Posted by: Joe English | November 26, 2007

Training: how does speed-work make you faster and how hard should intervals be?

A reader posed the following question recently: how does speed-work make you faster and how hard should intervals be done?

Good questions. These are meaty topics, so just think of this as the “quick answer” to the questions. I’ll write more about pacing intervals next spring when more of you have this on your mind.

How does speed work make you faster?
When we’re talking about speed-work here, we’re talking about intervals run on a track. There are actually lots of other types of speed workouts, like tempo runs and spin classes on spinning bikes. But here, I’m talking about running intervals from between 400M-1,600M on a track.

The best way to think of this type of speed work is that it improves your running efficiency, which you may want to think of like the “gas mileage” of a car. When you run faster in your speed workouts, you get more efficient at running, both reducing how much energy you burn and increasing the speed that you remove waste products from your muscles. By running at faster speeds, you become more efficient at running at slower speeds.

Think of your body like a car for a minute. If your body gets 25 miles to the gallon when running your long runs today, adding speed work (intervals on the track) might help push your gas mileage up to 30 miles per gallon on those long runs. This will make your long run pace feel easier and you’ll consume less energy at that pace.

A lot of endurance runners, especially marathon runners, feel that they don’t need to do speed work. They say, “hey, why do I have to run fast when I’m going to be running slower in my marathon?” Here’s is the reason: when you’re doing speed work, you are pushing your body harder than your marathon pace, but then when slow to marathon pace this improved efficiency makes you feel better and the pace feel easier.

That’s why speed work is so important for endurance runners.

How hard should you do speed work?
The best way to calculate your pace in your speed workouts is to actually measure your capability and then have time goals for each interval distance. These times goals are set based on the results of a time trial (usually a 1,500M or 1,600M race) and then your pace estimates from each interval are calculated based on your capabilities. This is something that your running coach can help you with. (Shameless plug: click here for more information on coaching services.)

But if you’re not working with a coach, a good way to sense if you’re doing your intervals hard enough is that you should be breathing hard enough at the end of the interval that you can’t talk (or maybe only get out a word or two) for at least 15-20 seconds after the end of the interval. You don’t need to be pushing so hard that you’re passing out, but the pace should be hard enough that you are struggling to finish the interval and then you need to “walk it off” afterward.

The recovery time between the intervals is also a critical component to the workout. Most people take too much time between their intervals. What you want to do is keep your heart rate somewhat elevated throughout the whole duration of the workout. The recovery time then should just be enough to allow you to get your breathing back under control and then take off running again. You don’t want to fully recover between intervals.

I usually find the recovery time to be correct when I don’t think I can start (or don’t want to start) another interval until about 5-10 seconds before I start the next one, but in those last 5-10 seconds I feel ready to go again.

This recovery time will vary throughout the season and will depend on the distance that you’re running. At the beginning of the season, you’ll need more recovery time. As you get in better shape, you’ll need less. For many runners, two minutes is plenty of recovery between intervals. For well trained runners, the recovery time could be as short as 15-20 seconds – or the intervals could even become continuous (meaning jogging between them).

I’d add that if you’re doing speed work and you feel like “hey, let’s go again” right after you’re done running – then you are definitely not doing your intervals hard enough. If you spend five minutes chatting between intervals with your friends, then you’re taking too much recovery. It’s a fine balance.

Marathoners: just do them!
The key thing to remember is that all runners, especially marathon runners, should be incorporating speed workouts into their routine. Speed work is a critical piece of the puzzle that helps keep you going in those last miles of the marathon when you’re really being tested. When you’re hitting about mile 22 or 23 of the marathon, what’s being tested is your strength, your efficiency, and your mental toughness. Speed work helps build all of these areas.

Thanks to Kat over on Myspace for the question. As always, questions are more than welcome!

Coach Joe English, Portland Oregon, USA


  1. I’ve been marvelling at the times of these marathon competitors – 4-5 minute miles, even near the middle. Are there any tips you can give us on stride? Sometimes I feel like I’m putting a bounce into my stride – a leap forward, but this tends to wear me down faster. Is there an appropriate stride for runners to improve on their time?

  2. Good question. I’ll answer this for you in another article soon.

    Coach Joe

  3. Thank-you!

  4. I have the same question about stride. In general, what’s more effective over the course of a long race: Longer strides or shorter / quicker strides? Looking forward to any tips you have on this subject.

  5. Let me take that up in a seperate article.

    Running speed is a function of both stride length and stride rate. Stride rate (or cadence) becomes optimal at a certain point, above which it becomes more important to take longer strides.

    So the short answer is that most people first need to quicken their stride and then later will work on increasing their stride once they’ve reached an optimal cadence.

    Coach Joe

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