Q&A: The Fourth Question – SpeedworkTempo Runs vs Interval Training, Part I

Now that we understand why it’s important to run slow(er) on your long runs (which, like many of you, I struggle with constantly), let’s move on to talk about a subject that I’m much more familiar with and love talking about…SPEEDWORK! My inquisitive reader continues…

Second, I have noticed (or I think I have) you don't do interval trianing for marathons, is that right? Just curious to your philosophy behind tempo runs vs intervals for marathon training. If you do both, when you do them? I feel like tempo/lactate threshold runs really help me out, but my training schedule doesn't have them towards the end. Instead, it goes into VO2 max intervals.

First of all, I’d like to commend my reader for another great question. She always asks the best questions, doesn’t she? In fact, the question is so awesome and the answer so important to everyone hoping to BQ or just run faster in marathons in general that I’m going to tackle this topic in two parts. In part one, I’ll try to explain, in layman’s terms, what tempo (or lactate threshold) running and interval training are and what physiologic roles they play in development of a marathon runner. Then, in part two, I’ll share how I’ve used each of those speedwork components in the past in my own marathon training as well as give some general guidelines on how you can incorporate them into your own training plans.

Part I – What is tempo training, why run intervals, and why should I care?

A. Tempo Runs

Anyone who has ever tried to run a race for time knows that the last mile is always harder and requires exponentially more effort to run than the first. The main reason that occurs is because as the distance increases while our physical exertion is kept at race effort, more and more lactic acid is being produced locally in our leg muscles and at a faster rate than what our body can do to metabolize and carry them away. As a result, we feel increasing fatigue and the inherent performance properties of the muscles decreases tremendously. That’s why it takes much more energy to pick up the pace and sprint in the last mile than it does to start a race at that same speed. A tired muscle full of lactate is the mortal enemy of runners because it not only results in pain and fatigue but the muscle itself just doesn’t work as well either. Tempo training then is the mechanism by which we adapt our bodies to running at a faster pace while still maintaining good efficiency so that we can delay the onset of lactic acid production begins. In other words, since lactic acid is a byproduct of anaerobic (without oxygen) respiration, we will minimize the rate of lactic acid production if we keep our running above the pace at which lactic acid is produced, which is referred to as the lactate threshold.

The purpose of a tempo run, or a lactate threshold (LT) run, as it is sometimes called, is to increase anaerobic threshold. They are run at 85-90% of your maximum heart rate, which translates to about 10-20 seconds per mile slower 10K race pace. They are usually done over 4-6 miles (~20-40 minutes) or even longer at peak training after an appropriate warmup, to be followed by a suitable cooldown.

B. Interval Training

Intervals on the other hand, are much shorter and are run much quicker. They are short segments (400m-1600m) run back-to-back at 95-98% of maximum heart rate (or about 5K race pace) with a recovery time equal to the length of the interval run time between each segment. Depending on the session and the length of each interval, a typically interval workout would involve running 3 to 8 of these segments, again with sufficient warmup and cooldown. For example, since my 5K pace is 6min/mi, my interval workouts are usually 3 or 4 x 1600m at 5:50-5:55 with 6 minutes of rest in between.

The purpose of interval running is to increase VO2max and the aerobic capacity. VO2max is the maximum speed at which oxygen can be absorbed by the lungs and delivered to the working muscles. I likened VO2max to the top speed of a car. Since nobody can sustain running at 100% of their absolute maximum speed for very long, this is intended strictly as an anaerobic workout. For this reason, the important point to remember when running intervals is to keep each segment short with an effort close to but not “all-out” and with sufficient rest time in between each segment to allow for proper recovery.

C. A Conceptual Model

In order to help some of you who are new to speedwork better understand the similar but distinct benefits of tempo and interval training, I’m going to use the functional model of our lungs as a conceptual model.

