Interval Training

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Once the training secret of the world’s best runners, interval training has become the new buzz term among elite and recreational runners alike. It seems as if everyone is doing it, from competitive athletes to grandma next door.  

Emil Zatopek of Czechoslovakia, who won the 10,000 metres at the 1948 Olympics and 5,000 metres, 10,000 metres, 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 Astrand discovered what many coaches and runners already knew – 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 Astrand’s simple observation is the basis for interval training.

One of the main reasons for all of the attention on interval training is that it can improve fitness quickly. Another reason is that 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).

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.” 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 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, 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 action from the tissues.

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.

Also during the recovery intervals, a significant portion of the muscular stores of quick energy – adenosine triphosphate (ATP) and creatine phosphate (CP) – that were depleted during the preceding work period is replenished via the aerobic system. During each work period that follows a recovery period, the replenished ATP and CP will again be available as an energy source.

Designing Interval Workouts

Interval training manipulates four variables: time (or distance) of each work period, the intensity of each work period, the time of each recovery period, and the 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.

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 work periods lasting three to five minutes and recovery periods equal to or slightly less than the time of the work periods (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 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 Intervals

Anaerobic capacity refers to the ability to regenerate energy (ATP) through glycolysis. Work periods lasting 30 seconds to two minutes target improvements in anaerobic capacity by using anaerobic glycolysis as the predominant energy system. These short, intense work periods with recovery intervals two to four 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 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 motor unit activation and the activity of creatine kinase, the enzyme responsible for breaking down creatine phosphate.

Incorporating interval training into your programme will dramatically improve your fitness. And if you train smart enough, not only will you be the fittest of all your competitors, you may even be able to outrun an Olympian (or at least grandma next door).

Sample Interval Workouts

Make sure you warm-up and cool-down before and after each workout.

Aerobic (Cardiovascular) Intervals:

  • 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

Anaerobic Capacity (Glycolytic) Intervals:

  • 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 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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