Muscle Mechanics Part 3: Isometric & Isotonic Contraction and Levers

Overview

This lecture focuses on two main topics:

• Isometric and isotonic contractions, including their graphical representation and examples in the body.
• The concept of levers, their classes, and examples in the human body.

Isometric Contraction

• Definition:
  • 'Iso' means same, 'metric' means measure.
  • Muscle contracts but does not change in length despite generating tension.
• Example: Trying to lift a heavy weight without success.
  • The muscle generates tension but the weight does not move.
• Load Force vs. Muscle Force:
  • Load force is greater than muscle force.
  • Muscle generates tension but doesn't shorten or lengthen.
• Graphical Representation:
  • Tension increases to a maximum point (e.g., 10 newtons) and then decreases.
  • Muscle length stays the same (horizontal line on the graph).

Isotonic Contraction

• Types:
  • Concentric: Muscle shortens while generating force (e.g., bicep curl up).
  • Eccentric: Muscle lengthens while generating force (e.g., lowering a weight).
• Load Force vs. Muscle Force:
  • Muscle force exceeds load force, allowing movement.
• Graphical Representation:
  • Maximal tension less than isometric (e.g., 6 newtons).
  • Muscle length changes, decreasing during contraction and returning during relaxation.

Levers in the Human Body

• Lever: Rigid structure where movement occurs around a fixed point (fulcrum).
• Classes of Levers:
  • Class 1: Rare, can exhibit both power and speed (e.g., neck muscles).
  • Class 2: Meant for power due to mechanical advantage (e.g., calf raises with gastrocnemius muscle).
  • Class 3: Most common, meant for speed (e.g., bicep curl, includes many muscles).

Class 1 Levers

• Example: Posterior neck muscles extending the neck.
• Fulcrum: Atlantooccipital joint.
• Load: Head's weight creating a downward force.
• Effort Force: Neck muscles generating an upward force.

Class 2 Levers

• Example: Calf raises using the gastrocnemius and soleus muscles.
• Fulcrum: Ball of the foot pushing into the ground.
• Load: Body weight pushing through the ankle.
• Effort Force: Muscles pulling on the Achilles tendon upwards.

Class 3 Levers

• Example: Bicep curl.
• Fulcrum: Elbow joint.
• Load: Weight in hand creating a downward force.
• Effort Force: Biceps pulling the forearm upwards.
• Commonality: Includes most muscles in the body like quadriceps, hamstrings, deltoids, pecs.

Key Takeaways

• Isometric contractions involve tension without change in muscle length.
• Isotonic contractions involve muscle length change with tension (concentric and eccentric).
• Levers in the body are classified into three types, with class three being the most common.

Additional Notes

• Class 1 levers are versatile in function.
• Class 2 levers focus on power due to the position of the force arm.
• Class 3 levers provide speed and are involved in many daily movements and exercises.

For a deeper understanding, practice identifying these lever types in various exercises and body movements.