Repetitive Movements and Assembly Line Ergonomics

Why are repetitive movements a separate risk topic?

Suppose the cycle time on a wiring harness assembly line is 45 seconds. Over 7.5 hours of net working time after breaks, this comes to about 600 cycles. An employee fitting eight connectors per cycle will have made the same pinching and pushing movement 4,800 times by the end of the day. None of them is heavy on its own; that is exactly why the risk from repetitive movements is overlooked.

Legislation names this risk explicitly. Art. 5 of Law No. 6331 lists among the principles of protection from risks adapting the work to the individual and, in particular, preventing the adverse effects of monotonous work and the pace of production on health and safety, or minimising them where they cannot be prevented. Turkish legislation sets no numerical limit on the number of repetitions; how the risk is measured and reduced is determined in the risk assessment.

In Bursa's automotive supply industry, wiring harness production for vehicles (NACE 29.31.04, hazardous class), seat cover and interior trim sewing, small parts assembly and quality control stations are the most typical places for this risk. The same picture is seen in sewing work in garment workshops. We covered the risks of carrying heavy loads in our article on manual handling and lifting technique; this article focuses on light but frequently repeated tasks.

Repetitive work risks: it is the combination, not repetition alone, that matters

Repetition count alone does not explain musculoskeletal disorders. The real risk grows when the following factors come together at the same workstation:

According to a criterion commonly used in the ergonomics literature, a job is considered "highly repetitive" if the cycle time is under 30 seconds or if more than half of the cycle is spent on the same basic movement. This is not a legal limit, but it is a good starting point for choosing which station to prioritise. For detailed analysis, methods such as OCRA, RULA or the Strain Index are used. None of these is named in legislation; the OHS specialist chooses according to the nature of the work. For vibrating tools, an assessment under the vibration regulation is also required.

Carpal tunnel risk and early symptoms

Carpal tunnel syndrome is compression of the median nerve passing through the narrow canal in the wrist. Work done with the wrist bent, involving force and repetition, increases the pressure in this canal. Typical symptoms are numbness and tingling in the thumb, index and middle fingers, complaints that wake the employee from sleep, especially at night, and reduced grip strength. Tendon sheath inflammation, pain on the outer side of the elbow and shoulder problems may also be seen in the same jobs.

These disorders start insidiously. When an employee says "my hand goes numb in the evenings", they have often had the complaint for weeks. Ways to catch it early:

• A simple complaint channel: Verbal reports to the shift supervisor or the workplace nurse should also be recorded.
• Musculoskeletal questioning at periodic examinations: The workplace physician asks about and examines hand, wrist, neck and shoulder complaints; the physician decides whether further tests such as a nerve conduction study are needed. We plan the necessary tests with authorised health institutions.
• Department-level monitoring: If complaints are concentrated at a single station, the problem lies with the station, not the person.

SGK decides whether a disorder counts as an occupational disease; for the process, see our article what is an occupational disease: diagnosis and notification.

Assembly line ergonomics: fix the workstation first

Rotation and breaks only share out the load of a poorly designed workstation. The permanent solution lies in the station itself. A checklist for assembly line ergonomics:

1. Working height: Precision work should be done slightly above elbow height, light assembly at elbow height, and work requiring force below elbow height. If employees of different heights use the same station, use an adjustable platform or table.
2. Reach: Frequently picked parts should be within the arm's natural reach zone and should not require reaching above the shoulder or twisting the trunk.
3. Part presentation: Inclined bins and sequenced feeding ensure the part arrives in the right orientation and close by; reaching into the bottom of the bin is eliminated.
4. Jigs and fixtures: Let a fixture hold the part instead of holding it in one hand and working with the other. Position it at an angle that keeps the wrist straight.
5. Hand tools: Hang heavy tools on a balancer, take up torque reaction with a reaction arm, and choose a handle diameter that suits the hand. For tools whose trigger is pressed continuously with one finger, consider changing the trigger type.
6. Insertion force: Address tight clip or connector problems together with product engineering and the supplier. A design change that lowers insertion force achieves an effect no amount of training can.
7. Sewing stations: Chair and table height, pedal position, machine table tilt and task lighting should be adjusted together; the place where the fabric pile is picked up and put down should not be behind the employee.

For other risks specific to garment and sewing workshops, see our article on OHS in garment workshops.

How do you set up a rotation plan?

Job rotation means the employee moving during the day between stations that load different muscle groups. A good rotation plan is set up with the following steps:

1. Classify the stations. For each station, determine which body region (hand-wrist, shoulder, lower back) it loads and to what degree.
2. Do not load the same region consecutively. Moving between two high hand-wrist stations is not rotation.
3. Set the frequency. A practical starting point is one change between each break. Shorten the time at high-risk stations.
4. Prepare a skills matrix. Everyone in the rotation should know the instructions and quality criteria for each station; for new starters, the induction training programme should be linked to this matrix.
5. Record personal restrictions. A restriction recommended by the workplace physician for an employee should appear in that person's rotation line.
6. Keep a record. The rotation schedule is evidence that the measure in the risk assessment is being applied.

A sample plan (three employees, four stations, two-hour slots):

Micro-breaks and work pace

Micro-breaks are very short, frequent pauses taken during work; for example, a pause of a few minutes every hour when the hands are completely at rest. They do not replace the statutory rest breaks under Labour Law No. 4857; they are added to them. For them to be effective, pay attention to the following:

• Review line balancing. At a station where the cycle load is constantly close to one hundred per cent, the employee has no seconds to breathe. A small buffer stock or redistribution of work content makes micro-breaks possible.
• Apply a gradual pace. Do not put an employee who is new or returning from long leave at full line speed in the first days.
• See stretching exercises as support. Simple hand and wrist exercises during breaks help, but they do not replace fixing the workstation.
• Take the shift pattern into account. Long shifts and overtime directly increase the number of repetitions; we described the effect of fatigue in multi-shift patterns in our article on OHS in shift-based production in Bursa's OIZs.

Repetitive movements in the risk assessment

Repetitive movement risk should not be squeezed into a general "ergonomic risk" line in the risk assessment. The following information should be written for each station: cycle time, main movements, observations of force and posture, the method used and its score, the measure to be taken, the person responsible and the deadline. A short video recording and a complaint survey given to employees are very helpful for observation. Repeat the same measurement after the measures and track how the number of complaints changes. For choosing a scoring method, see our article on the Fine-Kinney method.

In our risk assessment service, we observe assembly and sewing stations one by one and evaluate recommendations on station improvements, rotation and breaks together with the workplace physician's examination findings. Other sector-specific risks are on our automotive supply industry and textiles pages; you can track examination and review dates with the OHS calendar.

Frequently Asked Questions

Is there a legal limit for repetitive movements?

No. Turkish legislation has no numerical limit on the number of repetitions or the cycle time. Art. 5 of Law No. 6331 requires the adverse effects of monotonous work and the pace of production to be prevented or minimised; how this is done is determined in the risk assessment.

How often should job rotation take place?

Legislation does not set a period. A practical starting point is one change between each break. At stations with high hand-wrist load the period is shortened, and care is taken that two consecutive stations do not load the same body region.

Do wrist supports or bands prevent carpal tunnel syndrome?

Wrist supports do not replace fixing the workstation and are not a measure to be handed out to everyone. The workplace physician decides whether one should be used by an employee with symptoms.

Can an employee with carpal tunnel complaints keep working at the same station?

The decision lies with the workplace physician. Depending on the examination results, the physician may recommend a temporary restriction, rotation to lower-risk stations or further tests. If new complaints keep arising at the same station, also renew that station's risk assessment.