So you should do both aerobic and anaerobic exercises.

But the thing is, if I do anaerobic exercises, I am getting aerobic work done as well.

Say I go out and do interval training (i.e., anaerobic exercies). During each interval, it will be an anaerobic exercise. But if I do many intervals, and the entire exercise lasts me 30-60 minutes ... then my heart rate stays elevated throughout the exercise. In other words, it is also an aerobic exercise.

So what then is the point of doing aerobic exercises? Isn't doing an anaerobic exercise enough, since if you do it for at least 30 minutes, it automatically also becomes an aerobic exercise?


3 Answers 3


It really depends on your goals and what you're looking to get out of exercise. If you're looking to fit some quick workouts in throughout the week to lose weight/ build a little muscle then HIIT is fine and you don't need to be training different systems.

If you're looking to improve cardiovascular endurance and optimize your body's use of fat for fuel vs carbs for fuel you'd need to train at a lower heart rate for a longer period of time. Everyone has a point where this fuel source changes.

It really depends on your goals. A Thai fighter will do steady state cardio before essentially a HIIT style pad workout because they need both fast twitch and slow twitch muscle fibers trained as well as different energy systems optimized. The slow steady state cardio will improve your perfomance in the HIIT workouts.


If your goal is health and you only train this way 2-3 times a week this is probably the most effective approach. The Norwegian Cardiac Exercise Research Group "aim to define optimal exercise programs for “most people” in order to increase the likelihood of developing and preserving good health throughout life". They advocate 4x4 interval training which in effect is similar to what you propose. Reason being that high intensity training strengthens the heart and increases metabolism.

However if your goal is to perform well in an endurance event such as a half-marathon this is not the way to train. Stephen Seiler has shown that toplevel endurance athletes typically train with 80 % of their work-outs being low-moderate intensity and the rest 20 % very high intensity: polarised training. In order to gain endurance for say a half-marathon you need to run a lot of kms each week. So you have to train many days a week. This training plan for instance "takes you up to a regular 40 miles a week" and have you training 6 times a week. At this point recovery becomes a big problem. When you cross a certain intensity threshold your body produces stress hormons. These hormons increases recovery time. What more these hormons stay in the body for some time. So you can not mix low-medium intensity and high intensity work within the same workout. Instead you do mostly (80%) low-moderate intensity workouts that requires little recovery time and some (20%) very high intensity workouts.

Many people in their 30s and 40s train for half-marathon. From a motivational approach this is great. I have done it myself and it felt like an achievement. However from a health perspective I do not think it is optimal use of time. The same amount of time (or less) could be better spent on 2x45 minutes of 4x4 style running and 2x1 hour of strength training a week. That way you can have a strong heart, a low bodyfat percentage as well as strong muscles and tendons that protect you from injuries.


A quick answer but this is what really determines the quality of a workout:

Anaerobic alactic: work-rest ratio 1:10 Example. For each 10 seconds of sprints rest 2 minutes after

Anaerobic lactic: work-rest interval 1:2 Example.. weightlifting for 30 seconds and resting a minute. You more commonly see 60 seconds accompanied with 2 minutes rest.

Aerobic. Work-rest interval 2:1, 5:1, 10:1(really its working more than you rest) Example.. jogging for 10 minutes and resting 5 before continuing. Fun fact: you use aerobic energy for all 3 of the above but use it more in this work rest ratio.

The trick to these is intensity. Anaerobic is typically high while aerobic is typically low. Think about sprinting for as long as you can. After 20 seconds you're body will naturally run as it depletes it's first source of fuel. Then for 2 minutes it'll use lactic. After 5 it'll be aerobic because after so long you can't keep the intensity. Eventually you're other energy systems will replenish and let you Sprint again, etc..

The point being that during a high intensity anaerobic exercise.. Unless you're doing HIIT or tabata, you really aren't working out aerobic to its full capacity because you're putting a lot of power into an anaerobic exercise. If you are not resting and doing a 2:1 or greater work rest ratio.. then you're exercise, whether it's you jumping rope or running, is now purely aerobic because without resting you'll naturally lose power, just like the sprinting example above. Jump roping for instance is considered anaerobic but if you can do 30 minutes of jump roping without resting then you're doing an aerobic exercise, just a really really good aerobic exercise.

In your example it doesn't matter how long you exercise, what matters is how long you rest compared to the work. That's why HIIT is tricky because you get benefits of both even though you're doing a 2:1 ratio but it's because you're resting in intervals rather than doing sets. So HIIT can build both anaerobic and aerobic because it becomes a form of metabolic conditioning. You can also gain the same effects doing circuit training with low rep, heavy weight weightlifting which reduces your rest. You lose the efficiency of the anaerobic to some degree, for example circuit training with weights will cause you to use a lot less weight in your exercises but you can build both systems. With HIIT.. you lose building up your first two energy systems that use ATP and lactic, you're still training your heart and doing anaerobic exercise but you miss out on focusing on just the two energy systems . And in terms of weightlifting, you lose gains trying to combine the two

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