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Understanding the Difference Between Your Indoor and Outdoor Power Numbers

Did you know that most cyclists can produce higher power outdoors compared to indoors? It's true. Here's why it matters.

With the recent release of our new outdoor / indoor and event preparation training plans, subscribers to The Sufferfest have over 100 free training plans to choose from. Tailored to your Four-Dimensional Power™ (4DP) profile and Incorporating structured outdoor workouts on the weekends, these new plans will ensure that the quality of your training doesn’t go out the window when you head out the door.

If you’re training with power year-round, both inside and outside, you might have noticed that you hit your best power numbers while outside, or that the same power might feel easier outside compared to inside. This isn’t your mind playing tricks on you, but a well-documented phenomenon. This difference is more pronounced with shorter, higher-intensity efforts, especially when you’re out of the saddle (think sprints). The differences are smaller for longer, lower-intensity efforts, and can be caused by more factors. Before you read on, here are some key points to remember:

  1. Understanding why you can crank out more watts outside can help you identify specific weaknesses—like poor flexibility or core strength—that may be holding you back.
  2. There is no set formula for how much indoor power differs from outdoor power. Every athlete is different.
  3. If you have no idea what your individual differences are, using Relative Perceived Exertion (RPE) during training both indoors and outdoors will allow you to dial in your specific differences faster. 
  4. If you use a different power meter for indoor riding and outdoor riding, be aware that differences in accuracy and calibration between the two power meters may result in different readings for the same output.

 

Why Can You Produce Higher Power Outdoors?

When you ride outside, the bike is free to move underneath you. This is most apparent when you get out of the saddle to unleash the full fury of your sprint. With the wind rushing past your helmet and the bike dancing side to side beneath, you likely went above the peak power you hit on the trainer. Most people assume that this additional power comes from using your upper body to pull on the bars, effectively recruiting your arms and torso to pump out more watts. While this is true to a point (especially if you have a strong, stable core) there are other factors at play.  

Gravity Is Your Friend

The force that causes Sprinters to loath the mountains is the same force that adds a little extra power to their finish kick, gravity. When you’re standing, all of the weight that is normally supported by your saddle is now added to the force you’re putting into the pedals. This is a great example of Newton’s Third Law: “For every action, there is an equal and opposite reaction.”  

When seated, your weight is pushing into the saddle, and that saddle is pushing back into you. When standing, gravity is still pulling you down, but now that force is applied to the pedals rather than the saddle. To really take advantage of this boost, you want your center of gravity over the pedal you are pushing down.  Your two options are to move your whole body from one side of the bike to the other, or to move your bike back and forth beneath you. Considering that few people have a bike that weighs the same as their body, it’s easy to see how rocking your bike back and forth is the more efficient option.

Line It Up

The other piece to maximizing out of the saddle power production is proper alignment between your hip, knee and ankle. To illustrate how much joint alignment matters for muscle recruitment here’s an experiment:

  1. Do a regular push up with your hands shoulder-width apart.
  2. Now do another push up, this time with your hands aligned with the center of your chest, thumbs and index fingers touching. Not as easy, right?
  3. Go back to the starting position of the regular pushup, keep your body in the same position but slide your hands up 8 inches. Better, but not as good as the “regular” one right? 

In each scenario the same muscles of your upper arms and shoulders are recruited, but the force those muscles are able to exert is quite different. Only when your wrists, elbows, and shoulders are in optimal alignment can you unlock the full force of those muscle groups needed to complete a pushup. The same is true when you are pushing the pedals on a bike. We know that rocking the bike back and forth while standing maximizes your use of gravity, but that rocking also requires your ankles knees and hips to move dynamically to ensure they stay in optimal alignment.  When standing on the trainer, you can access the extra watts gravity provides by moving your whole body from side to side (assuming your trainer is stable enough to even do so), but you’ll miss out on optimal alignment. Maintain proper alignment and you miss out on the full impact of that gravity boost.

