Original article

Scand J Work Environ Health 2006;32(4):300-309    pdf

doi:10.5271/sjweh.1014

Changes in neuromuscular function due to intermittently increased workload during repetitive work in cold conditions

by Oksa J, Sormunen E, Koivukangas U, Rissanen S, Rintamäki H

Objectives This study attempted to determine whether repetitive work in the cold affects the number of electromyographic (EMG) gaps and whether cold-induced deterioration in neuromuscular function can be restored by altering work intensity.

Methods During 2 hours of simulated sausage packing, the occurrence of EMG gaps was studied in eight upper-extremity muscles at 19°C and 4°C. The additional effect of continuous, light repetitive work [wrist flexion–extension 10% of the maximal voluntary contraction (MVC), Cwork] and intermittently increased workload (10% or 30% MVC) (Iwork) on forearm muscle EMG gaps, the median frequency of the EMG spectrum, EMG activity, and muscle fatigue (as indicated by changes in the MVC of wrist flexion) at 4°C was studied.

Results During work simulation, the mean skin temperature decreased from 33.3 (SD 0.1)°C to 30.6 (SD 0.2)°C (P<0.05), and the number of EMG gaps diminished in seven muscles by 1.4–68.2% (P<0.05). During Iwork there were 44% and 37% more EMG gaps in the forearm flexors and extensors, respectively, and the median frequency shifted to higher frequencies (P<0.05) as compared with the situation in Cwork. The average EMG activity of the forearm flexors was 13% lower (P<0.05) during Iwork than during Cwork. Wrist flexion MVC decreased 18% and 15% in Cwork and Iwork, respectively.

Conclusions The cold-induced decrease in the number of EMG gaps and increased muscle strain and fatigue can be, at least partially, restored by intermittently increasing the workload (ie, breaking the monotonous work cycle).