IMAGES PROVIDED BY:
(1) Geri Lavrov/Superstock
(2) Peter Cade/Iconica
(3) Sean Murphy/Riser
(4) Adrian Green/Photographer's Choice
(5) Dorgie Productions/Photographer's Choice
(6) John Giustina/White
(7) Aurora Open/Kennan Harvey
(8) Sean Murphy/Stone+
(9) Craig Allen/Getty Images News
(10) Tim Platt/Iconica
(11) Howard Kingsnorth/Taxi
(12) Miquel Angel Munoz/Age Fotostock
(13) Tim Graham/The Image Bank
(14) David Nevala/UpperCut Images
(15) Gerard Brown/Dorling Kindersley
(16) Wallace and Wyant/Taxi
(17) Joe Michl/Workbook Stock
(18) Don Tremain/Photographer's Choice
(19) Michael Dalby/Flickr
(20) Justin Bailie/Aurora
(21) Stuart Redler/Photonica
American Kennel Club: "Summer Safety Tips."
American Society for the Prevention of Cruelty to Animals: "Exercise for Dogs."
American Veterinary Medical Association: "Advising Clients About Dog Parks."
Association for Pet Obesity Prevention.
British Columbia Society for the Prevention of Cruelty to Animals: "Exercising with Your Dog."
Dogchannel.com: "Exercise and Diet for Weight Loss" and "Team Up for Dog Weight Loss."
ExerciseMyDog.com: "Exercising and Dogs with Arthritis."
Kushner, R. Obesity, October 2006.
Midwest Skijorers Club: "Types of Skijoring."
Katherine Scott, DVM, internal medicine and emergency/critical care, Texas A&M University College of Veterinary Medicine.
University of Illinois at Urbana-Champaign, College of Veterinary Medicine: "Brain Exercise Keeps Older Dogs Sharp."