The antonyms for the phrase "were out of breath" are plentiful, as they relate to being in good shape and have ample oxygen in your lungs. Some possible antonyms could include "were energized," "were invigorated," "were refreshed," or "were revitalized." To be "out of breath" suggests that you have exerted yourself to the point of exhaustion, so the opposite might be "were relaxed" or "were calm." Alternatively, you might say you were feeling "strong," "powerful," or "vigorous," which implies that you have energy to spare. Overall, there are numerous ways to describe the opposite of being out of breath, all of which suggest a state of vitality, well-being, and readiness.