Your Threshold Session Doesn't Need to Be Longer. It Needs to Be Fresher.
Estimated read time: 4.52 minutes (about as long as it takes to convince yourself that two-a-days sound like a good idea 🤔)
Hey Performance Nerds! Jonah here. 🤓
Same total work. Two sessions instead of one. The athletes rated it easier and stayed sharper through the back half.
Kjosen Talsnes et al. (2024) split threshold intervals across two sessions in 14 trained male endurance athletes. Heart rate drift dropped 2.5%. Effort dropped from 7.0 to 6.0.
This isn't about your sessions being broken. It's a tool for accumulating more quality.
Here's what you'll learn today:
What double threshold actually is (and the logic behind all intervals)
What the crossover data shows about recovery and session quality
Who benefits from double days, and why most runners should learn the principle, not the practice
(Augie has never split a session in his life. One sprint to the mailbox, collapse, nap. Not the worst recovery protocol.)
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🔬 Double Threshold Uses the Same Logic as Intervals
You already split work to keep quality high. That's what intervals are.
Double threshold extends the same idea across a full day. Morning session. Afternoon session. Same total work, split in two.
Each bout stays fresher because fatigue erodes less of the back half. More high-quality volume across the week.
That may add up to a stronger training response over time.
🧬 Less Drift, Lower Lactate, Easier Effort at the Same Work
Kjosen Talsnes et al. (2024) tested 14 trained male endurance athletes. One group did 6x10-min threshold intervals in a single block.
The other split the same six intervals into 2x(3x10-min), with 6.5 hours between. Same intensity, roughly 85-90% of max heart rate.
Each session starts fresher. Less drift, lower lactate, less perceived effort.
More of the total volume stays at the intended intensity.
Tonnessen et al. (2024) calls doubles a "fundamental feature" of several elite Norwegian training programs. Elite runners run two double-threshold days per week.
Their accumulated weekly threshold volume is substantially higher than single-session approaches allow.
One honest caveat: This is one crossover study with 14 athletes measuring acute responses. The Norwegian elite data is observational.
No long-term trials yet comparing doubles vs. singles across a full training cycle.
🔧 Why the 6.5-Hour Gap Resets More Than Lactate
Multiple systems recover between sessions:
Core temperature and hydration restore. The second session starts fresh, not overheated.
Muscles, tendons, and your nervous system split the load across two shorter bouts. Less fatigue per session than one long block.
Neither session is as taxing alone. Cumulative fatigue for the rest of the week drops.
You eat and hydrate between sessions. Glycogen partially replenishes. Better fuel for round two.
The waste products that actually cause fatigue clear out. Acid buildup and byproducts from muscle contractions flush between bouts.
Lactate clears too, but it's a fuel, not a villain. Your body shuttles it between muscle fibers for energy.
More total volume at the intended intensity. That's the whole point.
🏃♂️ What a Double-Threshold Day Looks Like
Bakken, the Norwegian coach who originated the method, ran everything with clinical lactate monitoring.
AM session (longer reps): e.g., 5-6 x 6 min at threshold (roughly 2.5-3 mmol/L lactate), 1 min jog recovery.
Recovery gap: 6-6.5 hours minimum.
PM session (shorter reps): e.g., 20-30 x 1 min at threshold (roughly 3-4 mmol/L), 30s jog recovery. Slightly higher end of the threshold band.
Total daily threshold volume: 15-20 km of quality work, plus warm-up and cool-down on both sessions. That's likely more threshold volume than most single sessions can deliver at the same quality.
Frequency: 1-2x per week. Kelemen et al. (2023) found elite Norwegian runners keep 75-80% of training at low intensity, with about 20% at threshold.
Most of us don't have daily lactate testing. An effort level around 7 out of 10 is a solid guide for competitive runners.
You finish thinking "I could've done 5 more minutes."
🎯 Who Needs Double Days?
The principle applies broadly. The practice doesn't.
These are starting points, not rules. Double days are highly individual. Schedule, recovery capacity, and training history all matter. Some high-mileage runners do all their threshold work in singles and thrive.
