There should be no problem with a bike ride if you have been training.
Exercise can certainly help the immune system in moderation.
If you were running frequent marathons, then I would be concerned, but it sounds like you are doing it right by training beforehand. Experts appearing on this page are independent and are solely responsible for editing and fact-checking their material. Neither The Body nor any sponsor is the publisher or speaker of posted visitors' questions or the experts' material. Questions and messages posted to this forum are not statements of advice,opinion, or information of The Body, Body Health Resources Corporation or any sponsor of this forum. While neither The Body nor Body Health Resources Corporation regularly reviews posted content, we reserve the right to delete, move, or edit postings if we deem it appropriate under the circumstances.