A heart rate strap is much less prone to errors than an optical sensor on any watch.

The beauty of this strap is it also measures run dynamics such as Ground Contact Time, Ground Contact Time Balance, Cadence, Stride Length, Vertical Oscillation
Vertical Ratio and Running Power.

Before having this strap, I had the run dynamics pod, tiny and clipped to the back of my shorts. Long story short, I lost it when I ran my first marathon distance for the two-year post-heart attack “anniversary” run. This strap is convenient in having accurate heart rate and run dynamics in one unit!

The run dynamics displayed are dependent on the watch it is paired with, so check on the compatibility before you order.