Aching backs, stiff necks, sore ribs and battered hands are just some of the injuries common to gardeners. Some of this can be prevented, or at least lessened, through the use of proper tools. Gloves are an absolute must; lightweight cloth gloves are fine for jobs like weeding, but use heavy-duty leather ones for lifting rocks and other heavy objects.
Using a wheelbarrow beats carrying heavy items; even better for the back is a two-wheeled cart. Padded kneelers with hand grips, for greater ease in getting back up, are a boon to the lower body.
Long-handled tools can spare a lot of unnecessary bending; conversely, short people should not strain by using tools that are too big for them.
Raking, weeding, shoveling and hoeing are good aerobic exercises, with the added benefit of stretching many unused body parts. Best to warm up, though, as you would for any exercise.