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The Important Heart Health Number You’ve Never Heard Of

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If you’re only concerned about your blood pressure or cholesterol numbers, you’re missing the boat. There’s another way of gauging how healthy you are that’s just as important or maybe more so. It’s your cardiorespiratory fitness (CRF) level, a measure that not even your doctor might have mentioned to you.

What exactly is a CRF level? It’s a way to quantify how efficiently your body uses oxygen during heavy exercise and, in turn, pinpoints how aerobically healthy you are. CRF is an important part of being physically fit, along with endurance, flexibility, body weight status and muscle strength. But it goes beyond the vague sense of fitness you might feel you have—it’s a number you can track.

Think of it this way: CRF lets you know whether your cardio workouts are having the desired effect of improving heart health. Looked at in the opposite direction, a low CRF level has been strongly linked to a high risk for heart disease, stroke, type 2 diabetes, some cancers and even death.

WHY CRF MATTERS TO YOU

When you improve CRF, a number of physiological changes occur that strengthen your heart, blood vessels, lungs and muscles. Additionally, your resting blood pressure and blood levels of cholesterol, triglycerides (blood fats), glucose and insulin improve, said Steve Farrell, PhD, of The Cooper Institute in Dallas. The result is added protection against cardiovascular disease, the leading cause of death among US men and women.

A high CRF offers tangible benefits you’ll enjoy every day, such as being active—hiking, biking, swimming and even chasing kids or grandkids—without feeling winded in a flash.

Beyond improving your quality of life, it may extend your life—cardiorespiratory fitness can reduce your risk of heart attack or stroke, said Dr. Farrell, lead author of a study on CRF published in Mayo Clinic Proceedings.

Other studies have linked moderate-to-high levels of CRF to a reduced risk for cancer of the breast, colon, bladder, endometrium, esophagus, kidney, lung and stomach…type 2 diabetes and its precursor metabolic syndrome…and dementia.

HOW CRF IS MEASURED

Your CRF level is based on your “VO2 max”—how much oxygen you use during maximal aerobic (cardio) exercise. The most accurate way to measure this is with a maximal exercise test (also known as a maximal stress test). Typically done in a clinical setting such as a medical center, you’ll work out on a treadmill or stationary bike with increasing grade or resistance and speed while your electrocardiogram (ECG), heart rate and blood pressure are closely monitored.

On your own, you can get a good idea of your CRF level with either the Rockport One-Mile Fitness Walking Test or the Cooper 1.5-Mile Run/Walk Test on an outdoor track or indoor treadmill.

Which test should you opt for? If you have any signs or symptoms of cardiovascular disease or simply suspect that you have it, the clear choice is a clinical setting where you can be closely monitored as you exert yourself. A clinical test is also the way to get the most accurate reading. If you know you’re healthy and can walk at a fairly brisk pace with ease, opt for the Rockport test, while joggers might try the Cooper test, Dr. Farrell said.

Want a preview of your CRF? You can get a quick snapshot of your fitness level by answering questions about the types of physical activities you do at the online Duke Activity Status Index.

HOW TO RAISE YOUR CRF

If you set your mind to it, you can improve your cardiorespiratory fitness in pretty short order—about eight to 12 weeks. But check in with your health-care professional before making a change in your physical activity level, especially if you have a preexisting medical condition or have been sedentary.

Once you get the OK, pick an aerobic exercise that you enjoy and that fits your lifestyle so that you’ll be more likely to stick with it. To be aerobic, the activity must use large muscle groups, such as the legs and glutes, and large amounts of oxygen and be done continuously for at least several minutes, said Dr. Farrell. (If you’re new to exercise, “several” could mean five to 10, but over time you will be able to build to 20 minutes and more.) Examples include…

  • Brisk walking
  • Jogging
  • Bicycling
  • Elliptical or stair-climbing machine
  • Swimming
  • Cross-country skiing
  • Rowing

Another option: High-intensity interval training (HIIT). Exercising at near 100% intensity for brief periods followed by longer periods of low-intensity exercise is an effective and time-efficient way to improve cardiovascular fitness.

If using HIIT, you’ll have to push yourself so hard that you won’t be able to speak without being breathless during the high-intensity heart-pumping and sweat-inducing periods. On the elliptical machine, as one of many examples, you’d work at maximum intensity for 30 seconds and then recover at low intensity for 60 seconds before going hard again.

Caution: Dr. Farrell doesn’t recommend HIIT for beginners. If you’re brand new to vigorous exercise or haven’t exercised vigorously for a while, do moderate-intensity exercise for at least eight weeks before attempting an HIIT workout, he said. According to the American College of Sports Medicine, moderate intensity means reaching a heart rate between 65% and 75% of your predicted maximum heart rate. To calculate this, simply subtract your age from 220. Then take 65% and 75% of that number to find your recommended heart rate range during a moderate workout. For example, if you are 30 years old, then your predicted maximum is 190 [220 minus 30] beats per minute, and 65% to 75% of 190 is 124 to 143 beats per minute.

When you’re able to do HIIT, if you are very overweight and/or prone to injury, choose a low-impact type of exercise (biking, swimming or the elliptical) for your workout.

A SAMPLE PLAN FOR BOOSTING CRF

Here’s a progressive cardiovascular walking program perfect for starting at a moderate-intensity pace. Walking is ideal because almost anyone can do it without any special equipment, but if you prefer, you could follow this same program on a bike or elliptical machine.

  • Week 1: Walk 20 minutes, three times/week
  • Week 2: Walk 25 minutes, three times/week
  • Week 3: Walk 30 minutes, three times/week
  • Week 4: Walk 30 minutes, four times/week
  • Week 5: Walk 35 minutes, four times/week
  • Week 6: Walk 35 minutes, five times/week
  • Week 7: Walk 38 minutes, five times/week
  • Week 8: Walk 40 minutes, five times/week

This is just one example. The goal is to progress until you at least meet the American Heart Association’s recommended exercise guidelines for a healthy heart—30 minutes of moderate exercise at least five days a week for a total of 150 minutes.

Looking for more heart-healthy tips? Check out these articles:
The Heart Health Workout
30 Seconds of Exercise Boosts Heart Health

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Source: Steve Farrell, PhD, FACSM, senior investigator in the research division at The Cooper Institute in Dallas and coauthor of the study titled “Moderate to High Levels of Cardiorespiratory Fitness Attenuate the Effects of Triglyceride to High-Density Lipoprotein Cholesterol Ratio on Coronary Heart Disease Mortality in Men,” published in Mayo Clinic Proceedings. Date: May 22, 2018
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