By VeloPress with excerpts from RUN WITH POWER by Jim Vance.
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.
Windy, hot, or cold conditions can also affect pace negatively or positively, adding to the challenge of quantifying the intensity. Let’s say you are running on flat terrain on a windy day and your goal for today’s workout is to run hard intervals. To hold your prescribed interval times, you might feel as if you’re working much harder than on a calm day because of the wind. And you’d be right, but your pace wouldn’t show it because you held your times.
Pace Measures Speed, Not Intensity
The truth is that pace measures time and distance. Using pace is just like using a stopwatch that knows how far you’ve run and which does the speed calculation for you. Pace measures speed, but as you can see from the hill example, speed does not necessarily equal effort.
Why Does It Matter?
All of these tools are helpful in creating a snapshot to measure fitness, and yet none of them give us an impartial way to monitor training intensity with repeatable precision.
But when we measure stress incorrectly, our training suffers:
- We become more vulnerable to injury.
- We may not recover enough between workouts (or vice versa).
- We may do a workout at the wrong intensity and get the wrong adaptations from it (or no adaptations).
Any one of those setbacks can derail your training.
How Is Power Better?
What we need, clearly, is a better way to measure the stress we are inflicting in our daily training routines. And that’s exactly what the power meter provides, and it is why the power meter has the potential to revolutionize your run training.
In its simplest form, a power meter measures the force your feet put into the ground. That’s it.
A running power meter measures exactly how hard you are working and nothing else. It ignores all other variables. A power meter doesn’t care how much sleep you got last night, how much coffee you drank this morning, how hot it is outside, how steep the hill is, if it’s windy or calm.
Your power meter only sees one thing: how much power you’re putting out.
Your power meter directly measures the work you are doing during your workout. No other metric or tool can do that. All those other measurement tools just approximate our level of effort. Power eliminates the guesswork.
Since the research shows that working out at certain levels of effort causes specific changes that make us fitter, being able to accurately measure our workouts means we can be more precise in our training. Power meters can make every workout count more.
With a power meter, no longer will you wonder whether you are meeting the intensity, recovery, pace, and volume goals of your training plan. Instead, you will erase any doubts about your training, and you will be able to monitor changes and improvements in every aspect of your running fitness.
Power Is King of the Hill
Let’s head back to the hill for a workout with pace and then with a power meter. You’ll run normally this time, running a little harder up the hill and a little easier down the other side. Your GPS watch pace will show 10:00 min/mile heading up, 9:00 min/mile at the crest, and 8:00 min/mile heading down. From the perspective of your GPS watch, it will seem as if you slowed down, sped up, then sped up even more. Your pace will make it seem as if you were doing less work, more work, and then even more work, although the opposite is true.
What will your power meter show? Within a few steps into the hill, your wattage number will rise and plateau, showing you how hard you’re working as you head uphill. As soon as you hit the crest of the hill, your power will drop, then as you begin descending the hill, it will drop some more until it levels off at a lower wattage number. As you hit level ground, it will rise somewhat and level off at this new normal power output.
Your power meter will show you how hard you are working in real time. Since the goal of training is to exercise at specific levels to cause specific changes, only the power meter can accurately measure your effort on this hill and show you if you hit the right levels.
Take a look at this illustration from Run with Power:
A Workout with Pace and Power
Now let’s try a workout with pace and then with power. Pretend you’re training for a marathon with a goal finish time of 4 hours, which is 9:00 min/mile pace. You’ve just run a 2-mile warmup and plan to run a 2-mile cooldown.
Today’s workout is a strength workout (borrowed from Hansons Marathon Method):
6 x 1 mile at 10 seconds faster than race pace with ¼ mile jog recovery
Based on your goal finish time, you would run the mile intervals at 8:50 min/mile pace.
There are dozens of ways this hypothetical workout could go:
- Maybe you love training on treadmills so you could perform this workout with utter precision and control.
- You might live near a community track or in a pan-flat, windless area that’s always 65 degrees and be able to perform this workout exactly as prescribed.
- You might run on the actual race course for your upcoming marathon, making this workout nicely specific.
- You might live in an area with lots of rolling hills, every one of which distorts the intended intensity of the workout above.
Chances are, you run where you live and that means you have at least some variation in the terrain and weather. In any case, how would you get the most out of this workout? If you’re like most runners, you’d ignore all the variables and run exactly 6 x 1 mile at 8:50 min/mile with ¼ mile jog recoveries. Here’s how that might look:
- On the treadmill: You nailed the workout, performing it exactly as described. But is it worth doing all your workouts on the dreadmill?
