Take plenty of rest and deep breathing between sprints.
Usually, a two-bag sprint is all you need.

Now, some more of you get out and try it." Rapidly coach called off the names of those he wanted to try out.
Some of these young men did better than the starters, for they had learned from the criticisms, and from the showing of Luce's standard form.
Presently the young men were standing about in various parts of the field, for none came in until called.
"Ripley," said Mr.Luce, turning to that young man, "you have the build and the lines of a good sprinter." "Thank you, sir," nodded Fred.
"And yet your performance falls off.

Your lung capacity ought to be all right from your appearance.

What is the trouble?
Honestly, have you been smoking any cigarettes ?" "Not one," Fred declared promptly.
Mr.Luce lifted the boy's right hand, scanning it.
"If I were going to make such a denial," remarked coach coolly, "I'd be sure to have a piece of pumice stone, and I'd use it often to take away those yellowish stains." The light-brownish stains were faint on Fred's first and second fingers.

Yet, under careful scrutiny, they could be made out.
Ripley colored uncomfortably, jerking his hand away.
"Better cut out the paper pests," advised coach quietly.
"Only one, once in a while," murmured the boy.