Determining Exercise Intensity

The purpose of this document is to show how to determine intensity using several modes of aerobic exercise. Exercise testing provides the information needed to determine exercise intensity based on metabolic equations. The simplest way to do this is providing the equations for determining the appropriate intensity to reach a desired target heart rate. 

An individual who is apparently healthy and at an appropriate age, we may legally exercise test while not in the presence of a physician. Submaximal exercise testing with extrapolation of results may be used to provide results needed for determining exercise intensity. In certain subjects, it may be possible to maximally exercise test an individual to determine exercise intensity. No one over thirty-five years of age should be maximally exercise tested without a physician or medical professional present. An exercise test must reach ninety percent of age predicted maximum heart rate (APMHR)or a respiratory exchange ratio of 1.1 or greater to be considered a maximal exercise test. During a maximal. During a maximal exercise test, important physiological data is collected including resting heart rate, maximal heart rate, and volume of oxygen (VO2) maximum. The following metabolic equations will become essential for exercise intensity. 

-Walking on a motor driven treadmill: .1(m/min.) + (1.8 x m/min. x % grade) + 3.5 

-Cycle ergometry 

  Workload = RPM x flywheel travel x kg of resistance, fly wheel travel on Tunturi = 3m. Monark= 6m 

Metabolic equation  

   2 (kgm.) + 3.5 (BW in kg) 

-Arm ergometry 

 3 (kgm) + 3.5 (kg) 

The appropriate intensity for individuals who are apparently healthy without high blood pressure and documented heart disease is sixty to eighty percent of Age Predicted Maximum Heart Rate (APMHR). The formula for determination of APMHR is 220 – age. At this point, examples will be provided for determination of intensity for aerobic exercise using a motor driven treadmill, cycle, and arm ergometry. A subject completes a maximal exercise test or a submaximal with extrapolated values. The person is thirty-eight years old, weighs two hundred ponds or ninety kilograms, and achieved a VO2 maximum of 40 milliliters of oxygen per kilogram of bodyweight per minute expressed as 40 ml/kg/min.  

The first example will use a treadmill. At thirty- eight years of age, The APMHR equals 182 beats per minute (bpm). The target heart rate. The target heart rate is 109-146 bpm. Sixty to eighty percent of APMHR corresponds to fifty to seventy percent of VO2 max. Fifty percent of the VO2 max of 40 ml/kg/min. equals 20 ml/kg/min. In this example, the speed of the treadmill is 3.6 mph. To convert mile per hour to meters per minute (m/min.), miles per hour is multiplied by 26.8. The product equals 96.48 m/min. As stated, the metabolic equation for walking on a tread mill is .1 (m/min.) + (1.8 x m/min x % grade) + 3.5 with the first representing the horizontal component or speed, the second representing the vertical component or grade, and 3.5 is the resting component or one MET. 

In this example, the grade will be calculated by working backwards using the information provided. The calculation is as follows: 

20 ml/kg /min.= 9.648 + 173.7 x + 3.5 

6.85 = 173.7x 

.0394 = x 

4% = x 

At the low end of target heart rate or 109 bpm, the subject will exercise at 3.6 mph at a 4% grade. The upper target heart rate is 146 bpm and the intensity to produce this heart rate is as follows: 

28 ml/kg/min. = 9.648 +173.7x + 3.5 

14.85 = 173.7x 

.0855 = x 

9% = x 

The intensity needed to reach the target heart rate in this example of 109- 146 bpm is an intensity of 3.6 mph at a  4 to 9 % grade. 

The cycle metabolic equation as stated previously is the following: 2(kgm) + 3.5 (Kg). In this example, the subject’s weight is two hundred pounds or ninety kilograms. The value 20 ml/kg/min. Is multiplied by ninety kilograms to express the VO2 in absolute terms or 1800 ml/min leading to the calculation below. 

1800 = 2 (kgm) + 315 

1485 = 2x 

742.5 kgm = x   one watt = 6 kgm  watts= 742.5/ 6 = 124 watts to reach the heart rate of 109 bpm. 

28ml/kg/min. X 90 kg = 2520 ml/min. 

2520 ml/min. = 2(kgm) +3.5 (90) 

2520 =2(kgm) + 315 

2205 =2x 

1102.5 kgm = x   

 1102.5/6 = 184 watts 

The target heart rate of 109 to 146 bpm is accomplished by a cycle intensity of 124 to 184 watts. THe next example is very similar using the arm ergometry metabolic equation. 

20 ml/kg/min. X 90 kg = 1800 ml/min. 

1800 ml/min. = 3 (kgm) + 3.5 (90) 

1800 = 3x + 315 

1485 = 3x 

495 kgm = x   495/ 6 = 82.5 watts 

28 ml/kg/min. = 3 (kgm) + 3.5(90) 

2205 = 3x 

735 kgm = x    735/6 = 122.5 watts 

For the subject to reach a target heart rate of 109 to 146 bpm, this person will exercise at an intensity of 83 to 123 watts on the arm ergometer. 

The use of exercise testing and metabolic equations has become a lost art. The ability to reach proper intensities using these equations demonstrate that knowledge of them can lead to very accurate exercise intensity. They allow exercise professionals to tailor programs to the best heart rates to burn fat and treat chronic medical conditions. Patients treated by a physician for heart disease and taking medications affecting heart rate, rhythm, or dynamics should have a cardiac stress test annually. Determination of target heart rate in these cases should be accomplished using the heart rate reserve formula. The heart rate reserve formula calculates target heart rate by subtracting resting heart rate from the maximum heart rate. This value is called the heart rate reserve. The heart rate reserve is multiplied by the percentages desired and added back to the resting heart rate. The VO2 generally has the same relationship to heart rate described previously and the intensities calculated in a similar manner. Exercise physiologists use all these calculations to establish safe and effective programs and intensities tailored to the specific needs of clients and patients.