Measuring your Heart Rate for Training when over 50

We often hear about the "180 minus your age to give you your max heart rate" rule. For runners over 50 there is also an idea of "190 minus your age" idea. Is there any merit in it? Can this be used? And how can it be used? Sports Scientist, Lindsey Parry has the answers in this edition of the Ask Coach Parry Podcast.