The speed of an exercise has a lot to do with the intensity of cardiovascular exercise.
The more the speed of an exercise is the greater intensity of the workout is and the more you sweat. However after a certain time you get fatigued and tired out.
For example, if you had planned to do an exercise for 30 minutes and you increase the speed of the exercise then probably you might not be able to complete the 30 mins as youll get fatigued before that time due to the high intensity.
