Definition and preventive purpose
Dynamometry is the measurement of force using an appropriate instrument. In ergonomics it can help establish the external demand of pushing, pulling, operating or holding, provided the setup and instrument suit the quantity being investigated. It does not directly measure tissue damage or summarise the entire biomechanical load of a task.
Distinguish three questions: how much force the work requires, how that force is applied during the day and which changes can reduce the demand. Measuring a person’s grip strength answers a different question and does not replace job assessment. Nor does it justify selecting workers for a presumed ability to tolerate a deficient design.
Measurement is valuable when it informs a decision. It may compare a maintenance condition or locate unexpected resistance. Before measuring, establish the possible preventive action and the additional information needed to interpret the result. This prevents collecting attractive numbers that do not address the actual workplace problem.
Quantity, unit and direction
The newton, symbol N, is the International System unit of force. The kilogram expresses mass. A display showing kilograms or kilogram-force requires checking the manual and configuration; those readings must not be copied into a column labelled newtons without correct conversion and documentation.
Define the quantity before setting up: initial force to start movement, force during travel or force for a particular operation. Record direction and point of application as well. A force measured in one position is not automatically equivalent to a force measured elsewhere, even when the transported load is unchanged.
Do not confuse force with torque, pressure or trolley mass. Each quantity requires its own interpretation and potentially a different instrument. Preserve original units in the report and explain any transformation. The number of displayed decimal places does not establish measurement accuracy. Naming the quantity precisely is essential before comparing a result with any assessment criterion.
Sources: [3]
Instrument selection and metrological control
The instrument must suit the range, direction, resolution and behaviour of the force being recorded. NIST documentation distinguishes calibration of a transducer from calibration of the system with its readout. It also explains that traceability belongs to the result and requires a documented chain with uncertainty; a calibration label alone is insufficient.
As a proposed check, identify the instrument, serial number, accessories, configuration and applicable metrological records. Check that the intended working range is covered and that components have not been mixed without evaluating the effects. Follow instructions for zeroing, checks and operating limits.
If overload, impact damage, unstable readings or doubts about condition arise, do not keep producing data as if they remained comparable. Investigate the cause and decide whether the instrument should be withdrawn, controls repeated or a measurement series invalidated. Preserve that decision with the data so another reviewer can understand which results remain usable and why.
Designing a representative measurement
The measurement plan must describe a real task and a specific question. A proposed record includes load, equipment, maintenance condition, surface, route, grip and normal working method. Include conditions that may change the result, such as a turn, floor joint or initial wheel orientation.
Choose representative conditions and explain those that could not be observed. Testing on a smooth floor does not necessarily describe an outdoor delivery. Comparing an empty trolley with a loaded one and attributing the entire difference to the wheels is also invalid. Sampling should address expected variability; this entry does not prescribe a universal number of repetitions.
Preparation must preserve the safety of participants and observers. Do not create dangerous slopes, obstacles or loads to obtain an extreme reading. If the task cannot be reproduced safely, competent personnel must devise another assessment approach rather than asking the observed person to exert additional effort. Record this limitation explicitly in the plan.
Setup and observation
HSE pushing and pulling guidance highlights that the force being measured must pass through the dynamometer and that instruments commonly measure in one direction. A setup allowing part of the effort through another support can produce a misleading value. A competent person must verify the geometry and compatibility of the arrangement.
For the applied record, describe how the instrument was connected and how the procedure remained consistent between observations. Distinguish starting movement from sustained travel. Do not seek abrupt acceleration or maximum effort when the question concerns force needed to move the load under normal conditions.
Record relevant events during the series: jamming, slipping, grip changes or interruption. Do not selectively delete inconvenient readings; decide whether they represent a real condition or an experimental error and document the reasoning. Original files and contextual descriptions are needed for later review. A numerical summary without these records cannot explain why a particular peak occurred.
Sources: [1]
Variability, uncertainty and data quality
Variability and uncertainty are different. The former may reflect real differences between operations; the latter expresses limits to knowledge of the measured value. A widely scattered series may reveal surface or procedural changes as well as possible instrument problems. It should not be concealed by calculating an average alone.
