muscular skeletal system

Introduction

How movements occur contributes to successful performance. The skeletal and muscular systems work closely together and are referred to as the musculo-skeletal system. This system will support movement analysis and improvement in technique.

Content

  • Skeletal system – structure and function
  • Muscular system – structure and function
  • Antagonistic muscle action – prime movers, fixator, synergist
  • Muscle fibres – characteristics of Type I, Type IIa, Type IIb
  • Types of muscular contraction

Skeletal system

Knowledge of the skeletal system and how it works helps us to understand movement and explains how skills are performed. The skeleton provides attachments for the muscular system for movement and offers protection for vital organs such as the cardio-respiratory and vascular system.

The average human adult has 206 bones that are divided into the axial and appendicular skeletons. The main functions of these skeletal systems are:

Skeleton Function Bones Sporting example
AXIAL Protection
Shape
Red blood cell production		 Cranium
Thoracic cage
Cranium, thoracic cage, vertebral column, pelvis		 Heading the ball in football
Landing on floor after a tackle in rugby
Offers large surface area for muscle attachment
APPENDICULAR Movement
Muscle Attachment 		Upper Limbs: Humerus, Ulna, Radius
Lower Limbs: Femur, Tibia, Fibula 		Bowling in cricket
Running in rugby
Passing in netball

Structure of the skeletal system:

It is important to know the major bones that meet (articulate) at the shoulder, elbow, hip and knee.

How bones are formed

Bones are formed by the ossification of cartilage. This means is all bones start off as cartilage and they gradually turn to hard bone (ossification). Calcium is needed for strong bone growth.

Types of bones

The human body consists of 5 types of bones; long, short, flat, irregular and sesamoid bones.

Types of bone Function Example
Long
Growth plates at its ends 		Made up of compact bone for strength
Ends covered in articular (hyaline) cartilage aids with shock absorption
Creates leverage system for movement 		Femur
Short
As wide as long, with large amounts of bone marrow 		Provides support and stability Wrist, ankle
Flat Provides protection for vital organs
Base for muscular attachment
Highest number of red blood cells are formed 		Cranium, Scapular, Sternum
Irregular
Do not fall into any category 		Strength Mandible, vertebrae
Sesamoid
Embedded in a tendon (tendon attaches muscle to bone) 		To protect the tendon Patella

The muscular system

Skeletal Muscles are those that attach to bones and have the main function of contracting to create movement. They are also sometimes known as:

  • Striated muscles due to their appearance or
  • Voluntary because we have direct control over them contracting

There are over 600 muscles in the human body, all working in pairs (antagonistic muscle action). Knowing the major muscles that cause movement around the shoulder, elbow, hip and knee allows us to analyse movement, the generation of focus and how to improve sporting performance.

Forceful contractions can vary allowing, fast movements or small precision actions. Skeletal muscle can only pull, when contracting the muscle pulls one of the bones towards another across a synovial joint.

Antagonistic muscle action

As one muscle contracts to cause the movement another relaxes to allow the movement to take place. The muscle directly responsible for the movement is the agonist and the muscle that relaxes is the antagonist

Skeletal muscle fibre type

Not all skeletal muscles fibres are the same. The different fibre types contract at different speeds and are suited to different types of activity. The body is made up of a combination of slow and fast twitch muscle fibres. There are two main types:

Type I slow twitch oxidative aerobic
Type II fast twitch glycolytic anaerobic

There are two types of Type II:

Type IIa Fast oxidative glycolytic less force, more fatigue resistant
Type IIb Fast glycolytic greatest force

Depending upon the duration and intensity of training Type IIa fibres are able to take on the characteristics of either Type I or Type IIb muscle fibres

Characteristics of the muscle fibres:

Structural Differences
Characteristic Type I (oxidative) Type IIa (oxidative glycolytic) Type IIb(fast glycolytic)
Fibre size Small Large Large
No of capillaries Large Moderate Small
No of mitochondria Large Moderate Small
Myoglobin store High Moderate Low
CP stores Low High High
Glycogen stores Low High High
Functional Differences
Aerobic capacity High Low/moderate Low
Fatigue resistance High Low/moderate Low
Anaerobic capacity Low High/Moderate High
Speed of contraction Slow Fast Fastest
Force of contraction Low High Highest
Activity Long Distance 1500m Sprint

Immediate effects of exercise on skeletal muscle

As muscles contract over each other and along side bones it causes friction that is converted into heat, which in turn raises the core body temperature.

The effect of a raise in temperature of skeletal muscle:

  • Reduction in muscle viscosity, leading to improvement in efficiency of muscular contractions
  • Greater speed and force of contraction due to the higher speed of neural transmission
  • Increase in flexibility and elasticity of muscles, tendons and ligaments

Types of muscular contraction

Skeletal muscular contractions occur as a result of a stimulus being sent to the muscles to produce tension. Muscular contractions can be classified into either isotonic or isometric. Isotonic contractions can be sub divided into concentric and eccentric contractions.

The table below demonstrates the three types of contraction in relation top the biceps curl

Isotonic contraction
Concentric Eccentric
  • Muscle shortens and pulls
  • Upwards movement
  • Uses agonist
  • Most common contraction
  • Weight training
  • Muscle lengthens
  • Downwards movement
  • Uses antagonist
  • Control or deceleration
  • Opposite of concentric
  • Plyometrics
Isometric contraction
  • occurs with no change in length
  • tension stays the same length
  • stops flexion and extension
  • amount of force is related to the length of the muscle
  • Scrum in rugby

Quick Check

  • The skeleton provides attachments for the muscular system for movement and offers protection for vital organs such as the cardio-respiratory and vascular system.
  • The average human adult has 206 bones that are divided into the axial and appendicular skeletons.
  • The human body consists of 5 types of bones: long, short, flat, irregular and sesamoid bones.
  • Skeletal muscles are those that attach to bones and have the main function of contracting to create movement. They are also sometimes known as striated muscles due to their appearance or voluntary because we have direct control over them contracting.
  • As one muscle contracts to cause the movement, another relaxes to allow the movement to take place. The muscle directly responsible for the movement is the agonist and the muscle that relaxes is the antagonist.
  • The body is made up of a combination of slow- and fast-twitch muscle fibres.
  • Muscular contractions can be classified into either isotonic or isometric. Isotonic contractions can be sub-divided into concentricand eccentric contractions.