Chances are, you don’t have the speed or power of an Olympic sprinter or the endurance of a world-class marathoner. That’s okay. These are folks who are genetically gifted AND highly trained and it’s a pleasure to watch them in motion. It takes good genetics, training, and motivation to reach a world-class level. Yet, a speed and power athlete, like a sprinter, and a marathoner have very different talents.
The sprinter is fast-twitch dominant, meaning he or she has highly developed fast-twitch muscle fiber designed for contracting forcefully for short periods of time. In contrast, the marathon runner is slow-twitch dominant, meaning they rely mainly on slow-twitch fibers built for endurance. In this article, we’ll focus on aerobic or endurance exercise and the factors that go into giving you exceptional endurance. All in all, there are three main ones.
Aerobic Exercise Performance: Aerobic Capacity
You’ve probably familiar with the term aerobic capacity. You may have heard it described with scientific terminology as V02 max. In its simplest terms, aerobic capacity is the maximum capacity of your body to take up and use oxygen during endurance exercise. V02 max is measured in milliliters per kilogram of body weight per minute. A person with higher aerobic capacity can take up and deliver more milliliters of oxygen per kilogram of body weight per minute than someone with a lower aerobic capacity.
Now, you might wonder what factors impact aerobic capacity? One of the most important is an individual’s cardiovascular system – how efficient the heart is as a pump. In fact, research shows 70 to 85% of an individual’s V02 max is determined by how efficiently their heart can pump blood or oxygen. Another factor is how much oxygen-carrying hemoglobin you have in your bloodstream. If you have more hemoglobin, you can deliver a higher concentration of oxygen to tissues per heartbeat. That’s why anemia reduces exercise tolerance – you have less hemoglobin available to carry oxygen.
Another factor is the density of capillaries around muscles and tissues. If you have a high density of capillaries, you can deliver more oxygen per unit of time. Finally, the energy powerhouses inside cells, mitochondria, affect aerobic capacity. Remember, mitochondria use oxygen to make ATP, the energy currency that powers muscle contractions. More mitochondria and more efficient mitochondria increase aerobic capacity and exercise endurance since cells can get more oxygen to produce ATP.
There’s a genetic component to aerobic capacity but you can also improve your aerobic capacity through exercise training by as much as 20%. Training improves the efficiency at which your heart pumps oxygen. It also boosts capillary density around tissues and amplifies the number of mitochondria inside cells so there are more around to make ATP. It also increases the enzymes that produce ATP within muscle cells.
Aerobic Exercise Performance: Lactate Threshold
Another factor that affects aerobic exercise performance is the lactate threshold. If you go out and run, or do any form of aerobic exercise, and gradually increase the speed or intensity, you’ll eventually reach a point where lactate or lactic acid builds up in your bloodstream. Why does this happen?
When oxygen becomes limiting, your cells use an anaerobic pathway to make ATP. This pathway produces lactate or lactic acid. Your body has the ability to buffer lactic acid up to a certain point. However, when lactic acid production exceeds this threshold, known as the lactate threshold, lactic acid and hydrogen ions start to build up in the bloodstream. The hydrogen ions lower the PH. The drop in PH interferes with enzymes and cellular reaction and you begin to experience muscle burning and fatigue. At some point, you’ll be forced to slow down or stop. Keep in mind, it’s not lactate itself that causes fatigue but the drop in PH and the cellular disruptions that go along with it.
Lactate threshold is described as a percentage of V02 max, or aerobic capacity. An untrained person might only be able to exercise at 50% of their V02 max before experiencing lactic acid build-up and extreme fatigue. However, a highly trained individual can potentially exercise at a higher intensity of their V02 max, around 70 or 80%, before reaching their lactate threshold. So, when you have a lower lactate threshold, you can’t exercise at as high of a percentage of your V02 max.
Many experts believe that lactate threshold is a more important determinant of aerobic exercise performance than aerobic capacity. V02 max is most relevant when you’re doing a steady-state exercise like jogging at a moderate intensity. Yet, how many sports really follow that protocol? Even marathoners exercise at a higher intensity as they approach the finish line. A high lactate threshold helps you reach your maximal aerobic potential.
Your lactate threshold is higher when you have more mitochondria to produce oxygen aerobically. One way to increase the number of mitochondria and your lactate threshold is to do high-intensity interval training. In general, if two people have the same V0s max, the person with the higher lactate threshold will do better in an endurance-type event. The advantage of having a higher lactate threshold is you can exercise at a high intensity for a longer period of time before fatiguing and having to slow down or stop.
Aerobic Exercise Performance: Exercise Economy
Exercise economy is how much energy you expend to do a certain amount of work. It’s a measure of how efficient your movements are. Since you require oxygen to do work, it’s also indirectly a measure of how much oxygen you use to perform a specific task. An example would be two runners. One runner has smooth, fluid movements while the other has lots of extraneous movements when they run. If they run the same distance at the same pace, runner B expends more energy and uses more oxygen to run the same distance compared to runner A. Runner B is less efficient and has a lower running economy.
Factors that affect exercise economy include genetics, the degree of joint stability, flexibility (increased flexibility reduces exercise economy), neuromuscular coordination, as well as genetics. Greater muscle and tendon stiffness actually increases exercise economy by reducing the number of extraneous movements you make when you exercise.
The Bottom Line
These are the three main factors that influence aerobic exercise performance during aerobic exercise. Fortunately, you can improve these through training. Although running at a moderate, steady-state intensity for long distances will improve your aerobic capacity and, potentially, exercise economy, it won’t enhance your lactate threshold. That’s where high-intensity interval training comes in. Keep in mind that HIIT training can also improve your aerobic capacity as well. High-intensity interval training has multiple fitness benefits and now you know why.
References:
On Fiynrdd. September/October 2016. “Unraveling the Science of Oxygen”
The Physiological Factors Limiting Endurance Exercise Capacity by Len Kravitz, Ph.D and Lance C. Dalleck, M.S.
Sports Fitness Advisor. “Endurance Training Section”
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