Interval Training

Heart lung fitness remains a cornerstone of physical fitness. Much has been written about regular moderate exercise to achieve stamina and weight control. However, training for recreational sport differs from fitness for daily living. Sport involves a change in speed, ranging from low, through moderate, to full speed. The pursuit of the opponent, the ball, puck, or other sport object forces you to go for it. This so-called “intermittent work” requires different sources of muscle energy, and warrants changes to your core fitness program.

Interval training is a series of repeated work bouts, usually lasting between 10 and 90 seconds, followed by active or passive rest. The right selection of interval speed, duration, recovery, and repetition leads to strong gains in one or more of the three muscle energy systems.

Sport: A Case Study

Take soccer: it requires sprinting, jogging, walking and standing. Time motion studies of elite women’s soccer, reveal that athletes sprint for only 15 percent of the game. The remaining 85 percent is spent jogging, walking or standing. A typical pattern involves sprinting for about 6 seconds followed by a 20 to 30 second period of active rest and recovery. Hockey is similar; skaters exert themselves for 4 to 7 seconds, then coast, using momentum to move around the ice. A pattern forms: hard work, followed by reductions in work, followed by active or passive rest; and, the cycle repeats itself.

A Tale of Three Energy Superpowers

The muscle physiology to fuel physical activity comprises three distinct energy systems: the “fast and furious” (anaerobic alactic); “high power octane” (anaerobic lactic), and the most common “long slow distance” (aerobic). The anaerobic galactic system, assumes maximum effort for 2 to 20 seconds, uses carbohydrates as a fuel source and does not produce uncomfortable amounts of muscle burning lactic acid. The anaerobic lactic system, assumes a maximum effort to fatigue, lasting between 30 seconds to 2 minutes, uses carbohydrates as a source of fuel, and produces the maximum amount of lactic acid. The aerobic system, is engaged for activities that are moderate to vigorous, lasting greater than 2 to 3 minutes, and that may last for hours. It uses a combination of fat and carbohydrates as a fuel source, and is involved in recovery from vigorous short term exercise.

Practice How you Compete

A principle of athletic training is known as “specificity.” This means that you should train as you compete. If your sport involves intervals, it is wise to follow train using this pattern. A recent study supports this view[1]. A sprinting-type program was compared to an endurance (long slow distance) type program. A third study group did a combination of sprint and endurance training. No surprises in the observed results. The endurance-trained group improved their 30 minute run time more than the combo or sprint trained group. The sprinting group improved the most in the 100 metre sprint. The study showed that it is possible to combine sprint training with endurance training and show improvements in both measures.

Interval training leads to the following benefits:

  • Increased number of blood vessels, leading to better removal of exercise by-products;
  • strengthening of the heart muscles, leading to increased output with each beat;
  • improved muscle oxygen uptake during exercise;
  • improved performance, in particular within the cardiovascular system.

Researchers from Canada’s McMaster University observed these results about a study of interval exercise:[2]

  • A stationary cycling program, three times per week, comprised 4, 30 second intervals, followed by a 4 minute recovery;
  • By the seventh (7th) week, the number of intervals had increased to 10, while the rest intervals were gradually reduced to 2.5 min;
  • Maximal oxygen uptake (one of the leading measures of heart lung fitness) increased 9%;
  • In the first week of the program, each training session lasted 14 min, and the rest to work ratio was 8 to 1; and,
  • By the seventh (7th) week, the length of each training session had increased to 30 min, and the rest to work ratio was 5 to 1.

In summary, a small amount of interval training leads to impressive gains in heart-lung fitness. By the end of the seventh week, the people were performing only 5 minutes of work (10 reps x 30 seconds each). Good news: it takes weeks, not months or years to show benefits.

A team from Japan’s National Institute of Fitness and Sport found that a high-intensity intermittent training program achieved bigger gains in VO2max than a program of steady cycling.[3] Two groups: group one performed 60 minutes of moderate intensity exercise @ 70% of aerobic capacity, for a total of 5 hours per week. Their maximal aerobic capacity increased 9 percent. Group two, trained with the interval method: eight all-out work bouts, each lasting 20 seconds with 10 seconds of rest. This group cycled for a total of only 20 min per week, yet their VO2max improved by 15 percent.

Weight control programs are often linked to exercise programs employing long duration, modest intensity activities. The deal: exercise for 30 to 40 minutes and burn fat as a fuel source. Equipment vendors promote the notion of a “fat burning” zone; as if the only to lose fat is to work at a certain exercise heart rate. The following study indicates something very different, and uses good old interval training.

