Your body produces energy anaerobically at the start of any race.
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Running can take many forms, from a leisurely jog to an all-out sprint. But no matter what kind of running you do, your body needs to power itself through respiration. Lighter, long-distance running causes your body to use aerobic respiration, while more intense sprinting and interval training requires anaerobic respiration. Which is more beneficial depends on your personal fitness and competitive goals.
When it comes to distance and leisurely running, aerobic respiration is sufficient to power you across the finish line. Aerobic respiration uses oxygen as its main energy source and doesn't result in a significant buildup of lactic acid. Sprinting and high-intensity interval training, however, force your body to produce instant energy through the immediate breakdown of glycogen stores. You can't keep up anaerobic running as long as you can aerobic running, since it's harder on your heart and muscles.
Aerobic respiration involves a continuous, sustainable loop of oxygen intake, which is why distance running is often referred to as steady-state cardio exercise. Your heart rate remains constant during distance running, allowing your cardiovascular system to keep up with your rate of exertion. As long as you remain in a target heart rate zone between 60 and 80 percent of your maximum heart rate, you will use aerobic respiration as your primary energy source. Distance runners and those looking to improve their health without pushing themselves too hard should run at this pace.
Anaerobic respiration is the hallmark of explosive athletes such as sprinters, football players and wrestlers. When you need immediate energy for a short burst, anaerobic respiration provides it without delay. Anaerobic running pushes your heart rate above 80 percent of its maximum, which can be stressful on the body. You can dip into an anaerobic energy zone during a long-distance run if you want to use that final burst to get to the finish line. Contrary to popular belief, short anaerobic workouts can increase cardiovascular endurance as much as longer aerobic workouts.
If you don't want to wear a heart rate monitor during a race or workout, you can take your pulse on the inside of your wrist for six seconds and then multiply that number by 10. Experienced runners should be able to estimate their rate of exertion based on how they feel during a run, according to the Centers for Disease Control and Prevention.