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

Proposition for Debate - by Uli Julich and Terence Ho

Contents

• Statement of the Topic
• Affirmative Argument by Uli Julich
• Negative Argument by Terence Ho

Statement of the Topic

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

Affirmative Argument by Uli Julich

Introduction

Measurement of heart rate (HR) during training is commonly used to monitor athletes performance in mainly endurance based sports in order to give feedback. The physiological assessment with monitoring HR can help to identify weaknesses in the athlete's performance (status of overtraining), monitor the progress to determine the effectiveness of the training program and show physiological adaptations. HR increase during exercise is directly related to the intensity of work performed. Because of the ease of measurement HR is often used.

Reliability of Heart Rate as an Indicator for Intensity

The accuracy and variability of commercially available HR monitors is one of the greatest sources of error. In particular the use of "earlobe" and "finger" monitors are highly unreliable (Macfarlane et al 1989). Many HR monitors underestimate the HR according to Léger and Thirierge (1988). Errors from 20-54 bpm were found and the validity was lower at 85-95% HR max than for 65-75% HR max even for monitors of the 1. category. If two people perform close to each other their transmitter may interfere.

Factors Affecting Heart Rate

Temperature

Stannard and Thompson (1998) investigated HR as an indicator for exercise intensity under different environmental condition. In their study seven highly trained cyclist performed a 50 minute cycling session consisting of five 10 minute workloads of 150, 250, 350, 250, 150 Watts. The exercise tests were performed at 37 and 20 degree Celsius on the same day in random order with at least 21/2 hours between sessions. A constant wind flow of 14.5 m/s was provided.

The higher temperature induced a significant greater HR than the cooler conditions. With the onset of the exercise HR increases (average of 11bpm) and the difference increased with both intensity and duration of the task. At the end of the 4th stage, HR was an average 26 bpm higher in hot conditions. The 150 Watts workload at the end showed significant higher HR (average 18 bpm) than the same workload at the beginning of the task. But in cool conditions HR for the same workload were similar at the beginning and at the end of exercise.

Fig. 1. Stannard and Thompson (1989)

The authors concluded from these findings that in hot conditions power output is lower for the same HR in cool conditions. As a consequence an athlete with a maximal HR of 190 bpm might be in a E1 training zone (65-75% of HR max) while training in cool conditions in the morning but be training in E2 training zone (75-85% of HR max) in hotter environment during the day, although performing the exactly same training session. Another interesting fact coming from this study indicating that on a hot day once HR is elevated with an increase in intensity, the HR remains elevated even when the workload is reduced.

These findings have to be taken into consideration when designing an interval program with repeated submaximal efforts. On a hot day the power output will progressively drop, whereas under cooler conditions the same training session would have a quite different training effect. So if HR is used as an indicator, temperature has to be taken into account.

Effect of caffeine on HR and endurance

Caffeine is a substance that occurs naturally in many plants, including coca, coffee beans, and tea leaves. It is also found in numerous soft drinks, chocolate and analgesics. Caffeine can act through a variety of mechanism:

• Adrenergic receptor antagonist increase the permeability of the sarcoplasmatic reticulum to calcium and therefore increase muscle contractility
• Inhibition of enzyme activity such as phosphodiesterase
• Fascilitating neuromuscular impulse transmission

Caffeine has an effect on CNS at concentration of 85-200 mg. At this level it will decrease fatigue and increase mental alertness. The highest concentrations following absorption are found in tissue with the highest water content, primarily skeletal muscle.

Studies have shown that caffeine may improve endurance. In the study of Flinn et al 1990 nine cyclists were given a dose of 10 mg/kg caffeine 3 hours prior to an incremental cycle ergometer test. The subjects worked longer, performed more work, exhibited higher FFA levels in the caffeine trial than during control and placebo trials. The authors concluded that caffeine when taken 3-4 hours prior to exercise in subjects with diets normally low in caffeine.

Side effect seen with caffeine uptake include anxiety, tachycardia, irritability, restlessness. Caffeine has also a diuretic effect which may result in fluid imbalance and increased HR.

