Personal and occupational factors contributing to biomechanical risk of the distal upper limb among dairy workers in the Lombardy region of Italy

Abstract

Biomechanical overload in the wrist flexor and extensor muscles, together with awkward hand positions during work activities, can result in occupational wrist and hand disorders. Dairy workers, specifically those that work in the milking parlor, are exposed to highly repetitive and forceful exertions of the upper limb throughout their work shift. There are very few studies that have investigated the determinants that contribute to the risk of distal upper limb musculoskeletal disorders among dairy workers. The purpose of the present study was to identify the variables affecting the biomechanical overload of the distal upper limb among milking parlor workers, define risk profiles, and propose possible interventions to reduce the high physical loads to the distal upper limb during milking activities. Forty male workers from the three most common milking parlor systems in Lombardy Italy were recruited to participate in this study. Multiple correspondence analysis of personal characteristics and occupational risk factors, followed by cluster analysis, led to the identification of three distinct groups of workers. Low, medium and high risk profiles were assigned to each group based on the risk assessments performed using the Strain Index and electromyography of the distal upper limb. The main risk determinants were workstation characteristics, work organization and milking routine. A well-organized milking routine, milking cluster weight below 2.4 kg or the use of supporting arms for the milking cluster may reduce the risk of biomechanical overload.

Keywords: Dairy workers; Risk assessment; Strain index; Surface electromyography.

Fig. 1.

Milking tasks: (a) pre-dipping, (b) wipe-stripping, (c) milking unit attachment, (d) post dipping.

Fig. 2.

The three types of milking parlor systems predominantly used by dairy farms in the Lombardy region: (a) parallel, (b) herringbone, (c) rotary.

Fig. 3.

Personal and occupational variables investigated in the research framework.

Fig. 4.

The dimensional parameters of the milking parlor measured in this study.

Fig. 5.

Electrode placement protocol. An Italian worker equipped before starting the sEMG recording phase.

Fig. 6.

Infographic of the statistical analysis. 1: Sample of workers in herringbone, parallel and rotatory milking parlor systems. 2: 52 variables (characteristics) of workers collected. 3: Multiple correspondence analysis performed to identify the most important variables. 4: 14 variables out of 52 explained 97% of variability and selected for further analysis. 5: A sample of 40 workers and 14 most important variables analyzed further. 6: Cluster analysis identified 3 groups of workers (A, B, and C). 7: sEMG and Strain Index results compared among the three groups of workers to identify the Low, Medium, and High risk profiles.

Fig. 7.

Contribution of each variable to the first three factorial axes of the MCA.

Fig. 8.

Most important variables in the first factorial plane of the MCA.● Milking Parlor Systems: herringbone, parallel, rotary; Δ Herd size: ≷305 cows, ○ Pit height ≷ 92 cm; Cluster weight ≷ 2.4 kg; ◆ Nationality: European/Not European; ◊ relative shoulder height ≷15 cm.

Fig. 9.

Three Groups (A, B, C) of workers defined by the cluster analysis.