Overview
This lecture introduces the three main types of muscle contractions—concentric, eccentric, and isometric—and explains how muscles create movement by only pulling, with examples from sports.
Muscle Contraction Basics
- Muscles can only pull; they do not push.
- Despite this, muscles can shorten, lengthen, or remain stationary during contractions.
Types of Muscle Contractions
- There are three main types: isotonic concentric, isotonic eccentric, and isometric.
- Isotonic contractions involve movement; isometric contractions do not.
- Isokinetic contractions exist but are not covered in this lecture.
Isotonic Contractions
- Isotonic concentric contraction: the muscle shortens under tension (e.g., lifting a weight).
- Isotonic eccentric contraction: the muscle lengthens under tension (e.g., lowering a weight).
- Isotonic contractions are common in sporting movements.
Isometric Contractions
- Isometric contraction: muscle contracts but remains the same length under tension.
- Used to hold positions still (e.g., a sprint start, ski stance, or plank).
Antagonistic Muscle Pairs
- When the agonist (prime mover) contracts, the antagonist relaxes.
- During flexion, the biceps contract concentrically while the triceps relax; during extension, the triceps contract concentrically while the biceps relax.
Application Examples
- Throwing a football: biceps contract concentrically to flex the elbow; triceps contract concentrically to extend it.
- Press-up: triceps contract concentrically when pushing up, then contract eccentrically when lowering the body as a 'brake.'
- Leg extension: rectus femoris shortens concentrically to extend the knee; contracts eccentrically to slow landing.
- Isometric example: holding a static position (e.g., plank) requires both antagonistic muscles to contract isometrically.
Key Terms & Definitions
- Isotonic contraction — muscle changes length and movement occurs.
- Concentric contraction — muscle shortens while contracting.
- Eccentric contraction — muscle lengthens while contracting.
- Isometric contraction — muscle contracts with no change in length.
- Agonist — the muscle primarily responsible for movement.
- Antagonist — the muscle that opposes the agonist.
- Antagonistic pair — muscles that work in opposition to control movement.
Action Items / Next Steps
- Familiarize yourself with contraction terminology and corresponding muscle actions.
- Practice identifying types of contraction in daily movements or sporting activities.