Why You Struggle With Longer Intervals (And How to Fix It Fast!) - Lee Grantham

Aug 13, 2025

Intro

This is a quick summary of Why You Struggle With Longer Intervals (And How to Fix It Fast!) 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

Longer intervals fail because your VO₂‑max work is fine, but your lactate threshold and speed‑endurance haven’t caught up yet.
The fix is a progressive, mid‑week interval session that builds V₂‑max and pushes your threshold in small, controlled steps. For a deeper dive into the science behind these workouts, check out our guide on Mastering Interval Training: Science-Backed Workouts and How a Smart App Can Personalize Them.
Keep the session once a week, keep intensity around 8‑9/10 effort, and back off if you feel over‑reached.
Pair the interval session with weekend long runs and easy recovery runs to build your aerobic engine.

Workout Example

Week 1 – 20 × 1 min @ 4:00 min/km (6:26 mi) with 60 s rest

Week 2 – 13 × 90 s @ 4:00 km/min with 60 s rest (30 s longer each rep)

Week 3 – 10 × 2 min @ 4:00 km/min with 60 s rest

Progression (once you’re comfortable):

5 × 3 min @ 4:24 km/min (7:05 mi) + 60 s rest (10‑20 % slower than goal 5K pace)
Follow immediately with 6 × 1 min @ 4:00 km/min (6:26 mi) + 60 s rest

This progression is fantastic for improving your race times. If you’re targeting a new personal best, you can find more workouts like this in our guide to Mastering 5K Speed: Proven Interval Strategies to Cut Minutes off Your Time.

Later stage (if you can handle it):

5 × 4 min @ 4:24 km/min (7:05 mi) + 60 s rest (10 % slower than target 5K pace) – gradually increase reps or lengthen rest as needed.

Building the endurance to handle these 4-minute repeats is not just for the 5K; it’s also a cornerstone for longer races. The same principles of lactate threshold development are essential for Mastering the 10K: Proven Training Plans, Pace Strategies, and How a Smart App Can Elevate Your Performance.

Practical Tips

Start with short, manageable intervals (1 min) to get the feel of race‑pace effort.
Increase interval length by 30 s each week, reducing the number of reps to keep total volume ~20 min.
Keep the rest interval constant (60 s) to maintain a controlled, repeatable effort.
Aim for 8‑9/10 effort – you should feel in control, not scrambling for the finish.
If a session feels too hard, back off a week or add an extra recovery day.
Use the session to simultaneously boost VO₂‑max (short reps) and raise lactate threshold (longer reps at slightly slower pace).

Closing Note

Give this progressive interval plan a try and tweak the paces to match your current fitness in the Pacing app. Keep it consistent, stay patient, and you’ll watch those longer intervals become manageable—bringing you closer to that new PR! 🚀