5 Biomechanics of sports and physical exercise

Imkongtenla Pongen and Meenal Dhall

Contents:

1. Goals   of studying biomechanics of sport and physical activity

1.1. Ways of improving the goals

1.1.1. Training

1.1.2 . Technique

1.1.3. Equipment

2. Branches of biomechanics

2.1. External Biomechanics

2.1.1 Forces

2..1.2. Linear Kinematics

2.1.3 Linear Kinetics

2.1.4. Work, Power ,Energy

2.1.5. Torques and movements of force

2.1.6. Angular Kinematics

2.1.7. Angular Kinetics

2.2. Internal Biomechanics

2.2.1 Mechanical Properties of the Musculoskeletal System

2.2.2. Nervous System

3. Biomechanical Analysis to Improve Training

3.1 Biomechanics and Training

3.2 Technical Training

3.3 Physical Training

4 .Technology in Biomechanics

4.1 Tools for Measuring Kinematics

4.2 Tools for Measuring Kinetics

Summary

    Learning Objectives-

1.  To understand the meaning of biomechanics in terms of human physical activity and sport.

2.  Goals of studying biomechanics in sport and physical activity

3.  To distinguish between external and internal biomechanics

4 .To understand the different types of external biomechanics

5.  To evaluate the different types of internal biomechanics

6.  Understanding how the results of a qualitative analysis improve technical training

7.  To discuss the steps involved in a qualitative anatomical analysis

8.  Understanding the advantages of following a set of physical training

Introduction

Biomechanics is the study of forces and their impact on the living system. Human biomechanics or biomechanics of sports and physical exercise is the study of forces and their impact on the human body during physical exercise and sports.

1. Goals of studying biomechanics of sport and physical activity

1.1. Ways of improving the goals

i)  To improve performance in the given physical exercise or sport

ii)   To provide precautionary measures for injury and rehabilitation

iii)  To increase physical fitness

These goals can be improved through the process of:

1.1.1   Training

An athlete or an individual practicing physical exercise is or maybe limited by strength or endurance of certain muscle groups, speed of motion or by specific aspects of motion technique equipment and technique improvement .Therefore, the coach needs to analyse the mechanical values that may lead to threshold stimuli.

1.1.2  Technique

A qualitative analysis, can be used to correct the movement, for better execution of the movement, or to change the actions and positions of the sport performance.

Figure 1.1. To successfully complete triple jumps in figure skating human body requires strong arms and shoulders.

(Source Link: https://en.wikipedia.org/wiki/Glossary_of_figure_skating_terms)

1.1.3    Equipment-

Using the right equipment that will give advantage to the recreational athletes or to the elite.

2. Branches of biomechanics

2.1. External Biomechanics

External forces and their effects on the body and its movement – Movement of a body is determined by the external actions that acts on the body.

2.1.1.   Forces– Force is a push or a pull that are exerted by an object on another object . When a force acts on an object there is always action and a reaction i.e. the force exerted by one object on another is matched by an equal but oppositely directed force exerted by the second object on the first. Forces are classified into internal and external forces.

– Internal Forces-

Internal forces are forces that act within the object whose motion is being investigated. The human body consists of organs, bones, muscles, tendons, ligaments, cartilage, and other tissues and these structures exert forces on one another. The internal pulling forces are referred to as tensile forces . The internal pushing forces that act on the ends of an internal structure are referred to as compressive forces.

Muscles pull on tendons, which pull on bones and at joints, bones push on cartilage, which pushes on other cartilage and bones. When the structures are under tension or compression internal forces hold things together. Sometimes the internal forces is lesser than the tensile or compressive forces acting on a structure. When this happens, the structure fails and breaks. When muscles pull, tendons rupture, ligaments tear and bones break structural failure in the body occurs.

Figure 1.2. The forces acting on a shot-putter and a shot at the instant before release.

