The answer is to increase the minutes in which he is doing the exercise. He can just increase it by a couple of minutes and he will gradually improve his endurance.
Asthma Patients & Asthma Families network.
This would be the most accurate and reliable source to find information from for this particular topic.
Since someone would be performing wind sprint activities, it is guaranteed when performing any activity is to get better overtime so I would say to "work above your target heart rate"
