Podcast, Running, Training

How wind and air resistance impacts running with Evan Schwartz of Stryd | EP#197

 September 2, 2019

By  Mikael Eriksson

How wind and air resistance impacts running with Evan Schwartz of Stryd | EP#197

TTS197 - How wind and air resistance impacts running with Evan Schwartz of Stryd

The next generation of Stryd's running power meter is here, and it can now account for the differences in running power required depending on air resistance, wind, and drafting. Evan Schwartz from Stryd joins us to discuss the new device and the implications of wind on running with power.

Discuss this episode!

  • Let's discuss this episode and the topic in general. Post any comments or questions in the comments at the bottom of the shownotes. Join the discussion here!

In this Episode you'll learn about:

  • How much additional power do you need to produce in various wind conditions compared to a still day?
  • How much power can you save when drafting another runner?
  • How much power is required just to move through still air? In other words, what's the difference between running outdoors and on a treadmill?
  • Is Stryd catching on with elite runners and coaches?
  • What's next on the Stryd roadmap?

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Updates to the new Stryd device

5:05 -

  • Stryd is a running power metre.
  • The current version is a running foot pod.

    It's about 7 grams, the size of a power chip which you slip under your shoelaces and then go run.
  • It connects to your watch or your phone, you can see stuff in real time or you can just look at the data afterwards. 
  • We've been around since 2015 - Stryd originally started as a clip for shorts and measured biomechanics that way. 

    It then moved to a chest strap and then down to the foot in 2016. 
  • We're now entering into the next gen Stryd and the main feature that is included in the main upgrade is that it factors in air resistance now into the overall power output. 
  • There are also a ton of other great upgrades and new features that provide a great training environment for people. 
  • It's got sensors that are upgrades on previous things now. 
  • We've already started shipping out the first batch of the new Stryd, and we're making and shipping as many as we can!  

Wind resistance update

7:45 -

  • The main upgrade is the wind, and wind is a tricky thing in running! 
  • For runners, they're not necessarily thinking how air resistance and the wind impacts them. 

    If you compare it to cycling, you're trying to be as aero as possible, but for running it's never been a thing you can quantify besides 'it feels windy'. 
  • We've tried to make something to quantify and capture that and we found there's a reason nobody has done it before, because it's really tricky! 

    There's a lot of different equations you have to balance, and there are a lot of moving parts. 
  • It's been a rewarding, if very long, process.
  • Running on a treadmill inside a wind tunnel was an interesting thing, and then doing the same in the real world was exciting too.
  • We think it'll let people understand more completely what's going on when they're running, that maybe they had no idea what was going on before. 
  • It's the early stages now and we're currently very receptive to feedback. 

    We've always tried to engender this culture within the company. 
  • Currently, depending on your setup, you will see the overall power spike when you get a gust of wind. 
  • For example, I was doing a run at 2500m altitude in Boulder, and I was coming up a slight hill. I was running 4:30-5min/kms (7:30-8min/miles) and I didn't increase my pace, the elevation was staying the same.

    All of a sudden I get this huge gust of wind in my face, I look down at my watch and I was running 300 watts up this hill at an even effort, and it spiked to 380 and stayed there until the gust went away. 
  • You can see in real time how hard you're actually working and it can improve training, including confidence in your running. 

Examples of wind resistance impact

13:57 -

  • It's important to remember when running with power is that the weight you set can make a big difference. 

    When we talk about specific wattage it's important to remember that everybody has their individual power number that's accurate for them. 
  • You can be moving through a headwind or a tailwind but you are always moving through air resistance. 

    This is what Stryd is capturing, the air resistance that is interacting with your body. 
  • The concept of seeing your wattage go up is the amount of air resistance you're going through. 
  • Let's say you're doing 5x1km repeats, 3 are into a headwind and 2 are into a tailwind.

    You're trying to focus on 250 watts. 

    You notice that while you're pace is slower into the headwind, power is right at your goal.

    Then when you turn around, you might be running a couple of seconds faster. 
  • It will depend on the individual, the grade they're running on and the severity of the headwind. 

    If it's a still day, it's only going to be a few watts difference - maybe 2-3%.

    If the runner is moving at 14km/hour, they're going to have about 8-9 watts difference. 
  • Until you get to a fast speed moving through the air, you do not see that large of a wattage increase. 

    Probably greater than 15km/hour. 
  • If it seems like it's a still day and you're running faster through the air, that wattage will go up because you have to move through more air resistance. 
  • If you have a tailwind of 15km/hour and you're travelling a 15km/hour, that is a still air resistance. 

    If you have a headwind of 15km/hour and you're moving at 15km/hour, that's a lot more air resistance you have to overcome and the wattage will reflect that in real time. 
  • If you're running 1km repeats, running at 15km/hour and they experience a 10km/hour headwind, the wattage will go up by around 38-44. 

