Cardio-respiratory Fitness (CRF)
Cardio-respiratory Fitness (CRF) refers to the ability of the body’s circulatory system, which consists of the heart, blood vessels and blood, and the body’s respiratory system, which consists of the lungs and airways — to supply oxygen to the large skeletal muscles (shoulder, hamstring and abdominal muscles) when those muscles are in active use during any form of physical activity. Therefore, Cardio-respiratory Fitness provides the best measure of sustained physical activity (i.e. exercise) by any individual.
Cardio-respiratory Fitness (CRF) reflects the body’s ability to transport oxygen from the atmosphere through the circulatory system to perform physical activity. It relies upon the body’s respiratory and circulatory systems to transport blood from the heart to precisely matched oxygen requirements of the muscle cells. This enables the muscle cells to receive and use the oxygen and nutrients delivered by the blood. Cardio-respiratory Fitness is descriptive of the integrated function of numerous body systems, and it is thus considered a reflection of total body health.
As physicians begin to introduce a measure of Cardio-respiratory Fitness (CRF) during patient visits, the Physical Activity Guidelines published by the Department of Health and Human Services (HHS), as listed below, will provide a measurable and achievable “minimum” standard for setting patient expectations regarding the importance of regular physical activity to their health. In addition patient compliance in adopting “minimum physical activity habits” can be regularly assessed as a “preventive health” requirement of their “medical care” during encounters with their primary care physician.
HHS Physical Activity Guidelines
“For substantial health benefits: adults should do at least 150 minutes (2 hours and 30 minutes) to 300 minutes (5 hours) a week of moderate-intensity aerobic physical activity
OR
75 minutes (1 hour and 15 minutes) to 150 minutes (2 hours and 30 minutes) a week of vigorous-intensity aerobic physical activity,
……….or an equivalent combination of moderate- and vigorous-intensity aerobic physical activity. Preferably, aerobic physical activity should be spread throughout the week.”
These HHS Physical Activity Guidelines provide clear, quantifiable measures of “how often” you exercise, “how long” you exercise and “how hard” you exercise. In other words, the Guidelines specify the recommended minimum frequency (weekly), duration (# of minutes) and intensity (“moderate” or “vigorous” levels of intensity based on “measured” heart rate exertion during exercise).
The “frequency” and “duration” measures can be easily calculated. However, the “intensity” measure is determined by the individual’s pulse rate or heart rate, as calculated by the number of times the heart beats per minute (bpm).
Both “moderate” and “vigorous” levels of exercise intensity are, therefore, defined in terms of each individual’s maximum heart rate which varies by age. The maximum heart rate of a young person is higher than the maximum heart rate of an older individual. The formula for estimating the individual’s “age related” maximum heart rate is to subtract the age of the individual from 220.
The estimated “age related” exercise intensity measure is then defined in the form of a lower and upper percentage “range” of the individual’s maximum heart rate that is reached and maintained during exercise. The exercise intensity measure for the individual is calculated as a percentage of the individual’s age related maximum heart rate.
For example, a 45 year old person would have an age related maximum heart rate of 220 – 45 = 175 beats per minute.
Heart Rate Monitored Measurement of Exercise Intensity
For moderate-intensity physical activity, the target heart rate range should be between 64% and 76% of the individual’s age-related maximum heart rate.
The above identified 45 year old person with estimated maximum heart rate of 175 bpm would be required to maintain a heart rate range of 112 beats per minute (0.64 x 175) to 133 beats per minute (0.76 x 175)
For vigorous-intensity physical activity, the target heart rate range should be between 77% and 93% of the individual’s age-related maximum heart rate.
The above identified 45 year old person with estimated maximum heart rate of 175 bpm would be required to maintain a heart rate range of 134 beats per minute (0.77 x 175) to 163 beats per minute (0.93 x 175)
These physical activity guidelines provide clear, quantified measures of physical activity which define the minimum standards for physical activity compliance by individual consumers. These guidelines also serve as a reference point for the preventive care guidance which primary care physicians can provide to their patients regarding habitual physical activity.