Rest-allowance calculator for physical effort
Enter the workstation's energy expenditure and the reference limit: it tells you how much of the shift must be devoted to recovery (Murrell's formula).
Required rest
50.0% of the shift
In an 8-hour shift
240 min
Murrell's formula: rest = (W − limit) ÷ (W − 1.33), where W is the energy expenditure while working and 1.33 kcal/min is the resting expenditure. The preloaded values are the coal-shovelling case (9.33 kcal/min): half the shift. The limits are population averages quoted by Niebel; they serve to size a workstation, not to judge a person.
How it works
You enter the workstation's average energy expenditure (W, in kcal per minute) and choose the reference limit. Murrell's formula, according to Niebel and Freivalds:
R = (W − limit) ÷ (W − 1.33)
where R is the fraction of the total time that must be devoted to rest and 1.33 kcal per minute is the resting expenditure. The limits are those of Bink (1962) for an 8-hour shift: 5.33 kcal per minute (average for men) or 4 kcal per minute (average for women). If W does not exceed the limit, no additional rest is needed. The result is also shown in minutes per 480-minute shift.
The book's coal-shovelling example is preloaded, with 9.33 kcal per minute: half the shift is needed, about 4 hours. The limits by sex are population averages for sizing a workstation, not for evaluating an individual. And the calculation does not say how to distribute the rest: the book recommends short, frequent breaks.
If you prefer to work in Excel, there is an allowances and rest spreadsheet in Excel with these same calculations.
Sources
These are the ones from the article where the theory behind this tool is developed.
Where do the limits come from and how is the rest distributed? It is in the article Fatigue and rest breaks.