Biomekanik

Irfan Idris

Bagian Faal FK Unhas

Pendahuluan

Apa itu biomekanik ???

Anak usia 10-12 bulan mulai berjalan

Bagaimana pekerja menghindari LBP ?

Mengapa orangtua cenderung mudah jatuh ? Pakai tongkat ?

Ada orang yang dapat melakukan gerakan yang kompleks dengan mudah, tetapi ada yang tidak mampu melakukan gerakan yg sederhana

Definisi Biomekanik

The science involving the study of biological systems from a mechanical perspective

Use the tools of mechanics (branch of physics involving analysis of the action of forces) to study the anatomical and functional aspects of living organisms

Cabang utamanya : Static dan dynamics

Statics is the study of systems that are in a state of constant motion (rest or moving with constant velocity)

Dynamics is the study of systems in which acceleration is present

Kinematics is the description of motion including the pattern and speed of movement sequencing by the body segment that often translates to the degree of coordination an individual display

Kinetics is the study of the force associated with motion

Kinesiology : the study of human movement

Sport medicine : clinical and scientific aspects of sports and exercise The

American College of Sport Medicine

Masalah yang dipelajari

Binatang yang berkaki dua dan berkaki empat menggunakan energi yang sama saat bergerak; economy cost of energy (padahal berat badannya beda & jumlah otot yang terlibat beda)

Pada manusia, terdapat perbedaan individual “energy cost” saat lari dengan kecepatan tinggi

Latihan dan high altitude improve running economy; otot-otot menggunakan energi dan elastisitasnya lebih efisien

NASA : astronout yang hanya beberapa hari di luar angkasa atrofi otot, densitas tulang menurun (osteoporosis) terutama pada tulang kaki exercise (di luar angkasa)

Osteoporosis 40% usia > 50 thn dan 90% pada usia > 60 thn most common : vertebra & hip fracture

Usia tua gangguan keseimbangan : mudah jatuh (sway & fall)

Gait penderita cerebral palsy spastik dan muscle tension modifikasi otot hamstring, rectus femoris dan sartorius gait membaik

Amputasi prostetik yang mirip aslinya dapat digunaka sport/exercise

Occupational biomechanics is a field that focuses on the prevention of the work-related injuries Penelitian LBP akibat benda berat, posisi yg salah,

gerakan yg tiba2 & tdk direncanakan Pekerja harus siap secara fisik & mental pencegahan LBP

Carpal tunnel syndromes : repetitive keyboard use design keyboard yang sehat

Biomekanik penemuan sport equipment yang sehat Klapskate utk skating, aerodynamic helmet-clothes-cycle design utk olahraga bersepeda dsb

Biomekanik memperbaiki performance dan teknik atlit

Analisis biomekanik pada juara olimpiade lempar cakram 4 kali : mendapatkan lemparan yang maksimal bila : Speed of the discus when it is released by the

thrower The projection angle at which the discus is

released The height above the ground at which the discus

released The angle of attack (the orientation of the discus

relative to the prevailing air current)

Why study biomechanical ?

Why is swimming is not the best form of exercise for osteoporosis ?

What is the safest way to lift a heavy object ?

Is it possible to judge what movement are more/less economical from visual observation ?

At what angle should a ball be thrown for maximum distance ?

Why are some individuals unable to float ?

Beberapa aspek biomekanik tulang

Dua fase :

Fase 1 : mineral

Fase 2 : kolagen & substansi dasar

Aspek biomekanik yang terpenting dari tulang : kekuatan (strenght) dan kekakuan (stiffness)

Pembebanan (loading) untuk

mengerti aspek biomekanik pada tulang

B

A

C

D

D’

Ultimate failure

point

Plastic region

Yield

point

Deformation

Load

Load Deformation Curve for

pliable material

Strenght luasnya area dibawah curva

Stiffness makin curamnya slope elastic region

Load-deformation curve berguna

untuk mempelajari : karakter fraktur & repairing; respon tulang pada pembebanan; efek beberapa treatment pada tulang (prostetik implant)

Stress : load/force N/cm2 = Pascal

Strain : ketegangan linier (length

change) & shear (angular change)

A

B

C

B’

B” C”

C’

Strain (ε)

Str

ess (σ

)

E (elastisitas) = σ / ε

Curve stress-strain

E stiffness

Tulang cortical lbh kaku tulang cancellous (trabekular)

Tulang cortical dengan strain 1.5 – 2% fraktur; cancellous bone bisa tahan

strain sampai 50% sebab banyaknya pori-pori ~ banyaknya energi yang tersimpan

50

100

150

200

5 10 15 20 25 30

Strain %

Str

ess (

MP

a)

Cortical

bone

Trabecular bone

Mechanical behaviour of two bone

structures with compression test

metal

glass

bone

strain

str

ess

Beberapa aspek biomekanik pada otot

4 propereties :

Extensibility : increase length

Elasticity : return to the normal length (paralel elastic component/PEC and serial elastic component/SEC)

Irritability : ability to respond to a stimulus

Developed tension : contraction (contractile component)

SEC and PEC

SEC : tendon and contractile fiber

PEC : muscle membranes and muscles

Height of jump increase increased of

SEC lower extremity muscle

Increased muscle force increased

increased of PEC

Tipe otot

Karakteristik Type I (slow-twich oxidative)

Type IIA (Fast twich oxidative glycolytic/FOG)

Type IIB (Fast twich oxidative glycolytic/FG)

Kecepatan kontraksi

lambat cepat Cepat

Fatique lambat intermediate Cepat

Diameter kecil intermediate Besar

Jumlah ATPase rendah tinggi Tinggi

Jumlah mitokondria tinggi rendah Rendah

Jumlah enzim glikolitik

rendah intermediate Tinggi