A high aerobic capacity is an equivalent of being in good cardiovascular shape. Aerobic capacity is the body’s ability to deliver oxygen to muscle cells and the capacity of these cells to make ATP in the presence of oxygen. If you have a high aerobic capacity, your heart pumps blood and oxygen to your tissues in an efficient manner and your muscle cells have lots of mitochondria to make ATP. Plus, exercise increases the capillary density surrounding the muscles and that improves aerobic capacity as well since higher capillary density boosts oxygen delivery to the muscle. Aerobic capacity is referred to as V02 max and is the best indicator of aerobic fitness.
How’s YOUR aerobic capacity? If you don’t have the stamina and endurance you’d like, you can improve your V02 max through training. Studies show you can boost V02 max by as much as 25%. What type of exercise is best? You might think that moderate-intensity workouts, like jogging or cycling at a moderate pace, would be the best form of training to boost aerobic capacity – but is it?
Workouts for Improving Aerobic Capacity
There are several approaches to improving aerobic capacity. You can do low to moderate-intensity movements, like cycling, jogging, brisk walking, or swimming, for sustained periods of time. This is sometimes referred to as long, slow training. Sustained bouts of moderate-intensity exercise increase oxygen delivery to muscle cells and the muscle cells adapt in a way that helps them use that oxygen more efficiently. For example, the number of energy-producing mitochondria goes up to allow more ATP to be produced. Your heart also adapts by becoming a more efficient pump for greater oxygen delivery to the muscles.
Yet, this isn’t the only approach and isn’t necessarily the best approach to increase aerobic capacity. You can also get improvements in V02 max using high-intensity interval training. This approach alternates intense exercise, at 90-100% of your maximal heart rate, with low-intensity, recovery periods in-between the high-intensity intervals. During the high-intensity intervals, you tap into anaerobic pathways for energy production. Over time, this improves your body’s anaerobic capacity and the ability to clear lactic acid from your system. But during the recovery phase between active intervals you use aerobic energy pathways and this, over time, improves V02 max.
When you do high-intensity intervals, you place enough stress on your heart that it adapts and becomes more efficient at delivering oxygen to muscle cells during exercise. Just as your muscles hypertrophy in response to strength training, your heart muscle enlarges in size, especially the left ventricle that pumps blood to the body. A thicker left ventricle is able to pump with more force.
High-Intensity versus Moderate-Intensity Exercise
In fact, some studies show that high-intensity exercise is better for improving aerobic capacity than moderate-intensity exercise. In one study, researchers asked participants to take part in a 6-week training program. One group did 40 to 60 minutes of cycling at 65% of V02 max 5 days per week. The other group trained 3 days per week and did 4 to 6 maximal sprints on a bicycle that lasted for 30 seconds each. This was followed by 4.5 minutes of recovery after each active interval. After the training, the researchers looked at the mitochondria of both groups. The group who did the high-intensity interval training had higher levels of mitochondrial enzymes that make ATP during conditions when oxygen is present.
What does this mean? The mitochondria of the individuals who did the more intense training were better primed to make ATP during oxidative conditions than those who did the low to moderate-intensity sessions for 40 to 60 minutes. Plus, the high-intensity group spent less time training.
Why might this be? It appears that high-intensity interval training turns on the PGC-1 alpha pathway, a pathway that increases the density of energy-producing mitochondria inside muscle cells, but it does it via a different pathway that is activated by moderate-intensity exercise. Gaining more ATP-producing mitochondria is one way to improve V02 max since you can produce more ATP to sustain exercise under aerobic conditions and this gives you greater exercise endurance.
Another way to increase V02 max or aerobic capacity is to boost the amount of oxygen that’s delivered to the muscles you’re working. You can do this by making the heart a more efficient pump. Some studies show that high-intensity workouts improve stroke volume, the volume of blood the heart can pump with each beat more than sustained moderate-intensity exercise. Increased stroke volume leads to improvements in aerobic capacity.
High-intensity interval training also gives more of an after-burn than moderate-intensity aerobic training. After HIIT training, your body has to work harder to recover and, ultimately, burns more calories and body fat after the workout is over. It may be better for body fat loss than moderate-intensity exercise, even when you take into account the time differential.
Which Approach Should You Use?
If you’re trying to get into better cardiovascular shape and improve your V02 max, high-intensity interval training has a slight edge. However, it’s best to do some of each. If you only do high-intensity interval training, you risk exhaustion and burnout, as working at 90 to 100% of maximal heart rate is quite demanding. Yet these workouts are very time efficient. If you have limited time, you can get an excellent workout in a short period of time with HIIT routines. Since high-intensity interval workouts are shorter in duration, you’re at a lower risk of overuse and repetitive motion injuries. You can also vary the types of exercises you do during the high-intensity intervals for variety. All you really need for an intense workout is a stopwatch!
Why not do some of each type of training? Two sessions of high-intensity interval training weekly will help improve your aerobic capacity and you can also add another longer duration, lower intensity session that gets your heart rate up. That way you’ll get the best of both worlds!
American Council on Exercise. “8 Things to Know About Aerobic Capacity (And How to Improve It)”
Exp Physiol 101.1 (2016) pp 17–22.
Biomed Res Int. 2017; 2017: 5420840.