Monitoring Exercise Intensity
Monitoring exercise intensity is necessary to both the safety and effectiveness of the exercise session. It can provide useful information to both determine the success of the session in the short term, and provide a benchmark against which future sessions can be progressed to and compared against.

Methods

	Heart Rate
	Rate of Perceived Exertion (RPE)
	Subjective Methods
	Exercise Pace

Heart Rate:
This is traditionally most common method of monitoring exercise intensity and whilst very useful, some misconceptions have arisen surrounding this technique.

The main methods used for determine Heart Rate (HR) are to manually measure the pulse of the individual in the wrist or neck, or to use a heart rate monitor. The latter method is my preferred as the high heart rates experienced during exercise mean many people are very inaccurate in taking their own or someone else's pulse, whereas monitors are accurate to within a single beat.

Estimating Maximum Heart Rate
Many people are familiar with the equation for estimating Maximum Heart Rate (HR_max) which is:

Maximum Heart Rate (MHR) =

220 beats per minute (bpm) - age

(ACSM, 2000)

So for a 36 year old, the estimate HR_max would be 220 bpm - 36 which is 184 bpm.
However, what people are less familiar with is that this calculation has an error range of plus minus 11 bpm (ACSM, 2000; Howley, 2000), so in reality the estimated age related HR_max using this calculation would be somewhere between 173 bpm and 195bpm (184 plus or minus 11). The information derived from this calculation should, therefore, only be used as a guideline.

The only way of truly determine an individuals HR_max is to exercise them to exhaustion and measure their heart rate at the end, although common sense will determine as to which individuals are suitable for this.

Heart Rate Reserve
The Heart Rate Reserve (HRR) method is a better correlation to a persons VO₂ max, therefore, a more accurate method for prescribing exercise intensity. Both methods MHR and HRR are more accurate when true MHR has been determined.

HRR = MHR - Resting Heart Rate (RHR)

Training Heart Rate (THR) = HRR x (50 to 85%) + RHR

Maximum Heart Rate by:
Professional Olympic Triathlon Training Coach Mark Allen
No triathlete has gained the recognition or success that Mark Allen has. After competing and losing in the Ironman Triathlon Championships six times, he emerged victorious in 1989, winning the most difficult one-day sporting event in the world.

It would be the first of six Ironman victories for Allen, the last coming in 1995 at age 37, making him the oldest champion ever. He has also excelled at the Olympic distance, winning the sport's inaugural World Championships in 1989 in Avignon, France, by more than a minute. He went undefeated in 10 trips to the Nice International Championships, and from 1988-1990 he put together a winning streak of 20 races.

Over the course of his racing career, which ended in 1996, he maintained a 90% average in top-three finishes. He was named Triathlete of the Year six times by Triathlete magazine, and in 1997 Outside magazine tabbed him The World's Fittest Man.

The formula Allen uses to calculate an athlete's maximum aerobic training heart rate doesn't require you to know your maximum heart rate. Allen suggests the following:

1.	Take 180 and subtract your age.
2.	Take that number and correct it by the amount next to the statement that best describes your level of fitness:
	If you do not workout, subtract another 5 beats.
	If you workout only 1-2 days a week, only subtract 2 or 3 beats.
	If you workout 3-4 times a week keep the number where it is.
	If you workout 5-6 times a week keep the number where it is.
	If you workout 7 or more times a week and have done so for over a year, add 5 beats to the number.
	If you are over about 55 years old or younger than about 25 years old, add another 5 beats to whatever number you now have.
	If you are about 60 years old or older OR if you are about 20 years old or younger, add an additional 5 beats to the corrected number you now have.

(Note: if you are trying to decide between two of the above statements, it is much better to pick the one that gives you a lower training heart rate than the one that will give you the higher training heart rate.)

The number you now have is the upper heart rate limit that you can work out at and still develop your aerobic system. "This is the heart rate that will build the size of your engine!"

