Week 11 Lecture: MMH1 Flashcards
When can you use the ISO 11228-1 SCREENING FOR ASSESSMENT FOR LBD tool?
<3kg, no need to assess further = SAFE
> /= 3kg apply screening tool
RAPID ENTIRE BODY ASSESSMENT (REBA)
- items
- benefits
- limitations
- posture and force
- quick, easy to apply, user friendly
- does not consider contact stress, only looks at worst case scenario, does not look at frequency or duration, does not consider environmental factors
Describe where force assessment of the low back is performed and why
What are the limit values for disc compressive forces?
What are some tools you can use
Measured at l5/s1 or l4/L5 to capture compressive forces on spine or shear force or torsional force
Limit values for disc compressive force: 250kg for women and 350 kg for men
Direct measurement tools:
- measure weight of the load
- push/pull guages
- force plates
Indirect measurement tools:
- EMG
- modelling
How could you measure repetition of the low back
- IMUs –> programming
- task analysis
- observation
How can you measure back posture
- angles from photos (must be careful of angles tho - sagittal plane)
- electrogoniometers
- IMUS –> AI
What are the 3 possible approaches to assessing risk of back injury? Which is each ideal for?
biomechanical
- infrequent heavy work; takes into account muscle, bone, and disc limiting factors
physiological
- frequent, light to moderate work
- takes into account oxygen uptake, fatigue limiting factors
psychophysical
- combination
Describe the biomechanical assessment method of the low back
based on: A disc compression force greater than 350 kg for men and 250kg for women increases risk of LBP 4x (although, this was from a cadaver study that looked at one time loading and not cumulative loading)
hand arm torso model simplifies geometric complexity of joints
- back muscles must prod. a moment of force to counteract moment from hand force and weight of head, arms and torso in order for person to not tip over
pros:
- estimate of disc compressive force is about +/-10% for each person
- inter and intra-rater reliabilty is good
limitations:
- assumes that erector spinae moment arm is 5-6cm for everyone
- does not apply for 2 person lifts, twisting lifts, one handed lifts
- somewhat of an oversimplification though, making validity questionnable
- also can use 3DSSPP for a biomechanical assessment
perform the sample torque problem
what is shear force and the action limit for it?
Shear forces: A force that acts parallel or tangent to a surface to create sliding of one object with respect to another
The L4-L5 Joint Shear represents the resultant shear force due to the sum of the reaction shear and the muscle /ligament shear. It is this value, that includes the effect of muscle/ligament forces, which represents the actual shear experienced at the L4-L5 joint.
Action limit 500N males, 330N females
pros and cons of 3DSSPP
validity and reliability
Pros:
- Provides predictions of static strength at various joints
- Includes compression and sheer forces
- Provides strength capable for populations
- Best for back calculations
- Variety of actions including lifting, lowering, pushing, pulling, carrying, holding a static posture, one-handed actions, actions involving unequal hand forces
- Uses epidemiological data - compared to established limits and population strength data
Cons:
- steep learning curve
- static strength only
- less valid as you move toward the distal limbs
Validity: good for back, worse for wrist and shoulder
High inter and intra-rater reliabiltiy
Describe some assessment tools for the physiological approach and their validity and reliability
- heart rate
- borg scale
- energy expenditure prediction models
- metabolic rate from VO2 or estimated from HR
- note: Lack of epidemiological data linking fatigue to LBP
Reliability is not well understood
Validity studies are little and not well understood
Describe the psychophysical approach and their limitations and validity
The psychophysical approach aims to quantify human lifting capacity based on subjective perception of exertion, under the assumption that workers are able to determine with some accuracy the highest acceptable workload
Based on psychophysical ratings of industrial work groups, not strength or probability of injury
Only considers one task at a time, not cumulative
Less valid at high and low frequencies
Limited psychophysical studies that support this approach
Some individuals when asked about their ability to lift an object, they only consider their grip strength ability.
moderate validity and reliability
Describe how SNOOK tables were created and their limitations
Snook (ergonomist) conducted several experiments where he would have people perform manual material handling tasks and tell him if its too heavy and how long they could lift it for
- using this data and physiological limits for high frequency and low load lifts and biomechanical limits for high load and low frequency lifts, developed SNOOK tables
How to use the table
1. Find the correct table based on sex and start and end height
2. Find object weight (lbs)
3. Find hand distance from body
4. Find closest frequency of lift
5. Find lifting distance in inches
Only for 2 handed lifts
Don’t account for asymmetry
Assumes a good handhold on the object
Assumes that the object is stable, weight doesn’t shift
Assumes you’re not putting it in a confined space
Doesn’t consider temperature or slippery surface
Always a one person load
What are the Mital tables?
- provides limit values for non-traditional lifts using psychophysical data
One handed lifts
Confined spaces
Will help with two person lifts
