You've probably seen headlines: High-Intensity Training is superior...
Steve Magness@stevemagness
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Jul 06, 2025
~2 min read
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You've probably seen headlines: High-Intensity Training is superior to easy aerobic running.
But dig deeper and you'll notice a pattern: most of these studies are short: just 4 to 8 weeks.
A recent review tells a fuller story.
In the early weeks, HIT and Sprint Interval Training outperform easy endurance training (ET).
But over the long haul… the story changes
But dig deeper and you'll notice a pattern: most of these studies are short: just 4 to 8 weeks.
A recent review tells a fuller story.
In the early weeks, HIT and Sprint Interval Training outperform easy endurance training (ET).
But over the long haul… the story changes
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Easy aerobic work catches up...and then surpasses.
This isn’t anti-high intensity. You need it! You need every training intensity.
It’s about understanding timelines. Physiological adaptations don’t all happen at the same rate.
HIT gives you a quick jolt. It's the icing on the cake.
But endurance training lays the foundation for long-term progress. The gains come slower, but they go deeper.
This isn’t anti-high intensity. You need it! You need every training intensity.
It’s about understanding timelines. Physiological adaptations don’t all happen at the same rate.
HIT gives you a quick jolt. It's the icing on the cake.
But endurance training lays the foundation for long-term progress. The gains come slower, but they go deeper.
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We’re a culture obsessed with immediacy. And that holds in exercise:
“Get fit fast.”
“Only train for 10 minutes.”
But peak performance doesn’t play by TikTok timelines.
The mistake is mistaking speed of improvement for quality of adaptation. Just because something works fast doesn’t mean it works best.
“Get fit fast.”
“Only train for 10 minutes.”
But peak performance doesn’t play by TikTok timelines.
The mistake is mistaking speed of improvement for quality of adaptation. Just because something works fast doesn’t mean it works best.
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It's why research often is behind coaching theory...
Because of the constraints of studies, they are often short-term.
We see what happens for 6-8 weeks...
In addition, we often test things in isolation. All intervals or all easy...when it's the interaction and support that matters!
Because of the constraints of studies, they are often short-term.
We see what happens for 6-8 weeks...
In addition, we often test things in isolation. All intervals or all easy...when it's the interaction and support that matters!
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This is why the principles espoused by Arthur Lydiard in the 1960s still holds up.
Months of slow base-building, followed by hills and a sharpening phase.
That base? It's where aerobic development, mitochondrial growth, and capillary density happen.
They lay the foundation...allowing you to handle and absorb the harder training.
Months of slow base-building, followed by hills and a sharpening phase.
That base? It's where aerobic development, mitochondrial growth, and capillary density happen.
They lay the foundation...allowing you to handle and absorb the harder training.
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Coaches have known this for decades.
But science often lags behind coaching experience, especially when study design prioritizes short-term change.
A 6-week study might favor HIT. A 6-month season?
That’s where aerobic training shines. Time horizon changes the answer.
But science often lags behind coaching experience, especially when study design prioritizes short-term change.
A 6-week study might favor HIT. A 6-month season?
That’s where aerobic training shines. Time horizon changes the answer.
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But here’s the real kicker: it's not either/or.
That's the debate we had in the 1920s: All long walks or 7 days of intervals...
The best training blends all intensities. You need everything from long and easy to threshold to long/medium/short intervals and sprints.
They’re complementary.
That's the debate we had in the 1920s: All long walks or 7 days of intervals...
The best training blends all intensities. You need everything from long and easy to threshold to long/medium/short intervals and sprints.
They’re complementary.
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Easy training also does something else: it builds consistency.
It’s low stress, low injury risk, and sustainable.
It gives your body the reps it needs without pushing it toward burnout.
That’s why most endurance athletes spend 80–90% of their time running easy...
It’s low stress, low injury risk, and sustainable.
It gives your body the reps it needs without pushing it toward burnout.
That’s why most endurance athletes spend 80–90% of their time running easy...
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You can’t microwave aerobic development.
It’s like gardening: you can’t rush the soil. But if you nurture it, patiently, it produces season after season.
The best athletes? They respect the long arc.
It’s like gardening: you can’t rush the soil. But if you nurture it, patiently, it produces season after season.
The best athletes? They respect the long arc.
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To go deeper on this topic, read my new article:
Zone 2, HIIT, and the Flawed Science of Endurance Training
open.substack.com/pub/stevemagne…
Zone 2, HIIT, and the Flawed Science of Endurance Training
open.substack.com/pub/stevemagne…