(Source :Biomechanics of sport and exercise Peter M. Mc Ginnis )

External Forces

When objects interact with the environment surrounding is known as external forces. External forces can be divided into contact forces and noncontact forces.

In sports and exercise, the force of gravity is the only noncontact force and the most important contact forces in sports is between solid objects, such as the athlete and some other object . Friction and Normal Contact Force

Static friction – When dry friction acts between two surfaces that are not moving relative to each other. Limiting friction –When there is maximum amount of friction developing before two surfaces begin to slide.

Dynamic friction– When dry friction acts between two surfaces that moves relative to each other, also known as sliding friction and kinetic friction.

An important force in every sport and physical activity is friction . Locomotion requires frictional forces, so the shoes we wear are designed to provide proper frictional forces between our feet and the supporting surface. Thus we want large frictional forces in most athletic shoes, so that the materials used for the soles have large coefficients of friction.

2.1.2 Linear Kinematics

It is concerned with the description of linear motion. speed, distance and direction of an object Kinematics: Motion can be defined as the action or process of a change in position. Linear Motion-

Rectilinear translation – When all points on a body or object move in a straight line without changing the direction and the orientation of the object and all points on the object move the same distance. Curvilinear translation– When all points on a body or object move so that the orientation of the object does not change and all points on the object move the same distance.

Angular Motion –It is also known as rotator motion , occurs when all points on a body or object move in circles about the same fixed central line or axis. An example of angular motion is the body an ice-skater in a spin.

General Motion – It is a combination of both linear and angular motions.Example- running and walking.

2.1.3     Linear Kinetics

Newton’s first law –It explains that objects do not move or do not change their motion unless a net external force acts on them.

Newton’s Second Law of Motion or Law of Acceleration : The change of motion of an object is proportional to the force impressed; and is made in the direction of the straight line in which the force is impressed.

Newton’s second law explains a cause-and-effect relationship where it explains that acceleration is caused and is also the effect of force . An object accelerates if the net external force acts on it. If an object accelerates, a net external force must be acting to cause the acceleration. Impulse and Momentum

In sports and human physical activity, we are concerned with the final outcome resulting from external forces acting on an athlete or object over some duration of time than with the instantaneous acceleration of the athlete or object at some instant during the force application. Impulse is the product of force and the time during which force acts.

Momentum of an object depends on the velocity on sport and physical activity because the objects we deal with has a constant mass.

In certain other activities,we can use impulse to decrease momentum.

Newton’s Third Law of Motion –which states that to every reaction there is always an equal and opposite reaction. This law explains about the reaction –action.

2.1.4     Work, Power, and Energy

They explaining the causes of motion without Newton’s Law Work be defined as the product of force and displacement. Mathematically, it can be expressed as :

U = F(d)

where,

U = work done on an object (the letter W would be a better abbreviation for work, but we already used it to represent weight),

F = force applied to an object, and

d = displacement of an object along the line of action of the force

Energy is defined as the capacity to do work.We have two different types of energy:

Kinetic energy – energy due to motion

Potential energy – energy due to position

Gravitational potential energy is the potential energy due to an object’s position relative to the earth where the energy of an object is related to the object’s weight and its elevation or height above the ground.

Strain energy –The  energy caused due to the deformation of an object.

Work–Energy Relationship

Energy is transferred from one object or system to another which is a form of work. Also, the unit of measure for work and energy is joules.

-Doing Work to Increase Energy

-Doing Work to Decrease(or Absorb) Energy

-Conservation of Mechanical Energy: when no work can be done energy is conserved. Thus ,the total mechanical energy of the object remains constant if no external forces other than gravity act on the object.

Power is defined as the rate of doing work. It can be regarded as how quickly or slowly a work can be done. The maximum power output a human is capable of producing during exercise or sport is related to the duration of the activity involved that is dependant with the metabolic capabilities of the human body.

2.1.5 Torques and Moments of Force

Torque is the turning effect produced by a force.

