Biomechanic (Variables (SPATIOTEMPORAL
Lab application: Optogait (Spatio…
Walking and then running:
+ve: step / stride length, GRF, speed
-ve: Contact time during cycle time is shorter
Type of footwear
1) Mechanical tests (SHEI)
--> Stiffness (Nm/deg)
--> Hardness (40 Shore C)
(Shore D the hardest, Shore OO is softest
40 refers to material of outsole)
--> Impact Score
(Amt of force Received by platform when shoes is being worn)
-Energy return (% conserved from the run)
For the purpose of: ICA
3) Athletic purpose
2) Biomechanical Tests (J2P, GM)
combines mechanical results with human subj perf e test
--> Joint motions (rearfoot, forefoot motion)
-Ground reaction force
-->Loading rate eg rearfoot vs forefoot strike
--> Comparing 2 x 50kg persons with different foot sizes
Shoes must cater to both extremes
-Joint loadings (eg moments)
--> a larger foot has greater moment therefore req less force to walk vs a smaller foot with less moment therefore req more force
-->with the use of EMG, muscles can be purposely activated based on the design of the shoes.
Eg) MBT shoes are designed to activate the back muscles for better posture
3) Perception Tests (FACTS)
-Traction / grip
-rearfoot ctrl (stabilise the knee)
-climate (affects foot sensation)
- Centre of Mass (CM, average location of all masses in a system)
- Static balance aka ability to control equilibrium, maintaining CM within Base of Support (BOS)
-- BOS= area enclosed by outermost edges of the body in contact with the supporting surface (like a triangle)
- Centre of Pressure (COP) aka point at which resultant pressure acts on a body and causes a force that acts thru tt point
Y-balance Test (YBT)
- To predict risk of injury in athletes
FUNCTIONAL MOVEMENT SCREENING!?
2 types of tests
LOWER QUARTER TESTING (Legs)
1) Longest toe behind red line
2) Hands on hip
3) Heels contacting platform
4) Push reach indicator continuously in 3 directions (anterior, posterolateral and posteromedial)
5) Reach foot to maintain contact with red target indicator
6) Foot to touch only top of reach indicator
7) Return to original position under control w/o touching the ground
8) Repeat trial if fault is present
9) Repeat with other foot
UPPER QUARTER TESTING (Arms)
1) Push up position; feet shoulder width apart w/o shoes
2) Stance hand behind red line & hands underneath the shoulders
3) Push reach indicator continuously in 3 directions (medial, inferior lateral & superior lateral)
4) Return to original position under ctrl w/o touching ground
5) Reach hand in contact with red target indicator
6) Hand to touch only top of reach indicator
7) Repeat trial if fault is present
8) Repeat with other hand
Measuring the leg length:
- Anterior superior iliac spine (ASIS)
- to distal portion of inside of ankle
Right = 87.5com
Left = 88 cm
*Strength training doesn't benefit balance
- measurement of pre- and post-rehabilitation performance,
- improvement after performance enhancement programs, dynamic balance for fitness programs,
- and return-to-sport-readiness.
- To evaluate balance performance via a force platform and centre of pressure (COP) variables
What is measured?
1) postural sway variables
- Root mean squared (anteriorposterior)
- RMS (mediolateral, side to side)
Arabesque Balance Data:
Preferred leg (R) --> 0.267cm (front and back)
--> 0.405cm (side to side)**
Non-preferred leg (L) --> 0.47cm (front and back)
--> 0.836cm (side to side)
Ax postural control performance
- Balancing board that pivots ard the centre freely.
- Measuring 10 degree tilt
- Indicates postural sway during balance duration
- SO HOW IS COP MEASURED?
- Is how COP changes over time, used to reflect static balance perf
- VIA force platform or pressure sys
-- Older folks & eyes closed & fatigued have more sway
What variables are measured from COP?
