After a class or training session at the gym, your body increases its oxygen intake to assist the body in recovering. This increases the body's metabolism meaning that you continue to burn calories after your workout has finished. This is what we call the EPOC effect (excess post-exercise oxygen consumption).
The net calories burned in a high intensity workout (calories burned during and after exercise) will be the same if not more than the calories burned in a steady state session (think continuous running). Does than mean our fitness trackers are wrong? It means we don't just consider the calories burned during the workout, but those that follow.
Studies indicate that high intensity, anaerobic activity is the best type of exercise if you want a greater EPOC response. These workouts are usually high intensity circuit based training and/or heavy resistance training with short rests. It also results in a greater loss of body fat.
The other thing to keep in mind that these outcomes or results aren't based on the duration of the workout, but the intensity and type of the exercise.
If you have any questions feel free to contact us.