I think OP was comparing 5k running to 20 miles biking. That is still probably inaccurate, since a 20 mile bike is at least 60 minutes, and a 5k run is at most 30 minutes. It would be more accurate to compare a 10k or even 10 mile run to a 20mi bike.
Of course it also depends on the physical condition of the person, especially their susceptibility to stress related injuries, and the running surface. Generally speaking running is much higher impact than biking, which is why you so often see runners with a stress injury training on a stationary bike.
Of course it also depends on the physical condition of the person, especially their susceptibility to stress related injuries, and the running surface. Generally speaking running is much higher impact than biking, which is why you so often see runners with a stress injury training on a stationary bike.