- Range (min to max) ie most left to most right
- Total distance travelled (dist bet points)
- Root mean squared dist
- Sway area
- Mean velocity (average spd from 1 point to another)
#1 POSTURAL SWAY
Gymnasts consistently performed better than non-gymnasts
- 2 legged
- 1 legged
- 1 legged on foam surface
#2 RECOVERY FROM DESTABILIZATION
- Gymnasts reacted faster and used knees to stabilise therefore moving the CM to the medial point faster
- Non-gymnasts used hips instead therefore longer time to move CM past the medial point and closer to the edges of BOS
- Mx joint torque (rotational force)
- Reflects force prod by muscles
#1 Torque-Angle R/S
- sim to "force-length" curve
- bell shaped
- optimal angle near mid-range
#2 Torque-Angular Velocity R/S
- sim to "force-velocity" curve
- -ve velocity = eccentric contraction
- +ve velocity =concentric contraction
1) Subject to sit comfortably on isokinetic dynamometer
2) Align center of knee joint with the crank axis of rotation
3) Using the 3 pre-set protocols, measure the maximum isokinetic torque of the knee extensors (quads) and knee flexors (hamstrings) at an angular velocity of 180 deg / sec.
4) Calibrate the machine to set safe ROM for knee flexion
4) Save report in pdf
5) Extract data
Regardless of flexors / extensors, the torque produced is higher during eccentric contraction than in concentric contraction
Raw signal needs to be processed.
- filtered to 20-450Hz to remove 'noise'
- Raw EMG signal
- Rectification of waves (cut into half)
- RMS (averaged out)
HOW TO ASSESS FOR MUSCLE FATIGUE?
- With each rep the muscle's median frequency of EMG signals shifts to the left.
- The medium frequency slope (MFS) becomes steeper
- Constant angular velocity (60°/sec)
- Various joints (at knee, hip, shoulder)
- Both directions (flexion / extension)
Place electrodes on muscle belly (top and bottom) when it is contracted. A 3rd electrode which is the grounding electrode shld be placed on the elbow joint where no muscle activation occurs.
- Aligned along the longitudinal midline of the muscle
- Aligned parallel to the muscle fibre direction
PROCEDURES FOR COLLECTING A GOOD SIGNAL
- remove excessive hair that blocks muscle site
- Wipe with alcohol swab to remove sebum and other contaminants
- If dry skin is a hindrance, dab surface with medical tape to dislodge dry skin cells. wipe with alcohol swab again.
- If skin surface is too dry a small amt of ionic soap or saline soln can line EMG sensor contacts
- Refers to determination of forces & torques that must act in order for the motion to be produced
T = Iα
- I = moment of inertia
- α=angular acceleration (alpha symbol)
Process in which resultant joint forces & torques (rotational force) are indirectly est from
of moving bodies
- inertial properties
Eg) what is the hip force during SBJ?
Moment of inertia:
Level of force that has to be applied in. order to set the object, or keep the object, in motion about a defined axis of rotation.
Different from "forward dynamics"
- forces & torques are specified and aim to determine the resultant motion
F = maF = force
m = mass
a = acceleration
2 TYPES OF APPROACHES
#1 TOP-DOWN APPROACH
- Calculations begin from top or most distal segment all the way to the bottom
- Info needed:
-- body segmental inertial properties
(mass & moment of inertia of each segment)
#2 BOTTOM-UP APPROACH
- Calculations start from the ground all the way to the top
- Info needed:
-- body segmental inertial properties
-- & GRF
How to calculate inverse dynamics?
- Find out how many segments there are (chop them up)
- Draw linked segments
- Consider each segment independently
Armswing = 20% improvement in SBJ distance
- this 20% is broken down into 20% contribution in D(takeoff) and 70% in D(flight time).