Here is the program, and the results:

  • Two groups, one on a standard running program, steady pace for 30 to 45 minutes, and one interval trained group;
  • 20 week program, using an exercise cycle;
  • Interval group did 19 x 60 to 90 second intervals @ 60 % of maximum output, and 16 x 10 to 15 second @ 70 %, increasing 5 % every 3 weeks;
  • Recovery was complete when heart rates returned to 120 to 130 beats per minute;

The results:

  • The long slow distance group expended twice as many calories during the workouts as the interval training group;
  • Both groups lost an equal amount of body fat mass;
  • The interval group lost 3 times as much sub-cutaneous fat (skinfold measures) as the long slow distance training group.

Building the Interval Training Program

Here is a typical exercise prescription for an interval training workout. Let’s discuss the components.

  • 6 x 30 seconds sprints @ 80 % max output or speed; rest pauses of 120 seconds; rest:work ratio of 4 to 1.

This prescription, in plain language, says perform six, 30 sprints at 80 % of the maximum speed for a 30 second run. Rest 120 seconds (2 minutes) between each repetition. When we divide the work (30 seconds) into the rest period (120 seconds), we observe a rest to work ratio of 4 to 1.

To improve, or decrease the level of difficulty:

  • increase the number of repetitions;
  • reduce the amount of rest between repetitions (use the heart rate to determine if enough recovery has been taken to do another sprint, once a rate of 120 is achieved, depending on age, repeat the sprint);
  • Increase the speed or intensity of the work intervals; and / or,
  • Increase the number of workouts per week.

Adjust the interval training variables depending on your goals:

To achieve this… Do this…
Aerobic Capacity Intervals of 60 to 90 seconds;Rest to Work Ratios from 3:1 to 2:1Intensity @ 80 to 85 % of maximum effort

Reps: 2 to 3

Sets: 2 to 3

Increase number of reps

Shorten the recovery period

Anaerobic Lactic Capacity Intervals of 30 to 60 secondsRest to Work Ratios of 5:1 or 6:1Intensity @ 85 to 90 % of maximum effort

Reps: 3 to 6

Sets: 4 to 6

Increase the speed for the interval

Anaerobic Alactic Capacity Intervals of 10 to 30 secondsRest to Work Ratios of 5:1 to 12:1(more recovery leads to more quality and power, less endurance)

Intensity @ 85 to 90 % of maximum effort

Reps: 6 to 9

Sets: 4 to 6

Lengthen the amount of recovery

Increase the speed for each interval


Developed inSweden, for years, athletes have done “Fartlek.” It means an unstructured approach to changing the pace of workouts. Consider a 30 minute skate, bike or run. After a few minutes, pick up the pace for 20 to 30 seconds, then move to a slow jog for 60 seconds. This gives you more recovery. If you feel frisky, do the slow jog for only 30 seconds, giving yourself a work to rest ratio of 1 to 1. Then, as you feel the need, change the length of the intervals to say 60 seconds or 15 seconds, always allowing at least a rest to work ratio of 2 or 3 to 1.

The Annual Plan

Research and best practice suggest that doing the same fitness program week after week, will not produce maximum training results[4]. Enter the notion of “Periodization.” An annual program often has three main phases. Phase one is performed during an athlete’s “off-season,” and consists of several months of moderate intensity, long duration exercise (60 min or more per session). The athlete then enters Phase two, involving two interval sessions per week. These interval sessions replace two of the moderate intensity workouts. The work bouts during these interval workouts should consist of an intensity corresponding to race pace. For example, a typical program for distance cyclists includes eight work bouts (all carried out at race pace) each lasting 4 min with rest intervals of 90 s. Phase three, which begins approximately 21 days prior to the big event, involves high-intensity intermittent training at maximum effort, done three times per week, and includes 12 work bouts lasting 30 s, with rest intervals of 4-5 min. Notice the rest to work ratio of 8 to 10 to 1: lots of recovery to ensure great performance. Cross-country skiers showing little improvement in competitive performance after a year of high-volume low-intensity training made big gains using high-intensity intervals, with a volume reduction in low-intensity training.[5] The conclusion: interval training works.

[1] Calllister, et. al. “Performance Adaptations to Sprint, Endurance and Both Modes of Training,” Journal of Applied Sport Science Research, Vol. 2. No. 3, 1988.

[2] MacDougall JD, et. al. “Muscle performance and enzymatic adaptations to sprint interval training.” Journal of Applied Physiology, 84, pp. 2138-2142, 1998.

[3] Tabata I, et. al., “Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max, “ Medicine and Science in Sports and Exercise, 28, 1327-1330, 1997.

[4] Hawley JA, Myburgh KH, Noakes TD,Dennis,SC  “Training techniques to improve fatigue resistance and enhance endurance performance.” Journal of Sports Sciences, 15, 325-333, 1997.

[5] Gaskill SE, Serfass RC, Bacharach DW, Kelly JM “Responses to training in cross-country skiers.” Medicine and Science in Sports and Exercise, 31, 1211-1217, 1999.