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Heart Rate Monitoring 
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By Matthew Weston Matthew Weston BSc (Hons) MSc  PGMO Sports Scientist  mweston@fapl.co.uk

During exercise, the frequency at which the heart beats (heart rate, HR) increases in order to supply an increased amount of oxygen to the exercising muscles.  The harder the body exercises, then the faster the heart beats and the technological advances in HR monitoring have made it possible for athletes to record HR during training for subsequent analysis.1

HR monitors consist of a transmitter and a receiver.  The transmitter is attached to the chest and sends signals to the receiver, which is a watch-like monitor worn on the wrist.2  The illustration, courtesy of Wilmore and Costill,3 illustrates this set up.  HR monitors have been continually developed with larger memory capacities, which allows for significant data storage and subsequent data analysis through the downloading of the data onto a computer.4

The harder the body exercises, then the faster the heart beats.

In fact, HR monitoring is one of the best ways to monitor training load in athletes and its use is recommended to all referees, regardless of standard.  HR monitoring during training also permits the quantification of training into different exercise intensities, such as aerobic and anaerobic intensity.1  This helps to ensure that all aspects of physical fitness, i.e., speed, speed endurance, intensive aerobic training, recovery, etc. can be appropriately prescribed and monitored.  However, in order for accurate and reliable interpretation of HR training data, there are a number of factors can affect HR during exercise and these need to be controlled for.

Dehydration

HR’s are elevated during exercise in high ambient temperatures, when compared to exercise in cooler environments, with the rise in HR compensating for the extra fluids that are lost during sweating.  However, increasing levels of dehydration will impair physical performance.  Research has demonstrated that only a 1% loss in body weight owing to sweat losses is enough to impair performance, with further performance decrements being directly related to the amount of dehydration accrued.
The graph opposite demonstrates a referee's HR response to a fitness test (the YoYo Intermittent Recovery Test, Level 1).  The graph demonstrates the effect of heat stress upon HR, and ultimately performance, in that HR was higher during the test in 35º degree heat and ultimately performance was impaired (level 18 in heat vs. level 20 in normothermic environment).

Also, after the first few minutes of mild to moderate intensity exercise there is a gradual increase in HR as exercise progresses, termed cardiovascular drift – increases of up to 15% from 5 - 60` of exercise have been reported.4  This again is related to level of dehydration incurred during exercise. Therefore, when aiming for a certain HR zone during exercise this drift should be considered.4

A referee's HR response to a fitness test (the YoYo Intermittent Recovery Test, Level 1)

Time of Day

Reilly et al. 5 reported a considerable diurnal variation (5 - 15% variation across a 24hour period) on HR, with HR responses being highest late in the afternoon / early evening.  This is consistent with exercise performance being at its peak during the same time of day.

                                                            0300               0900               1500               2100

HRRest                                                 90                    96                    99                    96

HRmax                                                 176                 180                 182                 182

Anxiety

Psychological stress has been shown to increase HR with minimal physical activity.

 

Competition

During a competitive match, a referee’s HR response is likely to be affected by factors such as environmental conditions and emotional stress.  Consequently, HR’s recorded during matches may overestimate the amount of physical work undertaken by a referee.  Therefore, competitive HR’s will tend to be higher than training HR’s.  The data below collected from runners clearly demonstrates this:

                                                                  10km              21km              42km  
HR during race                                           163 + 13         166 + 10         156 + 6  
HR during training                                     143 + 22         151 + 13         137 + 17

 

Day to Day Variation

Astrand and Saltin6 reported a day to day variation of 3beats.min-1 difference for steady state exercise.  Whereas, Brisswater and Legros7 studied national class runners on a treadmill at sub maximal speed and reported a day to day variation of 6beats.min-1!

Effect of Training

The illustration below demonstrates the effect of training upon HR at rest, during sub maximal and maximal exercise.  Therefore, HR monitoring during graded exercise can be used to assess changes in fitness status.

The effect of training upon HR at rest, during sub maximal and maximal exercise.

    

HR Monitoring during Training

When undertaking fitness training, especially intensive training sessions, it is best that HR is expressed relative to each individual referee.  The reason for this is that referees of different ages and different fitness levels can attain the appropriate physiological overload from their training sessions. 

In order to achieve this, it is necessary to have the maximal heart rate (HRmax) accurately determined so that HR during training, and matches, can be expressed as a percentage of this value.  This is also a very easy way to prescribe training intensities as a % of HRmax.

HRmax can be determined via a maximal effort on a fitness test, either laboratory or field based, or taken as the highest 5second peak attained in a match or during an intensive training session.  However, it is important that this figure is reliable otherwise the goals of a particular training session, if using HR’s to monitor the training load, will not be met.  Therefore, it is important that the figure, which represents HRmax, is the highest recorded during any of the above sessions. 

