how I slayed my cardio demons

Happy belated Valentine's Day to Heart Rate Zone Training specifically

I used to be philosophically opposed to cardio.

Yes…I, someone who runs a product team that literally helps people optimize their cardio training, used to think cardio was Just Not For Me™. I love lifting weights and would occasionally drag myself through a HIIT class, but I had never once enjoyed a cardio-focused workout. Lifting made my back pain go away. Cardio just made me miserable. I figured some people's bodies just respond to different types of training, and cardio simply wasn't my thing.

Well. OK. Guess what? I was wrong. And the answer was not another “how to start running” program.

This is the tale of how I went so wrong, and how I eventually got on the cardio train bike.

(This is top of mind for me now because this week at WHOOP, we released some new features focused on Heart Rate Zone training. Learning about Heart Rate Zones fundamentally changed by approach to, and feelings toward, cardio exercise. If you, too, would like to transform your relationship to exercise, you can get a free month of WHOOP on me here :) )

I am going to wade into some basic scientific concepts of exercise physiology in this post. I promise you it will be interesting and helpful wherever you are on your fitness journey. Bear with me.

Let’s start with Vo2 Max.

It turns out that one of the biggest drivers of your long-term health—that is, not just how long you can expect to live, but specifically how many years you can expect to continue having a high quality of life—is something called VO2 Max.

VO2 Max is the maximum amount of oxygen your body can absorb and use when it's pushing itself hard during exercise. Like, if your body were a restaurant, what is the maximum number of people the kitchen can serve at peak capacity? When you're exercising hard, your muscles are like hungry tables all ordering at once during the dinner rush. VO2 Max measures how many orders (ie how much oxygen) your kitchen can actually handle when every table is full and demanding food at the same time. Within this tortured metaphor I am already regretting, a kitchen with a high VO2 Max would be well staffed and running at maximum efficiency. A kitchen with a low VO2 Max would be sluggish, easily overwhelmed, and immediately backed up.

OK, so what does this have to do with aging? This is explained in depth in books like Peter Attia’s Outlive, but I find this graph to be the most compelling:

This visual is showing you the required cardiorespiratory fitness levels (measured as VO2 Max) for daily life activities and exercise. VO2 Max naturally decreases as you get older, which means that if you work on improving it today, you will be better off in 20 or 30 years. Look at the black line in the middle representing a person of average fitness. At age 30, they can run at 6 MPH. By age 45, they will struggle to climb stairs. By age 65, they will struggle to walk 3 MPH up a steep hill.

Compare this to the green line, someone of high fitness. At age 30, they can run at 10 MPH. Even at age 75, they are still able to climb stairs without difficulty.

This all got me….thinking. Perhaps, as my sweet husband has long told me, I should not just write off cardio. But I've tried so many times to get into it before, and never once succeeded. What was I doing wrong?

The answer clicked once I started learning about Heart Rate Zone training. It turns out I wasn't actually bad at cardio. I just didn't understand how to train.

Around Zone 4 (high intensity), your body hits what's called an aerobic threshold. Below that threshold, the supply of oxygen meets or exceeds your body’s energy demand, so you can maintain this effort for a while. Above that threshold, your body can't get oxygen to your muscles fast enough, so it switches to local energy reserves (muscle glycogen) that burn out quickly.

When you push too hard too soon, you force yourself into anaerobic training without a sufficient fitness base. Here's what happens when you do that:

1. Your body switches to anaerobic energy production. As your muscles rapidly burn through their available muscle glycogen, the waste products build up in your muscles, causing intense burning sensations and much harder breathing as your system struggles to keep up.

2. This unsustainable energy production quickly depletes your glycogen stores. You experience a dramatic energy crash, like hitting an invisible wall. Your muscles feel heavy and weak, and you can't maintain the effort.

3. The physiological stress causes your form to break down. Your movements become increasingly sloppy and uncoordinated as your body fails to maintain proper technique under fatigue.

4. Your breathing becomes severely labored: You can't talk except in gasps, and you might feel light-headed from the rapid, shallow breathing as your body desperately tries to get enough oxygen.

Does this sound familiar? It does to me—it was what happened literally every time I tried to get into running. Once I started tracking my HR Zones, I realized that when I run, or go to a HIIT class, I quickly push myself into Zone 4/5 territory. I told myself I just needed to keep at it and eventually I would get “over the hump.” But instead I would just feel terrible, get frustrated, dread working out, and eventually stop doing cardio.

The key point is that all of this happened because I was trying to operate in an anaerobic state that my body wasn’t prepared to handle. I was forcing my body into emergency mode before building any foundation. This is why building an aerobic base first is so important.

And how do you build an aerobic base?

