STACK Science: How Muscles Produce Energy and How to Improve Endurance
Muscles are like a car engine. They convert a fuel source into energy to produce movement—more specifically, a contraction. Whether resting during the evening or competing at peak performance, muscles need a constant supply of energy to function.
Muscle fibers have unique structures that shorten for contractions, as detailed in STACK Science: How Muscles Work and How to Make Them Work Better. Each time a fiber contracts, energy in the form of ATP [Adenosine Triphosphate] is transferred. ATP is the "molecular unit of currency" for intracellular energy transfer, the basic form of energy used by the body.
Energy is produced via two primary pathways—anaerobic and aerobic metabolism—each of which has a specific role in sports performance that must be understood to achieve best results.
The anaerobic energy system provides an immediate source of ATP—for 30 to 60 seconds—and contributes power for up to three minutes for high-intensity activity such as sprinting, jumping or weightlifting. Unlike aerobic metabolism, anaerobic metabolism does not need oxygen. Instead, it uses stored ATP for about 10 seconds, then produces more ATP from sugars.
Although it generates immediate energy, the anaerobic energy system produces little ATP. It primarily depends on stored energy, which is limited. In general, higher intensity exercise consumes energy at a faster rate, shortening the duration of maximum performance. Also, lactic acid—a byproduct of anaerobic metabolism that causes an uncomfortable burning sensation—begins to build up during intense exercise, causing fatigue and limiting strong muscle contractions.
The aerobic system generates sustained energy for endurance activity lasting longer than three minutes, like jogging or swimming. It uses oxygen along with carbohydrate, fat and—to a lesser extent—protein to create a constant and large supply of ATP.
Aerobic metabolism cannot fuel the quick bursts of strength and energy needed for most sports. Its benefits are also limited by VO2 Max—the volume of oxygen you can consume while exercising at your maximum capacity.
What This Means for You
Athletes should perform conditioning workouts that closely mimic their sport. If your sport is primarily anaerobic, your training should include short and high intensity sprints. In fact, anaerobic athletes who run long distances may lose speed and strength. Click on the following links for examples of anaerobic training.
For aerobic training, athletes should perform workouts at moderate intensity for a long duration, such as cross-country running. Interval training [high-intensity exercise with specific rest periods] is valuable for both anaerobic and aerobic athletes, since the body can be challenged near max and rested in intervals that simulate competition. View the links below for aerobic workouts.