Ordinarily, going through the normal activities of daily living, we take about 12-20 breaths a minute, using about 25-40% of our lung capacities. With exercise, both of those parameters must increase to fulfill the oxygen requirements our muscles need to sustain the workout. Without even realizing it, we take deeper breaths and increase our rate of respiration to match the physiologic demands of our body. Although it would seem logical that the product (Lung Volume x Repiratory rate) should equal the oxygen requirement during exercise, this is not the case because our body is somewhat inefficient at utilizing all the oxygen absorbed by our lungs during each respiratory cycle. As such, the real formula for the metabolic quotient is more like (Lung Volume x Respiratory rate x Percent Efficiency). Therefore, we always must breathe a little deeper and a little harder to compensate for the inefficiencies of the system in order to get the job done.

Okay, so what does this have to do with speedwork, you ask? Well, speed training in a nutshell alters the mechanics of the body to make the system work a little better during intense exercise. Tempo training specifically increases the efficiency by which oxygen is utilized during each respiratory cycle, while interval runs increases your maximum lung volume so that you can (theoretically) take deeper breaths as you run. So as you can see, both types of speedwork work on different factors of the metabolic quotient to increase our ability to handle faster and longer runs and delay the appearance of lactic acid and fatigue.

(For the experts among us, I realize this is an over-simplified description of the benefits of speed training, but I’m just trying to explain the basics so people who are not so familiar with these concepts can understand the terms a bit better. There will be more resources at the end of this post for those who want to dig deeper and explore all the technical details.)

D. Tempo Training or Interval Runs, Which is Better For Marathoners?

Okay, so if interval runs increase VO2 max and our overall top speed and tempo training increases running efficiency, don’t they provide similar benefits for marathoners looking to run faster and improve their times? The answer might be surprising to some (it was to me when I first started training) but no, they really do not provide the same benefits. There are several reasons for this. First, the effort required to maintain a race pace over 26.2 miles is more similar to the sustained effort put forth in a long tempo session than to the quick energy bursts necessary to run short fast intervals. Second, since marathon pace more closely resembles tempo pace than interval pace, the specificity of training is higher when training at tempo speed because it teaches the body to practice at an effort close to what will be required on race day. Third, because running a marathon is almost entirely an aerobic exercise, it makes sense that we would have better results if we spend more of our time training under aerobic conditions (tempo training) rather in anaerobic conditions (interval training). The fourth, final, and in my mind the most important reason that tempo training is much more beneficial to marathoners than interval training is due to the fact that those of us who are pretty consistent runners and have done some racing/speedwork in the past are already running close to our physical VO2max anyway, so that the tiny incremental increase we might expect after intense interval training really doesn’t contribute that much to our overall running speed. (Remember that in practice, we spend very little time running close to our VO2max anyway, especially during a long endurance event like a marathon.) We get greater returns for our time and effort when we teach our bodies to become more efficient at oxygen transport and delivery, which is the crux of tempo training.

However, a word of caution. Although I’ve been singing the praises of tempo training and agree in principle that it should make up the bulk of speedwork during marathon training, a few interval sessions in between all the heavy miles can actually be quite helpful. Interval training not only reminds the body once in a while how to run fast (and yes the body operates on a use-it-or-lose-it physiologic model) but it also helps to correct posture and form problems when running (mainly because the body instinctively reverts to the most efficient running form when running at top speed). In fact, when I’m at the peak of marathon training and find myself running a lot of sluggish miles, I will often run an impromptu interval session to wake up the fast-twitch muscles, correct my posture and re-establish good running form. So yes, even if it plays second fiddle to tempo runs as far as marathon preparation goes, interval training is still important and deserves to be incorporated into every good marathon training program.

That concludes my introduction to speed training for marathoners. For those who are new to speed, I'd just like to say, What are you waiting for? For your sake, I hope I clarified the terms a bit and didn’t confuse things too much. (If I did, please ask either in the comments or by contacting me. Remember there are NO stupid questions!) In the next post, I’ll give examples of what I’ve done in terms of speedwork during marathon training and discuss a bit how to fit them into your own training plan. Thanks for reading and happy running.

For those who would like to read more into the topic of tempo training vs interval training as it relates to distance running, please visit the following sites for additional information:

Pete Pfitzinger: Improving Speed for Distance Runners

Planetultramarathon: The Merits of Tempo vs Interval Running

Stephen Seiler PhD: The Time Course of Training Adaptations