Check out the transcript of a message board discussion with Weather Expert, Ingrid Amberger. Dr. Jeffrey Masters, Director of Meteorology for the Weather Underground Web site, answered student weather and winter storm questions in the winter of 2001. Dr. Masters received his B.S. and M.S. degrees in Meteorology from the University of Michigan.
It is easier on the joints than running. It is non-impact and therefore safer and easier on the joints. Biking is an exercise that you can do even at an older age. It is a great aerobic exercise for losing weight and increasing cardio endurance.
Biking is not an upper body work out. As a matter of fact: on longer treks I have found my arms getting rather numb. Riding a stationary bicycle that works both arms and legs simultaneously is an upper body workout. Riding a stationary bicycle that just peddles like your standard bicycle is not an upper body work out. Sorry....