| Come ride with my pack on a Saturday 50-mile ride! We rarely dip below 20mph except at stop signs and lights and heavy traffic and average 19+ mph for the full 52 miles. My heart rate never drops below 135 and hits highs in the mid 150s, which for me is a very good heart rate for exercise. I do this for about 2.5 hours.
By the way, I am the junior in the pack at 48 and our pack includes a 49yo, 51yo and a very fast 68yo.
For three hours of elevated heart rate from running, you would have to run 15+ miles, depending on your speed and conditioning. | 
