Lecture 4 - Biomechanics Flashcards
define biomechanics
uses laws of physics and engineering concepts to describe motion undergone by the various body segments and the forces acting on these parts during normal daily living
define occupational biomechanics
study of the physical interactions of workers with their tools, machines, and materials so as to enhance the workers performance while minimizing the risk of musculoskeletal disorders
goals of occupational biomechanics (consider what we understand)
We understand that:
- > people have mechanical limitations (i.e. strength, ROM, fatigue) and that peoples excessive loading leads to fatigue, downtime, and injury
it is a goal of occupational biomechanics to generate “tolerable, acceptable and optimal” working condisions
Kinetics vs Kinematics
Kinematics
- > describes motion undergone by various body segments (displacement, vel, acc)
Kinetics
- > understand the forces acting on these segments (F=ma)
issues that may lead to injury, fatigue, ect. in the workforce
- > awkward & static posture
- > Force/Load (too much)
- > Repetition
- > Duration
- > Vibrations
define tendons and tendon sheaths (relate to biomechanics)
Tendon
- > ables transmitting muscle forces
Tendon Sheaths
- > pulley and sliding surfaces
questions to consider when evaluating the biomechanics and therefore the ergonomics of a workplace
- > what are the forces required to produce a movement
- > does it overload the person
- > can the force or motion requirements be reduced
what are the most common issue that we try and fix when we work for a workplace
Low back pain and Upper-extremity cumulative trauma disorder (CTD)
what causes tendon related cumulative trauma disorder (CTD)
loss of blood supply to the tendons and increased tension in the tendons
neuritis
damage to the nerves that can be caused by awkward posture and repeated use
ischemia
the sensation of tingling and numbness, and is caused by obstruction of blood flow to tissue
bursitis
the inflammation of a bursa sac, which contains viscous fluid and is located near joints
what are the different types of cumulative trauma disorders (CTD)
- > tendon related CTD
- > neuritis
- > ischemia
- > bursitis
parts of the musculoskeletal system
- > tendons
- > ligaments
- > fascia
- > cartilage
- > bone
- > muscle
characteristics of connective tissue
cells: produce extracellular matrix
extracellular matrix: consistency determines connective tissue physical properties
- > ground substance (viscous fluid)
- > fibers
fibroblasts
cells produce matrix of loose connective tissue (skin, tendons and ligaments)
chondroblast
cells produce matrix of cartilage (transform to chondrocytes)
osteoblasts
cells produce matrix of bone (transform to osteocytes)
force hierarchy of muscle contractions
- Eccentric
- > works at optimum length - Isometric
- > works at a non optimal length - Concentric
- > works away from optimal length
characteristics of tendons
- > connects muscle to bone
- > transmit muscle force
- > parallel collagen arrangements, minimal elastin
- > surrounded by fibrous tissue sheaths
- reduce friction
types of tendon damage
- > torn
- > tendonitis
- > tenosynovitis
characteristics of ligaments
- > provides stability to joints
- > non-parallel collagen arrangement, aligned in direction of imposed stress
explain stress-strain relationships
Stress: applied load
Strain: deformation
Plastic region: permanent disruption
Ultimate strength: complete tear
muscular endurance
ability of a muscle or group of muscles to sustain repeated contractions against a resistance for an extended period of time
axial vs appendicular bones
Axial bones
- > skull, verts, sternum, ribs, pelvis
Appendicular bones
- > limbs
functions of bone
- > provide support
- > allow movement
- > protection
- > mineral storage
- > blood cell formation
types of bone
Long bones
- > shafts (diaphysis)
- > two expanded ends (epiphyses)
Cortical (compact)
- > provides cortex or lining of bone
Cancellous (spongy, trabecular)
fractures
bone loaded to failure
- > can handle compressive loads (stronger compression than tension)
Traumatic fracture: single load
Stress fracture: repetitive loading
how to find/what are bone “hot spots”
- > computed topography (CT)scan or magnetic resonance imaging (MRI) will be necessary
bone scan will identify “hot spots”, which may indicate stress fractures or tumours
fatigue
Net effect of the central fatigue and muscle fatigue and psychological factors resulting in a progressive decline of observed force production
central vs muscle fatigue
central
- > reduction in MVC force not accompanied by same reduction in maximal evocable force
muscle
- > reduction in the capacity to generate force
how do we quantify the magnitude of the loading over a given time (refer this to cumulative loading and CTD)
we observe the…
- > posture
- > repetition
- > duration
- > force
main causes of CTD
- > inadequate recovery
- > awkward joint postures
- > excessive loads
how can repeated submaximal loading cause injury
tissue tolerance will decrease and eventually fail
how can sustained loading over time lead to injury
over time you will slowly degrade the tissue until your tolerance completely gives out
