
Physiological and biomechanical aspects of orienteering. Sports Medicine 24:409-418.
Eston RG and Williams JG (1988)
Reliability ratings of perceived effort regulation of exercise intensity. British Journal of Sports Medicine 22:153-155.
Gilman MB (1996)
The use of heart rate to monitor the intensity of endurance training. Sports Medicine 21:73-79.
Gnehm P, Reichenbach S, Altpeter E, Widmer H and Hoppeler H (1997)
Influence of different racing positions on metabolic cost in elite cyclists. Medicine and Science in Sports and Exercise 29:818-823.
Hills AP, Byrne NM and Ramage AJ (1998)
Submaximal markers of exercise intensity. Journal of Sports Sciences 16:S71-S76.
Jeukendrup A and Van Diemen A (1998)
Heart rate monitoring during training and competition in cyclists. Journal of Sports Sciences 16:S91-S99.
King CN and Senn MD (1996)
Exercise testing and prescription, practical recommendations for the sedentary. Sports Medicine 21:326-336.
Knopp WD, Wang TW and Bach BR (1997)
Ergogenic drugs in sport. Clinics in Sports Medicine 16:375-392.
Lambert MI, Mbambo ZH and St Clair Gibson A (1998)
Heart rate during training and competition for long-distance running. Journal of Sports Sciences 16:S85-S90.
Laukkanen RMT and Virtanen PK (1998)
Heart rate monitors: State of the art. Journal of Sports Sciences 16:S3-S7.
Lear SA, Brozic A, Myers JN and Ignaszewski A (1999)
Exercise stress testing: an overview of current guidelines. Sports Medicine 27:285-312.
Leger L and Thivierge M (1988)
Heart rate monitors: Validity, stability and functionality. Physician and Sports Medicine 16:143-151.
Levick JR (1996)
An Introduction to Cardiovascular Physiology. (2nd ed.) Oxford: Butterworth Heinemann.
Londeree BR, Thomas TR, Ziogas G, Smith TD and Zhang Q (1995)
%VO2max versus %HRmax regressions for six modes of exercise. Medicine and Science in Sports and Exercise 27:458-461.
McArdle WD, Katch FI and Katch VL (1996)
Exercise physiology: energy, nutrition and human performance. (4th ed.) Baltimore: Williams and Wilkins.
Meyer T, Gabriel HHW and Kindermann W (1999)
Is determination of exercise intensities as percentage of VO2max or HRmax adequate? Medicine and Science in Sport and Exercise 31:1342-1345.
Sutherland R, Wilson J, Aitchison T and Grant S (1999)
Physiological responses and perceptions of exertion in a step aerobics session. Journal of Sports Sciences 17:495-503.

Short Answer Review Questions

  1. What are the physiological responses to exercise, and how are these achieved in the initial stages of exercise?
  2. What are some of the uses of HR monitors by endurance athletes, and how could this assist with training?
  3. What factors can increase the HR during an endurance activity? Include both intrinsic and extrinsic factors.
  4. What are the main factors that can increase HR for a cyclist? What is the magnitude of these increases?
  5. What are some of the effects of body position and mode of exercise on HR?
  6. How can HR monitoring during exercise be used in the clinic, and for which population would this be most useful?

Exercise Physiology Educational Resources 1999