Training Tips

Running Speed and Distance Demystified

on July 16, 2020

It is reasonable to argue that, because most races are measured as distances, we should also plan our training around running distances.

We say things like, “I’ve got to run 5k tomorrow, then I have my 20-mile long run on Sunday.” And we may even run past our own homes just to ensure we complete a planned distance!

But how important are speed and distance, and how do we know how far we’ve run outside or how fast we are moving on a treadmill?

The Current State of Play

Aside from some timed events, almost every race you are likely to enter will be a distance-based event. 5k, 10k, Half Marathon, and Marathon are all set distances. The idea is that you cover that distance as fast as you can.

We take pride in beating our Personal Best times. In fact, the majority of us are not elite athletes and we are not expecting to win races, so beating ourselves is likely the primary goal for any race.

But How Far IS a Marathon?

The snag with distances is that they are all different. You will almost never run the same distance twice, for a variety of reasons:

  • Official Measurements - Rules in many countries state that a course must not be shorter than the advertised distance. In the UK, race organizers make courses slightly longer to account for this. A 10k race will actually measure 10010 meters. A marathon will measure over 40 meters further than the official 42.195km distance.
  • Weaving - You will never run the official racing line. You will be weaving between other runners, avoiding parked cars, crossing the road to get to the aid station. All this adds to the distance you actually run.
  • Measurement Errors - While big international races must adhere to strict rules, most smaller events are less regulated and distances may not be accurate. Indeed, in trail running, advertised distances are often merely a rough guide to how far you might run!

Arguably, the shorter the race, the more likely it is that you will run something approaching the advertised distance. But what’s important to remember is that the ‘correct distance’ of any race is from the start line to the finish line.

GPS and Footpods

You cross the finish line of your local 10k race. You look down at your watch and it says 10.25km. Or worse still it says 9.93km. How can this be?

In addition to our discussion above about course measurement, we also have to take into account the accuracy of the measurement device on our wrist.

In most cases, your watch will measure the distance you have run by bouncing a signal off a number of satellites. There are a few different arrays available such as GPS (USA), GLONASS (Russian), and GALILEO (European).

Some people use a footpod instead to measure speed and distance. The Stryd is a great example of a footpod that can produce a highly accurate distance measurement comparable to GPS.

However, both satellite and footpod methods are prone to errors. GPS will often fail in areas of dense woodland or in high rise city centers. It will always fail going through tunnels. Footpods rely on complex algorithms to work out your stride length and can easily be fooled in real-world running.

Treadmill Speed

You may think that running indoors on a treadmill offers increased accuracy over outdoors, but that isn't always the case. There are a variety of reasons why you might see different readings between your treadmill display and Zwift:

  • Motor Strength - The speed on your treadmill may not be the real speed of the belt. In many treadmills, the display is independent of the belt itself. If your treadmill is old or a particularly low-budget model, the motor may not be powerful enough to quite achieve the stated speed.
  • Belt Drag - In some low-end treadmills, the belt may drag on the deck as your foot strikes. This causes significant slowdown. Even though you feel like you’re working hard, your Zwift speed may be slower than the treadmill displays.
  • Footpod Calibration - A poorly calibrated footpod can give you wildly inaccurate speeds. You might appear to be going faster or slower than your treadmill display indicates. This can sometimes be rectified by using the Zwift Calibration Tool. However, often a poor footpod will always give questionable results.

It is often the case that all of these things are affecting accurate speed and therefore accurate distance within Zwift. There are methods we can use, beyond the scope of this article, to give us a more precise measure of the speed of the treadmill belt.

Work Rate and Time

The advice here is not to completely ignore speed and distance. Of course they are important. But don’t get hung up on the numbers because, as we have seen, you will never run exactly 10km, in training or in a race.

The important thing is work rate and time. The more races and training you do, the more you’ll start to understand how it feels to run at certain speeds, and you can balance your training with hard efforts and easier efforts, longer runs and shorter runs.

Vary your training so that you run on roads and trails as well as on Zwift. This will ensure you’re strengthening different muscle groups and keeps your sessions fresh and interesting.

In an outdoor race, use your watch for timing, but always use the course markers for distance, not your watch. On Zwift, use that big colorful heart rate display to monitor how hard you’re working and judge whether you could give just that little bit more.

Perhaps rather than running a 10k training session, do a one-hour session and forget about distance. Or try one of Zwift's new time-based run workouts such as the 33-minute Pick Ups which is designed to improve your kick at the end of a race.

Read about time-based Zwift Run workouts

Regardless of the workout you choose, just try not to be too concerned with running exactly 10k. Because we can guarantee that race you’re training for won’t measure 10k either!


Race Recon: London Greater London Loop 6 months ago