Running Intervals - How and Why

Synopsis: Running Intervals - How and Why explains what intervals can do for your training and how to do them.  This includes explaining the right pace, duration, and recovery.  It also describes the benefits and why the specific paces and durations prescribed are best.

If you are reading this, I have to assume that you want to run faster and are curious about how to do it.  Intervals were discovered as a training tool more than half a century ago but have endured to this day because scientific studies and individual experience have shown them to be very effective.

Intervals are a major tool in training for race performance.  They can lead to much faster times.

What are intervals?

Intervals are workouts that consist of a hard effort followed by an easy effort repeated several times.  The interval, technically, is the easy portion or the break between hard efforts.  However, that distinction has been pretty much lost over time.  The concept of the workout is that you run a hard effort of about 3 to 5 minutes.  This is followed by a recovery of 2 to 3 minutes, which is enough time to slow the heart and "catch your breath" before the next hard effort.  This is repeated several times.

A typical interval session might be 6 x 800 with a 400 jog recovery.  What does this mean?  It means you run 800 meters or 880 yards (2 laps on a track) at a fast pace followed by 400 meters or 440 yards (1 lap on a track) at a very easy pace to recover.  The "6 x" means that you repeat this pattern 6 times.

These workouts can be done on a trail, a track, or the roads.  They are often done on a track, only because the distance is known.  Knowing the time and distance allows you to control the pace and effort.  However, if you know your pace well enough or have a GPS, they can be done anywhere.

What is the right pace?

For the fast portion of your intervals you should be running at your 2 mile race pace.  If you don't know that pace, but have run a recent 5K, subtract 10 seconds per mile from your 5K race pace.  If you haven't run either one recently, go to our race prediction table and use the predicted 2 mile pace, or just do a 2 mile time trial, run as hard as you can.

Why this pace?  This pace maximizes your time at Max VO2 which maximizes the benefit of the workout.  This pace is fast enough to reach your Max VO2 within about a minute or so.  However, it is just easy enough that you can do multiple hard repeated efforts without running yourself into the ground or having to slow down or quit the workout early.  If you slow down a bit, you won't reach your Max VO2.  If you speed up a bit, you will slow down or quit entirely after a few repeats.  This pace maximizes the total time at maximal effort.  This has been shown in multiple scientific studies.

For the slow, recovery effort go slowly, very slowly.  The idea is to jog (or walk part of it if you must), but to go slowly enough that you recover some before your next hard interval.  However, you don't want to walk the entire recovery.  You don't want your heart rate to go back to your resting pace, just to get "off the roof" or out of your maximum range.

What is the right duration?

Each hard interval should be about 3 to 5 minutes.  Why this time?  It takes a minute or more to get to your max heart rate.  This makes short intervals like 1 minute or 2 minutes much less productive.  You only get a minute or less at your max heart rate for each interval completed.  However, each hard interval is going to wear on you.

If you go longer than 5 minutes, the effort is just too hard.  Remember, this is your race time for 2 miles.  This is flat out for 10 to 20 minutes, depending on your pace.  The idea of this workout is not to race over and over.  That is stressful and will leave you flat by the second or third interval.

Studies have shown that with an effort in this range and this duration, a well conditioned runner can repeat this several times.  If you do 5 minute intervals, you are getting perhaps as much as 4 minutes at max heart rate.  If you can do this 5 times, you will have accomplished 20 minutes at your max heart rate.  That is a best possible effort for any but the most elite athlete and will provide a huge benefit in your conditioning and future Max VO2.

The purpose of this workout is to spend as much time as possible at your Max VO2.  This is accomplished by running 3 to 5 minutes at a fast but controlled pace, followed by a recovery, and repeating this several times in order to maximize your time at your max heart rate / Max VO2.  Run at your 2 mile race pace for 3 to 5 minutes, then repeat after a 2 to 3 minute recovery!

Note that some runners use shorter intervals.  Intervals like 200's or 400's can be very useful for middle distance runners because they are run at their race pace.  This helps with efficiency.  However, runners training for distances of 5K or longer will want to focus on the longer intervals described (3 to 5 minutes).  These longer intervals are fast enough to gain efficiency by running at race pace or faster, but provide much more time at max VO2 effort, which maximizes the aerobic benefit.

Why run intervals?

Intervals are a way to stress your body without killing yourself.  They are hard, but the total work load achieved is much greater than you could do in a single steady run, at least on a regular basis.  They are much less stressful than a race, but provide a similar benefit.

Why stress your body?  Because that is the way you improve.  The basis of all improvement in body development or sports endurance is stress and recovery.  When you stress your body, you push it to near its limits.  When you recover from stress, it not only heals itself, it builds itself back stronger than ever.  This is the basis of all sports that develop the body.  Body builders do it and runners should too.  You are not trying to build bulky muscles, but the same principle holds for how to develop your body.  It is how the body gets stronger.

But why intervals?  Scientific studies have shown that by pushing yourself to your Max VO2 (maximum oxygen uptake, which is essentially your maximum heart rate also), you expand your capabilities; you improve your body's capability to take in and utilize oxygen.  Intervals allow you to stay at or near this maximum limit for longer than any other workout.  By doing this, you maximize the benefit.  There is no better workout for improving your body's capability to take in and use oxygen at a maximal level.  This is what makes a great miler or 5K runner.  It is less significant for a marathoner, but still important, since all other measures tend to be linked to your maximum capability.

Putting this into a complete training schedule:

Most runners will want to run intervals once per week to once every two weeks, depending on where they are in their seasonal cycle.  Elite runners may get to the point of doing intervals twice per week.  However, most recreational runners will want to limit the stress to once per week and maybe even substitute a race for the interval workout.  A 5K or 10K is also a Max Vo2 workout.  Our recommendation is to first read "Training Basics", which explains how this fits into a complete plan, and then to proceed to the plan that works for you, perhaps "Training for the Serious Runner (5K to 15K)" or "Marathon Training - Intermediate".

Good luck and maybe intervals will help you to that PR!  They are a key ingredient in any successful training program.

Copyright 2009 by Florida East Coast Runners and Frank Norris.  Reproduction or reprinting without written permission is illegal.

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