    Compared to the baseline condition you'd get around 30 extra watts, which is a significant increase.
  • I'd previously been someone who said I understand that I need to work harder into the wind but I don't know how hard I'm actually working. 
  • A constant headwind is hard to quantify but when you see the data it makes a lot more sense. 
  • The wind makes a huge difference, and it's a very different experience being able to quantify this difference. 
  • Also I previously expected a tailwind to help me as much as a headwind hurt me, but once you understand the concept of air resistance and you can look at the numbers, you understand why this isn't the case exactly. 
  • The wind is an invisible hill - you have no idea it's coming or that it's there, but once you can see how it affects you in real time it makes a big difference. 

Drafting & impact on air resistance

25:13 -

  • This is a complex topic for most people that have never drafted while running before. 
  • There's air resistance, and then there's things you can do to minimise the amount of air resistance you have to travel through. 
  • Let's say you're Eliud Kipchoge and you have nine people at the Breaking2 project that can run in front of you to break the air resistance, and you have a Tesla with a giant sign in front of them as well.

    Drafting in those scenarios is something that's very real. 
  • In the normal, day to day runners world, drafting is an obscure and abstract topic because it's hard to put it into practice. 
  • If you train by yourself and you go to a race and run by yourself the whole way, you have no idea that you're potentially leaving time on the table because you have no idea that the concept of drafting is a thing. 
  • Drafting in practice is also relatively difficult to do in a way that adheres to international racing rules. 
  • In practicality, there's not a lot of people that can pace the best in the world because they can't run that fast, and they're using a lot of effort to break the wind for them. 
  • There's been a good recent study about how many Eliud Kipchoge's would be needed to break a two hour marathon.
  • A non-elite may not be aware that they can run at the back of a pacing pack and use this to help them through their race and conserve more energy. 

    You have to be in a very specific place to take the maximum benefit. 
  • Stryd can show you the wattage you're conserving when running in a pocket of disturbed air resistance.
  • Drafting is a perfect thing to take advantage of in a race.  

How much power can drafting save?

30:29 - 

  • Using the example of a good amateur runner trying to run a 3-hour running, running around 15km per hour for example. 
  • The Pew study from 1971 talks about different athletes walking and running at different intensities. 

    If you perfectly draft for track running behind a subject 7.5-13% at different speed, running 1 metre behind them, virtually eliminates all air resistance. 

    They found that the VO2 cost was reduced by 6.5% at middle distance speed for high intensity. 
  • When you take the speed and effort down a bit the percentage still carries. 

    Talking about marathon, for a 250 watt runner you can save around 10-12 watts at that intensity if you're perfectly drafting the entire time. 
  • You'll probably be behind them around 90% of the time as there's different points where you'll slip out of the exact pocket behind them. 

Other upgrades for the new Stryd

34:27 - 

  • The design is completely new so the clip is now designed to funnel the wind into the front facing port. 
  • Aesthetically the new Stryd just looks more modern and sleek - these are the things the team geek out on! 
  • It's also a lot easier clip in and it stays better on your shoe. 
  • The IMU - the motion sensors - are completely next generation. 
  • We've added new environmental sensors for temperature and humidity. 
  • We hope to introduce the concept of tracking the temperature and humidity in training and use them to help you know what you can do on race day based off of what you've done in training based on that environment. 
  • For example, if you train in nice weather but the race is really hot and humid, it'll be able to tell you what wattage/output that you're going to be capable of in those conditions. 

    This is better than shooting over what you can actually do and trying to beat weather. 
  • We've also added in 64 times the amount of storage for internal data capture. 
  • The LED is completely new and it's a much more noticeable blink. 
  • The antenna on board is also new which will help with antenna range.
  • The phone app experience and integration with other models has improved as well as is now much better. 

    They're being improved and worked on day to day to provide a great training experience alongside the great hardware. 

Software integrations

38:58 - 

  • With Garmin you need to use the Garmin IQ connect apps. 
  • The big three sportswear brands that currently work with Stryd are Garmin, Polar and Suunto. 

    A fourth major player is the Apple watch. 
  • The Apple watch is my favourite integration because it's completely custom for what we want to do. 

    We have our own Stryd app so we can just change things as we feel, we don't have to wait for software updates on the other watches. 
  • Garmin is the biggest ecosystem in terms of number of users for us. 

    We've done a lot of work recently in terms of the Connect IQ data fields that we have. 

    We now have the Stryd zones data field which shows you what power zone you're in and it changes live and dynamically. 

    It's associated with out brand new feature called auto critical power which calculates your critical power based on your training over the past three months instead of estimating off a race or critical power test. 
  • This new feature will keep you in the right power output. 
  • Polar and Suunto have the easy option of just pairing as a footpod and then the power data shows up right there. 
  • There are some other watch brands we hope to work with in the future too! 
  • When it comes to structured workouts based on power we've done that with the Apple watch and you can get your training send from Training Peaks and you can run it as specific as you want. 

    E.g. if you want to do 60 minutes at a specific power range on Monday, then the next day you want to do 10x1 minute repeats it'll alert you when you're above and below. 

    As much as you want to design the experience the Apple watch will let you do that. 

    You can choose up to 7 different metrics on your screen and customise the averaging etc. 
  • With Garmin you're more restricted with the data fields.
  • I think the Apple watch will catch on with athletics because it's so customizable. 

