Made up of six different links: pathogen (infectious agent), reservoir(where germs live and multiply) , portal of exit (how germs leave the body), means of transmission (how germs are spread), portal of entry (how germs enter the body), and the new host. Each has a role in the chain but can be broken, or interrupted through various means.
The answer is infatuation. It means an intense strong feelings.
Exercise programs and sports activities can differ in number of participants from one person doing an activity like jogging or swimming, to hundreds of participants at a track meet. Structure can be loose in solo exercises where you can set your own pace, or be very strict in most competitive sports. Competition varies from none to highly competitive, and can be on an individual or team level. More complex sports and activities can present a high skill level.