Hi Hayley,

I have a heart rate monitor (chest strap) that I enjoy using; however, I really struggle to get into the more intense levels. I have a low resting heart rate and seem to be burning a lot of calories but my green zone is others’ red zones. We wear them for a specific spin class and while the entire class is at 90%+ I’m in the 70%. When I do get to orange I feel lightheaded. My spin instructor said that my muscles are giving out before my heart and that’s good, it’s a healthy heart. Is she right? Is there something I can do to push myself harder? Should I be pushing myself harder? Last class was 1 hour and I burned 500+ calories while in the green. The instructor burned closer to 600 and was in the red for much of it. She’s 2 years older than me and this is her life so she’s fit and strong and weighs less than me, but I don’t think I’m that far off. She said that she’s trained her heart to be able to do that. Is that true? Can I do that too?

Thank you!


Ok, there are a couple of things that can be going on here. The first is that your heart rate zones are totally wrong and maybe your green zone is actually your red zone. Any time you do a heart rate calculation based simply on numbers (such as your resting heart rate and your age) there is a large margin for error. Also, different activities have different thresholds, depending on how your body is moving. This may get a bit “sciencey” for a moment but I will do my best to keep it simple and use my own experience to explain it.

10 years ago I was competing in Ironman competitions and I worked with a physiologist to determine heart rate zones based on how much lactate my body produced (which is a by-product of aerobic and anaerobic exercise). I would be put through a test for each discipline and the physiologist would determine exactly at what point I went from my aerobic energy system to my anaerobic energy system (which are the science terms for the colours your spin class has you in). Here’s the thing – my running anaerobic heart rate was completely different from my cycling anaerobic heart rate and my swimming anaerobic heart rate. In other words, the colour green for me would be different heart rates in the 3 different disciplines. Make sense?

Another thing that could be happening is that you are not moving your legs fast enough to get yourself into an anaerobic threshold, aka the red zone. Your instructor could be correct in that your legs are fatiguing quicker than your heart, but it doesn’t mean you have a strong heart and weak legs. It means you are not pushing yourself hard enough to work your heart. Your resistance is too high and you are fatiguing your muscles before you even give your heart a chance to work. What you might need to do is lower your resistance on your bike and find a higher cadence. This will provide your heart with a better opportunity to be challenged without overloading your legs, which could be contributing to why you are feeling dizzy.

I just worked with someone who was battling with this exact same problem. She could never get her heart rate up, but every time I looked at her legs they were grinding a heavy gear. She liked that. She was more comfortable with a strong cadence than a fast cadence. I worked with her in keeping her resistance down but her legs fast and she started to see her heart rate increase. As her body became used to the faster legs she slowly started to up her resistance levels.
So how can you move forward without spending hundreds of dollars on physiological testing? Go by how you feel. If your heart is pumping and you are so tired that not only can you not speak to the person beside you but you can’t even think about speaking to them, then you are in your red zone no matter what the heart rate is telling you. Take the heart rate guidelines but combine them with your own rating of perceived exertion. If you are feeling like you are at a 9 out of 10 for effort then you are probably at 90%. But if you look at your heart rate and it is not moving, yet you feel like you could have a full conversation, lower the bike resistance, spin your legs faster and force that heart rate up. 

If you still can’t seem to hit that red zone, and it is really important for you to do so then go get your VO2 max or lactate threshold tested by a trainer professional. It will cost you a few hundred dollars but it will put your mind at ease as you will know the exact number when that screen should turn red.