You don’t need GPS (privacy invasion) to log your run workouts

Posted on March 30, 2020

(Last Updated On: March 30, 2020)

“You don’t need to worry about privacy if you have nothing to hide.”


Google tracked his bike ride past a burglarized home. That made him a suspect.

“I was using an app to see how many miles I rode my bike and now it was putting me at the scene of the crime,” the man said

(That app? RunKeeper. Quite a popular one.)

Read that article and the rebuttal to privacy advocates is more like,

“If you have nothing to hide, and money to pay a lawyer, then you might have nothing to worry about.”

You DO NOT need GPS

As watch and phone technology has improved, it’s common to use GPS to observe how far you’ve run. We need to emphasize how far. A lot of these apps will show you, and hence record, where you ran.

I think you know where you ran, since, you know, you ran there.

What we really care about then is how far we’ve run, and often what pace we’ve run at.

This can all be done with the smartwatch’s or smartphone’s accelerometer.

The accelerometer is a way the device tracks your body’s acceleration. It does not track your body’s location in a geographic sense.

Think of running as your legs constantly going through accelerating your body and DEcelerating your body.

Your foot pushes you forward? You’re accelerating your leg forward.

BUT, as your foot is about to land on the ground, your body, in other respects, is slowing yourself down. It produces force to move you forward, but it receives force as you land too. You know, so your leg doesn’t just collapse each time your foot hits the ground. (Your knee bends some when you land, but not too much, because the body slows that down.)

Perhaps more easily visualized is the arms. Just think about one arm.

You’re running. Your arm moves forward, but then it starts slowing down as it’s about to change direction i.e. go backward. It’s constantly alternating between accelerating one way, decelerating, then accelerating another way.

An accelerometer tracks this. Perhaps by syncing it to some data -such as your body measurements or using GPS one time to correlate GPS data with accelerometer data- or just making guesses based on how it’s being used (if you decelerate every X seconds, it can assume that’s a stride length), it can deduce what it measures with how far and fast you’re running.

Your arms are accelerating back and forth faster? You’re probably running faster => accelerometer shows us that.

Note an accelerometer does NOT track your body’s movement.

This needs to be crystal clear in this context. Accelerating and moving are not the same thing. You can be accelerating and moving, yes, but you can be moving and not accelerating.

The easiest way to understand this is think about being in a car.

When you hit the gas hard? Your body gets pushed back into the seat i.e. you can feel the acceleration.

When you’re at 70 mph, a constant 70 mph, like cruise control, you feel nothing. (Same thing in an airplane. You can be going 400 miles per hour and feel nothing.)

Have to hit the brakes hard? You feel a lot.

Riding a bike is different

This is why you-

-can track your run workouts with your Apple Watch even if it doesn’t have a cell or satellite signal. It can use just the accelerometer and be fine, and we don’t have to give it a recorded history of where we are.

-cannot track your bicycle workouts with your smart device unless it has an ability to use GPS

When you’re on a bike, think about a watch on your wrist. Your hand is on the handlebar, your watch is on your wrist, and…it never moves relative to your body. (Same idea for your phone in your pocket.) Even though it is moving geographically. Your wrist might have gone from your house to 5 miles away, but an accelerometer may pick up none of that, because a lot of bike riding is done at a constant speed.

It’s analogous to riding in the car on a highway at a smooth 70 miles per hour. To the accelerometer, nothing is changing speeds.

A tiny physics:

Velocity = distance / time

Velocity, speed, is dependent on how far you travel and how quickly you get there.

Acceleration = change in velocity / change in time

Acceleration is not how fast you’re going, it’s how fast you’re changing how fast you’re going.

In other words, if your speed is not changing, you have no acceleration. From the view of acceleration, standing in place and moving at a constant 400 miles per hour are the same thing. This is why sitting in a plane (with no turbulence) feels the same as sitting on the ground.

-> This is why the International Space Station can be moving around the Earth at 17,000 mph yet the astronauts don’t feel it.

This is why we can live on a planet constantly spinning and not feel it.

Conversely, this is why you can hit another vehicle at 70 miles per hour and die. Because you go from 70 to 0 so quickly. (Acceleration tends to be what we’re concerned with when it comes to injury. Not velocity.)

With running, even if your torso is moving at a constant 7 minutes per mile pace, your legs and arms are constantly accelerating and decelerating, so a smart device can pick up on that without GPS, do a little magic, spit out how far and fast metrics.

On a bike, everything is often moving at a constant speed, so it needs GPS to track your distance.

-> This is also why biking is not great for your bone density.

Notice the difference:


I know, I know.

“I already bring my phone everywhere. Even if I don’t use something like RunKeeper the phone knows where I am.”

I don’t want to go into the weeds on this, but some counters-

  • WHICH apps or services have your data can really matter

For example, Apple has a very strong privacy record. While Google, or Amazon, or Facebook, are ecstatic to attain, use and sell everything they can on you.

Using RunKeeper on an Android (owned by Google) phone is not the same as using Apple’s workout app on an iPhone.

  • Don’t bring your phone or change your phone’s setting when you workout

This is more so the telecoms aren’t getting your workout data either.

For example, when I run these days, I leave my phone at home. I use my Apple Watch to track my run, just using its accelerometer. It’s nice to not have to carry the phone, and frankly I think it’s never a bad idea for most of us to have our phones on us less, for a variety of reasons.

I know, I know.

“What are you going to do if something happens to you????”

I go the same route pretty much every time. If I’m not back after a certain amount of time, my family will know something is up.

If I need to make a call, I don’t know, I’ll knock on someone’s door.

For the times where I do need or want to bring my phone for some reason -usually something parent related- I put it on airplane mode (which is something I regularly do anyways, to help me not be on it too much).

-> Note GPS can still be used when you don’t have cell signal or when your phone is on airplane mode. Cell signal (towers on earth) and satellite signal (satellites in space) aren’t the same, but GPS does tend to be much less accurate on your phone on airplane mode. A positive thing in this context.

  • “An accelerometer isn’t as accurate!”

First, GPS ain’t golden either. I’ve used GPS while running laps around a track and it wasn’t spot on. If you’re doing sprints? Running in an area where signal isn’t that great? It can be terrible.

Second, this is like having a faulty scale to weigh yourself. As long as you’re using the same instrument each time, you can still grasp how you’re progressing. If your scale is always 5 lbs heavy, you can still answer whether you’ve lost weight.

Third, if you’re using any of this stuff for rigorous record keeping, you’re not in the right place. With run workouts, if you want to track things that closely, go to the track. If you’re out in the wilderness, there are higher tech options to go with as well. Lower tech approaches are often fine too. See below.

  • Biking or low tech

If you want to track your bike workouts, one thing you can do is have a few routes where you already know the distance. If you don’t already know it, you can map it e.g. look up the route using a map service, or use GPS one time to track the route.

-> If you’re doing trails, whether running or biking, there are tons of options out there to find the trail length ahead of time. The park service for one, the AllTrails app, etc.

Then, for the other times you do it, just track how long it takes you.

First, if you went faster, then you…went faster.

If you want to get more granular, like know your pace, then simply do,

distance / time

You know the distance, input your time => you know your average velocity.

For instance, you went 10 miles in an hour:

10 miles / 1 hour = 10 miles per hour

You went 10 miles in 2 hours:

10 miles / 2 hours = 5 miles per hour

You probably don’t need to be getting things too exact. You went 47 minutes? Just say you went 0.75 hours i.e. 3/4s of an hour.

Or you went 56 minutes? Then go another 4 minutes to make the math easier, you lazy ass.

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