The guy who invented rollerblades has come up with something that probably won't see quite as widespread adoption but damn does it look like you get a wicked workout doing it.
Check out the Rowbike and see what happens when you no longer pedal but you row with your upper body.
I love rowing and wish I had the space and cash for a rowing machine in the house. The Rowbike looks like fun but I don't see it doing any offroading or any real distance anytime soon. Part of the reason I love biking is to enjoy the ride and be able to look around, this looks like its a helluva lot of work.
But I wouldn't mind playing around on one for a little while.
Which reminds me, I need to get a second set of brake levers and grips so I can build up my other handlebars again for my cruiser. That way I can easily switch the bars in and out so I can use my WeeRide and take Grady out for rides or use the taller bars that I love so much. Always some project in the works.
Like the Szaz that needs a major overhaul and upgrade too!