Stryd and elite athletes

45:16 - 

  • I've always loved running and following it has been a passion of mine - my job is literally a dream come true for me. 
  • Using power in running is becoming more and more accepted. 
  • Stryd gives the benefit of the option of whatever they want to track. 
  • For example, say there's a really good marathon runner and their coach wants them not to focus on running with power, but they want to track their leg spring stiffness in different shoes and look at efficiency over a training block. 

    They could add in different plyometric exercises, or see what different shoes do for them at different paces. 
  • Another use case might be pacing distance as Stryd is very accurate for this. 

    If a team is going on a training camp that doesn't have GPS satellite locatable locations they can use Stryd to run on trails and still have a good idea of the actual mileage they're doing. 
  • In the current ecosystem, there's so many elite coaches and athletes we work with who have something that works for them and have got them to that level. 

    They don't need to switch their entire training plan but they can dip their toe in the water. 
  • They also use running stress score - which is your second by second current power related to your critical power multiplied by a coefficient.

    It gives a point to track stress, and they can notice when their athlete starts to become fatigued when they go over a certain cumulative running stress score. 
  • We don't want to say athletes have to use Stryd in a specific way, we're just excited to learn from all these great elite athletes and coaches. 

    We want to learn about their training structure and how we can then help them. 
  • We have a couple of people in Europe in the middle distance category (800-1500m runners).

    The main category is 5-10km on roads, up to marathon on the road. 
  • The US Olympic trials for the marathon are about half a year away. 

    I'd think there'd be 12-24 people repping Stryd on the start line. 
  • Over the next 200 days we might see people get more specific to the demands the course will have. 

    The tricky thing about this edition is it has 300m of elevation gain, which isn't a lot, but marathons are usually flat so this might need to be adjusted for. 

    Stryd will be great for pacing this. 
  • Also the trials are in Atlanta at the end of February so it'll be warm and humid, so prepping for this conditions will be important and Stryd can be helpful for that. 

Updating weight set in Stryd 

52:27 - 

  • Some coaches advocate leaving your weight set at a nice round number and never changing it again - e.g. 100kg - and track your progression that way. 

    E.g. tracking your increase in power and pace in workouts. 
  • Now in the Stryd ecosystem with the addition of critical power we're starting to track watts per kilogram so it's more important to update your weight. 
  • If you are within a kg of your weight it'll be accurate for seeing your watts per kilogram. 
  • We also have leg spring stiffness related to watts per kilogram which would need changing weight. 
  • If it's day to day and you're fluctuating between 1 kg or 2-3 lbs then you can leave it, but if it goes more than this you should change it. 

Running effectiveness with Stryd

55:52 - 

  • Running effectiveness, introduced by Andy Coggin, is something we've had a lot of discussion about. 
  • I was high on running effectiveness because it's a new metric I could look at and compare if somebody is running at this specific metres/second and their watts/kg is this, we can look at that interchange and relate it to their watts per kg. 
  • I think it's a great metric but for us to integrate it in our ecosystem we'd have to do a little bit of work to relate it to elevation. 
  • If I am running at a very flat even terrain all the time then I'm able to more handily use running effectiveness. 

    E.g. running effectiveness would be useful on a track workout. 
  • However if I'm mixing up road intervals on rolling terrain, or have uphill and downhill repeats, my running effectiveness will tell me I'm worse when running uphill and better downhill. 

    In reality, I might actually be the opposite but running effectiveness just looking at speed related to watts/kg won't paint the full picture of what's going on. 
  • If we were to add Stryd running effectiveness we wouldn't just take the equation and add it to our ecosystem. 

    We'd need to use all our resources and then create a Stryd running effectiveness based off heat, humidity, elevation, wind, past training etc. 
  • We'd want to tie in something to be very complete. It's something that might be worked on in the future but it would require more work than just inputting the equation.
  • We want to have actionable things at Stryd, we don't want to complicate running! 

What's next for Stryd?

1:01:39 - 

  • The most important thing now is the software side. 
  • We want to provide a great experience for people to use Stryd in their training and give them a reason to open the app right after their run. 
  • We want to be able to tell you something to do before your next run and even in the middle of your run. 
  • The specific next thing is to ship out all the new Stryds and get people running with the new Stryd. 
  • We want to increase the web and mobile support for Stryd specifically. 

Rapid fire questions

1:02:57 -

  • What is your favourite book, blog or resource related to running, triathlon or endurance sports? 
  • What is your favourite piece of gear or equipment other than Stryd?
    • My wireless running headphones - the Aftershokz.
    • They're bone conduction so they don't sit in your ears.
  • Who is somebody in running or endurance sports who you look up to?
    • For running specifically it would be my Dad, he instilled a love for running at a very early age for me. 

Key takeaway

  • The standard power cost of air resistance on a still day is around 8-9 watts, which becomes the difference in power demands when running on the treadmill when you're not moving through the air. 

    We've always heard the guidance of using a 1% grade on the treadmill because it's easier, but we can now quantify it with power numbers as well. 

Links, resources and contact

Links and resources mentioned

    Connect with Evan Schwartz

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