Diurnal changes

The HR shows a circadian variation during both rest and submaximal exercise (Davies and Sargeant 1975) that parallels the daily variation in body temperature. However, the maximal rate remains constant. The highest values are observed in the late afternoon and evenings, and the lowest values in the small hours of the morning.

Sympathetic neural stimulus

The HR is normal controlled by neural, hormonal, and intrinsic factors. Of these general control classification the control of HR by the nervous system is the most important. The heart is supplied with nerves from both sympathetic and parasympathetic divisions of the autonomic nervous system. The sympathetic cardiac accelerator nerves secretes noradrenaline and some adrenaline at their endings on the heart to make an increase in HR. The parasympathetic vagus nerve endings secrete acetylcholine, which slows the rhythm of the heart. The firing of the cardiac accelerator nerves and vagus nerves is controlled by nerves in the brain, primarily in the medulla. These cardiac control centers can be stimulated by emotional excitement, by nerve reflexes sensitive to changes in muscle chemistry, blood pressure, and arterial pH and many other factors.

Hormones circulating in the blood can directly affect the HR. Adrenaline and noradrenaline secreted directly from the adrenal glands are the most important ones. Under their influence HR increase as well as with thyroid gland hormones influence.

Psychological factors (motivation, anxiety)

There is evidence in the literature that high motivation alone can lead to an increased oxygen extraction by the working muscle without further HR increase.

Hormonal changes in the female athlete

During a menstrual cycle HR can differ (s.Fig. 2). In the menstrual phase HR is decreased at rest and increased during maximal exercise (Fox 1984).

Other Indicators of Exercise Intensity

Ratings of perceived exertion (RPE)

HR remains a somewhat labile measurement being influenced by such factors as emotional disturbances, effective environmental temperature, recent physical activity, consumption of food, caffeine and cigarettes.

As mentioned before there are problems associated with the use of HR leading to the use of perceived exertion, in conjunction with HR to estimate exercise intensity. It has been increasingly apparent that RPE as initially described by Borg (1982) can be of considerable value in testing and monitoring performance.

RPE has been shown to be a more accurate predictor of exercise capacity than HR. According to the American College of Sports Medicine (1986) RPE is a valid and reliable indicator of level of physical exertion during endurance exercise. They come to the conclusion that RPE can replace HR as the primary mean of monitoring exercise intensity distracting influence.

Koltyn and Morgan (1992) found similar results in their study. They showed in their study that the group employing RPE to monitor exercise intensity during aerobic dance had significant higher gain in endurance performance at the end of the training period than the group of HR monitoring.

VO_{2 max}

Maximal oxygen uptake (VO_{2 max}) is commonly accepted as the best criterion of cardiorespiratory endurance capacity or aerobic fitness. Because of the expense, inconvenience and discomfort associated with the direct assessment of VO_{2 max}, investigators have developed submaximal tests that provide accurate estimates of VO_{2 max}. These tests have limitations and include the potential source of error. For example with submaximal tests like 6 Min. Åstrand Test VO2 max in trained athletes is often overestimated (±10% of the true value). Maximal testing while providing more accurate estimates of VO_{2 max} is not applicable to most of the population whose age or medical history gives reason for caution.

Blood lactate

Blood lactate determination alone is not a good method to predict anaerobic threshold. Only if it is used in combination with respiratory determinations an accurate estimation is possible.

Macfarlane et al 1991 suggested that a training programme should be based on HR response, VO_{2 max} and anaerobic threshold, because every single measurement has its limitations. However, having evaluated these factors for each athlete, individuals exercising at a set percentage of their individually determined anaerobic threshold.

Conclusion

HR is a questionable indicator for exercise intensity because of its variation under hot conditions, ingestion of caffeine, food and cigarettes.

HR also changes with dehydration, with psychological factors, hormonal and vegetative stimuli.

Therefore the recommendation is not to use HR alone for assessment or monitoring, but to combine it with RPE, blood lactate measurement, and VO_{2 max} evaluation.

Response to Statements by the Negative Speaker

Statement 1: HR is an instant response and therefore an good indicator.

Response: If response is based on incorrect values because of inappropriate tests (submaximal), values are not useful.

