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.
The website notes a vigorous, 45-minute workout on the exercise bike will burn 774 calories -- the same as the elliptical trainer. The extra calorie burn from the elliptical trainer is due to the use of your arms, which are largely stationary during an exercise bike workout.