Biomechanics and Human Gait: An Engineering Introduction

Summer at Brown 2011

What do you think of when you hear Biomedical Engineering?

Biomedical Engineering: More than Biomechanics

• Biomaterials- Tissue engineering– Bladder– Kidney– Liver– Heart

Biochemical

• Biofuel from algae• Bioreactors

– Treating• Sewage• Landfills• Oil spills• Other environmental pollutants

• Biopharmaceuticals– Biological systems to produce medical drugs

• Insulin, anti-bodies

Neuroscience• Brain Gate

– Brown University– video– Chip implant– Brain Interface

Bio-sensing

• Analytical device for the detection of a biological factor using a bio and physiochemical detector

• Examples– Blood glucose biosensor– Food analysis

• Toxins and pathogens

– Counter-bioterrorism• Bio-warfare air detection

Bio-Nanotechnology• New Growing field• Cancer/Tumor

– Detection– Focused treatment

• Antimicrobial treatments – Catheters– Bone implants

• Carbon Nano tubes– Tissue engineering, scaffolds– Cancer therapy

A Day in the life of a Biomedical Engineering Student

• 1st and 2nd Year– Classes

• Chemistry, Organic Chem, Calculus, Physics, Ethics• 3rd and 4th Year

– Classes• Biomechanics, biomaterials, biosystems, electrical…

– Final Project– Research

• Grad School– Adding something new to science– Take classes relevant to research

A Day in the life of a Biomedical Engineer• Industry

– Companies large and small• Engineering Teams • Projects

– Why Biological Problems occur? Prevent? Solve?

• Interact with– Marketing, business, management

• Academia– Research at Institutions of higher learning– Universities– NIH

• Furthering Science and Engineering

What is Biomechanics?• The application of mechanical principles and

engineering techniques in biological systems.– Force body diagrams for bones and muscles

– Contact forces across a joint

– Bone motion• 3D X-ray tracking

– Mechanical properties of tissues• Max load, Stress (F/a), Strain (ΔL/L)

– Locomotion of organisms– Kinesiology- study of human movement

Why do we study it?• Two Reasons

• Why biological changes happen? • Can they be prevented?

• Once changes happen• How do we fix them?

• What causes changes?• Internal and external forces

acting on the human body have an impact on many factors ultimately affecting health.

– Examples:• Change- Torn ACL• Why? Prevent?

• How do you fix an ACL?

Examples Continued• Osteoporosis- Bone loss, Why? Prevent?

• Aging, lack of calcium• Force and vibrations on bones have

been linked to better bone health and density

• Shin Splints. Why? Prevent?• During running each stride results

in a cascade of forces in the joints of the body.

• Our Focus today- An increase in the popularity of running has caused researchers to focus on running injuries, proper running form, and shoe technology to hopefully prevent injuries.

Who studies Biomechanics?

• Academics– Orthopaedics

• Biomechanical influences on disease

– Evolutionary Biologists• Bat flight aerodynamics

• Medical Companies• Making bone implants

• The Military– Better gear for combat (body armor, shoes, med kits)

• Shoe companies – Nike– Adidas

– Running Technology

Waffle Irons and A Running Revolution• Background of Modern Running Technology

– Coach Bill Bowerman and Phil Knight • Oregon University Track Team

– 1962 Bowerman travels to New Zealand discovers Jogging as a fitness routine

• Fitness = Health; Modern discovery 1940s and 50s

– 1972 Cortez- waffle irons– Light cushioned shoe = extended running stride

• Heel strike was “good running form”– “…a shoe should be higher at the heel than at the ball of the foot, so

that the rear of the shoe lands first and absorbs most of the body’s weight. [it] minimizes stretching of the Achilles tendon, an important consideration if you’re a woman and wear high heels much of the time.” The Complete Runner 1st edition, 1974

How do you study running?• What is Gait?• The pattern of movement observed in limbs of animals

– Human running is the cycle of movement primarily in the lower extremities – Two phases and sub parts– Stance phase - When the foot is making contact with the ground

• Initial contact• Mid Stance• Take off

– Swing phase - When the foot is transitioning between periods of ground contact

• Initial swing• Mid swing• Terminal swing

Foot strike type• How your foot contacts the ground at initial contact• Recent research shows- Wearing running shoes (heels

first) may not be how humans evolved to run• “Non-evolutionary” style of running with sneakers could

result in injuries• What type of strike do you think you have?

