A Cardiologist's Guide to Power Zone Training on the Bike

Heart rate lies to you a little. It spikes with stress, a bad night's sleep, or an afternoon coffee, and if you're on a beta-blocker for blood pressure or a heart rhythm issue, it can stay artificially low even when you're working hard. That's a big part of why, when I clip into my Peloton at home after a long clinic day, I skip the high-energy music rides and head straight for an equally energetic Power Zone class — it trains off watts, not heart rate. Power Zone training uses a twenty-minute fitness test to estimate your Functional Threshold Power (FTP), the highest wattage you could hold steady for about an hour, and uses that number to set seven training zones. Unlike heart rate, watts measure the actual mechanical work your legs are doing in that moment, no matter what your pulse says. In my practice, I recommend this structured approach because it takes the guesswork out of pacing a workout — you're training off what your body is actually producing, not a number that medication or a rough night can distort. (To be clear: I'm not sponsored by Peloton — I just use it myself and find the power-zone format genuinely useful.)

Key Findings & Takeaways

• Why Power Beats Heart Rate (Especially on Heart Meds): Watts are a direct measure of output — they don't lag behind sudden efforts, drift with dehydration, or get blunted by beta-blockers the way heart rate can. If you're managing a cardiac condition or blood pressure with medication, power is often the more honest number to train by.
• Zones 1 and 2 (most of your training): An easy, conversational pace that trains your muscles to use oxygen more efficiently and helps your heart pump more blood with each beat. I tell patients to aim for roughly 75-80% of their weekly ride time here — the unglamorous base-building is doing most of the real work.
• Zone 3 (Tempo): A "comfortably hard" effort where talking takes real concentration. This builds muscular stamina without the recovery cost of harder intervals.
• Zone 4 (Threshold): Riding close to your FTP number teaches your body to clear the metabolic byproducts of hard effort faster, which is part of what lets trained riders sustain a hard pace longer before fatiguing.
• Zone 5 (Aerobic Capacity): Short, high-intensity intervals aimed at improving your VO2 max — the maximum amount of oxygen your heart and lungs can deliver to working muscle. Higher VO2 max is consistently linked to lower long-term cardiovascular risk in the research, which is part of why I don't skip this zone entirely even though it's a small slice of total training time.
• Zones 6 and 7 (short, all-out efforts): Brief bursts of maximum power lasting seconds to a couple of minutes. These are optional for most patients focused on general heart health — useful for building peak power, but not something you need to chase if your goal is a stronger, more efficient heart.

A word of caution before you test your own limits: if you have known heart disease, an arrhythmia, or you're on a beta-blocker or other medication that affects heart rate or blood pressure, talk to your own doctor before doing an FTP test or riding in the higher zones — that's exactly the kind of effort where it's worth getting individually cleared first. For most people without those issues, building a base in Zones 1 and 2 and adding intensity gradually is a safe, effective way to get more out of your rides without running yourself into the ground.

Reference Source: Peloton — Power Zone Training with Peloton: Everything You Need to Know

Journal Article: Circulation — Role of Physical Activity in Obesity Treatment and Cardiometabolic Health: A Scientific Statement From the American Heart Association