The Truth About Heart Rate and When It Doesn’t Matter

by Tony Bonvechio
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The Truth About Heart Rate and When It Doesn’t Matter

Listen to your heart, they say. That thumping in your chest can tell you when you’re excited, scared or in love. It can also tell you a lot about how hard you’re working during exercise; so much so that many people wear heart-rate monitors to quantify exactly how hard they’re training.

But is heart rate really the best indicator of exercise intensity? Should we trust that readout on the treadmill or that fancy wristwatch to tell us to push harder, back off or keep going?

Like many things in fitness, it depends. A basic understanding of what your heart does during different types of exercise helps determine whether you should worry about your heart rate or not.

WHAT YOUR HEART DOES

Your heart is a busy muscle. Its main job is to pump blood to other areas of the body that need it, delivering much-needed oxygen to muscles and organs. If you’re resting, the heart doesn’t pump very fast (the average HR of a healthy adult is about 60 beats per minute). But if you’re working hard, the heart beats faster to keep up with energy demands.

As you exercise, the heart pumps more blood to bring more oxygen to working muscles. Your HR is controlled by your sinoatrial node (SA node), also known as the body’s pacemaker. Luckily, you don’t have to consciously think about contracting your heart like you would your biceps; the SA node does that for you.

That said, your heart rate goes up during non-exercise activity, too. If you get scared, nervous or excited, there’s an increase in sympathetic nervous system activity, also known as “fight or flight” mode. While you’ll burn slightly more calories while excited, nobody got in shape by watching a scary movie, so we can’t rely on heart rate alone to determine exercise effectiveness.

So when does heart rate actually make a difference? It depends on what type of exercise you’re doing.

OPTION #1: AEROBIC EXERCISE

Aerobic exercise (literally, “with oxygen”), also known as cardio or long slow distance (LSD) training, typically comes in the form of jogging, biking, stair climbing or other similar exercises where you can sustain a steady pace for an extended period of time. HR is the most reliable measure of intensity for this type of exercise and is a surefire way to gauge your progress.

The reason HR works to quantify aerobic exercise intensity is because oxygen consumption (often called “VO2”) and HR are closely related during low-intensity exercise. HR and VO2 rise together steadily during aerobic exercise that isn’t too hard, meaning your heart is able to pump enough blood and deliver enough oxygen to meet the demands of your working muscles.

However, once exercise gets too hard (i.e. you start running faster, you run up a steep hill, etc.), it becomes anaerobic (literally, “without oxygen”) and your heart and lungs can no longer move enough blood and oxygen to meet energy demands. At this point, VO2 won’t increase (because you physically can’t consume any more oxygen), but your HR may continue to climb. It’s feasible that one’s HR might exceed 200 beats per minute during intense anaerobic exercise, but that doesn’t mean your VO2 keeps climbing.

That said, HR is a great indicator of aerobic exercise intensity, but it quickly becomes a poor indicator if exercise gets too hard and becomes anaerobic. So if you’re aiming to increase your aerobic fitness for endurance activities like jogging or biking, aim to keep your HR below 70% of your maximum heart rate (HRmax). How do you calculate your HRmax? The old-school method is:

HRmax = 220 – your age

This method is a bit dated, but works for most people. How do your find your HR? You can take your pulse at your wrist or neck for 15 seconds and multiply by four, or invest in a HR monitor for the most accurate measurement.

OPTION #2: HIGH-INTENSITY INTERVAL TRAINING

High-intensity interval training (HIIT) involves alternating short bursts of intense exercise (i.e. sprints, fast cycling, burpees, etc.) with longer periods of less intense exercise. This type of training is highly effective for losing fat because of the excess post-exercise oxygen consumption (EPOC) that it creates. It elevates your caloric expenditure for up to several hours after you stop exercising, making it a great bang-for-your-buck time investment. However, HIIT is anaerobic, meaning it’s too hard for oxygen consumption to match energy demands, making HR an unreliable measure of how hard you’re working.

As stated before, HR can keep climbing after you’ve reached your VO2 max (the most oxygen your body can possibly consume during exercise). We already know that at this point, HR and VO2 aren’t climbing together, and your only goal for HIIT is to consume as much oxygen as possible after exercise. So what’s the best way to measure your intensity? Rating of perceived exertion (RPE) is a good start, as well as keeping rest intervals short (60 seconds or less).

RPE is often measured on a scale from 1–10, with 1 being very easy and 10 being an all-out effort. For HIIT, keep your work intervals between 10–30 seconds at 8–10 RPE, and keep your rest intervals between 30–60 seconds at 4 RPE or less.

OPTION #3: LIFTING WEIGHTS

You often hear people say, “Wow, that heavy set of squats really got my heart rate up. I’m building strength and doing cardio!” This couldn’t be further from the truth. In fact, if you’re worried about your HR while lifting weights, you’re studying for the wrong test.

On the aerobic to anaerobic spectrum, lifting weights is as anaerobic as it gets. You’re using smaller muscle groups, heavier loads and higher efforts than you would while running or cycling, which makes lifting too hard to get enough oxygen to the working muscles to meet energy demands. If you’re actually lifting hard, your HR and VO2 never sync up, and that’s OK.

What’s more, while lifting weights, your muscles essentially “clamp down” on the surrounding veins and blood vessels, which reduces venous return (the rate of blood flow back to the heart). This increases blood pressure and therefore HR because the heart is trying like crazy to move blood around the body, but more and more blood is getting “trapped” in the working muscles. This partially explains that tight, burning feeling you get in your legs after a set of high-rep squats. This also explains why your HR skyrockets while lifting, but you’re not getting any cardio benefit from it.

