Virtually all world class athletes in sports which require significant physical performance have good posture all the time, not just when they are competing in their sport. From sprints to long distance running to power lifting, the best in the world have head-up, shoulders back, chest out posture, all the time! If a good athlete doesn't have good posture, it is simply an affirmation of how great their natural ability is, because if they had proper posture, they would be even better!
The reason for this posture-performance connection is that the balanced muscle strengths and flexibilities which produce proper posture also produce the the most muscular strength and endurance; the best force development for throwing, hitting, kicking, etc.; the most efficient movement capabilities in general; and the most efficient and highest possible heart and lung functions.
Anyone, of any age, who has posture that is the least bit round-shouldered, shrug-shouldered, slouchy, or forward head, will never be able to reach their athletic potential, no matter how long or hard they train, and no matter how well they eat and rest between workouts!
Correct posture which is the result of correct flexibility and muscle strength balances (as developed by the PowerPosture™ Program) is an absolute, foundational necessity for any athlete who wants to be the best that she or he can be, at any age!
So if your "automatic", relaxed posture is not perfect, use the PowerPosture™ Program to achieve the muscle strengths, flexibilities, and posture that will enable you to become the best that you can be. That way, you'll never have the "would have, could have, should have" regrets that so many people have, or miss the opportunity to have your once-in-a-lifetime performance!