Forefoot strike Heel strike

Important Mechanics Terms for Running

• Force = F– The push or pull on an object

• Spring– Elastic object that stores or

dissipates energy• Spring Constant = k

– ∆ Force/∆ distance– High K = stiff – Low K = bouncy

– In running is known as leg stiffness

• Deflection = X

Human Leg as a Spring• Muscles Tendons and Ligaments

together with joints operate like a single linear spring

• “Humans running; is like a mass bouncing along on two springs”

• Important joints– Foot Arch/Ankle– Knee– Hip

• Foot strike effect on spring– Midfoot/Forefoot

• Low K, bouncy spring (muscles/tendons)

– Heelstrike• High K, Stiff spring (bones)

What are other important factors in gait?

• Weight– Responsible for force

• Limb dimensions• Musculature (springs)• How these effect…

– Ground reaction force exerted during initial contact

Important Running Anatomy1?

2?

3?

4?

5?

6?

7?

A

B

Gait Labs• What do they measure?

– Muscle Activity (EMG)– Limb motion relative to each

other– Ground reaction forces (initial

contact)• How do they Measure it?

– Chronophotography– series of photographs

– Marker Systems-• Label Important anatomical

locations with sensors– Hip, Knee, Ankle

• Motion Capture• Reconstruct “stick figures”• Avatar

Gait Photo Collection ExerciseA series of measurement activitiesChoose a group representative runner

• Chronophotography - This exercise is a very simplified version of a process used in Gait labs. We will collect a series of photos of your runner’s gait.

– With shoes– And without

• We will then use these photos to make measurements

• Materials– Meter stick– Sony camera with continual capture function– Post processing using IMAGE J

• Why use a meter stick?– Calibration is the process of comparing/checking measurements of a known

instrument to those of unknown dimensions. I– We know how long your meter stick is and can use it as a digital ruler in our

photographs.

Collect data on your runner’s limb dimensions

• Mark your runners- Toe tip, ankle, knee and hip

• Using your meter stick record the following measurements

Distance from toe tip to heel ________m

Distance from ankle to knee ________m

Distance from knee to hip ________m

Calculating your Spring Constant (k) or Leg Stiffness

• Leg stiffness = step rate2 X Weight (lbs)/200– Changes with speed

• Step Rate= number of steps in one minute running in place (steps/min)– Keep feet close to the ground– What is your step rate? – Step off

• Who has the highest?

Step Rate

Calculating Leg Deflection (X)• Ground reaction force is the same for both forefoot

and heel strike– Force= 2.4*Body weight (lbs)

• Now using your calculated leg stiffness and F=KX– Calculate your deflection (X)– Where does that deflection go with

• Forefoot strike?– Joints bend

• Heel stirke?– Bone and cartilage deflection

– Which do you think is more likely to cause an injury?

Graph Paper for Foot Surface Area• Calculate area of foot

strike using graph paper– Stand on the graph paper

provided without shoes or socks

– Outline your footprint with a marker (include the toes and do your best to trace under the arch).

– Step four: Now count the number of blocks that make up your foot print, you may have to do some estimating.

1. What is your total foot surface area? ___________

2. What is the surface area of your runner’s foot if there was no arch? ___________

3. Calculate Foot surface area/Foot surface area with no arch (1/2) ___________

– Lower ratio = higher arch– Who has the lowest? What does that mean?

Example Result

Article Critical Review

• How does this article relate to what we just learned?

• Write a paragraph including three things you learned today about biomechanical engineering and gait analysis that influenced this study