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Interval Training: The Fastest Way to Get Fit

There’s been a lot of commotion about interval training. Once the training secret of the world’s best runners, interval training has become the new buzz term in the fitness industry. It seems as if everyone is doing it, from competitive athletes to grandma next door.

Learning Objectives:

  1. Become familiar with the research on interval training.
  2. Understand interval training from a historical perspective.
  3. Learn how to design interval workouts to target specific metabolic energy systems.

While many athletes used interval training in the first half of the 20th century, it was distance runner Emil Zatopek of Czechoslovakia, winner of the 10,000 meters at the 1948 Olympics and the 5,000 meters, 10,000 meters, and marathon at the 1952 Olympics, who popularized this method of training. However, it wasn’t until the 1960s that famous Swedish physiologist Per-Olaf Åstrand discovered, using a stationary bicycle in a laboratory, what many coaches and runners already knew—that by breaking up a set amount of work into smaller segments, you can perform a greater volume of work at a higher intensity. Sounds obvious, but Åstrand’s simple observation is the basis for interval training.

One of the main reasons for all the attention on interval training in the fitness industry is that it can improve fitness quickly, which is great news for busy people who don’t want to spend two hours in the gym. Interval training has also been shown to”

Furthermore, while aerobic training improves aerobic fitness, high-intensity, repeated anaerobic efforts improve both anaerobic and aerobic fitness, giving your clients two bangs for their workout buck (Tabata et al., 1996). While the energy for muscle contraction during maximal exercise lasting less than 20 seconds is primarily derived from anaerobic metabolism (i.e., phosphagen system and glycolysis), the contribution of aerobic metabolism increases when short sprints are repeated.

While interval training can be very effective, it is important to note that the results obtained (and thus the conclusions drawn) by most of these studies were a result of subjects performing repeated all-out sprints on a stationary bicycle multiple times per week, a protocol that would not likely be performed by the average personal training client due to its very strenuous nature. For example, many of the studies comparing the effects of interval training to continuous aerobic exercise come from the laboratory at McMaster University during which subjects performed 4 to 6 x 30-second all-out sprints (i.e., repeated Wingate tests) with 4 to 4½ minutes recovery three times per week for two to six weeks (Burgomaster et al., 2008; Gibala et al., 2009; Gibala et al., 2006; Rakobowchuk et al., 2008). The protocol used by Tabata and his colleagues (1996) (the so-called “Tabata intervals,” which have been getting a lot of attention lately in the fitness industry) included 7 to 8 x 20-second all-out sprints with just 10 seconds recovery five days per week for six weeks! In other words, the researchers hammered the subjects to induce molecular changes. Therefore, it cannot be assumed that if your clients do interval training once or twice per week when they see you for a session that they will achieve the same results as that reported in the literature.

Another reason interval training has become popular is because of its effect on metabolism and calorie burning. Its intense nature disrupts the body’s homeostasis, making interval training more effective than continuous cardiovascular exercise for increasing metabolic rate following a workout, as homeostasis is reestablished. Research has shown that subjects have a higher post-workout metabolic rate following an interval workout (20 x 1 minute at 105% VO2max with 2 minutes rest) compared to continuous exercise (30 minutes at 70% VO2max) and burn more calories during the 24 hours following an interval workout (15 x 2 minutes at 100% VO2max with 2 minutes rest) compared to continuous exercise (60 minutes at 50% VO2max) (Laforgia et al., 1997; Treuth et al., 1996). The more intense the workout, the greater and longer the post-workout elevation in metabolism (expressed as the excess post-exercise oxygen consumption, or EPOC) because recovery is an aerobic process. However, the acute increase in metabolic rate following an interval workout should not be used as an argument for doing it, as the number of calories burned post-workout is still minimal compared to the number burned during a workout. Furthermore, while interval workouts have the capacity to burn lots of calories if designed properly, the caloric expenditure during a 20-minute high-intensity interval workout is still less than during a longer (e.g., 60- to 120-minute) but lower intensity continuous workout.

Recovery Intervals

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” (Seiler & Tønnessen, 2009). 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 rep.

During the recovery interval, the heart rate declines at a proportionally greater rate than the return of blood to the heart, resulting in a brief increase in stroke volume (the amount of blood the heart pumps with each beat). 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.

Designing Interval Workouts

Interval training manipulates four variables:

  1. Time (or distance) of each rep.
  2. Intensity of each rep.
  3. Time of each recovery interval.
  4. Number of reps.

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 clients’ fitness levels.

Aerobic (Cardiovascular) Intervals

One of the best methods to improve the capacity of the cardiovascular system—specifically, the heart’s ability to pump blood and oxygen to the active muscles—is interval training using reps lasting three to five minutes and recovery intervals equal to or slightly less than the time of the reps (see Sample Interval Workouts). The cardiovascular adaptations associated with interval training, including hypertrophy of the left ventricle and a greater stroke volume and cardiac output, increase your clients’ VO2max, raising their aerobic ceiling. Since VO2max is achieved when maximum stroke volume and heart rate are reached, the reps should be performed at an intensity that elicits maximum heart rate during each rep (see Figure 1). This type of interval workout, which is very demanding, is one of the best workouts a client can do to improve cardiovascular conditioning.


Figure 1: The increase in oxygen consumption (VO2) and heart rate (HR) during an interval workout. The goal is to reach and sustain VO2max during each rep. In this example, VO2max is reached briefly during the second rep and is reached sooner during the third rep due to the elevated VO2 at the beginning of the third rep.

Anaerobic Capacity Intervals

Anaerobic capacity refers to the ability to regenerate energy (ATP) through glycolysis. Reps lasting 30 seconds to two minutes target improvements in anaerobic capacity by using anaerobic glycolysis as the predominant energy system. These short, intense reps, with recovery intervals two to four times as long as the reps, 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 Intervals

Anaerobic power refers to the ability to regenerate ATP through the phosphagen system. Reps 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 motor unit activation and the activity of creatine kinase: the enzyme responsible for catalyzing the chemical reaction that breaks down creatine phosphate and donating the phosphate to ADP to produce ATP for muscle contraction.

Sample Interval Workouts

Incorporating interval training into your clients’ programs will dramatically improve their fitness. And if your clients train smart enough, not only will they be the fittest and have the hottest bodies of all their friends, they may even be able to outrun an Olympian (or at least grandma next door).

Sample Interval Workouts
Make sure your clients warm-up and cool-down
before and after each workout.

Aerobic (Cardiovascular) Intervals:

  • 5 x 3 minutes @ VO2max intensity (95-100% max HR) with 2½-3 minutes active recovery
  • 3 x 4 minutes @ VO2max intensity (95-100% max HR) with 3½-4 minutes active recovery
  • 3, 4, 5, 4, 3 minutes @ VO2max intensity (95-100% max HR) with 2½-3 minutes active recovery

Anaerobic Capacity (Glycolytic) Intervals:

  • 4 to 8 x 30 seconds at 95% all-out with 2 minutes active recovery
  • 4 to 8 x 60 seconds at 90% all-out with 3 minutes active recovery
  • 2 to 3 sets of 30, 60, 90 seconds at 90-95% all-out with 2 to 3 minutes active recovery & 5 minutes recovery between sets

Anaerobic Power (Phosphagen System) Intervals:

  • 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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