The following is Part 1 of our three-part series showcasing the difference between running with power or with pace. You can read Part 2 and Part 3 here. These excerpts come from Jim Vance’s book Run With Power.
How Training Becomes Fitness
The entire point of training is to cause changes in your body that make you better able to tolerate the stresses of your sport. Exercise physiologists have long told us that exercising at certain intensities will cause specific changes in your body. Running lots of slow miles will boost your aerobic endurance. We expect that running hills should make you better at running hills.
Eventually, your body figures out what’s going on. Doing the same workouts over and over will eventually stop causing adaptations in your body because your body grows accustomed to them. That’s what we call fitness. When you’re fit, your body has changed so that those same workouts are no longer stressful for your body. To your body, those workouts have become normal life.
So if you want to keep getting fitter, you have to keep challenging your body in the right ways to cause those changes that create fitness. If your workouts are too easy, your body won’t be challenged and won’t adapt to become more fit. If your workouts are too hard, you ask your body for too much, which can cause overtraining and injuries.
What we want is find the Goldilocks training zone: not too easy, not too hard, but just right. Over time, we want to schedule our training so we do enough hills, enough speedwork, enough tempo, enough easy runs, etc. that we mold our bodies to become fit for the races we’ve entered or whatever challenge we have planned.
How do we know when we’re challenging our bodies the right way?
It’s simply said: We must measure the stress of our workouts. Since exercise physiologists tell us that certain exercise intensities cause specific, corresponding changes in our bodies, we can cause those changes more easily if we can tune our workouts to be just the right intensity.
For as long as runners have been training, that’s been much easier to say than to do. Until power meters, it’s been difficult to accurately measure the amount of stress we cause our bodies during workouts.
How can we measure workout stress?
Volume: It’s easy to track training volume using time or distance. Simple tools like a stopwatch on a track or known course or a GPS watch make this a cinch. But volume is not a very accurate way to measure the stress a workout inflicted on your body. It just doesn’t tell you much, and it loses meaning when you begin comparing athletes of different fitness. Volume is too broad a measure.
Intensity: The research shows us that exercise intensity is the real key to fitness, but measuring the intensity of a workout accurately is much more difficult than measuring volume. The usual ways we measure intensity, such as a scale of perceived exertion, are subjective measures. Intensity is tough to measure objectively.
Heart rate: Heart rate doesn’t measure intensity directly; it just shows one biological effect of exercising. Heart rate is affected by factors unrelated to exercise like diet, temperature, caffeine, fatigue, medications, stress, electrolytes, and hydration. Heart rate is too variable and derivative.
Rating of Perceived Exertion: RPE asks you to assign a number to how hard you feel you are working, so by definition, your RPE can’t be wrong as a measurement of how your workout feels. But RPE is a subjective measure of how you feel, not an objective measure of how hard you are actually working.
There are many non-training variables that can affect how a workout feels. Exercise physiologists and neuroscientists have made progress in identifying them. They include many of the variables that affect heart rate plus psychological and social variables like running with a partner, competing with a rival, the presence of a crowd of spectators, listening to music, etc.
In many ways, RPE is still a useful tool because how you feel really does matter! But are you more fit if a workout feels easier? Not necessarily. You just might be feeling better than usual that day. RPE isn’t a reliable way to judge the physiological demands of the workout. In the end, RPE is just too subjective.
What Does Pace Really Tell Us?
Pace seems like the answer to our measurement problem, right? Pace measures how long it takes us to cover a given distance. Isn’t that all a runner really needs to know? Thanks to GPS watches, we’re so accustomed to seeing minutes per mile on our wrists that we’ve become a little brainwashed about what pace truly measures.
Pace is a measure of how long it takes to go a given distance. With pace, we know how fast the athlete is running, but we still don’t know how hard this is for her.
We also don’t know the terrain or wind conditions. Pace doesn’t reflect the extra effort of running uphill or the ease of running with a tailwind or into a headwind. Varying terrain and elevation can markedly affect pace. Finally, pace has a margin of error of about 5%.
Running a Hill: The Classic Illustration of the Flaw of Pace
Running a hill is the classic way to show the flaw of relying on pace. Pretend you are running on flat terrain at 9:00 minutes per mile pace and you approach a hill. As you run up the hill, you slow down. Your GPS watch shows your pace has dropped to 11:00 min/mile. What is your pace telling you?
Your pace is telling you that you have slowed down. That’s all. Your pace doesn’t know you’re running up a hill because all it measures is time and distance. Your pace simply predicts how long it will take you to run 1 mile at your current speed.
There’s more. On flat terrain, 11:00 min/mile is easier than 9:00 min/mile. But now you’re running up a hill and your watch is showing you a pace of 11:00 min/mile. Is your pace on this hill reflecting an easier effort? Is running up this hill easier than running on the flat?
Of course not! Running up hills is harder than running on flat terrain!
Or is it?
Yeah, it probably is, unless running up hill slowly is physically easier for you than running faster on the flat. In this example, we really don’t know and the pace displayed on your wrist doesn’t help. Your pace just shows your speed in real time. Based on your experience, you have to make a subjective judgment about your performance. (A power meter can tell you exactly what’s harder by showing your actual work output.)
Running Down the Other Side
Now let’s say you crest the hill and run back down the other side. You speed up and your pace falls to 7:00 min/mile. What does your pace show? It simply shows that it will take you 7:00 minutes to run a mile at this rate of speed.
Is running down the hill easier or harder than running up the hill? We know it’s easier, yet your GPS watch’s pace display seems to be telling you that you are running faster and therefore working harder.
Running a Hill with Constant Effort
Let’s try one more example. Pretend you’re running on level ground at 9:00 min/mile pace and approach a hill. You decide not to tire yourself out too much because you’ve got a long race ahead. You decide to use RPE to maintain your current effort level from the flat terrain as you run up the hill and down the other side. As you run up the hill, you must slow down to keep what you feel is the same RPE, so your pace might rise to 12:00 min/mile. As you run down the other side, you’ll have to run a lot faster to keep the same perceived effort level, so your pace will fall to 6:00 min/mile. As you hit level ground, your effort level remains the same as before, so your speed will return to your previous 9:00 min/mile pace.
Did your GPS pace show you how hard you were working? Absolutely not. By design, you were working at the same level of effort the entire time (or so you estimated from your subjective RPE).
You maintained a consistent level of effort going up and coming down, but compared to running on flat terrain, your pace makes it seem as if you were barely jogging up the hill and then running for your life back down.