Practice makes perfect when it comes to getting in shape. Quite simply, if you want to increase your aerobic fitness you have to do aerobic activities. Endurance training such as running and biking will help, as will interval training, such as sprint workouts.
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A lot of what defines your fitness is your aerobic capacity. When your body uses oxygen to create energy it's considered aerobic. The truth is that you're constantly breathing and using oxygen to power your body. But, your fitness level depends on how effectively you can use oxygen at any given point in time during exertion.
If you do a slightly aerobic activity, like walking, you might not feel much of an increase in your breath rate. If you start to jog, you might breathe faster and faster. As you increase your speed to a full-out sprint you breathe even faster. At a certain point, you can't breathe any faster and your body starts to slow down.
Read more: Aerobic Exercise Adaptation
Distinct from your aerobic energy system is the anaerobic system. As your workout gets more intense your aerobic energy system simply can't power your muscles. The aerobic system is good for slow and steady exercises like long-distance jogging or swimming, but when you need short, fast and intense effort — such as sprinting to first base or squatting a super heavy weight — the aerobic system can't keep up.
The anaerobic energy system is what you use during intense activities like a sprint or vertical jump. It's more powerful and lets your muscles work faster, but you run out of this type of energy much faster.
It might seem like the best aerobic workout would be slow and steady, since that's when you're primarily using your aerobic energy system. However, the best aerobic workouts may actually be interval workouts that alternate between aerobic and anaerobic work, such as sprints.
Interval workouts can give you the same benefits as aerobic exercise. A 2015 research review from the Gatorade Sports Science Institute found that over two weeks, three interval workouts per week showed benefits that you would typically see from endurance training.
Similar to endurance training, interval training makes your heart more efficient. You increase the amount of blood that you can pump, which provides your body with more oxygen.
Your muscles also become more efficient. They can process more glucose and fat to create energy. Some of your muscle fibers adapt by switching from fast-twitch to slower, more energy efficient fibers.
In less than half the time it takes you to get a slow and steady aerobic workout — such as a 60-minute jog — you can do an interval workout that gets similar results. Think of interval training as a very concentrated dose of aerobic exercise to your body, which makes it adapt in a similar way.
Interval Training Setup
You can make almost any cardio exercise into an interval workout. Just alternate equal times work and rest for the duration of the session. For example, when you sprint, go close to your top speed for 30 to 90 seconds, and then recover at an easy jog or walk for an equal bout of time. When you sprint during an interval workout you're using your anaerobic energy system.
When you rest, you use your aerobic energy system to recover. During your workout, you constantly switch between the two energy systems to keep moving.
Running, cycling, rowing, swimming and stair climbing can all be easily converted to interval workouts. The big difference between intervals and continuous workouts is that you take rest periods in an interval workout. These rest periods let your body refuel for the next sprint, so you can keep the intensity high.
An example of an interval workout would be a 30-second sprint followed by a 30-second rest. You can keep that going for 10 to 20 minutes. You can do this style of workout about three days per week on non-consecutive days without overdoing it.
Read more: What Is Anaerobic Endurance?
Steady State Training
While the intensity of an interval workout makes it so effective, it also makes it much more difficult. Continuous aerobic workouts might be easier for you to do and, even though it may take longer to get the same results, they still improve your aerobic fitness.
For a continuous aerobic workout, pick an exercise like running, swimming, biking or rowing to do for an extended period of time, for example, 30 to 60 minutes. Do the exercise without any rest but at a low intensity — below 80 percent of your maximum heart rate. To find your maximum heart rate, simply subtract your age from 220. The key to this style of exercise is to pace yourself so that you're never completely exhausted. With a little bit of practice, you'll be able to find a pace that you can sustain for a while that isn't too easy or hard.
Since these workouts are less intense than interval training you can do them more frequently, like three to five days per week.