Your muscles require Glycogen when working out, which comes from Carbs. Your body does not require a heap of protein all of a sudden after a workout. This is a Myth that to many people still believe in.
There is no sudden burst of muscle-making after a workout. Building muscle tissue is a 24+ hour process, so getting Balanced protein throughout the day is far more Important than right after a workout. You only require a very small amount of protein to replace That which was burned as energy . The most important nutrient after a workout is carbohydrates. While muscle repair takes as much time as 24 - 72 hours after a workout, there is a small time slot of a few hours where your muscles are most ready to intake carbohydrates that were depleted during the workout.
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I wrote this when talking about resistance training, but the same applies to cardio