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.