Remain Seated

So far we’ve focused on why you see higher power numbers outdoors for maximal, out-of-the-saddle efforts. As the intensity of the effort decreases and you transition from standing to riding in the saddle most cyclists will still see lower power numbers indoors.

Riders with the greatest differences can usually be identified just from watching them ride outside.  They will be the ones rocking their bikes back and forth with each pedal stroke, even when they’re in the saddle. These are the Weavers, and despite their meandering riding style some have made quite a name for themselves. 

Weave the People

Jens Voigt: legendary hardman and famous silencer of noisy legs. He built a career on the ability to put down punishing, diesel-like power that shattered many a breakaway and more than a few podium dreams. Jens is a Weaver. Watch footage of him in a breakaway and you’ll see a man who looks like he’s trying to rip the bike to shreds. But strap Jensie to a static trainer and deprive him of the ability to rock the bike underneath him, and he would struggle to hold the same power he can while out on the road.

Weavers often have poor hip stability, which is typically caused by some combination of limited hip flexibility, and poor gluteus medius recruitment (that’s one of the three hip extensor muscles that make up the glutes).  Weavers move the bike underneath them while seated for the same reason riders rock their bike back and forth during a sprint, to optimize joint alignment. Remembering Newton’s 3rd law, every watt you push into the pedals pushes back into your hip. When someone has unstable hips, that force pushing into their hip is enough to shift their whole pelvis.  This shift on one side of your pelvis impacts the alignment of your hips, knees, and ankles on both sides of your body. Weavers solve this problem by synchronizing the rock of their pelvis with the rock of the bike, thus keeping their leg alignment closer to optimal.

Sways and Means

Take a Weaver and add in some poor core strength and you have yourself a Swayer. When you are pushing on the pedals hard, you need a strong backboard to counteract that force (Newtons 3rd law really is everywhere). Weavers can’t rely on their hips, so they fall back to using their core as that backboard. Remove that strong core and all you have left is the Sprinters frenemy: gravity. Swayers shift their center of mass over the downstroke pedal as they rock the bike back and forth, resulting in a swaying of the torso. This rocking motion is restricted when you are inside on a trainer, and a restricted backboard means restricted watts.

Cool Your Jets

There’s another, more basic reason for why you can generate more power outside than in the holy water-drenched confines of your bike torture chamber: Heat. We did a deep dive into the importance of staying cool when training indoors in this article. When your done here, we recommend you crank up the AC, curl up with an ice pack, and give it a read.

When you ride outside, you have the benefit (usually) of a nice, steady flow of cooling air. Not so inside. As the duration of an effort increases, overheating starts to limit how effectively your body can produce power. Unless your pain cave is in an uninsulated shed in the winter, or you live in a sweltering desert, your body will have an easier time staying cool outdoors. That means you are better able to produce higher power and sustain power for longer durations outdoors than on your trainer. If you want to improve your performance on the trainer, be like Fonzie. Cool.

 

What Do I Do If My Outdoor and Indoor Power Is Different?

Do not lose hope! If you see consistently lower power numbers for efforts indoors, your first step is trying to identify what might be the cause.  Poor hip stability? A weak core? Inadequate cooling on the turbo? The next step is doing what you can to address that issue.

  1. Start incorporating the yoga videos that specifically address hip flexibility and stability into your training. Hip Openers, Hip Openers II, and the Hips and Hamstrings yoga videos in The Sufferfest app are great for improving range of motion and activation of the gluteus medius muscle.
  2. Get hard core. A strong, stable core will dramatically improve power and efficiency, while also helping to prevent lower back pain (especially if you do a lot of seated climbing). Try the 30-day Yoga Core Challenge, available as a stand-alone training plan in TrainingPeaks. If you’re not ready to commit to 30 days, start easy and do one of the yoga videos that focus on core strength two to three times a week. You’ll be amazed at the difference it makes.
  3. Find some adoring fans.  When it comes to overheating inside, the simplest, and most effective solution is often getting a fan, or adding one to your collection.  If you do find that you struggle in the heat, this issue will not be limited to just riding inside. When that next heat wave hits be ready to see your power figures take a bit of a hit.  If you are really struggling, you can take a tip from the pros and make an ice sock to put in the back of your jersey on those really hot days. An ice sock is simply some store bought panty house stuffed with ice that can be placed in your middle jersey pocket.  Just make sure any electronics are in a waterproof bag if you attempt this one!

