I think no one should judge you whether you're faithful or not, this is a matter of conviction between you and God.

For me personally, I wouldn't arrange or take up any activity on a day meant for Christians to gather and worship God. I rather set it aside as Holy unto God and honor Him by coming together with other fellow believers.

For me, Man can exercise and eat healthy all he wants but good health and long life only comes from God and I believe only God can give us that.