Repetitive arm and hand work tires the muscles doing it. This calculator applies the ACGIH threshold limit value (TLV) for upper limb localized fatigue: enter how much of the work cycle the muscles are loaded (the duty cycle) and how hard they are working (the exertion, as a percent of maximum strength), and it tells you whether that combination stays within the limit — before fatigue outruns recovery.
Based on the ACGIH Upper Limb Localized Fatigue TLV documentation (2022), document 11DOC-782-PA, paraphrased in plain language.
The percentage of each work cycle during which the hand, wrist, forearm, elbow, or shoulder muscles are exerting force. Time spent below 5% MVC counts as recovery, not work — so a cycle of 4 seconds gripping and 16 seconds resting is a 20% duty cycle.
How hard the muscles work during the exertion, expressed as %MVC — the force required as a percentage of the strongest contraction that muscle group can produce. A light pinch grip might be 10–15% MVC; a hard squeeze on a stiff tool can exceed 50%.
The limit trades force against time: the longer the muscles stay loaded in each cycle, the lighter the exertion has to be. Your task is plotted against the curve — below the line is within the TLV, above it is not.
The limit was built for a specific kind of work. Check your task against these four points before relying on the result.
It covers the hand and wrist, forearm, elbow, and shoulder. It says nothing about the back, legs, or neck — those need their own assessment methods.
It applies to jobs built on repeated work cycles performed for two or more hours per day. Short or occasional tasks fall outside the model.
Time only counts as recovery when exertion drops below 5% MVC. Holding a part “lightly” while waiting may still be work, not rest.
Within the TLV, tiredness from a shift should recover and not persist from day to day. Symptoms lasting beyond 24 hours are a warning sign — investigate them as a possible musculoskeletal disorder, not ordinary fatigue.
You have two levers — the force and the duty cycle — and the curve shows exactly how much of either one buys compliance.
Send your numbers to NTSCS and get a straight answer on what they mean for your crew — and what to change first. On-site and virtual ergonomic assessments across North Texas and beyond.
Scott Weede, CIE — Certified Industrial Ergonomist, North Texas Safety Consulting Services.
This calculator is a free screening aid from North Texas Safety Consulting Services. It implements the published ACGIH equation for the upper limb localized fatigue TLV, which sets the highest exertion a muscle group should sustain for a given duty cycle:
Results are a starting point for a conversation about job design, not a diagnosis and not a substitute for an on-site ergonomic assessment — real tasks vary in posture, grip type, vibration, temperature, and the people doing them, and the TLV documentation weighs those factors too. Source: ACGIH, Upper Limb Localized Fatigue TLV documentation (2022), document 11DOC-782-PA. Content here is paraphrased; consult the official ACGIH documentation for formal assessments. TLVs are ACGIH guidelines intended to protect nearly all healthy workers, not fine lines between safe and dangerous conditions.