What Nobody Tells You About Those Long, Slow Zone 2 Runs

I started doing zone 2 training and have worked up to 3+ hour zone 2 runs in my weekly training. I thought I knew what to expect - keep my heart rate low, build my aerobic base, become a more efficient runner. The usual promises. What I didn’t expect were some of the bizarre side effects that nobody warns you about.

The Weird Stuff That Actually Happens

1. Your Muscles Will Betray You, But You Can Sing Your Lungs Out

Here’s something that completely caught me off guard: After a 3+ hour zone 2 run, I’m not out of breath at all but my muscles are screaming. This feels completely backwards from my normal running experience where I’m usually exhausted both muscle-wise AND gasping for air.

There’s a fascinating physiological reason for this. Zone 2 training keeps your blood lactate levels stable - your body clears lactate as fast as you produce it. You’re working your muscles for hours while your cardiovascular system cruises along, using fat as fuel instead of burning through carbs. Your muscles do serious work accumulating miles, but your heart and lungs are on a leisurely jog.

Normally when you run hard, everything fails together in one spectacular bonfire of exhaustion. With zone 2, your muscles do a slow burn while your cardiovascular system barely breaks a sweat.

2. Why Can’t I Fall Asleep?!

I’ve had a lifetime of great sleep - head-hits-pillow, wake-up-9-hours-later kind of sleep. Then I started these long zone 2 runs and suddenly I’m lying in bed at 2 AM wondering what happened to my superpower.

A key moment came as I browsed The Feed (nutrition shop for athletes) and noticed product lines dedicated to sleep-related nutrition. Why would athletes need help sleeping? Aren’t we supposed to be exhausted?

Marathon-level training can seriously deplete magnesium levels - up to 12% of your daily magnesium lost through sweat alone. Magnesium helps regulate cortisol and promotes deep sleep. Without it, you get the cruel irony of being physically exhausted but neurologically wired.

I’ve started supplementing with magnesium (glycinate, citrate) before bed. Who knew that running for hours could make you too tired to sleep?

3. Just Ran 3 Hours, You Must Be Not Hungry?!

Remember being a kid and your mom saying “you must be hungry after all that running around”? Turns out mom was wrong.

I noticed this during marathons in my younger days, but it’s happening again with long zone 2 runs: I finish a 3+ hour run having burned 1,000+ calories, and food is the last thing on my mind. My stomach feels like it’s hibernating.

As usual, the answer is science - intense or prolonged exercise actually suppresses your “hunger hormone” (ghrelin) and increases appetite-suppressing hormones like peptide YY. Your body essentially shuts down digestion to prioritize blood flow to working muscles, and this effect lingers after you stop running. Evolution probably designed this so our ancestors could hunt for hours without being distracted by hunger, but it means I have to force myself to eat recovery food when every instinct is saying “nah, I’m good.”

The Parts Nobody Mentions

Here are two notes on Zone 2 training which I will mention:

Walking. So. Much. Walking.

Want to feel like a fraud while “running”? Try zone 2 training on trails. Any slight incline and my heart rate monitor starts screaming at me to slow down. So I walk. And pause. And walk some more.

I’ve had to completely recalibrate my ego about what “going for a run” means. Sometimes my Strava looks like I’ve been out for a leisurely hike rather than a training run. But here’s the thing - this is exactly what you’re supposed to do. If you can’t maintain zone 2 while running up that hill, you walk. Period. Your ego will recover faster than your aerobic system will if you keep spiking into zone 3.

You NEED a Real Heart Rate Monitor

Let me save you some frustration: your fitness watch is lying to you about your heart rate, especially during zone 2 training where precision matters.

I use a Polar Verity Sense armband (because I hate chest straps with the fire of a thousand suns), and the difference is shocking. Wrist-based monitors lag, they get confused by arm movement, and they’ll have you thinking you’re in zone 2 when you’re actually cruising in zone 3.

When you’re trying to stay in such a narrow heart rate range for hours at a time, accuracy and responsiveness matter. Bite the bullet and get a proper monitor - armband or chest strap. Your Zone 2 training will thank you.

Bottom Line

Zone 2 training is simultaneously the most boring and most surprising type of running I’ve done. It’s exposed gaps in my fitness (strong heart, apparently weak muscles), created problems I didn’t know existed (who needs help sleeping after running for 3 hours?), and forced me to walk up hills like… like I’m old (I am old).

But here’s the thing - it’s working. My easy pace is getting faster while staying at the same heart rate. I can run for hours without feeling destroyed the next day. Despite all the sleep issues (which I will figure out).

Just don’t expect it to feel like “normal” running. Throw out your conceptions that running is hard. It’s its own weird, slow, surprisingly complex beast. Just prepare to do a lot of walking. Your ego might hate it, but your mitochondria will thank you.

Helpful Resources:

• Phil Maffetone’s MAF Method - The OG of zone 2 training
• Uphill Athlete’s Aerobic Capacity Guide - Great for understanding your zones
• Examine.com’s Magnesium Guide - Everything you need to know about magnesium supplementation
• The Science of Ultra Podcast - Deep dives into endurance physiology