This route begins and ends at the Lupine Meadows Trailhead in Grand Teton National Park. Following the Garnet Canyon Trail, it shares the first 4.5 miles of the approach with the route up the Grand Teton. Once it reaches The Meadows, the route takes a left onto the "trail" through the South Fork of Garnet Canyon. Some loose talus and strenuous boulder hopping leads runners up to the saddle between the Middle Teton and the South Teton, at 11,600ft. At the saddle, runners turn right, then follow the classic Southwest Couloir ascent route up to the Middle Teton summit at 12,804ft. After following the same route back down to the saddle, the route continues up the northwestern-most ridge to the summit of the South Teton at 12,514ft. After topping out at the second summit, the route returns down the same way to the saddle between the Middle and the South Tetons. And finally, runners retrace their steps down to the Meadows, rejoin the Garnet Canyon Trail, and then descend the 4.5 miles to Lupine Meadows trailhead in order to finish the route exactly where it started. Overall, the route is about 15.5 miles and 7000 feet of elevation gain trailhead-to-trailhead. Some photos of what to expect along the way can be found here: https://www.stavislost.com/hikes/trail/middle-teton-and-south-teton.
Route finding is imperative on the upper sections of this run due to the rocky nature of the terrain, but the route taken up each of these mountains is pretty closely replicable and well-known. A very common pairing of summits, this run up the Middle and South Tetons is less technical than the route up the Grand Teton (and therefore gets a tad less press) but it is a beautiful and beastly day in its own right -- especially if you're running for speed!