Once the training secret of the world’s best runners, interval training is now done by everyone, from competitive athletes to grandma next door.
Emil Zatopek of the former Czechoslovakia, who won the 10K at the 1948 Olympics and 5K, 10K, and marathon at the 1952 Olympics, was the first athlete to popularize interval training. However, it wasn’t until the 1960s that famous Swedish physiologist Per-Olaf Åstrand discovered that breaking up a set amount of work into smaller segments enables individuals to perform a greater volume of work at a high intensity. Sounds obvious, but Åstrand’s simple observation is the basis for interval training. 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 5 x 1,000 meters; and you can run 20 x 250 meters faster than 10 x 500 meters. However, this is where a lot of coaches and runners make mistakes. We’ll get to that in a minute.
When interval training was first studied in the 1930s by coach Waldemar Gerschler and physiologist Hans Reindell of Germany’s Freiburg University, they focused their attention on its cardiovascular aspects and believed that the stimulus for cardiovascular improvement occurs during the recovery intervals between work periods rather than during the periods of activity, as the heart rate decreases from an elevated value. Thus, the emphasis of the workout was placed on the recovery interval, prompting Gerschler and Reindell to call it an “interval workout” or “interval training.” Gerschler and Reindell’s original interval training method consisted of running periods ranging from 30 to 70 seconds at an intensity that elevated the heart rate to 170 to 180 beats per minute, followed by sufficient recovery to allow the heart rate to decrease to 120 beats per minute, signifying the readiness to perform the next work period.
During the recovery interval, the heart rate declines rapidly, but there is a lot of blood returning to the heart from the muscles, which leaves more time for the left ventricle to fill with a lot of blood, and subsequently eject a lot of blood with each beat (called the stroke volume). The increase in stroke volume places an overload on the heart, which makes the heart stronger. Since stroke volume peaks during the recovery interval, and because there are many 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. Pretty neat, huh?
Also during the recovery intervals, a significant portion of the muscular store of quick energy—creatine phosphate (CP)—that was depleted during the preceding work period is replenished via the aerobic system. During each work period that follows a recovery period, the replenished CP will again be available as an energy source.
Interval training manipulates four variables: time (or distance) of each work period, intensity of each work period, time of each recovery period, and number of repetitions. With so many possible combinations of these four variables, the potential to vary training sessions is nearly unlimited. Possibly the greatest use of interval training lies in its ability to target individual energy systems and physiological variables, improving specific aspects of your fitness level.
Back to the mistakes that coaches and runners make with interval training, and how to do interval workouts correctly.
(1) Know the purpose of the workout and match the pace to the purpose. If the purpose is to improve VO₂max, then run at your VO₂max pace, which you can determine from a recent race, from heart rate, and eventually by feel as you gain experience with these workouts. Do not run workouts at arbitrary paces, which is what most runners do. Always match the pace of the workout to its purpose.
(2) Run only as fast as you need to meet the purpose of the workout. If the purpose of the workout is to improve VO₂max, then run at your VO₂max pace, no faster. Make the workout harder by doing more volume at the right pace (or decrease the time of the recovery interval between reps) rather than run faster than the right pace. Just because you can run faster doesn’t mean you should. To stress the system, run at the upper limit of that system; there is no reason to run faster because that confers no greater benefit.
(3) Design interval workouts correctly, with an understanding of Åstrand’s research: By breaking up a period of work into periods of work and rest, you can perform a greater volume of work at a high intensity. For example, if you run 10 x 400 meters at 5K race pace, that workout doesn’t adhere to the purpose of an interval workout. It’s actually too easy of a workout because 10 x 400 meters is only 4,000 meters, which is less than the 5,000 meters that you could have held the pace for without any recovery intervals. So if you’re going to run 400-meter reps at 5K race pace, you need to run enough reps such that the total distance of the workout exceeds 5,000 meters, which is at least 13 reps. And since the reps are only 400 meters in length, which is only 8% of the distance that you can hold the pace, you should do many more than 13 reps at that pace to stress the system.
