Course Content I.Introduction to the Course II.Biomechanical Concepts Related to Human Movement III.Anatomical Concepts Related to Human Movement IV.Qualitative Analysis of Human Movement

Anatomical Concepts Related to Human Movement A.The Skeletal System B.The Muscular System C.The Nervous System

The Muscular System 1.Organ Level Structure & Function 2.System Level Structure & Function 3.Injury to the Musculoskeletal System

The Muscular System I.Organ Level Structure & Function II.System Level Structure & Function III.Injury to the Skeletal System IV.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: fibers Fiber:8000 fibrils

Muscle Compartments

Organ Level Structure and Function Structure 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 Muscle Muscle% % Obicularis oculi15Quadriceps52 Biceps brachii38-42First DI57 Triceps brachii33-50Abductor pollicis brevis63 Extensor digitorum brevis 45 Masseter60-70 Vastus lateralis46Tibialis anterior73 Gastrocnemius (L)49Adductor pollicis80 Diaphragm50Soleus80

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 Principle  Same fiber type within MU  fibers per MU  MUs / muscle  MU 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 MusclePennate Muscle

Ranges of Muscle Pennation in Humans (Yamaguchi et al., 1990) Muscle Pennation Angle (deg) Gluteus maximus Gluteus medius Gluteus minimus Biceps femoris Gastrocnemius (medial) Gastrocnemius (lateral)

Fiber Density - PCSA

Nonpennate MusclePennate Muscle

CSA & PCSA of Ankle Plantar Flexors (Fukunaga et al., 1992) Muscle CSA (cm 2 ) PCSA (cm 2 ) Medial gastrocnemius Lateral gastrocnemius Soleus Flexor hallucis longus Tibialis posterior Flexor digitorum longus

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:  m

Active Component

Passive component

Total Force

Single Joint Muscles 60% % 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

% isometric Biomechanical Factors: Force-Velocity Relationship EccentricConcentric Velocity

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.