What's the Elevation Gain? - Gary Valle's Photography on the Run

Friday, July 31, 2009

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Runner on the Hummingbird Trail.

"What's the elevation gain?" is a common question when talking about a trail run, because it makes such a huge difference in the difficulty of the run. All the technology we have for recording and analyzing trail runs is remarkable, but it can sometimes produce misleading and wildly inaccurate results. This is particularly the case when using a GPS track to calculate elevation gain and loss.

Last Sunday's trail run in the San Gabriel Mountains is a good example. The course started at Islip Saddle, dropped down to South Fork Campground, climbed to the summit of Mt. Baden-Powell by way of Vincent Gap, and then returned on the PCT to Islip Saddle. The GPS track was recorded on a Garmin Forerunner 205. So what was the elevation gain on the loop?

According to Garmin Training Center, the gain was about 10,500'. The same track in TOPO! calculated the gain at about 6,100'. SportTracks, using corrected SRTM-based elevations and moderate smoothing, came up with 5800'. When uploaded to Garmin Connect, the track produced a fanciful elevation gain of about 13,600'!

Last year I used a Polar 625X on this course. It measures elevation gain/loss based on changes in barometric pressure, and came up with a gain of 5400'. So which of these values is the closest to reality?

Fortunately, in the case of elevation gain/loss it's fairly easy to do a low tech sanity check of these high tech results. All that is required is to get out a topo map, either electronically or on paper, and do a little arithmetic.

In the case of Sunday's loop, the gain from South Fork Campground to the summit of Baden-Powell is about 4830'. The gain on the PCT up and over the shoulder of Throop Peak is about 375'. A couple of other minor climbs total 240'. This gives a total of 5445'. Adding in a fudge factor of 200' for very small climbs that were not included in the total, the result is a reality checked gain of about 5645'.

The title photograph is from a run on the Hummingbird Trail yesterday.

Note: A long-standing rule of thumb, Naismiths Rule, says that the additional time required to gain 1000 ft. on a run/hike, will be the same as the the time to run/hike 1.5 miles on the flat. See "Short and hilly or long and flat?" in the Mountaineering Council of Scotland's The SCOTTISH MOUNTAINEER (Issue 7, March 2001).