Question 4 of 4: Carpal Tunnel Syndrome and Other Repetitive Strain Injury Risk Factors
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
National Exams — Dec. 2016 — 98-Ind-B5 Ergonomics. Three-hour, open-book exam (all notes, books and any non-communicating calculator permitted; point-form answers requested); the paper requires 4 of its 5 questions (Part A's Questions 1–2 mandatory, plus one of Part B's Questions 3 or 4) — all five are solved below for completeness.
Reference texts: Sanders & McCormick, Human Factors in Engineering and Design (7th ed.) — manual-handling guidelines, human-computer interaction/usability evaluation methods, and MSD risk factors; Waters, Putz-Anderson & Garg, NIOSH Applications Manual for the Revised NIOSH Lifting Equation (1994) — the RWL/LI formula and multiplier tables reproduced on the exam's own pages 6–7; NIOSH, Elements of Ergonomics Programs (1997) and CSA Z1004 (Canada) — workplace musculoskeletal-disorder (MSD) prevention programs.
Question 4: Carpal Tunnel Syndrome and Other Repetitive Strain Injury Risk Factors (20 marks: a–6, b–14)
Carpal tunnel syndrome (CTS) results from repeated or sustained compression/irritation of the median nerve as it passes through the wrist's carpal tunnel – the defining risk factors are a non-neutral (flexed/extended or deviated) wrist posture combined with repetition, grip force, and/or direct pressure on the palm/wrist (and, separately, hand–arm vibration). Each task is assessed against those specific factors, not against "hand use" in general:
i. Wire-brush wall scrubbing – CTS risk: yes. Combines a sustained power grip with repetitive wrist flexion/extension (the scrubbing stroke) and often a deviated wrist angle to reach the work surface – the classic repetition + force + non-neutral-posture combination.
ii. Keyboard text entry – CTS risk: yes. High-repetition finger movement is often performed with the wrists extended (bent up/back) and/or resting on a hard edge, and sustained low-level static loading of the forearm/wrist flexor tendons over long typing sessions is a well-documented CTS risk factor, especially without a neutral-posture keyboard/wrist-rest setup.
iii. Ceiling painting – CTS risk: low/unlikely. The dominant load is shoulder/arm elevation and static shoulder-muscle fatigue, not repetitive wrist flexion under grip force – the wrist itself is typically held in a fairly neutral, low-force grip on the roller/brush handle, so this task's principal injury pathway is shoulder, not median-nerve.
iv. Mopping the floor – CTS risk: low/unlikely. The wrist is largely stabilized while the motion is driven from the shoulder/trunk in a sweeping arc; grip force is moderate and the wrist is not held in a sustained flexed/deviated posture, so this is again more a shoulder/low-back task than a CTS task.
v. Playing tennis – CTS risk: possible, secondary. Repeated forceful grip on the racquet with wrist snap/deviation on each stroke (especially topspin strokes) can contribute to CTS, though tennis is more classically associated with lateral epicondylitis ("tennis elbow") as the dominant injury – CTS is a real but secondary risk here.
vi. Playing the piano – CTS risk: yes. Rapid, highly repetitive finger movement performed with the wrist frequently held in extension over long practice/performance sessions is a recognized CTS (and broader hand overuse) risk among musicians.
vii. Jackhammer use – CTS risk: yes, and severe. Sustained high-force grip combined with intense hand–arm vibration is one of the strongest documented CTS/hand–arm vibration syndrome (HAVS) risk combinations in occupational ergonomics – vibration itself directly irritates the median nerve and surrounding soft tissue in addition to the grip-force component.
(b) Other Strain Injury Types and Risk Factors by Task
High-magnitude hand–arm vibration exposure; sustained high grip/push force to control the tool; whole-body reaction forces transmitted through a braced trunk posture
Across all seven tasks, three risk-factor categories recur in different combinations – repetition (ii, vi most acutely), force (i, v, vii), and awkward/sustained posture (iii overhead, iv trunk flexion) – with vibration (vii) as a fourth, distinct mechanism that compounds rather than substitutes for the force-related risk. A task with only one of these factors present (e.g. ceiling painting: posture-dominant, low force, low repetition) tends toward a single, localized injury type (shoulder), while a task combining several factors at once (jackhammer: force + vibration + posture) carries risk across multiple injury types simultaneously.
