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You may have heard the term aerobic fitness whilst flicking through your fitness mags. But what is aerobic fitness and how can you reap the benefits to reach your fitness goals.

What is Aerobic Fitness?

Your aerobic fitness is a reflection of your ability to take oxygen from the atmosphere and use it to produce energy for your muscle cells. Many factors influence aerobic fitness, including your lung efficiency, cardiac function, gender, age, training status and genetic makeup. Understanding the various components of aerobic fitness will help you train smarter to achieve optimal performance and reach your fitness goals.

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It’s All About the Oxygen

By definition, aerobic fitness refers to your ability to transport and utilise oxygen, measured by VO2 max, the maximal amount of oxygen you can use during intense exercise. Exercise scientist Len Kravitz, PhD of the University of New Mexico explains that VO2 max is influenced by central and peripheral components. The central component involves the ability of your lungs, heart and vascular system to deliver oxygen to your muscles via your blood stream. The peripheral component involves the ability of your muscle cells to extract oxygen from your blood and use it to make ATP, the fundamental unit of energy. VO2 max values are lower in women, and decrease incrementally with age.

Priming the Pump

Your heart and lungs play a central role in aerobic fitness, with your heart being the prime limiting factor. While your lungs must function efficiently in order to transfer oxygen from the atmosphere to your bloodstream, they take a backseat to your heart, which must contract forcefully to eject oxygenated blood into your system to reach your cells, accounting for 70 to 85 percent of VO2 max. According to Kravitz, aerobic exercise training increases your total blood volume, heart muscle size and contractility, resulting in a greater volume of blood being ejected per each heart beat. Increased stroke volume means your heart does not have to beat as frequently at rest, resulting in a lower resting heart rate.

Max Extraction

Regardless of how efficiently your heart pumps, aerobic fitness is also dependent on the ability of your muscle cells to extract oxygen from your blood and use it to make energy. Aerobic energy is produced in the mitochondria of your muscle cells, using carbohydrates and fats for fuel. Mitochondria are microscopic organelles that function as energy factories for aerobic metabolism. In response to repeated bouts of aerobic exercise, the density and number of mitochondria increases. High-intensity exercise that challenges your aerobic limit has a more profound effect on mitochondria adaptations and oxygen extraction than low- to moderate-intensity activity. During high-intensity exercise, you exceed your body’s ability to produce aerobic energy, forcing it to tap into anaerobic pathways. However, anaerobic energy can only be sustained for a very limited time, usually less than two minutes. Perpetually exceeding your anaerobic threshold causes your muscles to adapt to perform aerobically at higher intensities.

Measuring Up

While VO2 max is the ultimate measurement of aerobic fitness, it relies on a complex and invasive evaluation in a laboratory setting, conducted by trained technicians. According to “ACSM’s Complete Guide to Fitness and Health,” other methods may be used to measure your aerobic fitness. One way is to monitor your heart rate during maximal intensity exercise and translate it as a percent of your maximal heart rate, which you can calculate using the equation: 206.9 – (age in years × 0.67) = estimated maximal heart rate. The more fit you are, the higher your percent of max heart rate during exercise. Aerobic fitness classifications ranging from low to excellent are reflected by values of 60 to 90 percent of max heart rate, respectively.

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What are the Benefits? 

Now that we have an understanding of what aerobic exercise is, its important to know the benefits of including aerobic exercise in our exercise program.

Among the recognised benefits of aerobic exercise are:

  • Increased maximal oxygen consumption (VO2max)
  • Improvement in cardiovascular/cardio respiratory function (heart and lungs)
  • Increased blood supply to muscles and ability to use oxygen
  • Lower heart rate and blood pressure at any level of sub-maximal exercise
  • Increased threshold for lactic acid accumulation
  • Lower resting systolic and diastolic blood pressure in people with high blood pressure
  • Increased HDL Cholesterol (the good cholesterol)
  • Decreased blood triglycerides
  • Reduced body fat and improved weight control
  • Improved glucose tolerance and reduced insulin resistance

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The known benefits of doing regular aerobic exercise include:

  • Strengthening the muscles involved in respiration, to facilitate the flow of air in and out of the lungs
  • Strengthening and enlarging the heart muscle, to improve its pumping efficiency and reduce the resting heart rate
  • Toning muscles throughout the body, which can improve overall circulation and reduce blood pressure
  • Increasing the total number of red blood cells in the body, to facilitate transport of oxygen throughout the body
  • As a result, aerobic exercise can reduce the risk of death due to cardiovascular problems.

In addition to the health benefits of aerobic exercise, there are numerous performance benefits:

  • Increased storage of energy molecules such as fats and carbohydrates within the muscles, allowing for increased endurance
  • Increasing speed at which aerobic metabolism is activated within muscles, allowing a greater portion of energy for intense exercise to be generated aerobically
  • Improving the ability of muscles to use fats during exercise, preserving intramuscular glycogen

Reaping The Benefits 

“Simple” aerobic training

The simplest method of starting is just that, simple. Select the number of minutes you’d like to walk for (let’s say 20 minutes for your first walk) and head out the door or step on the treadmill and go for it. Remember that to make it aerobic you want to walk at a pace that leaves you feeling “warm and slightly out of breath” and one that you can sustain for the time that you planned. In this case, set your sights on completing 20 minutes and pace yourself to do it. If you start too quickly, then you may poop out too soon. It’s not important how fast you do it; it’s just important that you attempt to complete the time. If you find 20 minutes is too ambitious, then start with less. Again, the most important thing is to get started. You can always add more later on.

