This page provides engineering data on human work and energy expenditure, including metabolic rate, activity energy consumption and mechanical efficiency. The information supports ergonomic assessment of physical workload and human performance in industrial applications.
Work and energy requirements should be considered alongside human strength and endurance data and anthropometric measurements when designing equipment and tasks.
For control forces and operator interaction, see machine interfaces and control design.
The human body requires energy both to maintain essential physiological functions and to perform physical activity. In engineering and ergonomics, energy expenditure can provide an indication of physical workload and the demands placed on an operator during a task.
Human energy expenditure varies considerably with the individual, activity, working posture, task duration, work rate, environmental conditions and available recovery time. The values on this page should therefore be treated as indicative engineering data rather than fixed human capability limits.
For detailed ergonomic assessment, occupational health or safety-critical applications, appropriate current standards and validated data for the intended working population should be used.
The SI unit of energy and mechanical work is the joule (J). One joule is the work done when a force of one newton acts through a distance of one metre.
One kilojoule (kJ) is 1000 joules. Nutritional and physiological energy values are also commonly expressed in kilocalories (kcal).
1 kcal = 4.184 kJ
For example, an energy intake of 2500 kcal corresponds to approximately 10,460 kJ or 10.46 MJ.
Dietary energy requirements vary with body size, age, sex, activity level and other individual factors. Dietary intake figures should not be treated as engineering workload limits.
Metabolic rate is the rate at which the human body expends energy. Even when a person is resting, energy is required to maintain essential body functions. This minimum level of energy expenditure is commonly described as basal metabolism.
A legacy reference value for a 70 kg man is approximately 7000 kJ over 24 hours for basal metabolism. Additional energy is required for normal daily activities and occupational work.
Metabolic rate increases as physical workload increases and can therefore be useful when assessing the demands of industrial tasks, particularly where work is sustained for significant periods.
RoyMech has historically referenced:
BS EN ISO 8996:2004 — Ergonomics of the thermal environment — Determination of metabolic rate.
Standards are revised and replaced over time. Engineers should confirm the current applicable edition and requirements before carrying out a detailed ergonomic or thermal-environment assessment.
The following legacy values illustrate approximate daily energy expenditure associated with different levels of occupational activity.
These figures are retained as general engineering reference data and should not be interpreted as current dietary recommendations or precise energy requirements for individual workers.
| Type of Work | Example | Men (kJ/day) | Women (kJ/day) |
| Light work — sitting | Accountant | 9,600 | 8,400 |
| Normal manual work | Production engineer | 12,500 | 9,800 |
| Moderate bodily work | Bricklayer | 15,000 | 12,000 |
| Heavy manual work | Miner | 19,500 | — |
| Extreme effort | Lumberjack | 20,500 | — |
The occupational examples above are illustrative descriptions associated with the original data and should not be taken to imply that all people performing a particular occupation have the stated energy expenditure. Actual workload depends on the tasks being performed.
Different physical activities require different rates of energy expenditure. The following values provide indicative examples.
| Activity | Energy Consumption (kJ/min) |
| Mowing lawn | 30 |
| Level walking at 5 km/h | 17 |
| Light gardening | 12 – 15 |
| Digging soil | 33 |
| Walking uphill | 32 – 40 |
| Swimming | 20 – 40 |
| Sawing wood | 28 |
| Cycling at 20 km/h | 40 |
| Bowls | 16 |
| Jogging at 10 km/h | 40 – 48 |
These values represent approximate rates of energy expenditure. Actual energy consumption varies with factors including body mass, technique, speed, terrain, equipment and individual physical condition.
Only part of the metabolic energy used by the human body is converted into useful external mechanical work. The remainder is principally released as heat.
Mechanical efficiency depends strongly on the activity and working method. The following legacy values illustrate the approximate efficiency of different physical tasks.
| Activity | Approximate Efficiency (%) |
| Shovelling soil — stooped posture | 3 |
| Screw driving | 5 |
| Shovelling soil — upright posture | 6 |
| Lifting weights | 9 |
| Turning a handwheel | 13 |
| Carrying a load on the back on level ground — returning without load | 17 |
| Carrying a load on the back — returning without load | 20 |
| Climbing up and down ladders | 19 |
| Turning a handle or crank | 21 |
| Walking up and down stairs | 23 |
| Pulling a cart | 24 |
| Cycling | 24 |
| Pushing a cart | 27 |
| Level walking | 27 |
| Walking uphill | 30 |
The values above should be regarded as indicative rather than universal efficiencies. Human mechanical efficiency varies with the task, technique, speed, posture, load and individual.
The energy requirement of a task cannot be assessed from work rate alone. The duration and frequency of the activity and the opportunity for recovery are also important.
A relatively high work rate may be sustainable for a short period but unsuitable when maintained continuously. Conversely, an activity carried out only occasionally may impose a much lower total metabolic demand, although other ergonomic risks such as excessive force, awkward posture or manual handling hazards may still remain.
Environmental conditions can also influence the acceptable workload. High temperatures, protective clothing and restricted ventilation may increase thermal strain even when the mechanical work being performed has not changed.
Human energy data can help engineers assess whether a physical task is likely to be sustainable over the intended working period. It is particularly useful when considering repeated manual work, physically demanding operations and tasks performed in challenging thermal environments.
Energy expenditure should not be considered in isolation. Human strength, posture, reach, manual handling, task frequency, duration, environmental conditions and the consequences of fatigue or operator error should also be considered.
Human-factors guidance should be applied using engineering judgement. An occasional task may justify different ergonomic criteria from an operation performed hundreds of times during a shift, but low frequency does not automatically make a hazardous task acceptable.
Ergonomic requirements may also need to be considered alongside safety, security, maintainability and operational requirements. Where requirements conflict, mandatory requirements should be distinguished from recommendations and the resulting engineering decision appropriately assessed.
For workspace layout and reach considerations, see human access space requirements.
Human work and energy describes the energy expended by a person while performing physical tasks. In ergonomics it can be used to assess physical workload and whether a task is likely to be sustainable for the intended duration.
Metabolic rate is the rate at which the human body expends energy. It includes the energy required for basic physiological functions as well as the additional energy used during physical activity.
Energy expenditure provides an indication of physical workload and can help assess fatigue and the sustainability of a task. The work rate should be considered together with task duration, frequency, recovery time and environmental conditions.
Human mechanical efficiency varies considerably with the activity and working method. The indicative data on this page range from approximately 3% for inefficient physical tasks to around 30% for some activities.