To gain 0.5 second in a training macro-cycle is a very stretching target even for athletes in their teens. Hours and hours of training is spent on skill acquisition, fine-tuning technical models, lactic tolerance, speed, power, weights, intensive and extensive tempos. But the simple fact is, you might find that the biggest one-off gain that you can make will be in reading Jimson’s posts on pacing 400m and implementing them.
Learn more about pacing 400m
To find out how to pacing 400m can be correctly understood and developed, see this link.
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To know more about how to research your event and become a better athlete see The Sports Motivation Masterplan