Wheels
The major difference between roller skates and rollerblades (the commonly used name for inline skates) is the placement of the wheels. On roller skates, the wheels are placed two in front and two in back, just like the tires on a car. This makes balancing easier for beginners, but reduces speed and agility. Rollerblades, on the other hand, have all the wheels in a single row, resembling an ice skate with wheels. The wheels are also not as wide. It can be trickier to learn to rollerblade, but enthusiasts swear the effort is well worth it.
Muscles Used
Because of the difference in balancing and maneuvering, different muscles are used in rollerblading than in roller skating. Rollerblading takes more exertion, and provides a better workout if your purpose is fitness. Rollerblading can help tone your thighs, buttocks, calves and abdomen. It also provides a good cardiovascular workout. Roller skating can also be a good way to exercise, but it takes a more determined effort. It is possible to roller skate at a leisurely pace. Rollerblading at a slow pace requires skill and effort.
Turning and Stopping
Due to the difference in the alignment of the wheels, turning and stopping with rollerblades is very different than with roller skates. Rollerblades can make sharp, tight turns at fairly high speeds. Roller skates make much wider turns, and it's important to slow down enough if you're attempting a sharp turn. When it comes to stopping, it's much easier to stop and stand in roller skates, especially for beginners. Stopping rollerblades takes practice and skill.