In this article, I am going to present my thoughts on optimal intensity, duration, frequency, and modality. At the end, I will give you information on the best way to achieve both fat-loss and health benefits via aerobic training in terms of each topic.
In one of my more recent articles, "A Quasi-Comprehensive Definition & Explanation of Intensity," I defined intensity as a percentage of an individual's maximal capacity to do work. I also had skipped over the aerobic training component of intensity, so I'm now going to delve into this aspect.
Unlike resistance training, many cardiovascular measures can be used to assess aerobic exercise intensity. The most well known, and accurate measure is using a percentage of your VO2max. VO2max is the rate of oxygen uptake during maximal aerobic exercise, and is measured in either absolute terms (milliliters/minute), or relative terms (milliliters x kilograms/minute).
This measure reflects the capacity of the heart, lungs, and blood to transport oxygen to the working muscles and utilization of inspired oxygen by the muscles during exercise. Absolute VO2 is directly related to body size, so larger people will have a greater VO2. However, relative VO2 is expressed relative to an individual's body weight. Relative VO2 can be used in order to express VO2 relative to fat-free mass, allowing you to estimate changes in cardiorepiratory endurance. This measure reflects the capacity of the heart, lungs, and blood to transport oxygen to the working muscles and utilization of inspired oxygen by the muscles during exercise.
Having said that, VO2max is obtained by conducting a graded exercise test, in which an individual is usually placed on a treadmill or stationary bike. The person performs the exercise, and the exercise workloads are increased in regular intervals and sustained for a given amount of time. The time at which the workload is sustained is called a stage. Heart rate, blood pressure, and ratings of perceived exertion (RPE; see A Quasi-Comprehensive Definition & Explanation of Intensity for a definition) are taken throughout the stages. The person being tested is also connected to a spirometer so that the amount of inhaled oxygen and exhaled carbon dioxide can be measured. By using a spirometer, you can measure how much inhaled oxygen is being used and thus measure your VO2.
Taking these measurements at given intervals allows an individual to use their heart rate and RPE to predict their VO2 during exercise. For example, if you measure your heart rate during exercise to be 140 beats per minute (bpm), and you know that during the graded exercise test, 140 bpm was your heart rate when your VO2 was _____ ml x kg/min, you can say, "I know that my VO2 is _____ ml x kg/min because my heart rate is 140 bpm." You can also do the same thing with RPE, which is probably easier to use because you don't have to screw around with counting your heart beats.
The point at which you give out, and can no longer sustain a given workload at a given stage is when you can obtain your maximum RPE (which should be 19 or 20), maximum heart rate, and VO2max. Most treadmills/bikes have a chart that shows what your maximum heart rate should be according to your age. These charts are highly inaccurate because individual variability is high in terms of heart rate. In other words, your heart rate max may be 20 bpm different than someone else your age. Therefore, you can't always go by these charts. So, by obtaining your heart rate max, you can more accurately assess the intensity at which you are working by measuring your heart rate while you are working.
Also, since you know your heart rate max, VO2max, and RPE max, you can use your heart rate or RPE during exercise and compare it to your maximum measures and find out at what percentage of your max you are working. And what is a percentage of your max effort called? INTENSITY!
Obviously, being able to measure your inspired oxygen and expired carbon dioxide with a spirometer is not going to be feasible simply because spirometers are very expensive and are not readily available to the general public. However, you can still conduct a graded exercise test on yourself without a spirometer. Here's how:
Treadmill Test - The Bruce Treadmill Protocol Method
- Measure your resting heart rate and RPE
- Begin the test with a 2-3 minute warm-up at 1.7 mph at 10% grade
- Increase the grade by 2% and speed to 2.5 mph for 3 minutes
- Each stage thereafter, increase 2% grade and .8-.9 mph every 3 min.
- Continue to increase the workload until you completely exhaust
- Take heart rate and RPE at minute 2 and 3 of each stage, and at the point at which you exhaust
Bike Test - The McArdle Test Method
- Measure your resting heart rate and RPE
- Begin with a 2-3 minute warm-up at 60 rpm and 150 watts
- Increase the power by 30 watts every 2 min. until you completely exhaust
- Stay at 60 rpm throughout the entire test
- Take heart rate and RPE at minute 1 and 2 or each stage, and the point at which you exhaust
Now that you are up to speed and know everything about intensity, let's turn our attention to duration. Duration of aerobic exercise is the time per session that you spend performing the exercise. For example, if you run on a treadmill for 30 minutes, your duration of exercise is 30 minutes. The energy substrate that you burn is duration (and somewhat intensity) dependent. The reason that it's more dependent on duration is because generally, you assume a given intensity for a certain duration.
For the first 10 seconds of aerobic exercise, your major energy source comes from the adenosine triphosphate-phosphocreatine system (ATP-PC system). This fuel source is primarily what sprinters use for ultra short-term performances. The next 10 seconds to 3 minutes is characterized by a combination of fuels from the ATP-PC, glycolytic, and aerobic systems. Generally, you receive 40-90% of your energy from anaerobic (ATP-PC and glycolysis) systems and 10-60% from aerobic systems.
