"If you are used to going five innings and then go six or seven, you won't have your good stuff. They need to start that from the minor leagues and give pitchers strong arms"

This quote by Juan Marichal is describing the importance of developing strong arms in pitchers from a young age. He is suggesting that pitchers must be trained to go longer innings from the minor leagues, so that when they reach the major leagues, they are used to going longer innings and won't be as likely to lose their "great things" when they need to go longer. Marichal is highlighting the importance of training pitchers to go longer innings, as it will help them to preserve their strength and efficiency throughout the game. He is suggesting that if pitchers are used to going five innings and then need to go six or seven, they won't have their finest performance, as they are not utilized to going that long. Marichal is highlighting the value of training pitchers to go longer innings from the minor leagues, so that they can maintain their strength and performance when they reach the big leagues.