In terms of productivity, measuring a worker's workload generally could be started by studying their job desk and output per working hour. In terms of physiology, it generally could be done by measuring energy consumption per activity (measuring heart pulse before/after). Any method can be suitable case by case. I hope I could explain what you need to know.
On many occasions, physical fatigue is associated with the maintenance of a forced posture. Methods for evaluating physical workload taking posture into account include:
• OWAS.
• RULA.
• REBA
Cargo handling also causes overexertion. NIOSH equation can be helpful in evaluating lifting loads.
Measuring energy expenditure during the work period is a criterion that, when compared with the worker's physical work capacity, allows evaluating his aptitude for the type of work he performs and being able to establish adequate work and rest regimes. To measure energy expenditure, several methods can be used, among which are:
The NASA-TLX scales include a subscale for physical demand. Not sure how well it would work in your context, but have a look at it maybe and see for yourself.
Oxygen Consumption during the work maybe used to as a measure of calculating energy expenditure for which: Direct Calorimetry, Indirect Calorimetry maybe used.
However, many other factors may contribute to the workload percieved by the worker, not limited to physical factors.
The NASA Task Load Index is a scale which keeps into consideration psychophysics and has different subscales: Mental demand, Physical demand,Temporal demand, Frustation, Effort, Performance.
This scale can be used to measure the Subjective Workload of the worker.
Weightage of each factor can be calculated to see which factor contributes more to the percieved workload of the worker.
@Alicia Alonso Becerra Thank you for your answer. In the case of electrical workers, there is a categorization of types of work. This is what makes me have to determine the method used based on the type of work, then measurement and combining the measurement results from different methods.