- Importance of free arm movement
-- more force is produced when the arm is swung upward whilst standing on a weighing scale
- the armswing increases the height of the body's CM and take-off velocity
-- the increased spd comes from the arms storing energy in the early phases of the jump and then transferring it back to the body during the later phases
Practical tips for SBJ:
3) Increase distance at landing "D(landing)"
- Land with feet infront of CM
- Avoid falling backwards
2) Increase distance in flight phase "D(flight time)
- Increase take-off velocity
- Optimise take off angle (20°)
1) Increase dist at take-off "D(takeoff)"
- by leaning more forward (45°) toe-knee angle
- good armswing (extended with pull back)
Find out implications of low,
medium and high AI
Age vs AI
-Babies deceptively high AI (coz fat covers their arch)
-Adults (with age comes higher AI due to tendonitis, obesity and daily use which causes the tendon to weaken)
Procedures to determinee arch type
- Use Novel Emed, collect 3 left and 3 right footprints by walking using a 2 step-approach where 2nd step lands on pressure mat
- Calculate average of the 3 trials
- Generate geometry report of the averaged trial for each foot
- Obtain arch index from the report
- ID arch type based on the ranges provided
Further explanation of the joint augmentation theory:
- During the ﬁrst half of the ascent phase of the armswing jump where the muscle torque is greater, the joint velocity is lower, which leads to a reduced joint pwr and reduced perf over this period.
As a result, when referring back to the force-velocity graph, since the concentric conditions are slower due to the presence of armswing, this means that more force is actually generated and this explains why the take off velocity is higher.
- It has been found in this study that the augmentation of joint torque is associated with the period during which the muscles and tendons of the joint are storing energy and a greater joint torque would facilitate this. Thus, joint torque augmentation is actually associated with energy storage and it is the late rreturn of this energy that enhances performance, rather than the direct application of increased torque.
Draw the length - force graph where there is more power at the optimal length where the actin and myosin overlaps.
Eg) in a crouching start, there is an optimal overlap between the actin and myosin vs a standing start
What do authors say?
Medial longitudinal arch is responsible for shock absorption during barefoot running hence less injury prone than shod runners.
These adaptations ie shock absorption were brought forward by the sensory feedback as a result of barefoot running.
Conversely, shod runners experience sensory insulation which leads them to be injury prone.
Study fails to:
- mention mx of knee loading
- No correlation between MLA adaptation and lower injury freq
- they implied that MLA adaptation led to decreased injuries, moreover they need not mx and compare knee loading
Lieberman et al (2010)Foot strike patterns and collision forces in habitually barefoot vs shod runners
- FFS has lower rate of loading than in RFS due to drop in CM, because the feet adapts to the terrain and adjusts the stiffness of the leg
- There are only personal reports of reduced injuries in barefoot population
Barefoot-simulating Footwear Associated With Metatarsal Stress Injury in 2 Runners
Giuliani et al (2011)
- 2 metatarsal injuries
- No breaking-in period
-- runners to be mindful to adapt running style from heel toe strike to midfoot strike as a result of barefoot simulating footwear.
19.3 km/h ÷ 60 min ÷ 60 sec = 5.4 m/s
Since 1km = 1000 m, so take
1000 m ÷ 5.4 m = 186 sec/km = 3 min 6 sec/km
Draw the force - velocity (eccentric/concentric/isometric) relationship graph to show that
- In a jump phase, more force is needed for landing than is needed for jumping
- In a negative pull-up, more force is needed to resist the body weight than is needed to pull the body up.
1) Pressure - plantar pressure (2nd step on pressure mat called a NOVEL EMED)
2) Arch Index (AI)
- low arch (≥0.26)
- high arch AI ≤0.21
- neutral arch between 0.21-0.26
- The joint torque/work augmentation theory is acceptable only at the hips but not at the knees and ankles because only hip joint work is considerably increased.
- The pull/impart energy theory is also acceptable because shoulder joint work is responsible for about half of the additional energy created by arm swings.
Torque-angular velocity r/s
It is the ratio area of the arch portion of the plantar side of the foot in contact with the floor to the area of the entire plantar side of the foot in contact wit the floor excluding the toes.
+ve: Not biased
-ve: no perceptions mx
+ve: Both mechanical and biomechanical
-ve: Tedious but specialised tests
+ve: Meets demands of market
research has shown that only 1/7 of the data using a scale matches verbal answers
Dolnicar & Grun (2013)