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COACH, I CAN’T GET MY HEART UP (OR DOWN) … THE PHYSIOLOGY OF MEASURING HEART RATES

INTRODUCTION

The use of heart rate monitoring in swimming is almost universal in programs of all levels. The measurement of heart rate during swimming training is used for two main purposes … firstly, to control the training load (intensity) through the session … and secondly, to indicate changes in submaximal and maximal aerobic fitness levels during the season. A third application is the measurement of resting heart rate to indicate the current stage of the adaptation process. When combined with performances measures such as time, split times, stroke rate, stroke count, stroke mechanics (technique) and other physiological measures such as blood lactate, heart rate is a very useful monitoring tool for the coach. A key consideration, however, is that heart rate or any other measure, should not be used alone and can only be interpreted correctly in light of the other variables.

TRAINING ZONES

The control and prescription of training speeds by heart rate is the biggest application of heart rate testing in swimming. There are many different classification systems used by leading swimming coaches and sports scientists in Australia and around the world, although the validity of some has been questioned. The system used by the Australian Institute of Sport has been discussed previously in Australian Swim Coach. In recent years, many of the classification systems have been revised in order to accommodate individual differences in maximum heart rate levels. In their original form, the systems called for specific training sets to be defined by distinct levels of heart rate … e.g. low-intensity aerobic (A1) 120-140bpm, moderate-intensity aerobic (A2) 140-160bpm, anaerobic threshold (AT) 160-170bpm, and maximal oxygen uptake (VO2max) 180-190bpm. These training zones were developed using a model maximum heart rate of 200bpm – for many young swimmers this is reasonably accurate, however for others these zones will lead to a significant under-or-over estimation of the appropriate training heart rate and speed. To overcome this problem, many coaches now give their training heart rates as a fixed increment from maximal heart rate for each individual swimmer – i.e. A1 (60-80bpm below max), A2 (50-60bpm below max), AT (30-40bpm below max), and VO2max (10-20bpm below max).

For a swimmer with a maximum heart rate of 205bpm, the zones would be (in bpm)…

 

A1

A2

AT

MV02

125-145

145-165

165-175

185+

 

 

For a swimmer with a maximum heart rate of 185bpm the zones would be (in bpm)…

 

A1

A2

AT

MV02

105-125

125-145

145-155

165+

 

 

Finally, for short sprint work (25m and 50m) it is more appropriate to focus on the swimming and split times (and stroke mechanics) rather than the associated heart rates. For this type of work, the heart rate monitor should be replaced with the stopwatch. In this situation it is more important to know that a swimmer can hold, for example, 31.0 seconds for 50m Butterfly with a stroke count of 20 and a stroke rate of 38 strokes per minute, than the fact that the heart rate was, say 155bpm.

HOW TO MEASURE HEART RATE

By far the most common way to measure heart rate has been the self-reported manual palpation (counting) of heart rate by swimmers over a fixed duration (most commonly 10 seconds). Whilst this is the most practical method it is also the most inaccurate. With correct instruction and some experience, swimmers can be become reasonably proficient and accurate with this technique. The older swimmer should be able to calculate his or her post-exercise heart rate with an accuracy of +6 beats per minute. This can give you a reasonable indication as to the relative cardiovascular response to the training set. Remember you are trying to have the swimmers count the number of beats in a given 10 second period (using the pace clock) and this needs to occur as soon as the swimmer touches the wall. The heart rate will start to recover to a lower level within a few seconds of rest. This approach should be accurate enough to identify which training zone the swimmer is in, but more sophisticated measures would be required to indicate small changes in the relationship between heart rate and swimming speed.

At the elite level, the most common method for measuring heart rate has been the use of the Precision Heart Rate Monitor, designed and built by Dr Bob Treffene in Brisbane. Many coaches will have used or seen one of these hand-held units in action. In the hands of a skilled operator … i.e. coach or scientist … they give good service and are particularly useful when working with large squads. The monitors need to be well maintained in order to sustain their useful working life. Most coaches will have also seen the Sports Tester-type heart rate monitor, which attaches to the chest and transmits a signal to a wristwatch receiver. These do work reasonably well but with elite swimmers undertaking fairly dynamic work … e.g. dive starts, tumble turns … it is a difficult to keep them in a fixed position on the body and to obtain a clear and reliable signal. A number of other devices have been developed to measure heart rate in swimmers but these tend to be limited in two key areas … a lack of accuracy at higher heart rates and a lack of durability in the rough and tumble of the pool environment.

ANATOMY AND PHYSIOLOGY OF THE CARDIOVASCULAR AND NERVOUS SYSTEMS

To understand why heart rate can vary with fitness and fatigue levels it is necessary to examine some basic anatomy and physiology of the nervous system. The nervous system plays a major role in regulating the function of all the body’s systems including the cardiovascular system. The heart rate is, of course, the most identifiable indicator of the activity of the cardiovascular system and a major contributor to the metabolic (power) output of a swimmer. In basic terms the nervous system is divided into two parts … the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves that connect the different organs and tissues with the central nervous system) (see Figure 1).