 

Does it matter that my indoor and outdoor power numbers are different?

Short answer, yes. Here’s why: If you track your fitness using something like the Performance Management Chart in TrainingPeaks, and you have a significant difference in power production indoors versus outdoors, then depending on which FTP value you have set (indoor vs outdoor) your TSS values will either be artificially high when outside, or artificially low when inside.  As a metric dependent on FTP, TSS has limitations in a post-4DP world, so this issue really only affects athletes who put too much stock in TSS as the most important metric to track (check out this article for more information on TSS)

Where this difference does make an impact is when you try and take your indoor power zones outside, or when you take your outdoor power zones inside. Without being aware of your individual difference, your interval sessions can become impossibly difficult or wastefully easy, neither of which is ideal if you want to get the most out of your training.

Only by understanding “Why” your differences exist, and by paying attention to how efforts feel inside AND outside, will you figure out what adjustments you need to make when moving between outdoor and indoor workouts.

 

Should I use the 4DP numbers that I got indoors to set targets when I’m riding outside? If not, do I need to do a fitness test outside?

All of the outdoor workouts in The Sufferfest indoor / outdoor and event prep training plans include RPE, Heart Rate and Power Targets.  The Power targets will be based off of your FTP, Maximal Aerobic Power (MAP) or Anaerobic Capacity (AC). Since the TrainingPeaks Workout Builder only allows power targets to be based on FTP,  MAP and AC-based targets will be expressed as an FTP target with a much larger range to account for individual differences.

To start we recommend using your 4DP metrics from your most recent Full Frontal fitness test to set your specific power targets. Pay attention to your RPE and heart rate during these efforts so you can compare them to similar power efforts you have completed inside and adjust the targets accordingly.  

Another option is to complete the Full Frontal test outside to definitively set your outdoor power targets. That's easier said than done. Because of the variability in terrain, traffic, and road conditions completing Full Frontal outside is challenging. Not only do you need good roads that allow you to safely and legally ride for up to 20 minutes without stopping or slowing down, you also need roads that allow you to hit the exact recovery durations between the efforts. If you extend the recovery time between efforts while riding outside your results won't be accurate.

 

Should I be doing things to try to bring my indoor and outdoor power numbers closer together?

Yes! The greater your difference is the more work you will want to put into figuring out the main cause so you can address it.  When you overheat inside your power production drops significantly to keep your core temperature in a safe range, but your muscles will still have more to give.  That means you are not pushing them to the same limit they will be experiencing outside. If poor hip stability and or core strength is your issue, not only will addressing those decrease the gap between your indoor and outdoor power, but it should increase your power addition the the normal fitness improvements you will be seeing through consistent and well planned training.

 

If my power numbers are lower indoors than they are outside, does that mean I’m not training to my full potential indoors?

Even though you see lower power numbers inside—especially for shorter duration higher intensity efforts—that does not in any way mean that indoor workouts are a waste of time.  One of the major benefits of riding a stationary trainer is your ability to focus entirely on the effort to the point you can completely exhaust yourself. When doing efforts outside, part of your brain has to be focused on variables like traffic, road conditions, changes in terrain, weather and staying upright.  On the trainer it is just you and the effort (and sometimes a Minion with a stick). As long as your trainer is relatively stable, you can literally go until you collapse in a heap over your handlebars. That kind of Suffering pays dividends.

As you start to incorporate more outdoor sessions into your training schedule, remember that power numbers can be affected by a variety of factors. Understanding why there may be a difference between your indoor and outdoor power numbers can help you identify how to address specific weaknesses, get the most out of your workouts, and maximize your Return on Suffering.

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