Unleash Your Potential: How Interval Training Can Shatter Your Personal Bests - Lee Grantham

Aug 13, 2025

This is a quick summary of Unleash Your Potential: How Interval Training Can Shatter Your Personal Bests from Lee Grantham. 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

Interval training is the fastest way to break limiting personal‑best times for any distance (5K, 10K, half‑marathon, marathon, ultra) by adding speed work and shifting mindset.
Identify “gray‑zone” easy runs that are too fast; bring easy runs back to true recovery pace to allow quality speed sessions.
Use short, fast repeats (400 m) to develop leg speed, which then makes longer intervals and race‑pace feels easier.
Gradually increase the number of reps while keeping the target 400‑m time around 70 seconds (or 1:10 per 800 m) and keep rest at 60 seconds.

Workout Example

Warm‑up: 10‑15 min easy jog + dynamic drills
Main set: 20 × 400 m @ ~70 s per rep (or 1:10 per 800 m) with 60 s rest between reps.
Progression: start with 10–12 reps at goal pace, add 2‑3 reps each week until you can do 20 reps.
Cool‑down: 10 min easy jog.

Practical Tips

Keep easy runs truly easy (recovery pace) to avoid “gray‑zone” fatigue.
Treat speed work as a skill—practice regularly even if races are cancelled.
Monitor how your body feels; heart rate can rise but stay comfortable.
Use the Pacing app to adjust the 400 m target time to match your current pace.

Closing Note Give this interval session a try this week, tweak the 400 m target to suit your own paces in the Pacing app, and watch your marathon speed climb. You’ve got the tools—go smash that PB!