Course ContentI. Introduction to the CourseII. Biomechanical Concepts Related

to Human MovementIII. Anatomical Concepts Related to

Human MovementIV. Qualitative Analysis of Human

Movement

Anatomical Concepts Related to Human MovementA. The Skeletal SystemB. The Muscular SystemC. The Nervous System

The Muscular System1. Organ Level Structure &

Function2. System Level Structure &

Function3. Injury to the Musculoskeletal

System

The Muscular SystemI. Organ Level Structure &

FunctionII. System Level Structure &

FunctionIII. Injury to the Skeletal SystemIV. Musculoskeletal Function

General Structure ~ 434 muscles 40%-45% of body weight 75 pairs of muscles Organized into compartments Utilizes 50% of body’s metabolism Controlled by somatic nervous

system

General Function Provides force/torque for

movement Maintenance of upright posture Body transport Object manipulation

Aids in venous return Maintains body temperature

Organ Level Structure and Function Structure of the Muscle Organ Function of the Muscle Organ

Organ Level Structure and Function Structure of the Muscle Organ Function of the Muscle Organ

Muscle Tissue – Active Component

Properties of Skeletal Muscle Tissue Excitability (Irritability) Conductivity Contractility Extensibility Elasticity

Connective Tissue – Passive Component

Nerve Tissue – Passive Component

Structure of the Muscle Organ

Muscle organ: 40,000 -1,000,000 fibers

Fascicle: 10-200 fibers Fiber: 8000 fibrils

Muscle Compartments

Organ Level Structure and Function Structure of the Muscle Organ Function of the Muscle Organ

Function of the Muscle Organ

Force Production

Series & Parallel Elastic Tissue

Factors That Affect Force Output Physiological factors

Cross-sectional area Fiber type

Neural factors Muscle fiber activation Rate of motor unit activation

Biomechanical factors Muscle architecture Force-length relationship Force-velocity relationship

Physiological Factors: CSA

Training?

Physiological Factors: Muscle Fiber Type Type I

Red, SO, slow-twitch Type IIa

Red, FOG, fast-twitch, intermediate Type IIb

White, FG, fast-twitch

Training??

Percentage of Type I Fibers in Human Skeletal MuscleMuscle % Muscle %

Obicularis oculi 15 Quadriceps 52Biceps brachii 38-42 First DI 57Triceps brachii 33-50 Abductor pollicis

brevis63

Extensor digitorum brevis

45 Masseter 60-70

Vastus lateralis 46 Tibialis anterior 73Gastrocnemius (L)

49 Adductor pollicis 80

Diaphragm 50 Soleus 80

Factors That Affect Force Output Physiological factors

Cross-sectional area Fiber type

Neural factors Muscle fiber activation Rate of motor unit activation

Biomechanical factors Muscle architecture Force-length relationship Force-velocity relationship

Neurological Factors: Muscle Fiber Activation

All-or-None PrincipleSame fiber type within MU10-2000 fibers per MU120-580 MUs / muscleMU size influences precision & force of movement

Neurological Factors: Muscle Fiber Activation

# of activated MUs, force

Training?

Neurological Factors: Rate of Motor Unit Activation

rate of MU activation, force

Single Twitch

Multiple Twitch

Tetanus

Training??

Factors That Affect Force Output Physiological factors

Cross-sectional area Fiber type

Neural factors Muscle fiber activation Rate of motor unit activation

Biomechanical factors Muscle architecture Force-length relationship Force-velocity relationship

Nonpennate Muscle Pennate Muscle

Ranges of Muscle Pennation in Humans (Yamaguchi et al., 1990)

Muscle Pennation Angle (deg)

Gluteus maximus 3.4-5.0Gluteus medius 8.0-19.0Gluteus minimus 5.0-21.0Biceps femoris 7.0-17.0Gastrocnemius (medial) 6.5-25.0Gastrocnemius (lateral) 8.0-16.0

Fiber Density - PCSA

Nonpennate Muscle Pennate Muscle

CSA & PCSA of Ankle Plantar Flexors (Fukunaga et al., 1992)

Muscle CSA (cm2)

PCSA(cm2)

Medial gastrocnemius 16.49 68.34Lateral gastrocnemius 11.24 27.78Soleus 29.97 230.02Flexor hallucis longus 4.85 19.32Tibialis posterior 5.40 36.83Flexor digitorum longus 1.59 9.12

Biomechanical Factors: Muscle Architecture Pennate

Greater force (force ~ PCSA) Non-pennate

Greater range of muscle lengths Larger ROM Greater operating range Shorten at higher velocities

Training?

Factors That Affect Force Output Physiological factors

Cross-sectional area Fiber type

Neurological factors Muscle fiber activation Rate of motor unit activation

Biomechanical factors Muscle architecture Force-length relationship Force-velocity relationship

Humans: 2.6-2.8 m

Active Component

Passive component

Total Force

Single Joint Muscles

60% 110-120% 160%

Multi Joint Muscles

60% >160%

Factors That Affect Force Output Physiological factors

Cross-sectional area Fiber type

Neurological factors Muscle fiber activation Rate of motor unit activation

Biomechanical factors Muscle architecture Force-length relationship Force-velocity relationship

110-180%isometric

Biomechanical Factors: Force-Velocity Relationship

Eccentric ConcentricVelocity

Factors that Affect Force Output Physiological factors

Cross-sectional area Fiber type

Neurological factors Muscle fiber activation Rate of motor unit activation

Biomechanical factors Muscle architecture Length-tension relationship Force-velocity relationship

Summary Numerous factors affect the force

output of the muscle organ. Identification of these factors

allows us to better understand muscle strength and explore alternative training methods that may be effective in increasing muscle strength.