To be specific, exercise for health reasons increases CO2 levels for no reason other than to extend your life and, very possibly, to increase your muscle mass which increases your resting metabolic rate - you literally are generating CO2 with the effect of increasing your CO2 generation rate and the total duration you'll be producing CO2.

In a way, this hits exactly in my rant about where we worry about CO2 production: Getting out and getting in shape, or walking and biking places for fun is a negative but, like enjoying a reasonably-sized portion of animal protein in our diet, this is not the primary driver in causing Global Climate Change and there's a shit-ton of low hanging fruit (animal meat?) to be had but the people who make policy are the biggest offenders. We're literally banding together in the hundred of thousands to forego a chicken breast or hamburger so some celebrity can wipe out the entire savings by flying between their home and the harbor where their yacht is docked.