Statement 2: HR is an objective measure.

Response: According to Léger and Thivierge (1988) HR is underestimated by HR monitors. Even for the 1. category monitors errors were mentioned. Validity is also dependent on the intensity of exercise and underlie a great variability.

Only chest electrodes measure electrical activity valid and stable.

Statement 3: HR can be measured during a specific task.

Response: HR is not appropriate for swimming (too much arm movement, water contact). HR not an appropriate measure for cross country skiing

Statement 4: HR can be used to demonstrate overtraining.

Response: If HR is increased the athlete has already reached overtraining status, HR is not a valid predictor and HR is not always increased in overtrained athletes.

Statement 5: HR can be used not only for athletes but also for cardiac patients.

Response: not a valid measure because many cardiac patients take betablockers, therefore the HR is suppressed.

References

American College of Sports Medicine (ACSM) (1992)

Guidelines for Exercise Testing and Prescription. (3rd ed.). Philadelphia: Lea and Febiger.

Åstrand P and Rodahl K (1986)

Textbook of Work Physiology. (3rd ed.) New York: McGraw-Hill.

Borg GAV (1982)

Psychophysical bases of perceived exertion. Medicine and Science in Sports and Exercise 14: 377-387.

Bowers RW and Fox EL (1988)

Sports Physiology (3rd ed.). New York: Brown.

Davies and Sargeant (1975)

British Journal of Industrial Medicine 32: 110-114.

Flinn S, Gregory J, McNaughton LR, Tristam S, Davies P (1990)

Caffeine ingestion prior to incremental cycling to exhaustion in recreational cyclists. International Journal of Sports Medicine 11: 188-193.

Fox EL (1984)

Sports Physiology (2nd ed.). Tokyo: Saunders.

Koltyn KF and Morgan WP (1992)

Efficacy of perceptual versus heart rate monitoring in the development of endurance. British Journal of Sports Medicine 26: 132-134.

Knopp WD, Wang TW and Bach BR (1997)

Ergogenic Drugs in Sport. Clinics in Sports Medicine 16: 375-392.

Lamb DR (1984)

Physiology of Exercise. New York: MacMillan.

Léger and Thivierge (1988)

Heartrate Monitors: Validity, stability, and functionality. Physician and Sportsmedicine 16: 143-151.

McArdle, Katch FI, Katch VL (1996)

Exercise Physiology. (4th ed.) Baltimore: Williams & Wilkins.

Macfarlane D (1991)

Who do exercise physiologist test best - athletes or themselves. New Zealand Journal of Sports Medicine 19: 13-15.

Stannard S, Thompson M (1998)

Heart rate monitors: Coaches' friend or foe? Sports Coach 21: 36 37.

Thein LA, Thein JM and Laundry GL (1995)

Ergogenic aids. Physical Therapy 75: 426-439.

Negative Argument by Terence Ho

Physiological Significance of Heart Rate

During exercise, cardiac output must increase to match the demand by increasing the stroke volume and heart rate, however, these two parameters increase in different phases. In marathon runner, the cardiac output increases from its resting level of about 5.5 litres/min to 30 litres/min.(Leff, 1986).

The stroke volume increases from 105 to 162 millilitres, as an increase of about 50 %; whereas the heart rate increase from 50 to 185 beats per minute, an increase of 270%! Therefore, the heart rate increase accounts by far for a greater proportion of the increase in cardiac output than does the increase in stroke volume during strenuous exercise (Leff, 1986).

The stroke volume normally reaches its maximum by the time the cardiac output has increased only halfway to its maximum. Any further increase in cardiac output must occur by increasing the heart rate (Guyton, 1991).

Aim of Training

The main aim of training is to improve cardiovascular fitness/aerobic capacity and upgrade performance A training programme that lacks high intensity training will not improve aerobic fitness (Gilman, 1996). Therefore, the essential part of any coaching program is to be able to monitor the intensity of exercise at which the athlete trained (Stannard & Thompson, 1998).

