Exercises on Speed vs. Time

Speed and time are important factors to consider when designing a fitness program, but exercise isn’t one size fits all. Your workout intensity and duration depend on a number of health factors. Understanding how your body functions during high-intensity versus endurance exercise will help you reach your fitness goals.

  1. Your Body on Exercise

    • Your body uses two main energy sources for fuel during exercise: fat and carbohydrates. Of these two, fat is the most abundant. At rest, 33 percent of your body’s energy source comes from carbohydrates, and 66 percent comes from fat, according to ExRx. During aerobic exercise, carbohydrates, which are stored in your muscles and liver, are your body’s preferred source of energy. Carbohydrates are broken down into glucose, or sugar, to use as fuel, but once carbohydrates are no longer available, your body uses fat as energy.

    Speed and Intensity

    • Speed determines exercise intensity, or how hard you are working. The faster or harder you exercise, the higher the intensity. High-intensity interval training that alternates short bursts of speed followed by recovery produces results in a short period of time, according to the American Council on Exercise. These high-intensity workouts have aerobic and anaerobic benefits. Speed work using intervals that last three to five minutes followed by similar recovery time increases VO2 max, or your maximum aerobic capacity. Increasing VO2 max allows you to perform at a higher intensity for longer. These short bouts of intense aerobic activity allow your body to rely on glucose, or carbohydrates, for the majority of the workout. A 2012 study published in "BMJ Open," an online medical journal, found that exercising at a higher intensity is more effective at preventing metabolic syndrome than longer, lower-intensity exercise.

    Time and Exercise Duration

    • You can’t maintain your maximum aerobic capacity for very long, so when you exercise for a longer period of time, you do so at a lower intensity. Increasing the amount of time you exercise eventually forces your body to use fat as fuel, which usually happens after an hour and a half to two hours of aerobic activity. The American College of Sports Medicine recommends that adults get at least 150 minutes of moderate-intensity physical activity per week with gradual progression of time and intensity. A study published in the "Clinical Journal of Sport Medicine" found that the duration of exercise was more important than the intensity in helping sedentary, overweight women lose weight and improve cardiovascular fitness.

    Tips and Considerations

    • Both speed and time provide health benefits when exercising. If you’ve hit an exercise plateau, for example, integrating high-intensity interval training one to two days per week may help take your athletic performance to the next level. According to the American Council on Exercise, a cycling interval workout may look like this: warm up for five minutes and then perform three to four high-intensity, one-minute intervals followed by two minutes of recovery. Cool down for five minutes. Over time, your endurance will improve, you will be able to perform more intervals in one workout and you will increase your speed during longer-distance sessions. If you’re just starting a fitness or exercise program, focus on building endurance before increasing intensity. A beginning program may include 12 to 15 minutes of walking or jogging, gradually building up to 20 minutes of continuous exercise.