Joined: Dec 2004
Posts: 12,537
Likes: 791
From: Middle of da Mitten
Bikes: Trek 7500, RANS V-Rex, Optima Baron, Velokraft NoCom, M-5 Carbon Highracer, Catrike Speed
Just get a heart rate monitor and ride 40 minutes at the same HR as you'd have walking. Same workout, you'll just go further in the same amount of time.