Brief description of muscle Bio mechanics for Physiotherapists

1. Muscle biomechanics
Prof Subhash M Khatri

2. Motors

3. 1 January 1680
Giovanni Alfonso Borelli
De Motu Animalium book

4. Overview
• Mouse 640
• Organ of MVT
• Largest TIB
• 40-45% of TBW
• Respiration, circulation, digestion, locomotion,
communication

5. Classification
• Red &white:Red muscles contract slowly & white
muscle/skeletal contracts fastly
• Tonic & Phasic:Tonic/postural performs continuous low
level of contractile activity & phasic short durated high
level.

6. Classification
• Contractors& Expanders: Pulls the body in
approximate fetal positione.g flexors,
adductors, medial rotators. Expanders open
up the body e.g. extensors, abductors,
lateral rotators.
• Spurt & shunt: Muscle which attaches
closer to the joint axis has larger rotatory
component & is called spurt muscle

7. Fs
F
Fr

8. Mechanics
• Rotatory component & Stabilizing component
• Angle formed by the mechanical axis of muscle
with lever arm in which it is inserted
• Fr= F sin8
• Fs=F cos 8
• Both components equal if angle is 450 =0.70
• Most of muscle angles very small & hence
stabilizing component is >rotatory hence
position ,balance& stabilization is maintained very
well.

9. PCA
• Fm = (Amcosθ)σm
• where
Fm = max isometric contraction force
Amcosθ = physiological cross-sectional area
θ = angle of pennation
σm = maximum isometric stress

10. Series and parallel elastic elements in muscle.
A.Resting muscle contains elastic elements in series with the contractile elements (sarcomeres) and
in parallel with them.
B.During an isometric contraction, the muscle does not change length, but sarcomeres shorten,
stretching the series elastic elements.
C.During isotonic contraction, the contractile elements shorten, stretching the series elastic
elements, before they develop tension to lift the load.
D.Muscle begins to shorten when contractile elements shorten further.

11. Muscle can fail to produce force when slack (active
insufficiency) and can restrict range of motion when fully
stretched (passive insufficiency).

12. When a muscle develops concentric tension against a high load,
the velocity of muscle shortening must be relatively slow.

13. In single muscle fibers and isolated muscle preparations, force
generation is at its peak when the muscle is at normal resting
length (neither stretched nor contracted).

14. FORCE TIME RELATIONSHIP
Muscular power - the product of force and velocity.
Maximum power occurs at approximately one-third of
maximum velocity and at approximately one-third of
maximum concentric force.
Muscular endurance - the ability of the muscle to exert
tension over a period of time.
Effect of muscle temperature - as body temperature
elevates, the speeds of nerve and muscle functions
increase.

15. Rundown
1. Force time relationship
2. Length tension relationship
3. Length tension curve/stress & strain curve
4. Force velocity curve
5. Force & cross sectional area
6. Rotatory & stabilizing components