The peripheral nervous system is comprised of the somatic and autonomic components, with the autonomic nervous system that innervates (serves) the skeletal musculature being further divided into two branches … sympathetic and parasympathetic. These branches often produce opposite physiological effects. During strenuous exercise the sympathetic branch is stimulated, leading to release of adrenaline, increased heart rate, increased blood flow to muscles and eventually increased rates of metabolism and muscular contraction. This sympathetic activity remains elevated for some time after exercise. Problems may arise when sympathetic activity is chronically elevated during prolonged and intense training, particularly where recovery processes are not adequately restoring physiological equilibrium. On the other hand, one of the adaptations to training is for a reduction in sympathetic activity during training at a given speed. This is part of the explanation for the observation that heart rate is lower at submaximal speed after a successful period of training.

WHY CAN’T I GET MY HEART RATE DOWN?

(i) At Rest

The measurement of resting heart rate is one of the most well known methods to monitor training adaptation. An increase in resting heart rate may be evidence of elevated sympathetic activity … e.g. a swimmer whose resting heart rate is normally around 50bpm … e.g. 48-52bpm … may be experiencing some sympathetic stimulation if the levels are sustained at 55-60bpm over a period of a few days. A single occurrence of an elevated resting heart rate may be attributable to any one of a number of reasons, and action only needs to be taken if the rise is evident over several successive days. Many swimmers use daily training logs and it is good practice for them to record measures such as resting heart rate as well as the length and quality of sleep. The resting heart rate should be taken first thing in the morning and before the swimmer rises from his or her bed.

(ii) During Training

Experience shows that the swimmer unable to control their heart rate during steady state aerobic work needs further aerobic training. In simple terms, the activity of the sympathetic nervous system, and the aerobic and cardiovascular fitness of the swimmer, need to be improved. Physiological testing has shown that the heart rate-swimming speed relationship is a good indicator of overall cardiovascular fitness. If control of heart rate is lost during so-called steady state or even paced swimming and a consistent elevation is observed … i.e. an upward drift … there will be a concomitant transference from fat to carbohydrate metabolism. An example of this would be a set such as 12x200m Freestyle/Backstroke holding 2:40 with HR of 150bpm on 3:00 cycle…

Time: 2:40 2:40 2:41 2:39 2:40 2:42 2:38 2:40 2:41 2:41 2:42 2:38

HR: 137 145 148 151 152 156 159 157 162 166 164 170

One of the goals of low to moderate intensity aerobic work is to improve fat metabolism and this will not be achieved if higher heart rates (and a greater contribution of carbohydrates to energy supply) is evident in aerobic work. The key to improving heart rate and metabolic control is a program of carefully monitored aerobic intervals on short to moderate rest. An example of this work would be a set such as 6x200m Freestyle holding 2:30 pace at a heart rate of 150bpm on a cycle of 3:00. Swimmers should be encouraged to strictly maintain the required heart rate (in this case 150+5bpm … i.e. a range from 145-155bpm) and the required time (in this case 2:30). Measurement of blood lactate and blood glucose levels in this situation is useful to determine the extent of metabolic control. After a few sessions of this type, an improvement in the control of aerobic work should be observed. One feature of better (and usually older and more mature) swimmers is their ability to undertake aerobic work at the appropriate intensity and pace. Younger and less disciplined swimmers often do not maintain good control of swimming times and intensities. Starting too fast early and not finishing on strongly, or swimming descending sets … i.e. where the speed gets faster with each repeat … when a steady pace was called for, are common mistakes.

WHY CANT I GET MY HEART RATE UP?

The inability of a swimmer to get his or her heart rate up during training may be evidence of a disturbance or maladaptation in the parasympathetic nervous system. This is much less common than a training-induced sympathetic disturbance. The parasympathetic nervous system will tend to take over … i.e. compensate for … from the sympathetic system if the latter is exhausted by excessive training loads and/or inadequate recovery. A swimmer may sometimes exhibit the following signs during prolonged intense training: fatigue, lethargy, inability to maintain previous training levels, decreased body weight and, most notably with a parasympathetic disturbance, a decreased heart rate both at rest and during submaximal work (see Table 1). One of the most common signs is an extremely rapid return of the heart rate towards resting levels immediately upon the cessation of work. The lower heart rate can sometimes be mistaken for an improvement in fitness, but the full clinical picture (as the doctors would say) is one of deterioration rather than progress. Whilst we all strive for lower heart rates at a given submaximal speed, the combination of lower heart rates and other classical symptoms suggest a disturbance in the nervous system.

