What Causes Difficulty Breathing While Walking Inspite Of Being On Vyvanse?

I was in relatively good shape and enjoyed trail running. I m a 39 year old male, 205 lbs, 6 . I recently started taking Vyvanse 50 mg (week ago). I went for a slow, steady 3 mi trail run and couldn t make it a quarter of a mile before I was too winded to continue. I walked for a long while, but my heart rate and respiration took forever to recover somewhat. I can tell that I was still slightly aerobic for the remainder of the now hike. Is this change the result of starting Vyvanse?