Interval Training

Sara Fleming

*This is an excerpt from our textbook.  For more information on the science of interval training, see this comprehensive review of the research by Stephen Seiler.

High intensity interval training is a very popular training tool used in a lot of gyms.  The short duration and high intensity nature makes working out hard a bit more palatable for a lot of folks.  The short term improvements to the aerobic system increase one’s conditioning level very quickly, but only to a certain degree.  Although interval training is powerful medicine, it is no substitute for developing a substantial base of limit strength and aerobic capacity.  Interval training is only as powerful as the base that supports it.  Training at high intensities can be psychologically satisfying for many clients, but as a long-term training plan is not ideal.  Fun and satisfaction are important for our clients, but as a trainer, make sure you are using an appropriate amount of intensity and that the base you are building is substantial enough for the goals you are working towards, even if those goals are simply general fitness.  When used appropriately, interval training should not be utilized more than once or twice a week.  Its purpose is to enhance the base, not to be the base.

It is important to note that if a person has a desk job or is largely sedentary, working out intensely for 20-30 minutes does not increase their activity level significantly.  In fact, a person could run for an hour every day and still be considered sedentary if the bulk of their time is then spent sitting at a desk in front of a computer.  What changes this?  Simply getting up and moving, walking, or even playing golf.  For overall fitness, Intensity is important, but Volume is king.

Use of intervals in training beginners

Circuit training is great for beginners, but quickly
becomes limited to just cardio and strength endurance
as fitness levels increase.

Intervals can be very useful in training a broad range of individuals, but appropriate application is a must. For the beginner trainee, breaking a work period into smaller units can make the training session less overwhelming both physically and psychologically. A beginner exerciser will typically not be able to sustain the kinds of intensities that will elicit a positive change in body composition and/or overall fitness levels. Incorporating the concept of pacing intervals into a beginner’s workout will allow for more work to be done for longer. As a trainer, you must control the intensity of these sessions as it is easy to push the individual too hard too soon. Keep the rest periods short, 1-2 minutes so that the relative intensity stays low.

Because beginners will tend to improve most qualities of fitness simply by engaging in a new activity, circuit training is a very effective tool for the beginner. Circuit training with exercises that target different body parts deliver the effect of interval training in that the body parts not emphasized by a particular exercise will be able to “rest” while using another exercise. For beginner circuit training, use a relative intensity for the works sets such that by the completion of the work period or set of repetitions, the individual is starting to feel taxed, but still feels relatively strong and form is intact.

Either prescribe a rep range (6-10, 10-15) or a timed work period for each exercise and emphasize consistency between sets. For example, the workout is four minutes of total work broken up into one minute segments. During each segment, a different exercise is performed. The set is followed by one minute of rest and repeated 5 times. If the exercises are kettlebell swings, goblet squats, pushups and jump rope, you would want the exerciser to count the total number of reps of each exercise during the first round and try and repeat those numbers for each subsequent round. If the numbers fall off dramatically, the initial intensity was too high. If the number stay the same or go up, the initial intensity may have been too low.

Likewise, if simply training an individual to run, bike, or row a certain distance, you can use intervals to supplement and/or augment your base training. Start by dividing that distance up into manageable chunks such as 100, 200, 400, or 800 meters. Again, you want the relative intensity to be such that only a minute of recovery is required before beginning the next interval. Emphasize form, technique, and pacing during these intervals. The purpose of these intervals is to increase the individual’s ability to maintain a good pace with good form for longer periods of time. If the individual is unable to maintain the same pace for the prescribed time period, the interval is too long or the individual is not ready for true interval training. In this case, you can use “fartlek” intervals to help the individual make gains in both distance and speed.

Fartlek training is an unstructured method of interval training that allows the individual to vary pace and distance as needed during a set period of time. For the beginner endurance trainee, the ability to transition between slower and faster paces, for example a walk and a jog, will allow the individual to slowly work up a faster overall pace. Thirty to forty-five minutes is a good minimum work period for this type of training.

Use of intervals with intermediate athletes

In training for the Tough Mudder, we built our base first with
long steady distance training.  We could then use
sprint intervals to improve speed and stamina.

Intermediate athletes can begin to benefit from the use of VO2 max intervals in addition to cruise intervals. In these individuals, the relative intensity for these intervals will be higher than in the beginner because they are capable of sustaining more intense efforts. Interval training is no substitute for base training and should serve to help break through training plateaus. Interval intensity should be higher than one can sustain continuously and quality of movement is the priority. Using high intensity intervals with poor form will only result in form breakdown at high intensities. The purpose of using intervals is to sustain proper form, move more efficiently, and be able to compete in a more relaxed state.

The relative intensity for cruise intervals in the intermediate athlete will be higher than in that of beginners. Intermediate athletes should be able to sustain higher intensity efforts with less recovery time than beginners. VO2 max intervals, where the rest period is as long as the work period should be at an intensity that is on the edge of being unsustainable, but stops before form breakdown occurs. As the individual gets closer to one’s genetic capacity for improving VO2 max, VO2 max intervals become more about sustaining good movement economy at higher intensities. This enables the athlete to move in a relaxed and efficient manner at top speed on race day. Pace and form breakdown are fatigue indicators and should dictate the length of the interval for both of these intervals.

Circuit style workouts, including barbell complexes and strongman medleys, in intermediate and advanced athletes should not based solely on time, but should take into account load and total volume. The higher the intensity, the shorter the work period should be. Excessive training repetitions due to inappropriate resistance or longer work periods can lead to overuse injuries and may impair strength gains. If using rest periods in your strength conditioning work, use a heart rate monitor to gauge when the rest period is over. For improvements in VO2 max, the heart rate must return to an exercise baseline (generally between 120-150 bpm) before engaging in the next interval. Without this drop, appropriate intensity and volume with good technique cannot be reached on the following interval. Again, form and consistent pace are a priority with conditioning workouts.

Take home points

  • Intervals should emphasize quality, not quantity.
  • Beginners do not need to work at higher intensities until they develop a solid base of strength, endurance, and cardiovascular fitness. Intervals for beginners serve to break up the work period such that they can sustain their total efforts for longer periods of time.
  • If pace slows or form breaks down before the prescribed work period is over, the interval is too long or there are too many intervals in the training session.
  • High intensity interval training can help break through plateaus in work capacity, but having a solid base of strength, endurance and technique provides the platform for improvement to happen. The bigger your base, the bigger your benefit.

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