HR Measurement and Exercise

There's been a long held an assumption that heart rate (HR) and exercise intensity are linearly related: as workload increases, HR increases. This is true with the exception of the extremes. Through this relationship HR has been used to determine appropriate exercise intensities through knowledge of an individual's maximum HR (max HR).

Estimated max HR is typically used by fitness enthusiasts. This is determined by subtracting 220 from a person's age.

Percentages of maximum are used to determine exercise thresholds (minimum) and limits (maximum), which are known as the heart rate training zone (THRZ). Frequently, healthy adults are prescribed exercise intensities of 55/60 to 90 % of maximum heart rate. This is known as the % HR max method.

Many exercise professionals often use the Karvonean method, also known as the HR reserve method (% HRR method). Heart rate reserve is the difference between the maximal HR and resting HR. A percentage of HRR is added to the client's resting HR to determine the target HR.

HR={% exercise intensity x (HR max-HR rest)}+ HR rest.

The American College of Sports Medicine recommends using 40/50% to 85% HRR when prescribing exercise to healthy adults.

Compared to the Karvonen (% HRR ) method, the % HR max method tends to give a lower value when the same relative intensity is used. Therefore, more professionals used the %HHR method for healthy young to middle age adults. It's recommended that older people ( > 65 years ) use the  % HR max method. This method provides a more accurate estimate of % maximum. It should be stressed also with older adults that HR max should not be predicted from (220-age) due to the large variability in HR max in older adults and the likelihood that many in this age group will be using HR altering medications.

I suggest the following THRZ:

- THE APPROPRIATE HR FOR A UN-TRAINED INDIVIDUAL IS < 55 HR max or <40 HRR

- THE APPROPRIATE THRZ FOR A SOMEWHAT FIT INDIVIDUAL IS 55-85 HR max or 40-80 HRR

- THE APPROPRIATE THRZ FOR A HIGHLY FIT INDIVIDUAL IS 80-95 HR max or 70-90  HRR.

It's important to point out that the HR response to incremental exercise is different among exercise modes. At the same relative intensities, treadmill exercise has a lower and higher heart rate response compared to stepping and stationary cycling, respectively. Therefore. THRZ needs to be adjusted for the difference among exercise modes. 

When possible use a nonestimated, true maximal HR value when determining target THRZ and aerobic capacity. A nonestimated, true maximal HR value can be found during a multi-staged maximal exercise bout, where a person is brought to volitional exhaustion; a point where there's no longer an increase in HR with an increase in workload. This should only be attempted by a people who are fit with no existing medical condition.

The reason for suggesting not using estimated maximum heart rate is due to its standard of error of measurement of ±10 beats/min. This means that 68% of individuals would be expected to have a true maximum HR ± 10 beats/min of their age predicted HR and 95% would be within ± 20 beats/min, but, for the entire population, the true max heart rate would be within ± 30 beats/min.

Using a RPE Chart

A great way to judge exercise intensity is through the Rating of Perceived Exertion (RPE) scale. This scale is purely subjective: it is based on how you feel during physical activity. By perceived exertion, exercise scientists mean the total amount of exertion and physical fatigue. Don't concern yourself with any one factor such as leg pain, shortness of breath, or work grade, but try to concentrate on the total, inner feeling of exertion. The use of RPE has been shown to be more effective in determining appropriate exercise intensity for groups on heart altering medication than heart rate measures.

- THE APPROPRIATE RPE FOR A UN-TRAINED INDIVIDUAL IS 10 TO 12 (35-55 HR max)

- THE APPROPRIATE RPE FOR A SOMEWHAT FIT INDIVIDUAL IS 13 TO 15 (70-80 HR max)

- THE APPROPRIATE RPE FOR A HIGHLY FIT INDIVIDUAL IS 15 TO 17 (80-90 HR max)

I prefer using the Borg RPE 6-20 category scale over the 1-10 ratio scale.

6

7 VERY, VERY  LIGHT

8

9 VERY LIGHT

10

11 FAIRLY LIGHT

12

13 SOMEWHAT HARD

14

15 HARD

16

17 VERY HARD

18

19 VERY, VERY HARD

20 MAXIMAL

Measuring HR

Measuring heart rate manually takes some practice. When measuring manually, I prefer finger placement at the radial artery (thumb-side of wrist) over the carotid artery (neck) due to a possible receptor response, which some studies suggest may slow heart rate. I like to count the number of beats over 15 seconds then multiply by 4 to get beats per minute. If I feel a beat at the start of the 15 second count, I start counting from zero. I favor using a heart rate monitor, especially ones with a wireless sensor transmitting signals to a watch, over manually measuring heart rate.

Estimating Peak HR

Determining maximum heart rate is a painful and possibly dangerous task. It's even more risky if you're a fitness professional because you're dealing with the welfare of your client. I use a different way to estimate Max HR through an equation that uses the results of a physical challenge that takes into consideration the relationship between RPE and heart rate. You or your client is tested using the exercise mode that is going to be used in training. Exercise to a RPE of 14 if healthy and less than 45 years or 12 or 13 if older. Maintain RPE level for at least 3 minutes to achieve a steady state HR and then measure HR manually or with a HR monitor. Exercise steady state is where HR levels off with only a slight deviation of ± 3 beat/min. Place measured HR into one of the following equations.

If exercised to a RPE of 12, Peak Heart Rate=(sub maximal HR/.55)

If exercised to a RPE of 13, Peak Heart Rate=(sub maximal HR/.65)

If exercised to a RPE of 14, Peak Heart Rate=(sub maximal HR/.80)

I like to use the term Peak heart rate over estimated Max HR because it is a prediction of an exhaustion endpoint, not Max HR. Peak heart rate can be substituted for estimated Max HR in THRZ calculations.

Example: Submaximal HR at an RPE of 14 was 150. Peak Heart Rate 187.

TRHZ based on 55 to 80% is 104-150.

Estimating Peak HR hasn’t been validated yet through research as of yet, but through my own data collection it has been found to be more affective than estimating max heart rate in my practice.

Other factors to consider

After an initial conditioning period, HR at rest and during sub maximal exercise should decrease as the heart becomes more efficient. Endurance athletes typically have resting HR well below 60 beats per minute. Peak HR therefore should be reevaluated and THRZ adjusted.

Many factors influence heart rate during exercise including temperature, emotions, food intake, body position, the muscle area exercised, whether continuous or stop and go activity, or if the muscles are exercising isometrically or rhythmically.  Don't concern yourself with achieving an exact HR. Use the THRZ because of the submaximal HR day-to-day variability of about ± 5 beats per minute.