To start with, a general guideline should be used as reference of whether the exercise/training given is optimum or not. Heart rate provides useful guideline for exercise prescription for different groups of individual. This guideline not only applies to class I individual (apparently healthy subjects) but also provides information in calculating the formula for the class II (higher risk individuals) and class III (individuals with known cardiac, pulmonary or metabolic disease (Fig. 1)(King & Senn, 1996).

Background Information

"Heart rate is reflecting the performance of cardiovascular fitness"
Stannard & Thompson, 1998

"Heart rate is the relatively accurate indicator of cardiovascular work intensity, most exercise prescriptions use heart rate as a preferred measure of intensity"
King & Senn, 1996

"The cardiovascular response to physical training depends upon the type of exercise undertaken and the intensity, frequency and duration of training sessions"
Leff, 1986

"The intensity of training is critical to an athlete's performance"
Gilman, 1996

• Heart rate monitor
• Obtain the performance of cardiovascular fitness
• Produce training guideline and reference index to individual athlete
• Help upgrading performance/prevent over training
• Establish training plan in next season

Importance of Monitoring Heart Rate During Training

Instant response from athlete/patient to coach/medical profession

The performance of cardiovascular fitness is well reflected by Heart rate especially in endurance based sports, such as cycling, endurance running and triathlon where a highly developed aerobic energy system is fundamental for optimal performance (Stannard & Thompson, 1998). Increase in heart rate is a very important physiological response to exercise.

During the performance of dynamic exercise, cardiac output increases from resting levels of four to six litres per minute to maximal levels as high as 36 L/min in a well trained athlete.

This increase is achieved by relative increase in heart rate and venous return etc.. The heart rate increases from basal levels of approximately 70 to 200 beats/min during exercise in the young adult. This provides the major augmentation to the cardiac output during exercise (Leff, 1986).

Cardiovascular changes immediately before and at the onset of exercise are initiated from the neural command center above the medullary region. This feed-forward input suppresses parasympathetic activation and augments sympathetic outflow to increase heart rate and myocardial contractility (McArdle et al, 1996)

The instant result obtained can give an idea to coach/medical profession how hard is the intensity of the exercise prescribed to the athletes/patients

Objective response which is practical/accurate/valid and stable

The intensity of an exercise prescription has often been monitored with palpated heart rate that provides immediate feedback (Gilman & wells, 1993; Gilman, 1996; Stannard & Thompson, 1998). However, the reliability the obtained results are in doubt. Gilman & Wells (1993) demonstrated that the subjects self-reported perception of training intensity was actually overestimate the amount of time spent performing hard intensity training. It was suggested that a more precise way of monitoring training intensity, such as heart rate monitoring, is warranted.

Research showed that telemetry heart rate monitors both for immediate feedback and to store heart rates for later playback and analysis could provide a record of training intensity when downloaded to a personal computer and analyzed with software.

Some HR monitors available on the market are valid and stable, particularly those measuring electrical activity of the heart with conventional chest electrodes. Excellent correlation between readings obtained by ECG and HR monitors using conventional chest electrodes to measure electrical activity of the heart. The exercise heart rate obtained by heart rate monitor is valid and stable. Although many HR monitors systemically underestimated the ECG heart rate, this underestimation was small for the most valid monitors. (Léger and Thivierge, 1988).

Obtain the cardiovascular response during specific task

As mentioned before, subjective evaluation of performance may not be accurate. However, even though we have got the objective and practical measures, specificity is absolutely necessary. In order to obtain the "true performance" of the cardiovascular performance at specific task during certain time. The cardiovascular response at that particular moment should be recorded.

The general practice for establishing aerobic training intensity is direct measurement or estimation of the person's VO_{2 max} or HRmax, followed by assignation of an exercise level that corresponds to some percentage of these maximum. Although establishing training intensity from measures of oxygen uptake is reasonably accurate, it is impractical without sophisticated equipment. Therefore, the next effective alternative is to use Heart rate to classify exercise for relative intensity (McArdle et al, 1996)

The use of heart rate provides an acceptable estimate of energy expenditure for running over varied positive gradients up to 4% (Creagh, 1997)

An important safety measure

In the training situation, if no direct monitoring, excessive training which may cause illness and over-training. This is even more serious in those cardiac patient since heart rate at the ischemic ECG threshold was used as the upper limit of training intensity during jogging (Dressenddorfer et al, 1997).

