Cardiorespiratory Fitness: Assessment & Prescription

When it comes to being fit, cardiorespiratory endurance matters. Today we're talking all about endurance. What is it, how do you measure it, and how do I know where I currently stand?

What is cardiorespiratory endurance?

Cardiorespiratory endurance is the ability you have to exercise large muscles in the body for extended periods of time (ACSM, 2010). 

CE is really the product of two separate parts or systems: cardiovascular and respiratory systems. The cardiovascular system contains the heart, blood, and blood vessels. The respiratory system contains the lungs and oxygen. These two systems work together when you exercise. 

When you breathe in, oxygen flows to the lungs. Inside the lungs, carbon dioxide is eliminated, and oxygen enters the blood. The heart helps pump blood containing oxygen to working muscles through arteries, and deoxygenated blood returns to the heart through veins (Corbin, 2014). The heart of an active person pumps more blood per stroke compared to a sedentary individual.

5 ways to measure cardiorespiratory endurance

1. Graded exercise tests (GXT): GXT is the clinical gold standard for assessing VO2 max. All GXT uses linear increases in exercise intensity over time until the client is no longer able to adapt to increasing demands. This is done by increasing speed, incline, or resistance as the test progresses. Treadmills, cycles, rowing machines, and steps are common instruments used to administer a GXT. GXT can be maximal or submaximal depending upon the equipment available, risk classification of the client, and purpose behind the testing. 

2. Treadmill testing: While many different protocols exist for GXT on a treadmill, common protocols include the Balke, Bruce, and Modified Bruce. Generally, treadmills protocols involve the linear increase of %grade and/or speed until exhaustion from the client (Beltz, 2016).

• Balke: The initial grade of the treadmill is 0%, speed is 3.4pmh for the first minute of testing. Then treadmill grade is increased 2% at 1 minute, then increases by 1% every minute thereafter. Speed is held constant throughout the exercise (Balke, Ware 1959).
• Bruce: Unlike the Balke, both speed and grade are gradually increased. The initial workload is 1.7 mph at 10% grade for 3 minutes (0-5% high risk). Then at 3 minutes, the grade is increased by 2%, speed increased to 2.5. Then every 3 minutes after that the grade is increased by 2%, speed by .8-9 until exhaustion Bruce et al. 1973).
• Modified bruce:  Used for elderly and high-risk patients. From start to 3 minutes, the treadmill is set to 0% grade, 1.7 mph. The grade is increased by 5% at 3 and 6 minutes. Speed is increased to 2.5 mph at stage 3 and then every 3 minutes after.

3. Cycle ergometer: Two types of cycle ergometers are used to measure VO2 max: mechanically and electrically braked. In mechanically braked tests, the tester adds resistance throughout the test by turning a flywheel attached to the bike. Common protocols are the Astrand, Fox, and McArdle tests. Each of these tests uses a constant rpm while linearly increasing the W as time progresses. Tests continue until exhaustion or when the client can no longer maintain the set RPM (usually 50-60 rpm).

4. Bench stepping: Bench step tests use a constant bench height and have clients complete a certain number of steps per minute. As the test progresses, speed in the number of steps increases or bench height increases. 

5. Field tests: Common field tests include 12-minute run tests, 1-1.5 mile distance tests, and Rockport 1 mile walk tests. During timed tests, clients run as fast as they can to cover the greatest distance in the set time. During distance tests, clients run as fast as they can and the test ends when the allotted distance is traveled. 

Cardiorespiratory endurance standards

Standards for cardiorespiratory fitness are measured in VO2 max. A good VO2 max score ranges according to age and gender. For men, a good VO2 max ranges from 32-50+. For women, a good VO2 max ranges from 27-50+.

Cardiorespiratory recommendations

• Frequency: 3-5 days per week depending upon intensity
• Intensity: Moderate to vigorous intensity depending upon individual adaptation
• Time: ≥30 minutes per day of moderate activity on ≥5 days per week for a total of ≥150 minutes per week, OR ≥20 minutes per day of vigorous activity on ≥ 3 days per week for a total of ≥75 minutes per week, OR a combination of moderate to vigorous activity for 500–1000 MET min per wk.
• Type: Walking, jogging, cycling, running, rowing, stepping (Garber et al. 2011)

SOURCES

1. American College of Sports Medicine. 2010. ACSM’s guidelines for exercise testing and prescription, 8th ed. Philadelphia: Lippincott Williams & Wilkins.
2. Corbin, C. B., & Le Masurier, G. (2014). Fitness for life. Human Kinetics.
3. Garber, C. E., Blissmer, B., Deschenes, M. R., Franklin, B. A., Lamonte, M. J., Lee, I. M., ... & Swain, D. P. (2011). Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Medicine & Science in Sports & Exercise, 43(7), 1334-1359.