For me, it can be accurate once my blood pressure increases and I move it up my arm. But it can be 10 minutes into a workout before that moment kicks in. I'm usually on a stationary bike or an elliptical. I don't know how it would go while running.

Plus, it is much less accurate during weight lifting. Especially with any lifts that involve your arms.

So I would recommend against it if you are going to be doing high intensity workouts. Especially if that is what you are getting it for.