Download Skeletal Muscle and Force Production

Human skeletal muscles produce force and speed which provide the body with
movement. The muscles of the body do not directly exert force on the ground or objects. They
function through pulling on bones which rotate about joints. This creates torque and provides
force that is transmitted through the body to the external environment. Muscles only pull
(shorten) and create force through a systems of levers and pulley’s in the body. There are three
types of actions to which skeletal muscles work.
“Concentric Muscle Action – When the muscle shortens because the contractile force is greater
than the resistive force. The forces generated within the muscle acting to shorten it are greater
than the external forces acting at its tendons to stretch it.” (Baechle & Earle, 2000 pg. 41)
Example: (Bicep Curl – curling the weight up)
Figure 1
(Bench Press – Pressing the bar up
from the chest. Concentric muscles
involved; pectoralis major and minor,
triceps, deltoid, serratus anterior)
“Eccentric Muscle Action – A muscle action in which the
muscle lengthens because the contractile force is less
than the resistive force. The forces generated within the
muscle to shorten it are less than the external forces
acting at its tendons to stretch it. This occurs during the
lowering phase of any weightlifting exercise. During
standard weight training, the eccentric force exerted by
the muscle keeps the weight from being accelerated
downward by gravitational force. Thus, the weight
moves steadily downward rather than picking up speed
and impacting the floor to the lifters body.” (Baechle &
Earle, 2000 pg. 41)
Example: (Bicep Curl – lowering the weight back down)
(Bench Press – lowering the weight down to the chest. Eccentric muscles involved;
pectoralis major and minor, triceps, deltoid, serratus anterior)
“Isometric Muscle Action – a muscle action in which the muscle length does not change
because the contractile force is equal to the resistive force. The forces generated within the
muscle acting to shorten it are equal to the external forces acting at its tendon to stretch it.”
(Baechle & Earle, pg. 41)
Example: (Bicep Curl – holding the weight in place, halfway through the rep)
(Lateral deltoid raise – hold at shoulder height for 30 seconds. Muscles used are the
deltoids)
References
1.
Baechle, Thomas R., Earle, Roger. Essentials of Strength Training and Conditioning. National Strength and
Conditioning Association. 2000.
Illustrations
1.
Figure 1 - Anglican Beach Party. Concentric vs Eccentric Contractions for Spiritual Hypertrophy. Hot Rod
Anglican. Illustration can be viewed at: http://hotrodanglican.blogspot.com/2010/04/concentric-vseccentric-contractions.html. Posted on Saturday, April 10, 2011. 5/14/2011.