How can one piece of equipment be harder than another... Surely you can get your heart rate to the max just running in place???
I would normally agree directionally, then I bought an airdyne and doing max effort on it was unlike anything I've ever done. I think it's because it's an upper and lower body smash.
To put in perspective - I did a routine where I did 200 step ups on a box with a weighted ruck, followed by 1/2 mile run....repeat 5x in as short at time as possible - so 1000 step ups and 2.5 miles run. It was a chore, and a mind fuck, but I was fine.
Next day I did a 30 sec airdyne sprint for the first time and felt like I had never exercised before.