(4) Don’t run (or at least limit how much you run) at 5K, 10K, or half marathon race pace, unless you are specifically trying to practice running at race pace. These race distances don’t correspond to any specific physiological factor that influences performance. For example, 5K pace is too slow to achieve the benefits of a VO₂max workout and too fast to achieve the benefits of a lactate threshold workout. It’s much better to design workouts that specifically target the physiological variables that dictate your race performance. If you improve lactate threshold, VO₂max, running economy, anaerobic capacity, etc., your races will get better even without running at race pace because you will have improved the specific factors of your physiology that make you a better runner.
Aerobic Power (Cardiovascular) Intervals
One of the best methods to improve the capacity of your cardiovascular system—specifically, your heart’s ability to pump blood and oxygen to the active muscles—is interval training using work periods lasting 3 to 5 minutes and recovery periods equal to or slightly less than the time of the work periods. The cardiovascular adaptations associated with interval training, including hypertrophy of the left ventricle and a greater maximum stroke volume and cardiac output, increase your VO₂max (the maximum volume of oxygen muscles consume per minute), raising your aerobic ceiling. Since VO₂max is achieved when maximum stroke volume and heart rate are reached, the work periods should be performed at an intensity that elicits maximum heart rate during each work period. This type of interval workout, which is very demanding, is one of the best workouts you can do to improve cardiovascular conditioning.
Anaerobic Capacity (Speed Endurance) Intervals
Anaerobic capacity refers to the ability to regenerate energy (ATP) through glycolysis. Work periods lasting 30 seconds to 2 minutes target improvements in anaerobic capacity by using anaerobic glycolysis as the predominant energy system. These short, intense work periods with recovery intervals 2 to 4 times as long as the work periods increase muscle glycolytic enzyme activity so that glycolysis can regenerate ATP more quickly for muscle contraction and improve the ability to buffer the muscle acidosis that occurs when there is a large dependence on oxygen-independent (anaerobic) metabolism.
Anaerobic Power (Speed) Intervals
Anaerobic power refers to the ability to regenerate ATP through the phosphagen system. Work periods lasting 5 to 15 seconds target improvements in anaerobic power by using the phosphagen system as the predominant energy system. These very short, very fast sprints with 3- to 5-minute recovery intervals that allow for complete replenishment of creatine phosphate in the muscles increase fast-twitch muscle fiber activation and the activity of creatine kinase, the enzyme responsible for catalyzing the chemical reaction that breaks down creatine phosphate.
Sample Interval Workouts
Make sure you warm-up and cool-down before and after each workout.
Aerobic (Cardiovascular) Intervals (Aerobic Power):
• 5 x 3 minutes @ VO₂max pace (95-100% max HR) with 2½-3 minutes jog recovery
• 3 x 4 minutes @ VO₂max pace (95-100% max HR) with 3½-4 minutes jog recovery
• 3, 4, 5, 4, 3 minutes @ VO₂max pace (95-100% max HR) with 2½-3 minutes jog recovery
VO₂max pace = 3K (2-mile) race pace or slightly faster for good runners; about 1½-mile race pace for recreational runners
Anaerobic Capacity (Glycolytic) Intervals (Speed Endurance):
• 4 to 8 x 30 seconds at 95% all-out with 2 minutes jog recovery
• 4 to 8 x 60 seconds at 90% all-out with 3 minutes jog recovery
• 2 to 3 sets of 30, 60, 90 seconds at 90-95% all-out with 2 to 3 minutes jog recovery & 5 minutes rest between sets
Anaerobic Capacity pace = Mile race pace or slightly faster for good runners; about ½-mile race pace for recreational runners
Anaerobic Power (Phosphagen System) Intervals (Speed/Power):
• 2 sets of 8 x 5 seconds all-out with 3 minutes passive rest & 5 minutes rest between sets
• 5 x 10 seconds all-out with 3-4 minutes passive rest
• 2 to 3 sets of 15, 10, 5 seconds all-out with 3 minutes passive rest & 10 minutes rest between sets
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