Eccentric force – An external force that is not directed through the center of gravity of an object.

Muscular Torque – when a muscle contracts it creates a force by pulling on it’s point of attachments.

Figure 1.3. The biceps brachii exerts a torque around the axis of the elbow joint by producing a force (Fm) with a moment arm (r) around the joint.

(Source Link: https://www.tutelman.com/golf/swing/models1_.html)

Center of gravity –The point in a body or system where mass or weight is evenly distributed or balanced and where the force of gravity acts.

In sports and physical exercise centre of gravity provides stability i.e the capacity of an object to return to equilibrium or to its original position after it has been displaced.The stability of an object is affected by :

-the height of the center of gravity

–  size of the base of support

–  weight of the object

2.1.6 Angular Kinematics

Angular kinematics describes objects in angular motion.Angle is formed by intersection of a line and a plane or two lines ,two planes.Angular position is the orientation of a line with another line or plane. Absolute angular position – A position where a line or plane is fixed and immovable relative to the earth position.

Relative angular position – A position where a line or plane is capable of moving

Angular displacement- The change in absolute angular position experienced by a rotating line

Angular velocity -The rate of change of angular displacement

Relationship between linear and angular velocity

The  angular  displacement  and  linear  distance relationship  provides a good understanding  For instance, if we take into consideration a swinging golf club ,all points on the club undergo the same angular displacement and   the same average angular velocity. This is because they all take the same time to undergo that certain displacement.

Planes and Axes of Motion

Anatomical Planes:

Sagittal plane( anteroposterior plane) – An imaginary plane running anterior to posterior and superior to inferior dividing the body into right and left parts

Frontal plane (coronal or lateral plane) –It runs side to side and superior to inferior, dividing body into anterior and posterior parts

Transverse plane( horizontal plane)- runs from side to side and anterior to posterior, dividing body into superior and inferior parts.

Cardinal plane – A plane that passes through the midpoint or center of gravityof the body.

Table 1.1. – Anatomical Planes of Motion and Their Corresponding Axes of Motion

Figure 1.4 Anatomical Planes of Motion and Their Corresponding Axes of Motion

(Source Link : https://www.pinterest.com/pin/574771971165806104/)

2.1.7 Angular Kinetics

It explains the causes of angular motion

Angular inertia (rotary inertia) –is the property of an object to resist changes in its angular motion.

A body may have more than one moment of inertia because an object may rotate about more than one axis of rotation.

2. 2 Internal biomechanics

2.2.1 Mechanical Properties of the Musculoskeletal System

The important connective tissues important to the structure of the musculoskeletal of human body are bone, cartilage, ligament and tendon. Age and activity may also affect the mechanical properties of the connective tissues.

2.2.2 Nervous System

The nervous system controls of the musculoskeletal system. It is divided into the central nervous system and the peripheral nervous system. Central nervous system consists of the brain and spinal cord. Peripheral nervous system consists of all the nervous tissue that lies outside the skull and the vertebral column. According to function it performs ,it is again divided into:

Somatic nervous system – voluntary, involved in conscious sensations and actions

Autonomic nervous system– involuntary,  involved with unconscious sensations and actions.

There are three types of neurons:

(1)  Sensory or afferent neurons – responsible for sensations

(2)  motor or efferent neurons- receive stimuli from interneurons or sensory neurons

(3)  Interneurons

Sensory and motor neurons are situated in peripheral nervous system and the interneurons are situated within the central nervous system.

Figure 1.5 Scheme showing the pathways of a neural impulse from external stimulus to muscle action

(Source Link: http://leavingbio.net/the%20nervous%20system_files/the%20nervous%20system.htm)

3. Biomechanical Analysis to Improve Training

There are two types of analysis – qualitative and quantitative. A qualitative biomechanical analysis relies on subjective observations whereas a quantitative biomechanical analysis uses actual measurements to quantify the mechanical parameters of the performance.