So if HR doesn’t matter while lifting, how do you measure progress? Simple: lift more weight than you did before, or do more sets and reps with the same weight you did before. Follow this formula ad nauseam and you’ll make plenty of progress.

HAVE A HEART

It turns out HR isn’t the only way to measure exercise intensity. If you’re going for a jog, by all means track your HR and stay within your target HR zone. But if you’re doing HIIT or lifting weights, don’t worry about your HR and use other means to judge how hard you’re working.

Related

  • Dave Waters

    Thank you for that! My resting HR is around 80 so when I start biking/walking it quickly jumps past my HRmax of 128 (per your formula) if I slow down to let it come down I feel I’m at a crawl, I’m not going all out but just a comfortable pace. If I am comfortable maintaining that pace is it ok if it’s above my HRmax?

    • James Pierce

      Try using the 220 – Age = HR Max formula that was mentioned. It will be close to accurate for you. So, if you’re 30, it would be 220 – 30 = 190 max. When I’m exercising, I often range between 140-180 (at times), and that’s ok, based on your goals.

      • BuckeyeBeth7

        James, I think Dave might have been using that formula.

        “…aim to keep your HR below 70% of your maximum heart rate (HRmax). How do you calculate your HRmax? The old-school method is: HRmax = 220 – your age.”

        Are you working out at below 70% as the article above states or are you working out at between 75% to 85% as commenter Zoe claims is the exercise sweet spot? If I use that formula at below 70% my maxHR is 118. Nothing is getting done at those numbers especially since like Dave my resting HR has always been about 80 even as a teen.

    • DaBoss

      Dave if your max HR is 128 then you are 92 years old, so that must be a really old photo you are using.

  • Jaleela

    This was one of my personal favorite articles I’ve ever read on MyFitnessPal and I read them constantly! Thank you!

  • Zoe

    So I was once obese and now I am in a healthy weight range. I have always trained with a heart rate monitor and continue to do so. Here is why: a heart rate monitor helps to motivate you and keep all workouts real. Tony mentions RPE well my rate of perceived exertion is that all exercise is too hard and I will be staying on the couch. My heart rate monitor tells me otherwise. When doing cardio there is a sweet spot to train at at 75 to 85% your heart rate max, this is higher than the old school fat burning zone and is very effective for weight loss. If you train over 85% your body will burn (mostly) carbs this is when it gets anaerobic and will probably just make you ravenously hungry. Hiit May or may not be a good plan. You should try it for yourself. But here is the catch. Your body does not know if you are jogging on a treadmill or lifting heavy, all it knows is that the exercise is aerobic (mostly) up to 85% HRM then anaerobic (burning carbs) after that, so it makes perfect sense to wear your monitor whilst lifting to keep in that sweet zone with supersets or whatever to achieve great weight loss results.
    No need for a trainer and no need to constantly “assess” your exertion the monitor will tell you the actual facts. I recommend the book Heart Rate Training by Roy Benson if you want to know more and Suunto or Polar monitors with a chest strap.

    • BuckeyeBeth7

      Is the sweet spot 60% to 70% as this article and other people (employees at a fitness club) have told me or is it really 75% to 85% as you’ve claimed? Because quite frankly your numbers seem to make more sense. I (like commenter Dave Waters) have always had a resting HR at about 80, since I was about 19yo and about only 10 to 15lbs overweight. Does the math change for people with naturally higher resting HRs? Because the 220-age=HR formula puts my max workout HR at 118 which I can reach on a treadmill set on less than 2.0 speed with no incline, and with quite a few lbs to lose that not gonna get the job done.
      Anyone have any advice?

      • Angel Johnson

        220- your age is 118? Are you 102?

        • BuckeyeBeth7

          Nope. That would be cool to live that long only if I could still be independent and healthy! 😉
          You’ve forgotten to factor out the percentages. It’s 220 minus your age to find your maximum workout Heart Rate. You don’t want to workout at your maxHR number, but below it in the sweetspots for either fat burning or cardio zones. Certain experts suggest working out at between 60% to 70%, and others between 75% to 85% of that maximum Heart Rate number that the ‘220-age’ equation gives you.
          My question was does anyone know any research on which percentages to actually work at, the 60%-70% or the 75%-85% that Zoe’s post suggests?

  • DaBoss

    Max HR is individual for everyone and the ‘220-age’, (or any of the other more specific formulas for gender, age etc.) are only indicators. Resting heart rate is an indicator of cardio health/fitness and the ‘new’ thinking is that a RHR of around 60 indicates good heart health, down from the traditional 80 BPM. I have been a life-long athlete and my Max HR formula (220-age) is spot on and my RHR is 45-50. There is growing evidence that HIIT is not only highly efficient in improving fitness but also in slowing down ageing, one of the fastest growing areas in health and fitness research. Finally, it is interesting to talk about fitness and weight loss in the same sentence but in truth no type of fitness training is effective in losing weight in the way that food management is. The formula ‘calories in needs to be lower than calories out’ to achieve weight loss is still valid.

  • grout4cake

    If my heart rate is high- 195 but I am not winded, do I really need to slow down? I have just begun running with a HR tracker, indoors. Before I just ran outside, usually 5- 10 minute intervals with short resting periods to catch my breath. I am 65 and have no health problems