Aerobic Fitness, V02 max and Disease Prevention

 

What is Aerobic Fitness?

We here a lot about aerobic fitness, runners have it in spades, whilst couch potato's seek the latest infomercial with the hope of finding a small portion of it. But what is Aerobic Fitness. Aerobic Fitness is a combination of the delivery and utilization of oxygen. During aerobic training, the heart muscle enlarges, more blood vessels are grown and enzymes within muscle cells change in order to facilitate oxygen use. The oxygen that is delivered and used enables the body to perform exercise for prolonged periods with fatigue. 

The human body is able to create energy quickly but for short periods of time. This occurs without oxygen and is termed anaerobic metabolism. Think of a car with a turbo button. This turbo button is used for sports or movements such as sprinting or weightlifting involving speed and power. The energy created using the anaerobic system causes a build up of biproducts that eventually prevent the further formation of the molecules required for energy production. See Aerobic Metabolism and Energy Systems . 

In order to perform continuos exercise such as walking, jogging or bike riding the body has a requires oxygen. The need to increase your breathing rate when exercising is due to this extra demand for oxygen. Without the oxygen, you would be unable to exercise for over a minute

How is Aerobic Fitness Measured?

Aerobic Fitness is measured by what is known as VO2 max test. V stands for Velocity and O2 for oxygen. As the name indicates the test is a measurement of the rate of oxygen use by an individual. An Exercise Physiology Lab is required for the exact measurement of aerobic fitness. Maximal exercise tests such as the multi stage beep test (shuttle run) or the 1.5 mile run or 2.4 km run test are accurate predictors of VO2 Max and can be self performed. Both test contain population norms that have been been established due to the tests frequency and ease of testing.

A note of caution: Maximal Exercise tests can be dangerous. You shouldn't attempt these test if you are extremely overweight or have no history of exercise. Instead be evaluated by a professional or begin a gradual exercise program for several weeks before attempting the maximal tests. 

If you are a high risk individual submaximal predicative tests can be used to determine your aerobic fitness level

What is the average value for VO2 max

VO2 max values vary largely between individuals. Aerobic training is the biggest modifier of VO2 max. Endurance athletes record values of around 75-90 mls/kg/min. This means for every kilogram of body weight, the muscle consumes 75-90 milligrams of oxygen every minute. If the person weighs 60kg's the body will consume 80mls/kg/min = 80mlX60kg = 4.8Litres of Oxygen per minute. An average 40 year old might record a value of 40 mls/kg/min.

The higher the aerobic fitness level the more oxygen the body can utilize. The result is, continuous exercise can be performed at higher exercise intensities without fatigue. An elite marathon runner can sustain speeds of 20km/hour for 42.2 kilometres. The average social runner could hold this speed for maybe 400 metres. Both the marathon runner and the social runner may have almost the some top speed but the elite runners higher aerobic fitness level allows them to sustain this level for prolonged periods.

VO2 max values typically decline by on average 10% per decade (1,2) but training has been shown to slow that decline. Research on how much is dependent on the age of the individual as well as their current fitness level. A study of master's athletes showed their VO2 max values declined at half the rate of age matched sedentary individuals (2)

Why is Aerobic Fitness Important?

With large decreases in societies exercise levels and a concurrent rise in our rates of obesity large amounts of research have gone into the causes and the consequences of such changes. Research into the Mortality rates (death rates) of society, provides insights into the causes of premature death in a population group. Such research typically takes a group of individuals with no current signs of sickness or disease. The group is studied and certain variables tested, such as gender, body mass index, fitness level, occupation, sleep levels and other factors related to health. Research then follows the same group of individuals over a period of years and records the rates of occurrence of diseases such as diabetes and heart disease or death rates.

Findings from these studies show that an individuals aerobic fitness level is the strongest predictor of mortality in the years of follow up, rating as high as smoking and above high blood pressure, high cholesterol and obesity. (3,4)

The above graph was taken from a study of 2361 men aged 42-60 years old. Over a 13 year period the risk of death climbs 4.4 times for low risk individuals who are unfit compared to fit. For those with 2 or 3 risk factors death risk increases from 2.9 for fit individuals to 6.8 for unfit individuals, an approximate 2.5 fold increase. (5)

An earlier report on the same population group revealed the following death rates per aerobic fitness group (6)

The graph shows the increased rate of death in people with a lower aerobic fitness level. This is due to protective effect of a high aerobic fitness levels on diseases like diabetes and heart disease.

How does Aerobic Fitness Prevent disease?

Physical Exercise is how you improve aerobic fitness level. Performing physical exercise decreases certain diseases risk factors such as obesity, high blood pressure and high cholesterol. Individuals with a high fitness level tend to also have higher levels of physical activity. This is one possible reason behind the longer life spans associated with a higher level of aerobic fitness. Apart from this aerobic fitness even without exercise is protective of disease. As a high fitness level indicates an improved oxygen delivery system, a stronger heart and an exhanced ability to burn fats.

Directly modifying aerobic fitness through gene manipulation or drugs has in animal studies been shown to cause changes that are advantages in preventing mortality.  Therefore those who are genetically fitter will experience an advantage. Despite this aerobic exercise in any individual will modify disease risk factors and increase life span

How can you improve your Aerobic Fitness Level?

Exercise that is of a continuos nature will improve aerobic fitness. Using a number of muscle groups such as in running or swimming allows the heart rate to increase and places a demand on the aerobic system. Strength training doesn't improve aerobic fitness as the muscle fatigues before a substantial demand is placed on the heart. Performing circuit strenght training or boxing though will result in an increased aerobic fitness level.

The longer an exercise goes the lower the intensity the exercise becomes, aerobic fitness benefits result from exercise that is approximatly 20-40 minutes in duration. This can be a series of running intervals of 1-3 minutes with rests between, or it can be a continuous run. Exercise that is extemely long still produces improvments but these improvements are less then that seen with medium duration exercise. This is due to the fact that extremely prolonged exercise happens at an intensity that is below what is required to stimulate large aerobic adaptions. Therefore walking for several hours will produce benefits but these benefits will be less then those experienced during a high intensity 30 minute run

(1) Aerobic fitness norms for males and females aged 6 to 75 years: a review.

E Shvartz, RC Reibold - Aviation, space, and environmental …, 1990

(2) Decline in VO2max with aging in master athletes and sedentary men

M. A. Rogers et al, 1990, American Physiological Society

(3) Relationship Between Low Cardiorespiratory Fitness and Mortality in Normal-Weight, Overweight, and Obese Men

Ming Wei et al, JAMA. 1999;282(16):1547-1553

(4) Influences of Cardiorespiratory Fitness and Other Precursors on Cardiovascular Disease and All-Cause Mortality in Men and Women:

Steven N. Blair et al, JAMA. 1996;276(3):205-210

(5) The predictive value of cardiorespiratory fitness for cardiovascular events in men with various risk profiles: a prospective population-based cohort study

J. Laukkanena, et al, Oxford Journals Medicine European Heart Journal Volume 25, Issue 16 Pp. 1428 1437.

(6) Cardiovascular Fitness as a Predictor of Mortality in MenFREE

J Laukkanen, et al. Arch Intern Med. 2001;161(6):825-831. doi:10-1001/pubs.Arch Intern Med.-ISSN-0003-9926-161-6-ioi00420