A proposed record preserves individual values, the condition of each observation and the summarising rule. Choosing a maximum, mean or another statistic must match the method and question, not whichever result appears most favourable. State resolution, working range and relevant setup limitations; do not invent numerical uncertainty without a technical basis.
If differences between two conditions are small relative to variation and uncertainty, avoid asserting that one is clearly better. The comparison may need redesigning or additional information. A rigorous assessment can conclude that available data do not distinguish the effect of a modification. This is a meaningful limitation to document, rather than a reason to overstate precision.
Ergonomic interpretation and limits
Force must be considered with posture, frequency, duration, recovery and environmental conditions. ART addresses factors in repetitive upper-limb tasks; RAPP concerns pushing and pulling involving whole-body effort. No score makes a task safe by itself or replaces technical judgement about factors outside the method’s scope.
HSE warns that RAPP can underestimate some movements involving small wheels when irregularities or gradients substantially change force. This limitation supports observing the actual route and extending assessment where appropriate. It does not mean every pallet truck is unsuitable or that a measurement at any single point represents the entire route.
In the report, explain which reference was used and why it applies. Do not present foreign guidance figures as Spanish legal limits. Avoid extrapolating a pushing result to pinch work, a two-handed effort to one-handed work or a brief episode to an entire shift. State what the measurement can support and what further evidence remains necessary.
From measurement to improvement
Assessment should lead to eliminating or reducing demands, rather than normalising them. Under Spain’s framework, manual handling should be avoided where possible and assessed where it remains necessary. A measurement may help choose between technical changes but does not replace that priority.
Options to investigate include wheels, maintenance, surfaces, material presentation, mechanical aids and handle design. Selection depends on the process. Telling people to push more slowly is insufficient if a permanent obstacle is the problem; buying a trolley that cannot enter the area where it is needed is also ineffective.
After modification, repeat a planned comparison under equivalent conditions and observe unintended effects. An aid may reduce force while increasing reach, instability or braking difficulty. Verification should include those dimensions and users’ experience as well as the new dynamometer reading. Confirm that the improvement remains usable during normal operations, including the loading and unloading stages surrounding the measured movement.
Example of a before-and-after comparison
Hypothetical example: a team identifies difficulty starting a supply trolley. The proposal compares the same route and load before and after a defined maintenance intervention, without attributing figures or outcomes to a real company.
Load, surface, wheel orientation, point of application and procedure are documented. Starting and travelling observations are distinguished and incidents retained. If the load changes or part of the route is cleaned during the second series, that change must be recorded because it prevents attributing the entire difference to maintenance.
The report may conclude that the comparison supports a reduction in observed demand, requires more information or cannot separate the effects. Posture and normal use still require review in every case. The example illustrates an interpretable comparison; it does not prescribe a minimum number of trials or universally acceptable force. Any proposed improvement remains subject to checking that the equipment is suitable for the complete operation.
Reporting, confidentiality and traceability
A useful report lets another person understand what was measured and reconstruct the reasoning. A proposed structure includes objective, task, instrument, metrological records, setup, conditions, original data, analysis rule, limitations and decisions. Preserve dates and versions to avoid mixing measurements taken before and after a modification.
Workstation information must not be confused with a clinical record. If an investigation includes health information or personal tests, it needs the appropriate professional and confidentiality framework. Do not publish individual strength rankings or infer medical fitness from a series collected to assess equipment.
Proposed indicators include measurements with complete context, valid comparisons and preventive measures verified after implementation. Success is not the quantity of numbers stored. Links with biomechanics, pushing and pulling, physical workload and ergonomic assessment place dynamometry within a broader, technically justified preventive decision. Keep unresolved questions visible so that the report does not imply more certainty than the measurement process actually supports.
Frequently asked questions
Does a dynamometer measure the whole task risk?
No. It measures force under the setup conditions; assessment also includes posture, repetition, duration and environment.
Are kilograms and newtons interchangeable?
No. Kilogram is a mass unit and newton a force unit. Check the instrument setting and any conversion.
Is a calibration certificate enough?
No. The result also depends on setup, procedure, range, conditions and uncertainty.
Can it determine medical fitness?
Measuring job demand is not a fitness test. Occupational health assessment requires its own professional and confidentiality framework.
