The release of Garmin’s newest GPS running watch, the Forerunner 620, introduces the running community to two new features not available on any other GPS watch: ground contact and vertical oscillation. Garmin describes these as functions created to help runners improve their running form.
Ground contact tracks how much time your foot touches the ground each stride. From Garmin's website: "Most running ground contact times are between 160 — 300 milliseconds. Elite runners typically spend under 200-milliseconds in contact with the ground each step."
Vertical oscillation measures the amount of “bounce” – i.e. vertical up and down movement – generated while running. The Forerunner 620 measures “bounce” by tracking the number of centimeters your torso moves from a fixed point during each stride. According to Garmin, elite runners oscillate less, although they don’t make it clear how much less.
(It should also be noted that both of these features require HRM-Run, the new heart rate monitor Garmin developed.)
While Garmin has proudly announced these features as part of the overall Forerunner 620 package – there is little information about how to actually use these metrics while training.
Which raises the question: are these features useful to the everyday runner?
To find out, we asked James Dunne of Kinetic Revolution.
James is professional running coach, specializing in correcting inefficient (and potentially injury-inducing) running movement patterns. His website, Kinetic Revolution, has a wealth of information and articles about proper running form, training, and nutrition. Additionally, he offers a six-week online course to improve form and efficiency.
According to James, ground contact is just another way of measuring running cadence.
“Contact time and cadence are inextricably linked, and essentially the same thing, expressed in differing ways. Contact time decreases as cadence increases, and vice versa.”
In essence, Garmin has simply provided a secondary metric to track cadence (which the Forerunner 620 measures as well). Cadence increases --> Ground contact time decreases.
At its core, tracking vertical oscillation is really about improving running efficiency by reducing wasted energy. But just how much energy might be lost?
“A runner who runs a 3:30:00 marathon with an average cadence of 168 strides per minute makes 35,280 strides. If each of these strides contains 1 inch excessive vertical oscillation (bounce), the runner has to spend excessive and unnecessary effort in 'bouncing' well over half a mile (in total) vertically during the race!”
Clearly, it’s beneficially to try to reduce “bounce” as much as possible. But according to James, the running stride itself will always include some bounce. Fortunately, increasing cadence will have significant benefits in reducing bounce to a more appropriate level.
Both ground contact and vertical oscillation are beneficial but only as secondary metrics to track running cadence. So while they are not groundbreaking features, they do provide useful information.
Knowing this, the proper way to use these metrics while training is to measure current cadence, ground contact, and vertical oscillation, then slowly work on increasing cadence. Decreases in ground contact time and vertical oscillation should follow.
James has written a great article explaining the correct method to increase cadence. The key is to make a gradual change, slowly working towards a faster cadence.
Once you’ve increased cadence to an appropriate level, track these metrics to stay on target and spot any inconsistent trends. A change in any of these could signal degradation in running form and/or other potential issues that should be investigated.
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By Ben Drew
Photo by Josiah Mackenzie
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