Work-Rest Scheduling
Proper work-rest schedules are essential for preventing fatigue and musculoskeletal disorders. This calculator helps determine appropriate work durations and rest periods based on workload intensity.
Rest Allowance (Murrell) = (W - B) / (W - R) × 100 [% of work time]
Where:
- AWT (Allowable Work Time) - Maximum percentage of time that should be spent on a given task
- Rest Allowance - Percentage of work time that should be allocated to rest
- EEL (Energy Expenditure Limit) - Maximum recommended energy expenditure (kcal/min)
- EM (Energy Measurement) - Measured energy expenditure of the task (kcal/min)
- RMR (Resting Metabolic Rate) - Baseline energy expenditure at rest (~1.2 kcal/min)
- W (Work Energy) - Energy expenditure during work (kcal/min)
- B (Basal Metabolic Rate) - ~1.2 kcal/min
- R (Rest Energy) - Energy expenditure during rest (~1.5 kcal/min)
Calculation Method
Select which calculation you want to perform:
Allowable Work Time (AWT)
Calculate the maximum percentage of time that should be spent on a given task based on energy expenditure.
Results
Allowable Work Time
Percentage of shift
Required Rest Time
Percentage of shift
Recommended Work Period
Minutes per hour
Recommended Work-Rest Schedule
For a hour shift:
Interpretation Guidelines
| AWT Range | Workload Classification | Recommendation |
|---|---|---|
| < 30% | Extremely Heavy | Task should be redesigned or automated |
| 30-50% | Heavy | Requires frequent rest periods |
| 50-80% | Moderate | Standard work-rest cycles |
| > 80% | Light | Minimal rest required |
Rest Allowance (Murrell's Equation)
Calculate the percentage of work time that should be allocated to rest based on Murrell's equation.
Results
Rest Allowance
Percentage of work time
Rest Time
Minutes per work period
Recommended Work-Rest Cycle
For a minute work period:
Rest Allowance Guidelines
| Work Intensity | Energy Expenditure (kcal/min) | Typical Rest Allowance |
|---|---|---|
| Light | 2.0-3.5 | 0-10% |
| Moderate | 3.5-5.0 | 10-20% |
| Heavy | 5.0-6.5 | 20-30% |
| Very Heavy | >6.5 | 30-50% |
Practical Examples
Example 1: Light Assembly Work
EM = 3.0 kcal/min, EEL = 5.0 kcal/min (8-hour shift)
AWT = (5.0 - 1.2)/(3.0 - 1.2) × 100 = 211% → Capped at 100%
Interpretation: This light work can be performed continuously without additional rest.
Example 2: Heavy Lifting
EM = 6.0 kcal/min, EEL = 5.0 kcal/min (8-hour shift)
AWT = (5.0 - 1.2)/(6.0 - 1.2) × 100 = 79%
Interpretation: Workers should spend no more than 47 minutes per hour on this task (with 13 minutes rest).
Example 3: Murrell's Equation
W = 5.5 kcal/min, R = 1.5 kcal/min
Rest Allowance = (5.5 - 1.2)/(5.5 - 1.5) × 100 = 107.5%
Interpretation: This extremely heavy work requires more rest time than work time (alternating 1:1 work:rest ratio).
Energy Expenditure Reference
| Activity | Energy Expenditure (kcal/min) | Typical AWT |
|---|---|---|
| Sitting at rest | 1.2 | N/A |
| Light assembly | 2.0-3.5 | 100% |
| Machine operation | 3.5-5.0 | 80-100% |
| Heavy lifting | 5.0-7.0 | 30-80% |
| Very heavy labor | 7.0-10.0 | <30% |