Hello Ali

What do you mean by breezing by the way? Heart rate decreases due to an overdrive of parasympathetic tone, as during training the sympathetic system is in overdrive. This would be a rather physiological, as the body must begin the regeneration process shortly after an endurance session. 

Hi Mike.

many thanks for your answer, i mean problems in respiratory system or breathing.

anyway, i found it in regeneration process and especially i can relate it with muscle storage depletion.

Reductions in autonomic tone, specifically the sympathetic tone, are apparent after exercise, as this is a fundamental part of the recovery process. After metabolic rate is increased during physical activity,  decreases occur afterwards. Given enough time and intensity, one sees things like the "athletes heart" in which there can a be a resting bradycardia, offset by a larger stroke volume, due to plasticity and morphological changes after a longer term training interval (adaptation). The Respiratory drive decreases just as heart rate decreases as well. I was wondering in which time intervals are you talking about? Immediately after a training session, or hours or days following training?  Heres is quite a good article detailing some of the facets mentioned above. 

Article Basic science behind the cardiovascular benefits of exercise

Autonomic dysfunction  Athlets due to increased vagal tone

i think that parasympathetic system over activity may implicated by decreasing heart by action on M2 receptors in heart causing slowing in heart rate and on M3 receptors  in bronchi casing difficulty in breathing due to  bronchospasm