Biomechanics & Surgery: Muscle Structure and Contraction

Muscle Function and Classification

• The main or prime mover in a movement is known as the agonist muscle.
• Tonic or stability muscles predominantly consist of slow-twitch muscle fibers (Type I), which are endurance-oriented.
• Synergist muscles assist the prime mover by stabilizing joints and helping to produce a smoother motion.
• The length-tension relationship describes how optimal muscle length increases the force production capability of muscles.
• Cocontraction refers to the simultaneous contraction of agonist and antagonist muscles.

Muscle Contraction Types

• Fast-twitch fibers (Type II) are primarily used for short, powerful actions.
• The primary function of muscles is to facilitate movement and provide stability.
• Mono-articular muscles cross one joint, while multi-articular muscles span multiple joints.

Muscle Mechanics and Forces

• An increase in the number of cross bridges attached to actin filaments enhances muscle contraction strength.
• Tendons connect muscles to bones, transmitting force generated by muscle contractions.
• A twitch response in a muscle fiber is a single contraction cycle in response to a stimulus.

Muscle Attachment and Roles

• The origin of a muscle is the attachment point that remains stationary, while the insertion moves during contraction.
• Multi-articular muscles are involved in complex movements, allowing them to function across different joints.
• An increase in the frequency of stimuli to a muscle fiber leads to tetanus, a sustained contraction.

Muscle Contraction Characteristics

• Isometric contractions occur when the joint angle remains constant, producing tension without movement.
• Isokinetic contractions are performed with a constant speed against resistance, often using a dynamometer.
• Mono-articular muscles primarily function to produce movement at a single joint.

Muscle Fiber Characteristics

• Characteristics of bi-articular muscles include being able to cross more than one joint, allowing for versatility in movement.
• The typical range for muscle cross-sectional area impacting maximal torque is about 30-50 cm².
• The force-velocity relationship suggests a trade-off between force and the speed of contraction with a lower FL/ML ratio indicating higher velocity.

Torque and Functional Insights

• The type of muscular contraction that produces the highest torque is the eccentric contraction.
• The primary function of the gastrocnemius muscle is to facilitate plantarflexion of the foot.
• In real-world situations, gravity significantly influences muscle movement by providing resistance.
• The interaction between muscle contraction speed and torque typically indicates that slower contractions yield higher torque output.

Purpose of Studying Muscle Mechanics

• Understanding muscle mechanics aids in optimizing performance in sports, rehabilitation strategies, and preventing injuries, thus enhancing overall movement efficacy.

Explore the structure of muscle and the mechanism of skeletal muscle contraction. Learn about the factors influencing muscle's motion and force production, and how muscle architecture is optimized for force production and joint motion. Understand how this knowledge can enhance performance.