You don't need double days to benefit from this. Protecting quality within sessions applies at every level.
My version: I use the same splitting logic for running and lifting.
Wednesday: AM track session, PM lower-body lift with 6+ hours between. Sunday: AM long run, PM lower-body lift. Hard days stay hard so easy days stay easy.
🎯 Practical Takeaways
Double threshold splits threshold work into two daily sessions. Same logic as intervals: rest preserves quality.
Less drift, lower lactate, easier effort at the same work. Each session starts fresher.
The real benefit is weekly accumulation. More high-quality threshold volume across the training week.
Most runners don't need double days. But the accumulation principle applies to everyone.
Under 7 hours/week? Focus on singles first. Doubles are an advanced tool for high-volume athletes.
Bottom line: Your threshold session doesn't need to be longer. It needs to be fresher.
Jonah
Are You a True Running Nerd? Prove it.. 🧐
Welcome to the prove you’re a nerd section. Each week, I ask a question about a common running science myth.
Answer correctly, and you’ll be entered into a weekly raffle to win a package of Jonah’s favorite supplements.
Why does hitting 60–90g carbs/hr suddenly feel harder on hot race days, even if you’ve trained your gut for it?
- A. Carbs sit longer in your stomach in the heat, leading to sloshing and poor absorption 🤢🥤
- B. Your body switches to burning more fat in the heat, so ingested carbs aren’t used as much 🔥🥑
- C. Blood is pulled away from your gut to cool you, so less of what you take in actually gets absorbed 🌡️🩸
- D. Heavy sweating makes it harder for your body to break down carbs during exercise 💧⚠️
Last Week’s Results: The Bounce Myth 📉🏃♂️
Most runners think efficiency is about “quick feet” or “less time on the ground.” But when it comes to running economy, the biggest wins are often hiding in plain sight.
The correct answer?
A. Reducing vertical oscillation (less up-and-down bounce) by ~1–2 cm 📉 ✅
A recent meta-analysis shows vertical oscillation has one of the strongest relationships with running economy. More bounce means more work against gravity, which means more wasted energy every step.
Here’s how the votes shook out:
🟨 A. Reducing vertical oscillation (less up-and-down bounce) by ~1–2 cm 📉 – 90
🟨 B. Increasing cadence by ~5–7% above preferred 🔁 – 75
🟩 C. Shortening ground contact time ⚡ – 98 ❌
⬜️ D. Switching from heel strike to mid/forefoot 🦶 – 5
A lot of you went with ground contact time.
Makes sense. It feels like faster, lighter steps should be more efficient. But across 50+ studies, contact time shows basically no meaningful relationship with running economy when speed is controlled.
What about cadence?
There is a small benefit there. But it is weaker and more individual. Cadence tweaks help at the margins, not as a primary lever.
Bottom line?
If you want “free speed,” stop thinking about faster feet. Start thinking about less bounce.
🚀 Jonah's Stryd Training Tip: Why Splitting Sessions Saves Your Springs
I ran a 40-minute threshold effort two weeks ago. Felt sharp through minute 20. By minute 35, my legs were cement. Same pace, way more effort.
I checked my Stryd data afterward. Leg Spring Stiffness dropped steadily across that session.
By the final 10 minutes, my tendons were returning less elastic energy. Muscles were picking up the slack at a higher energy cost.
That's the case for splitting threshold days. When you break the same volume into AM and PM sessions, LSS should stay closer to baseline in both bouts.
Fresh tendons return elastic energy cheaply. Fatigued tendons don't.
The 6.5-hour reset in the Talsnes protocol lets your springs recharge.
Why it matters:
Quality stays high. Preserved LSS means each rep costs less energy. More work at the intended stimulus.
Fatigue shows up early. A declining LSS trend tells you quality is eroding before pace does.
Track it across blocks. If your second-session LSS matches your first, the split is working.
After your next threshold day, compare LSS from the first and last intervals. That gap is your fatigue tax.