Simultaneous assessment of upper limb usage and sedentary behavior time among white- and blue-collar workers using wrist-worn accelerometers
Authors: Porta Micaela , Leban Bruno , Pau Massimiliano 
Published: June 2022

The use of wrist-worn accelerometers to perform assessment of physical activity features and posture recognition, has significantly increased in the last decades, but remains limited in ergonomic contexts. In particular, to our knowledge, no studies employed them to investigate symmetry of use of upper limb (UL) during actual work shifts, even though such information would be useful to identify potentially unbalanced use of dominant and non-dominant limb. In the present study we aimed to estimate intensity and symmetry of use of UL while, at the same time, analyzing the amount of time spent in sedentary behavior in workers engaged in physically demanding and sedentary tasks.2.MethodsTwenty-two full-time workers employed in a metalworking company were recruited for the study and divided into two groups (n=11 each) according to the task they usually performed as follows:1)Machine tools operators, who are required to perform several kinds of machining processes such as cutting, turning, milling, etc.2)Administrative staff, who spend most of their shift time on a desk, in a sitting position using a PC, mouse and keyboard. Upper limb activity was measured for 4 consecutive hours of a regular working shift using two wrist-worn tri-axial accelerometers (Actigraph GT3X-BT, Acticorp Co., USA). The raw accelerations were processed to calculate the following parameters:a) vector magnitude (VM) counts, a composite measure of the accelerometric counts on the three planes of motion;b) Bilateral Magnitude (BLM), which is the sum of the VM values of dominant and non-dominant limb;c) Use Ratio (UR): is the ratio between the minutes of use calculated for the non-dominant and the dominant limb respectively. UR = 1 indicates an equal use of dominant and non-dominant limb, while UR < 1 (>1) indicates longer periods of use for the dominant (non-dominant) limb;d) Magnitude Ratio (MR) is the natural logarithm of the ratio between the VM counts calculated for the non-dominant and the dominant limbs respectively. A value of MR = 0 indicates perfect symmetric use of both limbs in terms of movement intensity. MR < 0 (> 0) denotes higher intensity activity of the dominant (non-dominant) limb;e) Time spent in sedentary (sitting) behaviour calculated according to the procedure proposed by Straczkiewicz et al. (2020)We performed one-way MANCOVA and ANCOVA using the number of steps as covariate because the arm swing associated with walking represents a source of accelerometric counts. The independent variable was the group (i.e. machine tools operator or administrative staff), while the dependent variables were: 1.The three UL activity parameters (i.e., BLM, MR and UR); 2.The time spend in sedentary (sitting) behavior.The level of significance was set at p = 0.05 and the effect of size was assessed using the eta-squared coefficient. Univariate ANOVAs were carried out as a post-hoc test on the adjusted group means.3.ResultsAfter controlling for number of steps, MANCOVA detected a significant main effect of group on UL activity and symmetry parameters [F(3,17) = 5.512; p = 0.008 Wilks’ λ = 0.507; η2 = 0.493]. In particular, the follow-up analysis revealed that machine tool operators performed a more asymmetrical activity in favor of their dominant limb with respect to those engaged in office tasks both in terms of intensity (MR = -0.18 vs. -0.02, p=0.004) and minutes of use (UR = 0.89 vs. 0.99, p=0.001). As regards the sedentary behavior, the ANCOVA revealed that the administrative staff spent significantly longer time in sitting position with respect to machine tools workers (158 minutes vs. 70, p=0.021). This value represents approximately 66% of the monitoring period.4.Discussion and conclusionThe results obtained from the experimental analysis identified the existence of significant asymmetry in the machine tools workers in terms of both duration of UL use and activity intensity. In particular, their markedly higher intensity of use of dominant limb is probably due to the fact that during activities such as cutting, turning, milling, etc. the dominant arm tends to perform dynamic tasks, while the non-dominant is devoted more to stabilizing position by contrasting the forces imposed by the dominant limb. Also, as expected, they spend little time in sitting position (30% of the monitoring period) compared with administrative staff, which perform a typical sedentary work. The findings of the present study, although carried out on a restricted sample in terms of working activities and number of subjects tested, suggest that accelerometer-based data allow discriminating among important features of different job occupations, at the same time highlighting potentially harmful conditions associated with the asymmetrical use of the dominant and non-dominant limbs. This can be extremely important in properly planning suitable ergonomic interventions.