Vibrations

Accelerometry

The quantification of the biomechanic load through direct measures is essential for an accurate comprehension of the physiopathological mechanisms for WRMSD development. Accelerometry is one of the most used methods to perform an objective evaluation of superior members’ activity. This method allows one to identify movement patterns risk among operators at risk for various occupational contexts (at the field or the laboratory), especially in repetitive tasks identifying, empirically:

  • Joint amplitude range of gestures;

  • Execution velocity of gestures;

  • Similar patterns of daily movements performed during the work activity;

  • Accelerometry signals from long duration records.

From accelerometry signals it is also possible to:

  • Identify and analyze frequency of activity cycles;

  • Study cycles' variability (analysis based on algorithms used in heart function study which might reveal relevant modifications throughout activity period);

  • Identify and analyze vibrations;

  • Evaluate impact level on members in order to identify maximum values and define biomechanic strategies to reduce impact values.

Accelerometry data are conceptually related with dynamic components – “repeatability”.

Accelerometry has been used for movement patterns quantification among operators at risk for WRMSD development. For example, we referred Grant et. al. (1995) developed work; authors used accelerometry to counterweight the repeatability of actions performed by supermarket cashiers with the developed activity by workers assigned to the logistic sector.

In industrial context, Anderson et al. (1996) performed a pilot study for movement patterns evaluation during activities performance, in real context, with different levels of physical requirements, establishing differential movement profiles according to different conditions of activity conduction.

Diary Exposure

In some activity sectors the human body is exposed to mechanical vibrations harmful to health that can afect productivity and cause irreversible and disabling injuries. These vibrations come from machines or portable tools motorized (of small or big ensembly). The sustained use of a high number of vibrating tools in occupacional level represents a risk to operators health.

The risks to health due to this sustained exposure are various in the medium and long term. Concerning tools that affect the hand-arm system, there could be neurological, muscular or vascular disturbances and osteoarticular injuries. The use of tools of big ensembly that affect the whole body may cause pathologies in the lombar region and injuries in the vertebral column.

The main variable used to describe the amplitude of the vibrations should be the effective acceleration weighted in frequency, expressed in m/s 2. The frequency weighting reflects the importance of the different frequencies in causing injuries.

The total diary exposure measure is made taking into account the total vibration of all tasks to which the operators are exposed during the work day.

The limit values of diary exposure registered for the hand-arm and whole-body system are:

hand-arm system:

  • action level: 2.5 m/s 2A(8)

  • exposure limit value: 5 m/s 2A(8)

whole-body system:

  • action level: 0.5 m/s 2A(8)

  • exposure limit value: 1.15m/s 2A(8)

Representation of the exposure zones.