In the athletes group, despite generally the greater the relative training intensity above threshold, the greater the training improvement, the maximum intensity of training is still unknown. With heavy and prolonged regular training, especially in endurance sports, certain athletes experience the syndrome of over-training. The over trained condition is more than just a short term inability to train as hard as usual but rather, it involves a more chronic fatigue, the symptoms may included persistent poor performance, increases the chance for injury to bones, joints and muscles (McArdle et al, 1996). Therefore, a long term monitoring should be carried out to prevent unnecessary injury.

Heart rate monitoring is a good way to establish optimum training intensity

Assess training intensity: Gilman (1996) showed that heart rate associated with exercise intensity provides a reasonable marker of training intensity. In his study, the heart rate of a fourth-year male collegiate ski racer (21 years of age) was obtained by telemetry heart rate monitor. The results obtained were partitioned into 3 zones to represent easy, moderate and hard intensity.

The heart rate at aerobic and anaerobic intensities was determined by a ski-walk test in laboratory. The lower reference heart rate was closely associated with 2 mmol/L of blood lactate and this intensity of exercise is primarily aerobic energy metabolism.

Hence, the heart beat per minute (in this case is 150 beats/min) was used as reference heart rate for the upper limit of the aerobic training zone. On the other hand, hard intensity zone was heart rate which as closely associated with 4 mmol/L of blood lactate which was proposed that this is the anaerobic threshold (Gilman, 1996).

Some of the metabolic variables e.g. OBLA (onset of blood lactic acid) can be the reference points occur at different percentages of maximum heart rate. Therefore it may be possible to design individualised training programs based on the heart rates at ventilatory threshold (the anaerobic threshold as the point of non-linear rise in minute ventilation or carbon dioxide production in relation to VO₂), OBLA and VO_{2 max} (Gilman & Wells, 1993).

Different training zones are defined according to the percentage of maximum heart rate. For example, the basic aerobic endurance is defined within the range of 65% and 75% of maximum heart rate; the general aerobic endurance is defined within the range between 75% and 85% of maximum heart rate. The anaerobic threshold is defined as the range between 85% to 92% of maximum heart rate (Stannard & Thompson, 1998).

Conclusion

To conclude, heart rate monitoring during training is essential. It can provide instant response to athlete/patient and coach/medical profession as an objective measure. Besides, the cardiovascular response at specific training task can also be obtained.

In both athletic and patient group, heart rate monitoring can be an important measure to prevent over training. Above all, the use of heart rate monitoring is a good way to establish optimum training intensity to upgrade performance.

References

Creagh U and Reilly T (1997)

Physiological and biomechanical aspects of orienteering. Sports Medicine 24(6):409-418.

Dressendorfer RH, Franklin BA, Smith JL, Gordon S and Timmis GC (1997)

Rapid cardiac deconditioning in joggers restricted to walking. Chest 112(4):1107-1111.

Gilman MB (1996)

The use of heart rate to monitor the intensity of endurance training. Sports Medicine 21(2):73-79.

Gilman MB and Wells CL (1993)

The use of heart rate to monitor exercise intensity in relation to metabolic variables. International Journals of Sports Medicine 14: 339-344.

Guyton AC (1991)

Textbook of Medical Physiology. (8th ed.) Philadelphia: Saunder.

King CN and Mark DS (1996)

Exercise Testing and Prescription. Sports Medicine 21(5):326-336.

Leff AR (1986)

Cardiopulmonary Exercise Testing. London: Grune & Stratton.

Léger L and Thivierge M (1988)

Heart rate monitors: Validity, stability, and functionality. Physician and Sportsmedicine 16(5):143-151.

McArdle WD, Katch FI and Katch VL (1996)

Exercise Physiology: Energy, Nutrition and Human Performance. (4th ed.) Philadelphia: Williams & Wilkins.

Stannard S and Thompson M (1998)

Heart rate monitors: Coaches' friend or foe? Sports Coach 21(12):36-37.

Exercise Physiology Educational Resources 1998