Muscle Contractions Lecture Notes

Types of Muscle Contractions

Isometric Contraction

• Muscle contracts but does not change length.
• Example: Holding a tray steady without moving it.

Isotonic Contraction

• Muscle contracts with the same resistance, but speed may vary.
• Two types: Concentric and Eccentric contractions.

Concentric Contraction

• Muscle shortens during contraction.
• Example: Bicep curl - lifting the dumbbell.
• Works against gravity.

Eccentric Contraction

• Muscle lengthens during contraction.
• Example: Lowering the dumbbell slowly during a bicep curl.
• Works with gravity.

Isokinetic Contraction

• Muscle contraction speed is constant while resistance varies.
• Typically performed using external devices.
• Used in clinical practices to aid passive range of motion exercises.

Functional Roles of Muscles in Movements

Agonist (Prime Mover)

• Main muscle responsible for the movement.
• Example: Bicep in bicep curl.

Antagonist

• Muscle that opposes the movement of the agonist.
• Example: Triceps during elbow flexion in bicep curl.

Synergist

• Muscles that assist the agonist in performing the movement.
• Example: Core muscles stabilizing during arm movements.

Stabilizer

• Muscles that support the body to allow other muscles to perform movements efficiently.
• Example: Core muscles acting as stabilizers during a push-up.

Neutralizer

• Muscles that counteract unwanted movements during a primary movement.
• Example: Pronators stabilizing the forearm during bicep curls to avoid unwanted supination.

Role of Co-Contraction

• When agonist and antagonist muscles contract simultaneously.
• Ensures accurate and controlled movements.
• Example: Holding and manipulating a hammer requires co-contraction of wrist extensors and flexors.

Practical Examples

Elbow Flexion (Bicep Curl)

• Agonist: Biceps Brachii
• Antagonist: Triceps
• Synergist: Brachialis

Push-up

• Agonist: Triceps Brachii
• Antagonist: Biceps
• Stabilizers: Core and back muscles

Wrist Flexion and Extension

• Neutralizer: Extensor carpi ulnaris and flexor carpi ulnaris canceling out ulnar deviation.

Key Points

• Different contractions: Isometric, Isotonic (Concentric, Eccentric), Isokinetic.
• Muscle roles: Agonist, Antagonist, Synergist, Stabilizer, Neutralizer.
• Co-contraction ensures movement accuracy and control.

Conclusion

Understanding muscle contractions and their roles is crucial for clinical practice and improving movement efficiency.