15 Kilometers - Seth James DeMoor

Aug 13, 2025

Intro: This is a quick summary of 15 Kilometers from Seth James DeMoor. It’s a great watch — we’re breaking it down so you can try the workout today. Be sure to check out the full video for all the details.

Key Points

The run is a speed‑endurance (threshold) workout on rolling hills, targeting a steady mile‑pace in the 5:15–5:23 range.
Seth uses a Koros watch to lock in the first 1,500 m (≈1 mi) at the exact target pace, then lets the run settle into the zone.
He monitors cadence (≈190–194 spm) and heart‑rate (150 bpm early, 161–163 bpm later) to stay in the intended effort.
Total vertical gain is modest (~280 ft) – the course is mostly undulating, not a mountain climb.

Workout Example

Warm‑up – 5‑10 min easy on flat ground.
Threshold start – Run the first 1,500 m (≈1 mi) at your goal pace (e.g., 5:22 / mi). Use your watch to confirm you’re on target.
Settle in – Continue for the remaining 13.5 km at the same pace, staying in the 5:15–5:23 / mi range. Let the hills provide brief speed bursts.
Cool‑down – 5‑10 min easy, focusing on relaxed cadence.

Practical Tips

Pace‑check early: Glance at the watch after the first 1.5 km to verify you’re dialing in the right speed.
Cadence cue: Aim for ~190 spm; if you drop below, pick it up on the next hill.
Heart‑rate band: Keep HR between 150 bpm and 165 bpm; if it spikes, back off a second.
Hill strategy: Use the rolling rollers to naturally vary effort – stay smooth, don’t sprint.
Data‑driven: Record splits (e.g., 5:24, 5:24, 5:21, 5:20, 5:19, 5:34) and adjust future runs based on the trend.

Closing Note: Give this 15 km threshold run a go, tweak the pace to fit your own speed in the Pacing app, and watch your endurance click into place. Happy running!