TLDR: It's a lot harder to overdo it than you think. And for women, it usually isn't the workout that's the problem, it's running on coffee until noon.

In 2006, I was producing Dr. Oz's first radio show for Oprah's radio network. He was famous then for the book YOU: The Owner's Manual, and for explaining how the body works in ways that made people interested in their health in new ways.

One day he interviewed an endurance athlete. And I remember him saying that more than two hours of cardio creates so much oxidative stress, it may take years off your life.

I never forgot it. Twenty years later, this idea came up again in a conversation about biohacking and the risk of overtraining. Is long-distance anything, whether biking, running or hiking, or even weight training, actually good for you?

TBH, from what I see, too much exercise is very few people's problem. (Certainly not mine.) But now we all wear a Whoop that grades our recovery every morning. So the question is back: how much is too much, and why?

So I went back through 20 years of science on overtraining, the heart and the forces on our artery walls. The short answer: it's very hard to overdo it, and when people do, they're mostly men. What women do overdo is different. We under-recover and under-fuel.

Here's how.

Don't train less. Recover more and eat enough to keep going.

👉 Forward this to the friend who trains through everything and eats lunch at 3.

❌ The old assumption: More than two hours of cardio takes years off your life.

I looked. I couldn't find a strong study that shows it.

✅ It's really hard to overdo it. In 116,221 adults followed for 30 years, the benefits leveled off at 150–300 minutes a week of hard exercise, or 300–600 of moderate. More didn't add much. It didn't clearly cause harm either (Circulation, 2022). Even Tour de France riders had 41% lower mortality than other French men (European Heart Journal, 2013).

✅ When people do overdo it, they're mostly men. At very high doses of hard exercise, men's risk of AFib, an irregular heart rhythm, went up. Women's kept going down (European Heart Journal, 2020). Men who race for decades also build more calcified plaque in their arteries. Women who race for decades don't (Circulation, 2024).

What about too many shear forces on your artery walls? The steady blood flow you get from exercise is one of the main ways it protects them—it’s a good thing, not bad (Physiological Reviews, 2017).

✅ Oxidative stress is the point. Exercise creates free radicals. That's the signal that tells your body to build its own defenses. People who took vitamin C and E while training lost the boost in insulin sensitivity everyone else got (PNAS, 2009). The stress isn't the problem. Stress without recovery is.

✅ What women overdo: under-recovering and under-fueling. When you don't eat enough to cover your training, your body cuts corners on bone, hormones, metabolism, immunity, sleep and mood. It's called REDs, and it isn't just an elite athlete problem (British Journal of Sports Medicine, 2023).

In my practice, this is what I see far more than an overworked heart. Women training hard, eating light, sleeping 6 hours and wondering why they feel worse. And in perimenopause, when your cycle is already changing, you lose the missed-period warning sign.

1️⃣ Aim for the sweet spot, not the max. 150–300 minutes of hard exercise a week, or 300–600 of moderate, or a mix. That's about 30–60 minutes of real effort, 5 days a week.

2️⃣ Keep most of it easy. Make the hard stuff count. Build your week on Zone 2: walking, easy cycling, jogging where you can still talk. Add a few truly hard sessions, not an all-out effort every day. In men, it was the very hard efforts, not the total hours, that tracked with more calcium in the arteries (Circulation, 2023).

3️⃣ Read your Whoop recovery score as a trend. One red day means nothing. A week of them means something. Back off when the numbers and your body agree:

An easy day isn't a day off. Walk, stretch, do yoga.

4️⃣ Eat enough to cover your training. You can't recover from a workout you didn't fuel.

5️⃣ Know when to get checked. Palpitations, fainting or chest pain during exercise? Stop and see a doctor. And if you're a man over 40 who's done hard endurance training for decades, ask about a Cleerly CTA, a non-invasive 3D image of the heart, to look at soft and hard plaques in the artery walls. We order them at Parsley routinely.

The goal: Don't exercise less. Recover more, and eat enough to keep doing it for decades.

Does this resonate? Hit reply and tell me: does your recovery score run your day, or do you ignore it? I read every one.

A calcium score only shows the hard, calcified plaque. A Cleerly scan goes further. It's an AI-analyzed heart CT that also shows the soft plaque a calcium score misses, which is the kind that worries me more.

If you've been training hard for years, or heart disease runs in your family, this is the scan I'd want. Work with us at Parsley and we'll order your Cleerly scan and walk you through the results. Get started here →

Stay strong, stay curious, and breathe,
Robin

Medical disclaimer: As always, this newsletter is for informational and educational purposes only and is not intended as medical advice. Always consult your healthcare provider before making any health decisions or changes to your treatment plan.