Muscle Contraction Glossary 

To learn about muscle contractions in sports science, you must first learn the following part definitions.

1. Contraction = Tension

Note: You must think of muscle contraction in sport science as a "tension", not shortening because contracting a muscle can be shortening, lengthening or remaining the same length. When contraction is used as a normal vocabulary word it does mean shortening but not in sport science or physical education. 

2. Iso = Constant

3. Tonic = Movement

4. Metric = Measure of the distance moved

5. Concentric = Shorten

6. Eccentric = Lengthen

If you learn these part definitions you will then be able to understand all the following sports science terms:

1. Isotonic contraction =

• Constant movement
• Muscle in tension

In other words = Muscle tension that results in limb movement. 

This can be one of two ways:

A. Concentric Contraction =

• Shortening of the muscle
• The muscle is in tension.

In other words = Shortening of the muscles.

Example: Lifting a dumbbell in a bicep curl. 

B. Eccentric Contraction =

• Lengthening of the muscle
• Muscle is in tension

In other words = Lengthening of the muscle.

Example: Slowly putting down a dumbbell.

2. Isometric Contraction =

• Constant length
• Muscle is in tension

In other words = Muscle length does not alter under tension

Example: Pushing against a load but not moving, or pulling a door that won't open.