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Five-out, five-back training plan

As discussed above, I like the simplicity of the five-minute out, five-minute back aerobic training plan. And like I said, you can increase gradually to 15 minutes out, 15 minutes back. It’s aerobic and you’ll get a training effect as long as you feel warm and slightly out of breath when you do it.

Interval training

Interval training is more intense than simple aerobic training. It’s a very effective way to increase your fitness level (remember stroke volume and mitochondria activity!), but it’s tough, and so I recommend holding off until you build up to 20-30 minutes of aerobic exercise. The idea to intervals is to set up work to active-rest ratios (work:active-rest), and as you get more fit, decrease the active-rest interval and increase the work interval. The work interval of the ratio is a speed that is faster than what you usually do, and the active-rest interval is your usual speed. To do it, you start at your usual speed for five to eight minutes, then increase the speed to the work interval for one to three minutes, then slow down to your usual speed for a few minutes to catch your breath (this is the active-rest interval), and then you repeat the cycling for the duration of your workout.

Here are some examples of interval training using walking as the activity:

Training Plan #1

Try the following if you currently walk for 30 minutes at 3.5 mph on the treadmill.

Interval 1: 3.5 mph for five minutes to warm up

Interval 2: 3.8 mph for one minute

Interval 3: 3.5 mph for three minutes to catch your breath (active-rest)

Interval 4: 3.8 mph for one minute

Interval 5: 3.5 mph for three more minutes, and so on until you reach 30 minutes.

After a few weeks you can try increasing using plan #2.

Training Plan #2

The work:active-rest ratio in the above example is 1:3. Over the course of weeks and months, you increase the work interval and decrease the active-rest. For example:

Interval 1: 3.5 mph for five minutes to warm up

Interval 2: 3.8 mph for two minutes

Interval 3: 3.5 mph for two minutes (active-rest)

Interval 4: 3.8 mph for two minutes

Interval 5: 3.5 mph for two more minutes, and so on until you reach 30 minutes.

Training Plan #3

The work:active-rest ratio in the above example is 1:3. Over the course of weeks and months you increase the work interval and decrease the active-rest. For example:

Interval 1: 3.5 mph for five minutes to warm up

Interval 2: 3.8 mph for three minutes

Interval 3: 3.5 mph for one minutes (active-rest)

Interval 4: 3.8 mph for three minutes

Interval 5: 3.5 mph for one more minute, and so on until you reach 30 minutes.

As you can see, the ratio changed from 1:3 to 3:1 (work to active-rest). The next step would be to do all four minutes at 3.8 mph (the new active-rest) and increase the work interval for one minute to 4.0 mph.

One final note. Spin class is interval training. It’s done at gyms on special spin cycles with an instructor who barks out orders to increase the intensity and then slow down to catch your breath. It’s addictive, and people who do it regularly swear by it. You should already be doing some aerobic exercise and be reasonably conditioned before you try it, but I recommend it if you’re looking for one of the toughest workouts around.

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Heart rate training

You can get more specific with your aerobic interval training and use heart rate since it’s an excellent indication of how hard you are working. Let’s use jogging on a treadmill as the aerobic activity in this example. For example, if your heart rate is at 70% of your predicted maximum when you jog at 6 mph, then start at that speed and either increase the speed or elevation so that your heart rate increases to 85% or even 90% for one minute, then back to your usual jogging speed for three minutes to elicit a heart rate of 70%. Start with a 1:3 work:active-rest ratio. That’s a good starting point, and as you increase the work intervals and decrease the active-rest ratios like in the examples above, you’ll notice that your conditioning improves so that your heart rate will be lower at the higher speeds.

It’s a good idea to plan your intervals in advance. Write them down so that you don’t have to think about it while you’re working out. I also suggest intervals no more than one to two times per week because they are tough workouts and you will need some time to recover. It’s okay to do aerobic activity on days in between your intervals, but give your body a chance to recover from the intervals before doing them again.

Matt Williams, Personal Trainer, Fitness Blog

Increasing duration and intensity

The general rule for increasing aerobic activity is 10% per week. Interestingly, there’s no evidence to suggest that a 10% increase is the safest and most effective amount of time to increase, but that’s the rule of thumb and it seems to work pretty well. So, if you’re walking for 20 minutes then the next increase ought to be two minutes for the following week. The bottom line though is to listen to your body. If you find that increasing by 10% is very easy, then go ahead and try a little more. But if you find that you are tired for hours after your workout, or chronically sore or achy from your workouts, then you know you need to cut back to 10% increases. Learn how to listen to your body and everything should be OK.


author: Matt Williams


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