NOT BY RUNNING UNTIL YOU WANT TO DIE, IT TURNS OUT.

The actual right approach: focused Zone 2 training. I got a smart trainer and a bike and started using Zwift, which is basically like Mario Kart but for cyclists. (I'll go on a small tangent about how I've never enjoyed spin classes because I hate when people talk at me while I exercise - but Zwift? I LOVE Zwift. It's so fun to bike around fake worlds with real people from Japan and Sweden and see all the creatures that live in the fake world. You can even go underwater!)

The transformation was incredible. 30+ minutes of Zone 2 exercise 3-5 times a week got me in shape so much faster and more effectively than all my previous failed running attempts combined. In January, I aimed for just 20 minutes of Zone 2 every day. I was amazed at how quickly I saw improvement - I could output more power while keeping my heart rate lower, a clear sign my cardiovascular fitness was getting better.

And, as much as I used to think cardio wasn’t doing anything for me, once I had the data in WHOOP I could see the positive downstream results pretty quickly. With consistent Zone 2, I was falling asleep faster and sleeping better, and I had better recoveries and more energy throughout the day.

(I’m talking about this in the context of getting into shape, but for the Real Athletes out there…I would be remiss if I didn't mention that Colin has said the biggest mistake he made in offseason training for rowing in college was feeling like he needed to go hard for training to be helpful – to get on an erg and feel pain. If he had realized that low-intensity volume was what he needed, he might have had an easier time cutting out excuses and spinning the flywheel instead. An athlete who trains enough volume at low intensities pushes their sub-threshold outputs higher and higher until their aerobic pace outstrips their old race pace…AND without all that lactate and pain. Even if you are an elite athlete, you still need to work your aerobic system with long (90 minute) Zone 2 workouts to increase endurance. If you approach every workout like "time to push myself as hard as I can for as long as I can," you will plateau very quickly because you're not building your aerobic capacity.)

Want to try this approach yourself? Here’s what I recommend based on my conversations with experts in this space:

Getting Started with Zone 2 training

• Start with just 20-30 minutes of Zone 2 exercise 3-5 times a week.

• You can use an online calculator to get your Z2 BPM ranges, though of course I’d recommend using WHOOP or another type of heart monitor.

• The key is staying well below that aerobic threshold. You should be able to hold a conversation while working out. If you're gasping for air, you're going too hard.

Types of workouts

It's very difficult to stay in Zone 2 while running if you are not an elite athlete. That's why I started with cycling. You could also try:

• Walking uphill on a treadmill

• Using an elliptical

• Swimming at an easy pace

How to actually improve VO2 Max

Once you've built up that aerobic base (which happens surprisingly quickly!), you can start improving your VO2 max by adding short bursts of higher intensity. Try this once a week:

• 4 intervals of 3 minutes hard effort (Zone 4/5)

• Each followed by 2 minutes easy recovery (Zone 1/2)

• As you improve, add more intervals, increase the time of intense bursts, and do this more days per week

Track it all in WHOOP

This is exactly what WHOOP helps you track now. We just launched some upgrades to make it easier:

• See a historical trend of time spent in different Heart Rate Zones

• Set HR Zone targets in your Weekly Plan

• Get specific workout recommendations each day from WHOOP Coach based on your zone training history

Did I mention you can get a free month of WHOOP here? Yee haw!

Miscellaneous recommendations

1. You guys are NOT going to believe this. Remember when I went on this whole mission to find a new hand soap because my beloved Muji soap was discontinued? WELL. I FOUND IT. When I was at Muji recently I noticed a sign that said all their cosmetics are made in partnership with Public Goods. So I got on the Public Goods website and looked up their hand soap. The scent profile matched my beloved Muji soap, so I bought it, and ….. IT’S THE SAME SOAP. I AM SO BACK!!! If you want the hand soap that I have DEFINITELY overhyped, it’s available here (refills here).

2. I also need to share an anchovy-based experience I had recently. I got these Cantabrian Anchovies from the Rancho Gordo website with my last bean order. Inspired by a recipe in Justine Cooks, I draped a couple over a halved boiled egg with some chopped herbs. First of all these anchovies are AMAZING, the best I have ever had by a long shot. Second of all I have never had anchovies on eggs before but it’s now a top snack for me.

3. Speaking of my last bean order, I got Rancho Gordo split peas to make Thomas Keller’s Split Pea Soup and it turned out impeccably. I make a few edits to the recipe; first I use a regular ham hock rather than a smoked one for a more subtle meat flavor, second I don’t put shreds of meat or peas in the final soup because I prefer a smooth texture. But either way, it’s a top soup in my book, and perfect for this endless onslaught of snow we’re getting.

That’s all for now.

xoxo,

hils