Background

Estimating cardiorespiratory fitness

To classify cardiorespiratory fitness (CRF), we measure maximum oxygen consumption (VO_2max). It is well accepted that the gold standard method of measuring VO_2max is by using a gas analyses system. However, these gas analyses systems are costly and take time to calibrate for each test. In addition, only one person at a time can be tested.

Field tests for CRF avoid all three of this cons: they are inexpensive, requirer a shorter time than a gas analyses system test, and more than one person at a time can be tested. There are cons of field tests, the biggest one being that it is an estimation method. Another is that if the method is conducted outside, the environmental conditions can introduce variability into the test.

Another option for  measuring VO_2max besides a gas analysis system or a field test method is a sub-maximal VO_2max estimation test. These tests are typically completed on a treadmill or bike, are shorter in time than using a gas analyses system, but usually only one person at a time is tested. One advantage over a field test is that they can be conducted inside in a temperature controlled room.

Estimation methods–whether using a field test or a sub-maximal test–can estimate VO_2max because during sub maximal work there is generally a linear relationship between oxygen update and heart rate. The slope of the line changes with the state of physical fitness; that is, a fit person is able to transport the same amount of oxygen at a lower heart rate than an unfit person.

Because many of the estimation methods rely on the relationship between oxygen uptake and heart rate, it is crucial that the method to measure heart rate (or pulse rate) is as accurate as possible. It is essential to follow the test instructions if the measure is a heart rate, pulse rate, or recovery.

Class activity

Activity 1: The Forestry Step Test

Equipment: Step bench and risers, stop watch, metronome (or metronome app on phone), scale to measure body weight, tables posted on Blackboard

Participant: Everyone will complete this activity, unless someone has an orthopedic or other reason to not be a participant. If you are not a participant, make sure you record the information of your partner so you can practice using the data in the tables.

Instructions: Prior to starting the test, be sure you can locate pulse rate on your partner. Do not use a heart rate monitor, and be sure to count the pulse for the fun 15 seconds. 

1. The participants stands facing the step bench (height = 40 cm for men, 33 cm for women).
2. The technician starts metronome, which is set for 90 beats per minute (step rate = 22.5 steps per min)
3. Start the timer as soon as the participant steps up on the bench. Have the person continue stepping for exactly 5 minutes (test time 0:00-5:00).
4. The participant should should straighten back and legs at top of step, and make sure to plant the entire foot on the step.
5. At the end of the five minutes, the participant stops stepping.
6. Immediately after ending the test, the participant sits down on the bench or a chair next to the bench for a 15 second rest (test time 5:00-5:15). The technician needs to use this time to find the participant’s pulse.
7. Count the pulse rate for 15 seconds, 15 seconds after subject stops stepping. (test time 5:15-5:30)
8. Record the 15-sec use rate. (do not multiply by 4)
9. Estimate VO_2max using the Forestry heart rate tables 13.5 and 13.6. (find tables in the Blackboard folder for this lab)
10. If the participant is not 25 years ±2.5 years, use table 13.7 adjust VO_2max for age.
11. Use the table 3.2 in your REP textbook to determine CRF classification.

Activity 2: Two-stage treadmill test

Note: This test frequently appears on the ACSM-EP exam. The metabolic equations will be provided during the test, but conversions are not. Expect the same on your exams for this course. 

Equipment: Treadmill, heart rate monitor and watch

Participant: Each group will have one person perform this test. The other members of the group will need to monitor the test to adjust TM speed as needed.

Instructions: It is important to follow the instructions exactly as written. If the heart rates are not in the zones listed, the test will not be accurate and it will be difficult to interpret.

This test consists of two stages of 3 minutes each. The test works best if the heart rate is between about 110 and 150 BPM for both stages, with at least a 20-30 BPM difference between stages, and a 3-5% point grade difference between stages. The person can run or walk for the test, but be sure to use the correct equations for walking or running. The results work best if the person does the same exercise (walking or running) for both stages.

1. Stage 1: start treadmill at 0% grade and 3.5 mph. (suggested. Please discuss with your participant their fitness and determine if they need to perform this as a running test instead)
2. After one minute look at HR. If needed, adjust TM grade/speed to be at the lower end of the 110-150 BPM recommendation. (i.e. 110±10 BPM)
3. Record HR during the last 15 seconds of stage 1. Also record TM grade and speed.
4. Stage 2: increase TM grade by 3-5 percentage points.
5. After one minute look at HR. If needed, adjust TM grade/speed to be at least 20 BPM higher than the end of stage 1 (and 30 BPM higher is better) and at the higher end of the 110-150 BPM recommendation. (i.e. 140-150 BPM)
6. Record HR during the last 15 seconds of stage 2. Also record TM grade and speed.
7. After the last HR reading, lower grade to 0% and decrease speed to a slow walk. Allow the subject to cooldown for 2-3 minutes. (HR should noticeably drop from stage 2 and ideally be lower than the end of stage 1)
8. Use equations below to calculate estimated VO_2max.
9. Compare your results with REP textbook table 3.2.

Calculations

1. Calculate estimated VO₂ for each stage.

Change speed mph to m/min by multiplying speed in mph by 26.8. Be sure to use incline value as a decimal.

Calculated walking VO₂= 3.5 + (speed*0.1) + (speed*incline*1.8)

Calculated running VO₂= 3.5 + (speed*0.2) + (speed*incline*0.9)

2. Calculate the slope of the line between the two stages

b = (VO₂ stage 2 – VO₂ stage 1) ÷ (HR stage 2 – HR stage 1)

3. Use the slope to calculate estimated VO_2max

VO_2max = VO₂stage 2 + (b * (estimated HR_max– HR stage 2))

Self-test your comprehension