Reading for Control of Human Movement 2:
pp. 138-142 in Smith, L.K., Weiss, E.L. & Lehmkuhl, L.D. (1996). Brunnstrom's clinical kinesiology (5th ed.). Philadelphia: F.A. Davis.
(optional) Langton, P. (17 Nov 2000). Element 3. Nerves, the neuromuscular junction and muscle. Bristol, UK, Bristol University, Department of Physiology. Retrieved January 17, 2001, from the World Wide Web: http://www.bris.ac.uk/Depts/Physiology/ugteach/ugindex/m1_index/nm_tension/nm_tension.htm
Clinical implications of muscles' length-tension properties
Students in Control of Human Movement I consider two implications of muscles' elastic properties:
- A MUSCLE DEVELOPS GREATER FORCE WHEN IT IS ELONGATED.
People frequently permit muscles to elongate just prior to activating them concentrically. For example, just before activating the knee extensors to perform a vertical jump, they permit the knees to flex, thereby elongating the knee extensors.
AN ELONGATED MUSCLE DEVELOPS GREATER FORCE BECAUSE ITS CONNECTIVE TISSUE STRUCTURES CONTRIBUTE RELATIVELY LARGE PASSIVE (ELASTIC) FORCES.
- A MUSCLE DEVELOPS LESS FORCE WHEN IT IS SHORT.
One cannot make an effective fist, for instance, when the wrist is flexed. Flexing the wrist, Then flexing the digits to make a fist, causes the finger flexors to become very short.
A VERY SHORT MUSCLE DEVELOPS LESS FORCE BECAUSE ITS CONTRACTILE STRUCTURES (ACTIN-MYOSIN) CONTRIBUTE RELATIVELY LITTLE ACTIVE FORCE.
In Control of Human Movement II students additionally consider the consequences of muscles' viscous properties.
- TO ELONGATE A SHORT MUSCLE, SLOW STRETCHING IS MORE EFFECTIVE THAN FAST STRETCHING .
Stretching muscle or other soft tissue involves overcoming the tissue's resistance to elongation. AT LOW SPEEDS OF ELONGATION, MUSCLES DEVELOP LESS VISCOUS FORCE, AND SO OFFER LESS RESISTANCE TO STRETCHING.
In this sense, muscles behave like a viscous material, one whose properties are similar to those of "Silly Putty."
Knowledge of properties like elasticity and viscosity influence our approach to developing clinical prescriptions for stretching exercise.
- MUSCLES DEVELOP MORE FORCE DURING CONCENTRIC ACTIVATION IF THAT ACTIVATION IS PRECEDED BY A 'QUICK STRETCH' THAN IF IT IS PRECEDED BY A SLOW STRETCH.
Not only do people permit a muscle to elongate just before activating it concentrically, they permit it to do so quickly. They allow the knees to flex quickly, not slowly, prior to jumping so that the knee extensors elongate quickly.
RAPID ELONGATION CAUSES THE MUSCLE TISSUE TO DEVELOP GREATER VISCOUS FORCE, WHICH CONTRIBUTES TO THE MUSCLE'S OVERALL FORCE PRODUCTION.
MUSCLE STRUCTURES THAT PRODUCE ACTIVE OR PASSIVE FORCE
ACTIVE FORCE IS PRODUCED IN
PASSIVE FORCE IS PRODUCED IN:
connective tissue structures:
- tendon, aponeurosis, or other structure attaches muscle to the skeleton
- epimysium surrounds entire muscle
- perimysium surrounds individual fascicles
- endomysium surrounds individual fibers
- sarcolemma penetrates individual fibers
- large proteins like titin connect myosin filaments to sarcomere's Z lines