Every swimmer and coach knows that a lack of fitness is highlighted by an increase in submaximal heart rates. At the same low to moderate speeds, a swimmer’s heart rate will be lower as they get fitter. Or expressed another way, they can swim faster at the same heart rate. Physiologists use heart rate in this way to track changes in general cardiovascular fitness with standard test sets such as the 5x200m or 10x100m incremental step tests.

Table 1: Comparison of the signs and symptoms of sympathetic and parasympathetic nervous system disturbance in athletes undertaking prolonged and/or intensive training

Sympathetic Disturbance

Parasympathetic Disturbance

Increased resting heart rate

Decreased resting and exercise heart rates

Increased resting blood pressure

Normal blood pressure

Normal recovery of heart rate after exercise

Rapid recovery of heart rate after exercise

Decreased body weight

Normal body weight

Poor appetite

Normal appetite

Sleep disturbance

Sleep patterns may be normal

Irritable and emotional

Depressed and apathetic

Decreased ability to metabolise glycogen

Rapid recovery (days-weeks)

Decreased blood lactate levels

Decreased physical work capacity

Slower recovery (weeks-months)

WHAT ARE ‘HEART RATE’ SETS?

Within the culture of Australian swimming, particularly at the elite level, the term ‘heart rate set’ is well known to most coaches. Coined by leading Australian physiologist ‘Heart Rate Bob’ Treffene, the term ‘heart rate set’ refers to a high intensity aerobic set designed to improve endurance fitness including the so-called maximal oxygen uptake (VO2max). Many coaches would be familiar with the sets of 2000m to 3000m (30 minutes work) at a pace that elicits a heart rate 10 beats from maximum level … e.g. 20x100m Butterfly/Backstroke aiming for 185bpm on a 1:45 cycle (for a swimmer with a maximum heart rate of 195bpm). These sets when properly designed and monitored are a very effective way to improve aerobic fitness. Given their high intensity and associated stress, they need to be introduced and developed gradually in order to avoid excessive fatigue. A maximum of two or three heart rate sets per week is recommended for well-conditioned swimmers.

WHAT DO I DO IF THE HEART RATE IS UNEXPECTEDLY UP OR DOWN?

The easy answer to this question is MORE RECOVERY. Irrespective of the origin of the disturbance in the nervous system … i.e. sympathetic or parasympathetic … the appropriate course of action is to review and implement appropriate recovery practices. In terms of planning, this may mean the need for a reduction in volume and intensity of training, an increase in the absolute and/or relative volume of low- to moderate-intensity aerobic recovery work. If the majority of swimmers in the squad are breaking down or not responding to training it is prudent to review the short- and medium-term training plans. If a quality session is planned it is a good idea to change this to a low- to moderate-intensity aerobic workout. In more severe cases of fatigue it may be more appropriate to skip the session altogether. The other area to be considered is the aggressive use of recovery modalities such as massage, hot or cold therapies with showers, spas and plunge pools. Replacement of fluids and adequate nutrition is also an essential component of the recovery process.

SUMMARY

  1. The use of heart rate is almost universal within swimming programs at all levels and is an effective tool to prescribe training loads and monitor changes in aerobic fitness levels.
  2. Heart rate is most easily measured by swimmers themselves with self-reported palpitation at the neck or chest. Elite coaches commonly use the Precision Heart Rate Monitor to assess the cardiovascular demands of particular training sets.
  3. The regulation of heart rate is governed by the sympathetic and parasympathetic branches of the autonomic nervous system. With sympathetic disturbance, heart rates are normally higher, whilst disturbance of the parasympathetic system is characterised by lower heart rates.
  4. A lack of fitness will be evident with higher heart rates at submaximal speeds. Further attention to training in well-controlled moderate-intensity aerobic sets should improve cardiovascular fitness.
  5. Over stimulation of the sympathetic nervous system can lead to the physiological and psychological signs and symptoms of overtraining … e.g. an increased resting heart rate and/or higher heart rates during submaximal work.
  6. An exhausted sympathetic nervous system may result in the parasympathetic system becoming dominant. This may lead to unusual depression of the heart rate at rest and during exercise, with a concomitant reduction in physical work capacity.
  7. An understanding of the physiological responses to acute work and prolonged training will assist the coach in interpreting heart rate measurements and ultimately in optimising the training program.
  8. The term ‘heart rate set’ refers to a high intensity maximal aerobic (VO2max) set where the intensity of the set is controlled by heart rate (and swimming times). Swimmers are encouraged to swim at the appropriate pace necessary to elevate and hold the post-exercise heart rate at level that is approximately 10 beats below each individual swimmers maximum heart rate.
  9. A disturbance in the sympathetic and/or parasympathetic nervous system as indicated by heart rate responses at rest or during exercise should be addressed immediately. Training programs may need to be adjusted and recovery programs emphasised. The timing of the return to full training should be determined on a case-by-case basis.

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