TOUGHEST Marathon Workout I’ve EVER done! 2:29 Marathoner training for a BIG PB in Valencia Marathon - The Welsh Runner

Aug 13, 2025

Intro

This is a quick summary of “TOUGHEST Marathon Workout I’ve EVER done! 2:29 Marathoner training for a BIG PB in Valencia Marathon” from The Welsh Runner. It’s an inspiring 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 workout is a 5 km steady warm‑up, followed by 13 repeats of an “on‑off” kilometer pattern, then a 4 km cooldown – a total of 35 km. This type of structured session is a fantastic example of the concepts we cover in our guide to mastering interval training.
“On” kilometers are run faster than marathon pace (around 3:15–3:20 min/km). Pushing your pace like this is a key technique for building top-end speed, whether for a marathon or for mastering 5K speed.
“Off” kilometers are 20‑30 seconds slower (about 3:40–3:50 min/km), giving a slight recovery before the next fast kilometer.
The goal is to build lactate tolerance, burn glycogen and simulate marathon fatigue without actually running a marathon distance.
Nutrition tips: take a Morton gel 5 minutes before the start, a 200 mg caffeine tablet (or homemade gel) in the pocket, and stay hydrated with a homemade drink.
Practical advice: after a rest day, do a light jog instead of staying completely still, and use a flip belt to keep bottles from bouncing.

Workout Example

5 km easy warm‑up (steady, ~6:12 min/mile or ~3:50 min/km)

Repeat 13×:
  • 1 km “on” – 3:15‑3:20 min/km (faster than marathon pace)
  • 1 km “off” – 3:40‑3:50 min/km (20‑30 s slower than the “on” pace)

4 km cool‑down (easy pace)

Total: 35 km (≈19 mi) with about 26 km of hard work.

Adjust the paces to match your current marathon pace and use the Pacing app to customise the intervals.

Closing Note

Give this tough “on‑off” marathon session a try, tweak the paces to fit your own marathon goal, and use the Pacing app to tailor the intervals. While this workout is geared towards the marathon, the core principles of alternating pace and building endurance are universal. They’re just as effective when you’re mastering the 10K. You’ve got the strength – now go turn that confidence into a new PB