Set
Fixed number of repetitions. For example, 10 repetitions may comprise one set.

Slow Twitch
Muscle cells that contract slowly are resistant to fatigue and are utilized in endurance activities such as long-distance running, cycling or swimming.

Snatch
Olympic lift where weight is lifted from floor to overhead, (with arms extended) in one continuous movement.

Spot
Assist if called upon by someone performing an exercise.

Spotter
Person who watches a person closely to see if any help is needed during a specific exercise.

Static Stretch
A stretch that is held within the stretched position for several seconds, without movement.

Sticking Point
Most difficult part of a movement.

Stiffness
A condition that is often felt after exercise, especially weight orientated, or excessive running. Caused by the micro tears within your muscles as part of the body rebuilding phase. Will generally last 24 / 72 hours, with feelings felt normally the day after exercise.

Straight Sets
Groups of repetitions (SETS) interrupted by only brief pauses, (30-90) seconds.

Strength
The ability of a muscle to produce maximum force.

Strength Training
Using resistance weight training to build maximum muscle force.

Stretch Marks
Tears (slight scars) in skin caused if muscle or fat tissue has expanded in volume faster than the skin can grow.

Striations
Grooves or ridge marks seen under the skin, the ultimate degree of muscle definition.

Stroke 
A condition which occurs from insufficient oxygen supply to the brain.

Super Set
Alternating back and forth between two exercises until the prescribed number of sets is completed.

Sympathetic Nervous System
Part of the autonomic nervous system that prepares the body for activity by speeding up the heart rate.