Frequency of Force Exertion FF

Seyyed Ali Moussavi-Najarkola AJE Vol.9 2009 63-78 70 Lack of enough recovery periods hour 0 1 2 3 4 5 6 7 8 Multiplier factor 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 Table 9. Elements for achieving the multiplier factor for age factor AF Age rating year ≤ 40 41-50 51-60 60 Multiplier factor 0.6 0.8 0.9 1

3.8. Lack of Recovery Periods RP

A recovery period is defined as “period of time between or within cycles, during which no repetitive movements are carried out” 10. A recovery period consists of relatively long pauses after periods of mechanical movements; during these periods muscles can recoved metabolically 10. Lack of recovery periods can create oxygen debt and produce accumulation of lactic acid, which induces muscle fatigue 4. Therefore, providing formal and informal rest intervals between work cycles during tasks can prevent muscle fatigue and UEMSDs 1, 3, 5. The multiplier factor for lack of recovery period Table 8 was derived from 15 and 16 using the OCRA method 10.

3.9. Age Factor AF

Age is the most important factor in force exertion and biomechanical models 18; it has a direct relationship with FE and Maximal Aerobic Capacity in hand activities 4. For example, a 40 year old person has the maximal power, but at later ages this capability and power decrease slowly 18. The age factor multiplier Table 9 was obtained using the European Coal and Steel Community ECSC studies that quantified the effect of age on inducing and exacerbating UEMSDs 21, 22, 23.

3.10. Effective Item EI

EIs are factors that have indirect effects on the incidence rate of UEMSDs 10.These items may be present in repetitive tasks, but not necessarily or always 10. Their type, intensity and duration lead to an increased level of overall exposure to risk of developing UEMSDs 2. These items are considered to be relevant in the production and development of UEMSDs 3. They are always work-related, and must be considered when assessing risk exposure 5. For an item to be considered, it must have an association with UEMSD occurrence, so that it would have a collective impact rather than an individual impact 10. To obtain EI, a score of 1 is allocated to any item whenever that item is present 10. • Extreme precision at working