The Job strain index is an evaluation method created to estimate the level of risk of developing a musculoskeletal disorder by hand, wrist, forearm or elbow for tasks Repetitive intensive.
This method does not take into account:
- The vibrations
- Local constraints.
- The environment: temperature…
Step 1 – Observing the activity
The first step in the method is to observe the movement carried out by the operator. For this, the best is to make a video of the activity. The use of the video allows to evaluate the same situation to several, key point for the quality of this evaluation.
It should be noted that the assessment of the left hand and the right hand is done separately.
Step 2-Evaluate according to the 6 criteria
Task intensity (IT)
We estimate the effort required to complete the task once. This assessment is carried out on a scale of Borg and aims to compare our effort to the maximum effort that can be exerted.
Task Duration (DT)
The duration of the task is calculated by making the relationship between the time of the task on the total observation time. Depending on its percentage of the observation time and posture while one has to perform the task, it is allocated a score.
Frequency of effort (FE)
For this criterion, we count the number of times the task appears for the duration of the observation, reported by the minute. According to this frequency a score is allocated to it.
Hand and wrist posture (PMP)
The posture of the hand and wrist is to compare its position (extension, bending and deflection) vis-a-vis a neutral posture. Depending on this position, a score is allocated.
Execution Speed (VE)
Speed is an estimation of the operator’s working speed. The score is allocated according to the speed with respect to the standard of the MTM1.
Task duration per day (DTJ)
The duration is to measure how long per working day the person performs the task analyzed. Depending on this duration, a score is allocated.
To get the final score, it is enough to multiply each of the multiplier factors obtained via the different tables. As well:
index = IT * DT * FE * PMP * VE * DTJ
J. S. MOORE, A. GARG (1995)-The Strain Index: A proposed Method To Analyze Jobs For Risk Of distal Upper extremity disorders