Chapter 6, Problem 1IP

Summary Introduction

To list: The three examples of activities requiring concentric muscle action and three examples of activities requiring eccentric muscle action and also identify the specific muscle and muscle groups that are involved in these actions.

Concept introduction: Muscle tissue is a well-vascularized soft tissue present in the muscles of animal body. Muscles are elastic and extensible usually attached with bones, which enable the movement of the various parts of the body. Muscles also respond to stimulation.

Explanation of Solution

Concentric muscle action: In concentric muscle action, the contraction of muscles permits the muscle to be shortened. In this muscle action, the force that is generated by the muscle is always less than the muscle’s maximum force. Three examples of activities that requires concentric muscle action are as follows:

• Weight lifting
• The upward motion of a full squat
• The upright motion during pushups.

The muscles that are involved in concentric muscles are as follows:

• In the case of weight lifting, the following muscles contracts concentrically during lifting.
  • Quadriceps
  • Hamstrings
  • Calves
  • Pectorals
  • Triceps and the front deltoids
  • Lats
  • Trapezius
• Contraction of rectus abdominis during a sit-up to raise the trunk.
• During pushups, the muscles used are as follows:
  • Pectoral muscles
  • Deltoids
  • Triceps
  • Biceps
  • Rhomboids and trapezius
  • Latissimus dorsi

Eccentric muscle action: The muscle actions are involved in lengthening. In concentric action, the muscular load increases and reaches the final point where the external force on the muscle is greater than the force generated by the muscle. Under this condition, the muscles are activated and due to high external load, the muscles are forced to lengthen. Three examples of activities that requires eccentric muscle action are as follows:

• Lowering of the barbell in weightlifting.
• The downward phase of a squat.
• The upward phage of pull-down.

The muscles and the muscle groups that are involved in eccentric muscle action are as follows:

• Quadriceps
• Hamstrings
• Calves
• Pectorals
• Triceps and the front deltoids
• Lats
• Pectoral muscles
• Deltoids
• Triceps
• Biceps
• Rhomboids and trapezius