Steps of a Qualitative Biomechanical Analysis

It consists of four steps:

1. Description – To develop a theoretical model of the most effective technique and to describe what it would look like.

2.  Observation- To observe the performance

3.  Evaluation – To compare the ideal technique to the observed performance.

4.  Instruction – Educate or instruct advice to correct

Quantitative Biomechanical Analysis: This analysis is limited however, teachers or coaches may make some performance measurements and thus do some limited quantitative biomechanical analysis.

For instance, equipement such as stopwatch and a tape measure may be used to measure and quantify the biomechanical parameters.

3.1 Biomechanics and Training

The principle of specificity is a fundamental principle of training . Therefore as the principle suggests exercises and drills must be specific to sport and physical activity. If the exercises and drills used in training are closely matching the aspects of the skill we are training for, we will have greater gains in performance.

3.2 Technical Training

Training time and practice for specific sport or physical activities are usually devoted to improving technique (technical training) or physical condition (physical training). The time proportion allocated to technical training depends in part on the technical difficulty of the activity. Technical training may involve performing drills or performing the actual skill that mimic specific aspects of the skill. Biomechanics can thus contribute to improvements in sport and various physical activity.

Technical training may have some effect on the performer’s physical condition, and physical training may have some effect on the performer’s technical proficiency.

3.3 Physical Training

The other part of training is the physical training, physical training is directed at altering performance limitations due to the physical condition of the performer whereas technical training is directed primarily at correcting or improving aspects of technique training.

Physical training is directed at improving the various components of physical fitness that includes :

1.  muscular strength,

2.  muscular power,

3.  muscular endurance,

4.  flexibility,

5.  cardiovascular fitness, and

6.  body composition.

4. Technology in Biomechanics

As technology improves measurement techniques are constantly evolving .There are various tools for measuring biomechanical variables that vary in cost and sophistication from simple stop watches to highly sensitive force platforms and multi-camera motion capture systems. The tools has been categorized as tools for measuring kinetics and tools for measuring kinematics .

4.1 Tools for Measuring Kinematics

Popular tools for measuring kinematic includes; timing systems,velocity-measuring systems (based on radar or laser light), accelerometers, microelectromechanical systems (MEMS) inertial sensors and optical imaging systems (film cameras, video cameras, etc.)

4.2 Tools for Measuring Kinetics

Kinetic variables are based depending on the force of the cause of change in motion. Some popular tools for measuring kinetic variables in biomechanics force platforms, strain gauges,

Summary

Human biomechanics or biomechanics of sports and physical exercise is the study of forces and their impact on the human body during physical exercise and sports. Forces play a major role in the movement ,motion and co-ordination of the body whereas, Work, Power, and Energy explains the causes of motion without Newton. Torques and Moments of Force.

Center of gravity is the point in a body or system where mass or weight is evenly distributed or balanced and where the force of gravity acts. In sports and physical exercise centre of gravity provides stability i.e the capacity of an object to return to equilibrium or to its original position after it has been displaced. Angular Kinematics describes objects in Angular Motion. Angular Kinetics explains the causes of Angular Motion mechanical properties of the Musculoskeletal System. Also, the Nervous System controls Musculoskeletal System. We have two types of analysis that can improve the performance which are the qualitative biomechanical analysis that relies on subjective observations of the performance, whereas the quantitative biomechanical analysis uses actual measurements to quantify certain mechanical parameters of the performance.

Biomechanics can be used to improve performance by improving training for that performance. A basic principle of training is specificity. Biomechanics can improve the specificity of training by identifying specific aspects of technique that need to be perfected by identifying exercises and drills that mimic specific aspects of the exercise technique or specific muscle groups used during the performance; and by identifying the specific muscles whose strength, power, or flexibility limit the performance. A study on the qualitative anatomical analysis of a performance also identifies the specific muscles that are active during a movement or performance.