WouterB wrote:If I cycle for 30min at a heart rate of 160bpm, or I run for 30min at a heart rate of 160bpm, I should have the same cardio workout. No?
If you are in fact doing each of these activities at the same heart rate, I would agree with you. Like you said, you are training differenct muscles, but from a cardio/calorie burning standpoint I wouldn't expect much difference. But hey, I'm not a doctor...
Consider yourself fortunate though that you can do both at the same heart rate. I can't, most people I know can't, and it doesn't surprise me that people are telling you you have to cycle longer than bike to get the same workout, because they probably experience the same problem I do. I can run at 80% MHR for a long time. But cycling, my legs would be toast after a few minutes riding at 80% MHR. At 70% MHR I can ride for maybe as long as I run but my legs would be very uncomfortable. At 60-65% MHR is where I prefer to ride at...(although I don't train with a heart rate monitor much anymore).
WouterB wrote:Additionally cycling seems to put far less strain on my knees.
Not an uncommon issue, which is why so many people switch over to cycling if they start having knee problems.