VO2 Max???
Lazy Runners may of heard me mention this when they had their Health and Fitness Assessment, specifically when you did your beep test, and I will be bringing it up again next week. The shuttle test score is converted into a VO2 max level which is a standard reading to measure cardio fitness.

VO2 max is the maximum volume of oxygen the body is able to  use during exercise. It is measured as milliliters per kilo of bodyweight per minute(ml/kilo/min). Not to get too scientific... but, every cell consumes oxygen to stay alive and well. Our muscle cells are the greatest oxygen consumers in the body therefore, muscles that are working harder have a higher need for oxygen. The efficiency in which your muscles consume that oxygen can be measured as VO2 max, the higher your score the fitter you are...simple.

As per usual though some factors have a bearing on that score-
HEREDITY- If your parents had a good score you will too, if not...keep training hard
AGE-After age 25, VO2 max steadily declines at a rate of 1% per year..so much for improving with age
GENDER- Sorry girls but our scores are 15-20% lower than the boys... something ridiculous about higher bodyfat in women and higher blood levels in men! 
CONDITIONING-training, especially endurance, can raise your VO2 max by 6-20% and in some cases up to 50%.. we all get a big tick in that box

Most of the highest scores of  VO2 max have been recorded by the best runners in the world, with their top scores reaching past 90 ml/kg/min. Level 20 of the Beep test would give you a VO2 max of 84 ml/kg/min, that is something to work towards!..However,  it may also be of benefit if you are under 25, a man, you train three hours a day and your dad was Emil Zatopek...otherwise just stick with Lazy Runner!