Interval Running – The Key to Increased Speed, Endurance, and Strength

If you want to be a faster, stronger, more resilient runner, interval running should be a part of your weekly regiment. This type of training takes a runner through alternating intervals of aerobic and anaerobic exercise. By doing so, the runner gets a full range of fitness conditioning. Interval training also helps increase performance levels while minimizing the risk for injuries.

While low intensity running works on basic sustainable endurance, high intensity running works on strength, speed, and agility. Oxygen intake during low intensity work is sufficient to fuel ATP energy generation (for muscle contractions). Anaerobic metabolism works without oxygen. Instead, the body uses stored creatine phosphate to provide ATP energy. As in aerobic activity, glycogen is converted to pyruvate to aid glucose transportation. However, the lack of oxygen causes the fermenting to lactic acid, which causes the burning sensation one gets during high intensity activity.

The stress levels of high intensity intervals force the body to adapt over time to accommodate larger work loads. The anaerobic threshold, which is the point at which lactic acid build up is faster than the body’s ability to remove it, increases. The heart and lungs become stronger to deliver more oxygenated blood throughout the body. In addition, capillaries form and grow throughout the body to receive this oxygen more efficiently. Lastly, interval training increases lean muscle mass. After a few weeks of interval running, these adaptations build and help the runner run hard longer.

Although high intensity running produces increased performance levels, prolonged training at this level greatly increases the risk for injuries and burnout. By working in a few occasional bursts of high intensity running (30 seconds, for example) you can still push the envelope and get a good performance workout, all the while staying injury free. This is not so much different than strength training in the gym where one would perform a set and rest for a bit before doing the next set.

A good side benefit of interval running is the tremendous weight loss affects it has. High intensity running simply burns more calories than low intensity running. Some people would argue that low intensity running burns a higher percentage of fat calories. However, a high intensity run of comparable distance or time would burn more absolute total calories, and comparable or more absolute fat calories. A typical jog (4-5 mph) burns about 500 calories per hour. Low intensity calorie burning typically involves 50% fat, which would turn out to be 250 calories in our current example. High intensity calorie burning typically involves 40% fat. For example, a 60 minute run at 6-7 mph will burn an average of 700-800 total calories, and 280-320 fat calories. Alternatively, running at 6-7 mph would burn the same amount of fat in 46-53 minutes as you would running 5 mph at 60 minutes.

There are a couple different ways to do interval running. The first method, is known as fartlek, which is Swedish for « speed play. » As the translation suggests, it approaches high intensity training informally. This allows the runner to experiment, and keep things fresh as she can throw in her own mix of intervals and speeds. I remember doing fartlek one time, and getting so into it that I was able to sustain a fifteen minute high intensity interval. Tiring, but exhilarating as well. Usually, I keep it to 30-60 seconds or I just pick out a landmark ahead and race to it. The point is fartlek will allow you to have fun while increasing performance.

Another, more formal method of interval running is High Intensity Interval Training, commonly known just as HIIT. It requires a little more conformity and discipline than fartlek. High intensity intervals last 30-60 seconds at full effort with 2-3 minute rest intervals in between. I do 5-10 intervals each session. Other HIIT programs allow less than full effort but require longer high intensity intervals and shorter rest intervals. For example, a runner may be required to do 3/4 effort at 1-2 minutes, and rest intervals of 1-2 minutes in between. Furthermore, other HIIT programs require using a heart rate monitor to help the runner maintain a certain range per interval. When using a heart rate monitor, set your first interval at 75% of maximum heart rate. Increase the percentage a little with each following interval, eventually reaching max heart rate.

Before you start incorporating interval training into your schedule, I suggest you establish a strong endurance base. You should be able to run for at least one hour at moderate effort prior to your first interval training session. A strong base better ensures that you can perform the high intensity intervals adequately and with good form. It will also help your body cope with the taxing nature of high intensity intervals. If you’re in doubt about your ability to perform this type of training, consult your physician.

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