In situations where one value is significantly higher that all other peaks, it is necessary to check the HR readings carefully to ensure that this figure is not an error.  If the value appears to be true, then it may be that a central mean HRmax value is used from the highest 5second peaks attained during fitness tests, matches and intensive training sessions.  This will minimise the potential risk of under or over estimation when calibrating exercise intensities with HR.8  It is also necessary to monitor HRmax directly throughout the training year, perhaps once every 2 months as HRmax can be sensitive to training status.9 

Once an accurate and reliable HRmax has been determined, it is possible to add HR zones into the training monitoring process.  Therefore, training is prescribed as a range as opposed to a fixed figure.

 

Heart Rate Zones

% HRmax                                 Type of Training                    Perceived Exertion

Below 60%HRmax                  Recovery                                Very Easy

60 - 75%HRmax                      Low Intensity                          Easy to Comfortable

76 - 85%HRmax                      Medium Intensity                   Uncomfortable to Slightly Hard

86 - 93%HRmax                      High Intensity                         Hard to Very Hard

Over 93%HRmax                    Maximal Effort                          Maximal!!

HR analysis of training sessions enables an examination of whether or not the goals of individual training sessions have been met.  For example, high intensity aerobic training sessions should ideally be performed at an intensity corresponding to 86 – 95% HRmax.  Whereas, for recovery sessions and speed training, HR’s should be used to ensure the physical load is kept to a minimum and that recovery is complete in between repetitions.

HR during Training

The following section provides an illustration of typical HR traces during training sessions aimed at improving different aspects of physical fitness.

1. High Intensity Aerobic Training

-Steady state running at an intensity 86 - 93% HRmax

-Average work rate over session is important

-Can be continuous (20 - 30’) or interval based (15” - 8’)

Example given – 3’, 2’, 1’, 1’, 2’, 3’, 3’, 2’, 1’ running at 90 - 93%HRmax, with 1’ recovery intervals in between.

High Intensity Aerobic Training

2. Speed Endurance Training

-Interval running at high speeds, with incomplete recovery in between running bouts

-HR peaks should be >90% HRmax

-Cumulative fatigue as session progresses

-Peak work rate over session is important

Example given (starting on goal-line) – 5x 90% sprints to far goal line & back, 5x 90% sprints to far penalty box & back, 5x 90% sprints to half way & back, 5x 90% sprints to near penalty box & back.

Speed Endurance Training

3. Medium Intensity Aerobic Training

-Continuous running at 75 – 85%HRmax

- Average work rate over session is important

Example given – 45’ continuous run.

Medium Intensity Aerobic Training
4. Speed Training

-Emphasis on quality not quantity
-Recovery periods much longer than work periods (at least 15:1 ratio)
-Thus keeping HR low (<80%HRmax)
-Use HR to make sure workload is not too high and that recovery is sufficient in between repetitions.

Example given - 4x 20m, 4x 15m, 4x 10m sprints.

Speed Training

Summary

HR monitoring offers one of the best and easiest ways to monitor training load as they are practical to use, relatively cheap and provide immediate feedback, which enables the individual referee / coach / sports scientist to:  

i) Objectively assess the physical effort during all training sessions.

ii) To ensure that the aims of individual training sessions are met.

iii) To ensure that training sessions are varied in terms of duration and intensity, and, most importantly, that the referees’ training load is tapered (gradually reduced) towards matches.

iv) Ensure an appropriate level of all-round physical fitness is developed which will enable a referee to meet the physical demands of their matches.

 HR monitors of all ranges can be purchased at www.bodycare.co.uk (PGMO discount)  

References

1.      Gilman, M.B.  (1996)  The use of heart rate to monitor the intensity of endurance training.  Sports Medicine, 21 (2), 73-79.

2.      Laukkanen, R.M.T. and Virtanen, P.K.  (1998)  Heart rate monitors: state of the art.  Journal of Sports Sciences, 16, S3-7.

3.      Wilmore J.H. and Costill, D.L.  (1999)  Physiology of Sport and Exercise.  2nd Edition.  Human Kinetics:Illinois, pp394.

4.      Achten, J. and Jeukendrup, A.E.  (2003)  Heart rate monitoring.  Applications and limitations.  Sports Medicine, 33 (7), 517-538

5.      Reilly, T., Robinson, G. and Minors, D.S.  (1984)  Some circulatory responses to exercise at different times of day.  Medicine and Science in Sports and Exercise, 16, 477-482.

6.      Astrand, P.-O. and Saltin, B.  (1961)  Oxygen uptake during the first minutes of heavy muscular exercise.  Journal of Applied Physiology, 16, 971-976.

7.      Brisswalter, J. and Legros, P.  (1994)  Daily stability in energy cost of running, respiratory parameters and stride rate among well-trained middle distance runners.  International Journal of Sports Medicine, 15, 238-241

8.      Boudet, G., Garet, M., Bedu, M., Albuisson, E. and Chamoux, A.  (2002)  Median maximal heart rate for heart rate calibration in different conditions: laboratory, field and competition.  International Journal of Sports Medicine, 23, 290-297.

9.      Zavorsky, G.S. (2000) Evidence for possible mechanisms of altered maximum heart rate with endurance training and tapering.  Sports Medicine, 29 (1), 13-26.

Source of information: Matthew Weston mweston@fapl.co.uk