Why Your Intervals Aren’t Working (And How to Fix Them)

Optimising VO₂max and Lactate Testing for Better Running and HYROX Performance

Intervals are one of the most effective tools in endurance and hybrid training. They help improve aerobic capacity, boost threshold power, and sharpen top-end speed. But only if they’re used properly.

Whether you’re training for running performance or preparing for a HYROX event, understanding how to structure your intervals using VO₂max and lactate testing data is a game changer.

The problem? Most people are either doing the wrong type of intervals for their goal... or they’re matching the wrong rest to the wrong intensity.

Let’s clear it up.

Your Intensity Dictates Your Recovery

Every interval has a purpose — and each purpose demands a different structure.

1. VO₂max Intervals (Red Zone Work)

These are your high-intensity, maximal aerobic power sessions. You’re working at or just above your VO₂max. It’s brutal, but effective for driving up your ceiling.

• Work time: 2–4 minutes per interval

• Recovery time: 1:1 work:rest ratio (e.g. 2 min hard, 2 min easy)

As fitness improves, you might progress to sessions like:

• 4 x 2 minutes at red zone with equal recovery

The key? Full recovery between reps to repeat high-quality efforts. If your power or pace drops off after rep 2, you’re under-recovered and not training what you think you are.

VO₂max testing can help identify the right intensity zones for this type of training, ensuring your efforts match your physiology.

2. Threshold Intervals (Zone 4 Work)

Threshold work is all about control. You're sitting right at the edge of lactate accumulation — training your body to sustain strong, steady efforts without tipping over.

• Work time: 6–20 minutes total (e.g. 2 x 10 min, or 4 x 5 min)

• Recovery time: Short. 2:1 or even 4:1 work:rest ratio

  • (e.g. 8 minutes on → 2–4 minutes easy)

The key? Consistency across intervals. This isn't a time to sprint — it's about locking into a strong, repeatable pace. If you're needing full recovery or can't maintain your pace, you're probably going too hard.

Lactate testing allows you to pinpoint your lactate threshold (LT2), which aligns closely with this zone. It helps fine-tune pace and recovery so you don't burn out too early.

The Big Mistake?

Most people mix up the systems.

• They push VO₂max intensity… but don’t take enough rest.

• They hit threshold efforts… but go too hard and need full recovery.

What ends up happening? Everything turns into a grey-zone grind: not hard enough to build speed or power, not easy enough to build aerobic efficiency.

Fix It With Structure

The best interval sessions aren’t the flashiest — they’re the most intentional.

Ask yourself:

• Am I training aerobic base, threshold, or power?

• Is my recovery matching the effort?

• Can I maintain quality across all intervals?

• 
  

If the answer is no, it’s time to reassess. Not every session should feel like a sufferfest — and the smart ones usually don’t.

Need help structuring your own intervals?

If you’ve done a VO₂max or lactate threshold test recently (or are planning to), I can help you build sessions that actually reflect your physiology — whether you're training for a 10K, a marathon, or a HYROX event.

Ready to take it a step further?

✅ You can book in for VO₂max or lactate testing here in the UK — just message me directly.✅ Or buy a portable device like the one I use (happy to share recs).✅ Or just Google "VO₂max or lactate testing near me" to find a local lab or clinic.

It’s not just for elites — it’s for anyone who wants to stop guessing and start progressing.