The Bleep Test This is one way of measuring VO2 Max

VO2 max (Maximal oxygen uptake) is widely accepted as the single best measure of cardiovascular fitness and maximal aerobic power. VO2max are typically 40-60% higher in men than in women. These scores can improve with training and decrease with age,

Improving your VO2 max by 10 % without changing any other performance factors, can take more than a minute off your 5k time. There are two ways to improve VO2 max; increased volume and increased intensity of training.

Volume. Sedentary people can improve VO2 max by over 20% when they begin a running program of 25 miles per week. By increasing mileage to 50 miles per week, VO2 max is improved a further 10%.

Intensity is a more potent enhancer of VO2 max. Running intervals at 75-80% of max heart rate is the best thing you can do to elevate your VO2 max. This corresponds to about two mile race pace, so use intervals of three to five minutes at 3k to 5k race pace with about equal recovery between each interval.

Children typically have VO2 max scores of 40-50. Short efforts run at 85%max HR are more beneficial for them. Their hearts reach their full size when they reach full height