We know that exercise that's of 60 minutes in duration or less and that is intense but not all-out effort... If you do that sort of exercise for about 60 minutes or less, you promote the exchange of components between the blood and the lymphatic system that increases the circulation of those cells and chemicals within the innate immune system such that not just during exercise but for many, many hours afterwards... your innate immune system level of baseline activity is ramped up...