You could be sabotaging your workout right from the start if you skip a warm-up. All too often you will see people who jump right into their cardio activity at full speed right away and then find they are unable to maintain that pace for long enough to get in an effective workout. A common misconception is that if you go for as hard as you can right away for as long as you can you will get the most out of your cardio; you will feel exhausted and spent so that means you worked hard, right?

While you probably did work hard and are panting, you may have only worked out for a very short amount of time. Most likely you tapped into your anaerobic system instead of your aerobic system which is not the one you were intending to stress to improve cardio fitness. Say you put the treadmill on as fast as you could run without being sent flying off of the back end, you most likely were not able to stay on more than a few minutes, if that. Instead if you were to gradually work up to that pace you not only would have been able to run longer, but you would have felt much better by the time you reached an all out sprint and then would have been able to maintain that pace longer and with better form.

Even the fastest runners in the world won't set to the track for a race without warming up before hand. Your muscles need time to get limber and your body needs an acclimation period to get into the right motions. This means that by gradually working into the pace that you are running at, or workout out at for any cardio activity, you will reap more rewards from each outing and improve your fitness far better than doing a few all-out minutes off of cold muscles. Physiologically you will be more efficient at using the glycogen out of your muscles and you will actually be able to go faster and for longer after a proper warm-up. Finally you are more apt to getting injured if you go into a hard workout without warming-up first because your muscles are not loose or limber.

So if you are looking to improve the effectiveness of your workouts and feel far better both during and after them you will do well to warm-up and gradually work into the pace you plan on sustaining.