Power meters have been prevalent in cycling since Greg Lemond brought SRM to the mainstream in the 1980's. They revolutionised the way that cyclists measure their training & performance and completely revolutionised the sport. Most racing cyclists won't even leave the house without their power meters!
Excitingly, it seems the same thing is about to happen with running. Two running power meter systems have recently come to light; Stryd and RPm2. Funnily enough they both claim to be the first to market.If both live up to their marketing hype then they will offer runners a consistent and reliable metric to measure their training by.
Most athletes will know that heart rate is far too variable day by day to rely on. Too many coffees or a change in temperature can easily send you a dozen beats per minute higher for the same effort the previous day. The same goes for measuring your run training by pace. A change in terrain or wind can easily alter your speed for the same effort.
The golden nugget that a power meter provides is knowing for certain that your effort today is the same as your effort tomorrow. Knowing your maximum sustainable running power for one hour gives a far more accurate and reliable way to set training zones and ensure you're getting the right adaptions from every single run session.
I just hope they live up to the hype!
Power meters for running are a very new technology, and there is still a lot to learn ahead. However, to begin using it effectively to learn about your training and training response, you should begin as you would if you were using a cycling power meter.