Wrist-based or chest strap HR monitoring?

There are a lot of questions on different forums if it worth to buy an HR monitoring chest strap or the wrist-based is enough. My answer usually depends on two factors:

1. Do you have some extra money to buy the strap?
2. How accurate data do you want to get about your training?

If the answer is yes and accurate, my reply is: yes, definitely.

How they work?

Newer and newer watches with wrist-based HR monitoring are being released every day, and they deliver more and more accurate sensors. In their User Manual they ask you to tighten the wristband around your wrist, keep the sensors clear, unscratched, and, of course, don’t wear anything between the watch and your skin. The problem is that even if you comply with all of this, there’s a chance the watch will move, your skin get wet, things you can’t avoid when you train or run. It also worth to know the OHRM (Optical Heart Rate Monitor) checks the blood flow dynamics changes by measuring the amount of light that is scattered by the blood in your veins. It means, if the above conditions aren’t met, it’ll deliver inaccurate data.
On the other hand, the chest strap uses ECG that checks the electrical activity of the heart; it should be placed as close to your heart as possible, but due to the nature of our skin, it can read electrical changes well a few centimeters away too, and, for the same reason, even if it moves a bit the collected information is more accurate.

So, the OHRM isn’t trustworthy?

That is trustworthy, however, simply it has much more factors that can interfere the sampling and with that, the result.
I’m training for a long time now, I feel when my pulse is above 100 beats per minute. Last week I was in the gym, doing resistance training. For this sessions I don’t bring my chest strap. I checked my watch and it showed my heart beats 104 times per minute. 5 seconds later only 78 times. 2 seconds and 85 times. Then 75, and short after that 110 times. Pushing weights doesn’t require knowing your HR, but having inaccurate records for your runs may mislead you with your required sessions.

If you want to know more

• Generally about Heart Rate Monitors, check the Heart rate monitor article on Wikipedia.
• Valencell has a very good and detailed article about OHRMs: Optical Heart Rate Monitoring: What You Need to Know.
• About ECG, there’s Electrocardiography on Wikipedia.
• Biomedcentral compared the wrist-worn optical and the chest strap ECG HR monitors in their Wrist-worn optical and chest strap heart rate comparison in a heterogeneous sample of healthy individuals and in coronary artery disease patients research article.