- On ideal running terrain: Congratulations on your selection of hometowns! You nailed the workout.
- On the actual racecourse: In this case, your race day plan is probably a tempo run, not intervals. But kudos for specificity!
- On rolling hills: You could be in trouble. On the uphills, you were holding your 8:50 pace, meaning you were working much harder than the workout intended. On the downhills, you were just coasting along. Does it all even out? No, not really. Your workout called for a intensity and duration equivalent to exactly 6 x 1 mile at 10 seconds faster than race pace with ¼ mile jog recovery. You nailed the duration, but your intensity was all over the map.
Now put on your power meter and try this workout again.
Using a power meter, this workout could be written this way:
6 x 1 mile in Zone 3-4. Recover between intervals with 2 min. jog/walk in Zone 1-2.
Here’s how this workout would look:
- On the treadmill: You nailed the workout, performing it exactly as described. Now you also have feedback (and hard data) on your running form efficiency and can compare it to your pace, RPE, and heart rate. Again, is it worth doing all your workouts on the dreadmill?
- On ideal running terrain: Kudos on your choice of hometowns! You nailed the workout and you have a lot of power data you can use to improve efficiency and monitor performance over time.
- On the actual racecourse: In this case, your race day plan is probably a tempo run, not intervals. But kudos for specificity! Your power meter gives you hard data on exactly how hard you’ll need to work on race day on this section of the course to hit your goal time. This is invaluable knowledge.
- On rolling hills: You nailed the workout. How? You adjusted your pace going uphill to stay in Zone 3 or 4. You increased your pace going downhill, too, to maintain the ideal intensity of Zone 3 or 4. Same with the recovery intervals. In this example, your power meter enabled you to perform this workout as written, despite the terrain.
In all these scenarios, you were able to perform the workout correctly, but three of those scenarios are pretty unlikely. Most runners enjoy running outdoors. Most of us live in places that aren’t pan-flat and windless. And a major difference in using a power meter is that you know you did the workout correctly. It eliminated all doubt, even on the hilly terrain.
Windy Hills Are Just One Limited Use for Power
The power number on your wrist gives you instant feedback on your workout intensity and your running form efficiency, but it’s just one way to use the power meter for running. The power meter can unlock your potential in vastly more powerful ways as you use it over time to monitor changes in your performance.
In all the workout examples above, you’ve taken a baseline measurement of your direct work output for a strength workout of this structure. By boiling down your workout intensity to a single number, your wattage, you can compare it to the other data, like speed, to begin understanding yourself as a runner in all new ways.
For example, perhaps you ran your early intervals with a higher speed per watt ratio. This means your earlier intervals were more efficient and your form broke down a little toward to end of the workout. Why is this? Only you or your coach can interpret the data your power meter reveals. Maybe an old injury was bugging you a bit in later intervals. Your power meter shows that it adversely affected your form, so maybe it’s time to revisit therapy to heal that injury.
Efficiency: Speed per Watt
Jim Vance’s concept of “Efficiency Index” is a simple ratio that GPS watches cannot measure. The EI measures the ratio of your speed against your power output. Runners who can squeeze more speed out of the same power have become more efficient runners, and as well all know, efficient running form can be a critical determinant of race performance, particularly in longer race distances.
Measuring Your Training Matters
If you care about your running performance, you need to care about how you measure your workouts. Put simply, there’s no better metric for runners than power. Pace, heart rate, and RPE give us part of the picture, but adding power to those measures gives runners and coaches unprecedented insight in your workouts and your fitness.
In what other ways is running with power different from running with pace? Please add your comments and questions below!
RUN WITH POWER is the groundbreaking guide you need to tap the true potential of your running power meter like SHFT, Stryd, or RPM2. From 5K to ultramarathon, a power meter can make you faster—but only if you know how to use it. Just viewing your numbers is not enough; you can only become a faster, stronger, more efficient runner when you know what your key numbers mean for your workouts, races, and your season-long training. In Run with Power, TrainingBible coach Jim Vance offers the comprehensive guide you need to find the speed you want.
Run with Power is available now from your local bookstore, tri or running shop, and from these online retailers:
Coach Jim Vance
Limited offers: Get Run with Power FREE with purchase of a SHFT, RPM2, or Stryd power meter while supplies last.