If your cat eats dry food, he's more prone to constipation than a cat who eats wet food due to the decreased moisture content. Your vet will do a simple test to determine your cat's hydration level by pinching a fold of skin on his shoulders and pulling up. If it snaps back into place when released, he's well hydrated.
Comparing the Calorie Burn. In terms of calories, a 30 minute treadmill running session at 6mph for an 155lb adult will burn around 350 calories. The same size adult will burn around 260 calories in 30 minutes on a Spin bike at a steady pace. However, a Spinning class is much more intense so you can expect to burn anywhere from 400-600 calories if you push yourself.
I know calorie counts vary quite a bit, but a rough ballpark for cycling at a 20 mph pace is 450 calories per 15 minutes according to this calorie calculator. Running a 6 minute mile is expected to burn a similar 450 calorie count on the same calculator with the same settings. So, if you do the math, and the calculator is assumed to be reasonably accurate, then 5 miles on a bike at 20mph, is roughly equivalent to 1 mile run at a very fast pace.