Weight lifting — heart rate is inaccurate

While lifting weights, heart rate monitors on your wrist (including the heart rate monitor on the apple watch) are very inaccurate (this is normal). This is because when you contrict your muscles when lifting weights the muscles in your arms tighten up and restrict blood flow to your wrist, as a result your BPM will read lower then expected. When you stop lifting the weight and rest a while (in your case you stop lifting weight to restart your apple watch) your muscles relax and allow the blood to reach your wrist, as a result your BPM will be more accurate. Heart rate monitors on your wrist are not accurate when your are lifting weights, but they are very accurste when you do activitys that do not use your arm muscles, such as running, yoga, and normal activities. Don't worry your apple watch is running properly, it is just that heart weight monitors on wrists do not give accurate results when weight lifting.

If you watch this guys video on YouTube he explains how the apple watch works when weight lifting (skip to about 5:30 in the video because that's when he starts to explain what happening when you lift weights with the apple watch) http://youtu.be/LA9RG-9nx2U

Found a solution. I wore the Apple Watch on my ankle when doing upper body. Much more accurate!!

I Am having the same issue when lifting weight. I have noticed this especially doing movements that are over my head. I am wondering if it has to do with the blood flow being altered from raising my arms and how the watch is reading it. I have also noticed that I have has to pause and restart to get an accurate reading. When at the end of good workout my average heart rate is way lower then it should be and my calories burn is also too low.

I had the same issue and was very disappointed. Apple was deceptive in their advertising as they made no mention that it wouldn't work well while lifting weights. I purchased it specifically to replace my chest strap. Had I known it's not meant for any activities that you use your arms then I wouldn't have gotten it. I guess that's why they don't list it as an activity in the workout app...they know it doesn't work.

I'll take your word for the explanations on the physiology of it but it doesn't make a whole lot of sense. For one, even when I did squats I experienced the same issue as the original poster did. And when doing curls or anything else you use a tight grip then blood is certainly rushing to your hands.

Thanks. I checked out the video and the same measurements are happening with me, around 60-75BMP just after workout, then 125-160BPM during rest. I'm not particularly worried about it taking readings after the weights, if thats normal with optical sensors then thats fine. I don't really want to buy a chest heart rate monitor though.

I'm hoping that Apple can find a way to let us input a weight workout. Perhaps, by using the movement sensors to work out the reps we have done and combine that with resting heart rate and an input of the weights in kilograms?

I am having the exact same problem. When weightlifting, my heart rate is usually half my actual heart rate. If I rest for 2-3 minutes, it captures my actual heart rate. This is disappointing since I can't really do without a heart rate strap to capture all types of physical activity.

I Have been using a separate chest strap heart rate monitor with my Apple Watch and I still have concerns that the Other category is not quite right. A 90 minute yoga class registers the same active calorie burn as 90 minutes of weight lifting. So I'm not sure that can be right.

i Had previously used the polar fitness app and the Apple Watch reports much lower calorie burn with the same chest strap than the polar fitness app did.

Yep, same problem.

I've ended up pairing the watch with a bluetooth heart rate chest strap during any sort of work out, to maintain a more accurate reading for the duration.