CIEE Repetitive Motion & CTD Prevention 2 — Questions and Answers
Question 1: A production line worker performs the same pinching motion 3,000 times per shift. Which factor MOST directly amplifies the CTD risk from this repetition rate?
- Prolonged static posture of the neck
- Simultaneous forceful grip exceeding 10% MVC (Correct answer)
- Irregular shift scheduling
- Ambient noise above 85 dB
Correct answer: Simultaneous forceful grip exceeding 10% MVC
Force and repetition interact multiplicatively, so combining high repetition with force exceeding ~10% of maximum voluntary contraction dramatically increases cumulative tissue load.
Question 2: Which physiological structure is PRIMARILY damaged in de Quervain's tenosynovitis, a common CTD in assembly workers?
- Ulnar nerve at Guyon's canal
- Abductor pollicis longus and extensor pollicis brevis tendons (Correct answer)
- Carpal tunnel median nerve
- Radial head bursa
Correct answer: Abductor pollicis longus and extensor pollicis brevis tendons
De Quervain's tenosynovitis involves inflammation of the tendon sheaths surrounding the abductor pollicis longus and extensor pollicis brevis at the radial styloid.
Question 3: An ergonomic evaluator observes a job with a Strain Index score of 12. What does this indicate about CTD risk?
- The job is safe and no controls are needed
- Moderate risk; monitor but no immediate action
- High risk; the job is probably hazardous and redesign is warranted (Correct answer)
- The score is invalid because Strain Index maximum is 10
Correct answer: High risk; the job is probably hazardous and redesign is warranted
A Strain Index score ≥7 is generally considered hazardous, and a score of 12 indicates the job is likely to cause upper-extremity CTDs and requires intervention.
Question 4: Micro-break schedules are most effective at reducing CTD risk when breaks are structured to allow which physiological process to occur?
- Maximal muscle fiber recruitment
- Tissue perfusion and metabolite clearance from tendons (Correct answer)
- Accelerated nerve conduction velocity
- Synovial fluid degradation
Correct answer: Tissue perfusion and metabolite clearance from tendons
Short, frequent breaks allow blood flow to restore oxygen and clear lactate and other metabolites from avascular tendon tissue, reducing cumulative damage.
Question 5: Which NIOSH revised lifting equation variable specifically accounts for repetitive lifting over a full work shift?
- Coupling multiplier (CM)
- Frequency multiplier (FM) (Correct answer)
- Asymmetry multiplier (AM)
- Horizontal multiplier (HM)
Correct answer: Frequency multiplier (FM)
The Frequency Multiplier (FM) in the NIOSH equation adjusts the Recommended Weight Limit based on lifts per minute and duration of lifting task.
Question 6: A worker develops trigger finger (stenosing tenosynovitis) after six months on a gripping task. Which intervention addresses the ROOT CAUSE most directly?
- Prescribing anti-inflammatory medication only
- Redesigning the tool to reduce grip force and repetition (Correct answer)
- Providing a wrist splint to wear at night
- Rotating the worker to a different department permanently
Correct answer: Redesigning the tool to reduce grip force and repetition
Reducing grip force and repetition directly eliminates the mechanical loading that causes tendon sheath inflammation, addressing the root ergonomic cause.
Question 7: When applying the ACGIH TLV for hand-arm repetition, a task with a repetition rate of 30 exertions per minute at moderate force level falls into which risk category?
- Below action limit — no controls needed
- At or above action limit but below TLV — administrative controls recommended
- At or above TLV — engineering controls required (Correct answer)
- Insufficient data to classify without a force measurement
Correct answer: At or above TLV — engineering controls required
The ACGIH hand activity TLV uses a graph of force vs. hand activity level; high repetition combined with even moderate force typically places tasks at or above the TLV requiring engineering controls.
CIEE Repetitive Motion & CTD Prevention 2
A production line worker performs the same pinching motion 3,000 times per shift.
Which factor MOST directly amplifies the CTD risk from this repetition rate?