Nutrition - The sum of the processes by which an animal or plant takes in and utilizes food substances.

Osteoporosis - A condition that affects especially older women and is characterized by decrease in bone mass with decreased density and enlargement of bone spaces producing porosity and fragility.
Overpronation - Excessive inward foot motion during running that can lead to injury. Learn how to choose running shoes.

Pectorals or "pecs" - The 2 pairs of muscles in the chest that work to pull the upper arms toward or across the chest. The pectoralis major covers the chest from the top of the arm to the collarbone, down to the sternum and upper 6 ribs. The smaller pectoralis minor is located underneath, and runs from mid-chest to shoulder blade.
Perceived exertion - The level of intensity you feel your body is exerting during exercise on a scale of 0 to 10. An unscientific way of staying within your target heart rate zone. Pronation - The natural inward motion of the foot after heel strike and before pushing off again with the ball of the foot. Overpronation is excessive inward motion and can lead to running injuries. Learn how to choose running shoes.
Pull buoy - A foam flotation device designed to fit between your legs and keep the lower part of your body afloat without kicking. It allows you to work only your upper body and concentrate on your swimming stroke.
Pyruvate - A nutritional supplement that has been found to enhance athletic performance and possibly aid in burning fat.

Quadriceps or "quads" - The group of 4 muscles that make up the front of the thigh. Quads straighten the knee, and keeping them strong can help ward off knee injuries. Cycling, skiing, running and hiking downhill work these muscles.

Rectus abdominis - The muscle extending the entire length of the abdomen, from the lower 3 ribs to the top of the pubic bone (below the navel). Works to keep you upright and lets you bend at the waist. Strengthening this muscle can help prevent lower back pain.
Recumbent bike - A bicycle on which you sit in a reclined position with your back supported and your feet out in front. It can be an indoor, stationary-type or a moving, outdoor-style bike. It works the buttocks and hamstrings more than upright bicycles, and unlike uprights, supports the back.
Repetition or "rep" - A single movement, as in doing one squat. This is going down and then going back up. For toning, strength and endurance, do more reps at a lower weight.
Resistive cuffs and boots - Foam buoyancy devices placed on the ankles and/or wrists to create extra resistance for water aerobics and water running. Shown to increase workout intensity up to 5 times.
Rhomboids - The muscles that pull your shoulder blades inward. They attach to the vertebrae at the base of the neck and go diagonally to the inside edges of the shoulder blades.
R.I.C.E. - The formula for treating an injury such as a strain or sprain. The acronym stands for Rest, Ice, Compression and Elevation.