Heart Rate Zones
Once an individual's HR_max has been determined, we can decide on what proportion of this represents an effective aerobic training intensity. Research indicates that an exercise intensity equivalent to 60% - 90% of HR_max is appropriate for most individuals (ACSM, 1993)

Example:
Maximum Heart Rate = 194
Multiply 194 by 0.6 and 0.9 to get the lower and upper limits of the target heart rate zone:
194 x 0.6 and 194 x 0.9 = a Target Heart Rate Zone of 124 to 186 beats per minute (bpm)

Identifying Training Zones
As these thresholds will occur at different intensities and different heart rates for each individual, with the data obtained I'll be able to prescribe a personal aerobic training programme for you.
The table below shows for simplicity the 4 training zones and demonstrates the physiological correlation between the different zones and methods of monitoring and prescribing intensity:

Zone	Upper Limit	Physiological Correlates
		Blood Lactate	%MHR	%HRR	RPE
1	Recovery	Resting level	50 - 60	40 - 50	< 10
2	Aerobic Threshold (AeT)	Sustained increase above resting level	60 - 75	50 - 65	11 - 12
3	Anaerobic Threshold (AnT)	Rapid rise	75 - 90	65 - 85	13 - 15
4	Anaerobic 1	> 4mmol/l	80 - 95	80 - 95	16 - 17
4	Anaerobic 2	VO2 max	95 - 100	95 - 100	19

Beginners will exercise at the lower end of their range and increase intensity slowly as the body becomes more conditioned to exercise. It should be noted that with very unfit individuals 50% of HR_max may have an aerobic training effect (ACSM, 1997).

A major myth associated with aerobic training zones and heart rates is that lower training heart rates represent a 'fat burning zone'. No such direct relationship between an individual's heart rate and their metabolism of fat whilst exercising exists! Some individuals have been recorded as metabolising fat at up to 97% of their HR_max, whilst others stopped metabolising fat at 54% of their HR_max. The point here is that individual's respond very differently to exercise, and any attempt to provide standard calculations or zone can be very problematic. Please ignore those little graphs on the treadmills and steppers!

Rating of Perceived Exertion (RPE):
This method was developed by a Scandinavian physiologist called Gunnar Borg and is a scale of how hard an individual feels they are working when they exercise. The response of the participant should take into account all of the symptoms of exertion such as breathing, muscular fatigue and the subjective feeling of effort. The classic Borg scale given below rates effort between 6 and 20.

RPE has been related to heart rate with some accuracy.

Heart Rate:	RPE:	Classification:
> 90 bpm	> 9	very light
100 - 110 bpm	10 - 11	light
120 - 130 bpm	12 - 13	moderate
140 - 160 bpm	14 - 16	heavy
> 160 bpm	> 16	very heavy

Subjective methods:
Subjective methods are the least accurate methods of measuring intensity and would include such observation as sweating/redness technique, and talking. Whilst these may provide some general indication of fatigue, particularly if the individual response is well known, there is no direct research based evidence on their validity.

Metabolic Threshold and Rating of Perceived Exertion (RPE)
Although Metabolic Thresholds cannot be identified outside the laboratory, there is a remarkable consistent relationship between Metabolic Thresholds and Rating of Perceived Exertion. Exercise at the Aerobic Threshold (AeT) is perceived as 'light' (RPE = 11), whilst exercise at the Anaerobic Threshold (AnT) is perceived as 'somewhat hard' to 'hard' (RPE = 13 -15). What's more, the ability of RPE to identify the AnT is dependent of mode of exercise, gender and training status.

The relationship between RPE and metabolic thresholds allows me to identify training zones using RPE data obtained in an exercise test (Zone 1-4). New individuals will be tested to identify the exercise intensity associated with an RPE of 11-12 (Zone 2). After two to three months of regular training, a second exercise test should reveal substantial improvements in fitness, as indicated by lower heart rates at each level. The goal now is to increase exercise intensity without unduly taxing the individual. Intermediate exercisers will not tolerate exercise beyond the AnT, and an RPE of 13-15 is appropriate at this stage (Zone 3).

Intermediate to advanced status is probably best facilitated by interval training. Interval training (Zone 4-5) is characterized by bouts of high-intensity exercise interspersed with lower-intensity recovery periods. To prescribe interval training 'in the field' we'll turn again to RPE data obtained from regular exercise tests.

Beyond the AnT, lactate starts to accumulate rapidly. RPE is strongly influenced by blood lactate, consistently producing scores of 16-17 at concentrations > 4 mmol/l. Initially, intervals at RPE 16-17
won't be tolerated for more than one or two minutes. With training, however, these work periods will lengthen at the expense of recovery periods.