The wide range of percentages reflects the range of duration of the exercise. For example, if you exercise for 10-15 seconds, you are probably using about 90% anaerobic and 10% aerobic systems. From 3 to 10 minutes, your energy sources range from 40%-15% for anaerobic systems and 60-85% for aerobic systems depending on if you are closer to 3 or 10 minutes duration. Finally, for 10 minutes to 1 hour, you are using 15-20% anaerobic systems and 85-98% aerobic sources. It is important you understand that anaerobic systems use fuel in the form of phosphocreatine, blood glucose, and stored glycogen in order to produce energy for exercise. Aerobic systems use fat in order to produce energy for exercise. Also, during resting conditions, your body uses a slightly larger amount of fat than blood glucose/stored glycogen for energy. As you can see, duration of exercise determines to a large extent what source of fuel that you use.
Frequency refers to how many aerobic workout sessions that you have over a given period. For example, if you run 3 days per week, your frequency is three days per week. Since this is a pretty obvious and simple concept, I am going to move right into modality.
For those of you unfamiliar with modality, it is simply the mode of exercise that you are performing. For example, if you run on a treadmill, the modality is running on a treadmill. Pretty simple stuff, right? Good, let's get down to what you really came here forâ€¦what to do in order to achieve your goals.
Now that I've given you all of this hodgepodge, I'm going to show you how to apply it. What you decide on for an exercise program depends on what you are trying to achieve. For example, if you are seeking to improve your general fitness, here are some basic guidelines:
Basic Guidelines To Improve Your General Finess:
- Perform weight bearing exercises on most exercise days
- Exercise at a frequency range of 3-4 days per week
- Exercise for 20-30 minutes per session
- Exercise at about 75-90% of your heart rate max or 55-75% VO2max for the given duration
Health Benefits From Improving Your General Fitness Will Reduce Your Risk For:
- Cardiovascular diseases
- Musculoskeletal disorders
- Psychological disorders
- Pulmonary diseases
- Metabolic disorders
If you are seeking solely to reduce fat, there are generally two approaches to aerobic training. You either try to exercise at a higher intensity for a shorter duration or at a lower intensity for a longer duration. Continuous, low-intensity training is termed "LSD," or Long Slow Distance. This form of training is a constant intensity, usually sustained for at least 20 minutes, and the intensity is less than 75% VO2max. Individuals who use this type of training either jog, swim, or cycle. The advantages of LSD training are that it can be used for beginners, deconditioned individuals, weight-loss programs, weight maintenance, and general health benefits. The disadvantages are that fat-loss takes a longer time to achieve and the increase in metabolic rate during and after exercise is less than other forms of training.
A more intense form of training is called interval training. Many of you have heard of this before. Basically, you can accomplish the same or greater volume of exercise at a higher intensity than LSD training. For example, running continuous for 3 miles at 8 min/mile is LSD training. Running 400 meters at a faster pace for 12 laps with rest intervals at a 8 min/mile pace is interval training. In interval training, you either want to manipulate the duration of your work intervals or your rest intervals.
Say that you can run 400 meters in 60 seconds (this is your fastest time). You would want to run those laps in 61-65 second intervals if you were training. Likewise, if you run the same 400 meters in 60 seconds, you would want to rest for about 120 seconds between work intervals. If you want to manipulate your training to make it more intense, you would either want to run the laps in a shorter time or rest for a shorter period of time. You could also determine your rest intervals by measuring your heart rate and begin another work interval when you reach a desired heart rate. For example, resting until your heart rate reaches 130 bpm and then doing another work interval.
Both of these methods are effective, however, studies have shown that you can accomplish in LSD training with what you accomplish in interval training, however, it takes a lot longer with LSD training. The following changes and percentages are expressed in terms of interval training vs. LSD training over a given period of time.
In Interval Training, You Achieve:
- 40% increase in glycogen
- 100% increase resting ATP levels
- 65% increase in resting phosphocreatine levels
- 35% increase in resting creatine levels
- 35% increase in maximum lactate levels
- 50% increase in max stroke volume
- 75% increase in max cardiac output
- 45% decrease in resting heart rate
- 107% increase in VO2max
- 25% increase in heart volume
- 30% increase in blood volume
- 30% decrease in body fat
The two figures that struck you the most were probably the increase in VO2max, and the decrease in body fat compared to LSD training. Obviously, if you want to achieve faster results, higher intensity, interval training is the way to go.
Another major benefit to higher intensity aerobic training is the change in metabolic rate. When you exercise, you metabolic rate increases and then slowly decreases throughout the day with cessation of exercise. If you train at a higher intensity, your resting metabolic rate will remain elevated over a greater amount of time than lower intensity training.
This is why I stress doing two a days for high intensity aerobic training. If you train in the morning, your resting metabolic rate remains higher throughout the day, and if you train in the evening, your metabolic rate remains higher throughout the night as well.
Finally, I think that running is superior to all other forms of aerobic training simply because it is more of a compound movement (since it does involve your arms) and it is weight bearing, which will strengthen your bones. Don't get me wrong, cycling and swimming are both effective as well, but both exercises have either one or the other benefits of running. Now that you have the knowledge to design your own program, good luck getting ready for summer!