Understanding Interval Training

When Swedish physiologist Dr. Per Olaf Åstrand discovered in the 1960s on a stationary bicycle in the laboratory that if you take a set amount of physical work and break that work up into periods of work and rest, you can accomplish more work at the same or higher intensity, the interval training that runners were doing in the 1930s & 1940s gained the credibility it needed to propel it into the training programs of athletes everywhere. 

The secret of interval training is in the amount of work you can accomplish. For example, you can run 5 x 1,000 meters faster than you can run 5,000 meters; you can run 10 x 500 meters faster than you can run 5 x 1,000 meters; and you can run 20 x 250 meters faster than you can run 10 x 500 meters. Sounds obvious, but Åstrand’s simple observation is important when designing workouts.

Interval training actually originated in Europe in the 1930s to develop fitness in track athletes. While athletes used interval training without knowing exactly why it worked, coach and physiologist Waldemar Gerschler and Hans Reindell of Germany’s Freiburg University believed that the primary stimulus for cardiovascular improvement occurs during the recovery interval when the heart rate is reduced from 170-180 to 120-140 beats per minute.

During the recovery interval, the heart rate declines quickly since the runner has stopped running fast, but there is a lot of blood returning back to the heart. Since the heart rate declines rapidly, there’s a greater filling time in the left ventricle to accommodate the return of the large volume of blood to the heart, resulting in a brief increase in stroke volume. The increase in stroke volume places an overload on the heart, which makes the heart stronger, and enables the skeletal muscles to be cleared of waste products quickly due to the elevated rate of blood flow when there is little demand for activity from the tissues. Since stroke volume peaks during the recovery interval, and because there are multiple recovery intervals during an interval workout, stroke volume peaks many times, providing a stimulus for improving maximum stroke volume and thus the capacity of the oxygen transport system. Hence the term interval workout—to place the emphasis on the recovery interval between reps.

Gerschler and Reindell’s original interval workout required running for 30 to 70 seconds at a speed that elevated the heart rate to about 180 beats per minute. The run was followed by sufficient recovery to allow the heart rate to return to 120 beats per minute. 

In the late 1940s and early 1950s, interval training was made popular by Emil Zatopek of Czechoslovakia, the only runner to win the 5,000 meters, 10,000 meters, and marathon in the same Olympics. Also during that time, Hungarian coach Mihaly Igloi developed the concept of sets of short distances run quickly to permit a greater total training stimulus. His coaching centered on large amounts of interval training, believing that a large amount of speed training also built stamina. This opinion was echoed by Zatopek himself in response to those who told him he was spending too much time training with short distances as if he were a sprinter: “…but if I run 100 meters twenty times, that is two kilometers and that is no longer a sprint.”

To do an interval workout correctly, either do more volume at race pace (e.g., 5 x 1 mile at 5K race pace or 6-8 x 400 meters at 1-mile race pace) or run the same volume at faster than race pace (e.g., 6 x 1/2 mile at faster than 5K race pace). Thus, if you’re going to run mile reps at 5K race pace, you need to run more than 3 because a 5K is 3 miles and you could run that pace without taking breaks. By breaking those 3 miles into 1 mile segments, you either need to run each mile faster than 5K race pace or run more than 3 miles in the workout at 5K race pace. Likewise, if you run 20 x 200-meter reps, run them faster than 5K race pace because 20 x 200 meters is only 4K. Remember the purpose of an interval workout.

Learn all the details of interval training (and a whole lot more!) with the REVO₂LUTION RUNNING™ certification.

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