Life style, environment toxins, and Gene mutations
I think Greg needs to start small than go bigger on the excersise .
He shouldn't rush on the process and he should be careful.Take everything slow.
He should work hard but not to the point where he gets hurt again or more.
Remind him to stretch before he does
Excersising.
He should run shorter distances and than later increase the number of miles or laps he is running .
I hope I helped I am not really a athletic person though
A. Virus - flu
B. Fungus - yeast infection
C. Protist - malaria
External or internal and an example is how you feel about yourself I think
