1. 9 Neuromuscular Factors Affecting Muscle Force Production
Fiber Type
Number of Muscle Fibers
Rate of Stimulation
% Fiber Recruitment
Force-velocity Relationship
Fiber Architecture
Muscle Temperature
Elastic Properties
Angle of Pull

2. Sliding Filament Theory

3. 1. Fiber Type Fast twitch muscle fiber (Type IIb)
Contraction speed is fast – high force production
Fatigues relatively fast
Slow twitch muscle fiber (Type I)
Contraction speed is slow – lower force production
Slow to fatigue
Intermediate muscle fiber (Type IIa)
Population distribution is bell-shaped curve

4. 2. Number of Muscle Fibers
The more muscle fibers one possesses the more force production they create
Largely genetically pre-disposed
Increase cross-sectional area of muscle fiber will increase force production

5. 3. Rate of Stimulation
The faster the rate of stimulation the more force production
Based on the “All or None Principle”
twitch → summation → tetanus
Electromechanical Delay (EMD) – due to the elasticity of tendons and muscle

7. 4. % Fiber Recruitment
Largely dependent on the resistive forces that the muscle deals with – slow twitch (ST) fibers have a lower activation threshold than fast twitch (FT) fibers
As the speed and force requirement of the muscle increases more FT fibers are activated

8. 5. Force-Velocity Relationship
As speed of contraction increases force production decreases and vice-versa
Force-Velocity Curve

9. Force-Velocity Curve

10. 6. Fiber Architecture
Fusiform or Parallel (parallel tendons) – specializes in greater ROM and speed of ROM
Pennate – specializes in greater force production (contains greater # of fibers w/n a cross sectional area)

12. 7. Muscle Temperature Warm muscles will result in:
↑ elasticity of muscles
↑ conduction velocity (↑ rate of stimulation)
↓ internal friction

13. 8. Elastic Properties Tissue Elastic Properties
Series Elastic Component (SEC)
Parallel Elastic Component (PEC)
Proportional Length of Muscle
Under isolated conditions the muscle fiber produces greatest force when at resting length
Inclusion of SEC and PEC than greatest force production is produced when slightly stretched
Stretch-reflex (Stretch-shortening Cycle)

14. Musculotendon Unit Model

15. Proportional Length of Muscle

17. 9. Angle of Pull Two important functions of muscle contraction:
Rotation of the bone segment
Stabilization of the bone segment
Near 90 degrees of pull the muscle work best to rotate the joint. As it goes away from 90 degrees it works more towards joint stability