[yibg]

Depends on what your body is telling you. If your kneed are killing you half way through you might want to stop and take a break for a few days.

[lvturner]

Or change shoes - my knees constantly hurt whenever I ran until I switched to more barefoot style shoes.

Really transformed running for me. It went from something I was terrible at, which hurt and I hated, to something I merely hated.