Many cats and dogs become suddenly homeless when their owner moves or passes away, or when someone in the family develops allergies. Even if you can't permanently welcome animals into your home, you can help facilitate a happy ending to their story by boarding them until the right adoptive parent comes along. Nearly every animal-rescue group and shelter depends on foster volunteers because the staff just doesn't have as much time as they'd like to pet, play with and hang out with the cats and dogs; go to Petfinder.com to find an organization near you.
Calories burned: 143 for a half-hour of playing and walking with animals, 30 for feeding them for 10 minutes.
Muscles worked: Biceps, shoulders (hurling sticks and balls); wrists (holding a taut leash); legs (keeping up with a pup); quads (squatting for kisses).
Karmic bonus: A puppy gets a fairy godmother.