From The Ergoweb® Learning Center

Research: A Circadian Rhythms Based Work Scheduling for High Voltage Live Line Electricians

Editing and the "What This Might Mean to Ergonomists" section by Peter Budnick, PhD, CPE

The few ergonomics studies on the work of grid electricians point to the consequences of the constraints imposed, ranging from states of:

  • fatigue;
  • pain;
  • musculoskeletal disorders risk; and
  • in the final instance, death, mainly under emergency situations when the work conditions are more critical. 

Most often, however, even in the case of supply of electric energy services, where the different tasks are not necessarily sequential, work design does not consider the incompatibility between work demands and worker’s capabilities (whether physical or mental). Generally, the Operation Centre programs the service provision, without any regard to the human factors involved, and the team renders this service without question, despite the constraints that may be involved. Assuming there is no reason for not designing work according to human predisposition, a proposal for scheduling service calls by a team of live line electricians was developed, prototyped and validated in this study.


The study was conducted during two weeks in an electric energy utility (CEEE) company, which employs 10 men for live line operations for energy distribution in the city of Porto Alegre, Brazil. The work consists of preventive and corrective maintenance of the network and its sub-stations with grids energized at 13.8 kV or 22.4 kV. Most tasks are independent of each other, and about 95% of the services are not emergencies.

In the first week, a five electrician team worked normally, as scheduled by the Operation Centre, while in the second week ("circadian-based ergonomics” week), the team worked according to the circadian cycles and homeostatic processes (the maintenance of metabolic equilibrium), with activities scheduled in accordance with:

  • the level of mental and physical demand (light, medium and heavy), as evaluated by the workers;
  • time of day (because of the heat and circadian rhythms) and day of week (depending on the workers predisposition and accumulation of fatigue). 

In the second week:

  • tasks with a predominantly mental demand were allocated to the end morning and afternoon shift;
  • tasks with a predominantly physical demand were allocated to the morning shift;
  • both mental and physical loads were higher on Mondays, Tuesdays (primarily) and Wednesdays decreasing until Fridays;
  • at the end of each day, time was set aside for planning activities for the next day, as well as sorting and organizing the materials and equipment needed; and
  • considering the mid-afternoon dip, the lighter activities were also scheduled for the 2:00-4:00 PM period in all days of the second week.

Three physiological indices were used to assess the impact of having re-organized the work on the electrician’s level of stress:

  • heart frequency (HF, also known as heart rate);
  • levels of two urinary catecholamine:

    • adrenaline (A, an index of mental stress); and
    • noradrenaline (NA, an index of physical stress).

Additionally, in order to minimize the effect of individual catecholamine fluctuations as well as day-to-day variations in the excretion of both catecholamines, the “Q-index” was proposed to assess catecholamine behavior during the work journey in the first and second weeks. Hence, the ratio of NA to A after work (NA/Aafter) was compared to the ratio of NA/A before the work (NA/Abefore), so that the overall ratio Q-index [Q = (NA/Aafter)/(NA/Abefore)] indicates whether the maneuvers had been of more mental demand (Q-index falls) or of less mental demand (Q-index raises).  

The level of tiredness, and consequently, the level of attention of a person, was evaluated by two attention tests:

  • the perception of a minute; and
  • the dexterity in fitting matchsticks into a matchbox.

Given the influence of heat on stress, daily temperature (kept by CEEE’s meteorological department) was also considered in the two weeks. Attention and HF data were collected from all 5 electricians, while catecholamine data were collected only from two out of five electricians due to the costs involved and grant limitations.  Both attention and Q-index paired data obtained at the start and end of the workday in the two types of working week (traditional and circadian-based ergonomic intervention) were evaluated by analysis of variance (repeated measures ANOVA). HF from all workers was measured at the beginning of the day (at rest) and every 20 minutes, on average, during the working day.


HF increased with temperature increase during the day throughout the two weeks. There were significant differences in the Q-indices and attention results from week 1 (no intervention) and week 2 (circadian-based ergonomics intervention). In week 2, the Q-index measured in both workers were lower, showing a decrease in physical and mental effort, which is an important benefit, since the reduction in stress reduces the likelihood of accidents and fosters an increase in attention.

More specifically, Q-index values clearly evidenced a sharp decrease in mental stress after the circadian-based ergonomic intervention. In week 1 there was a statistically significant difference in the time taken for the two attention tests before and after the daily work journey, while there is no difference in week 2. This shows that the perception of the individuals was not affected by the load imposed by the work journey, possibly because they came to and left work feeling less tired in the second week. Since the nature of the activities did not undergo any significant changes in week 2, work organization is assumed to be the beneficial factor.

Together, physiological and attention data provided evidence of a reduction in the stress experienced in week 2, indicating that taking circadian-based ergonomics principles into account when organizing work provides a positive impact on worker's performance. Also, the “Q-index” appeared to be a robust parameter to assess the impact of physical/mental work demands, and therefore may be useful to assess physical-to-mental load when designing ergonomics interventions.

What This Might Mean to Ergonomists

Thanks to researchers Buarque de Macedo Guimarães et al for writing the above summary of their study for The Ergonomics Report™. We were intrigued when we saw it published, because it touches on a subject that is intuitively real, yet the scientific methods to study it, and the tools to carry it into real-world practice are lacking. Ergoweb has covered other research regarding circadian rhythms (see related articles on this page, or search the terms using our keyword search for examples), but they tend to focus on shift work, particularly "graveyard" or night shifts. Whether or not you can begin to apply this knowledge to your work environments — and keeping the usual caveats of study limitations, like a small sample size in this case — two things in particular strike us as important in this study:

  1. Circadian rhythm based work scheduling can be effective, particularly for stressful and high-risk tasks; and
  2. Participatory ergonomics, where the workers are directly involved in improvement processes, can be effective (in this study, the workers used a team approach to identify work demands and develop schedules according to the researchers guidelines, like "Tasks with a predominantly mental demand should be allocated to the late morning and afternoon shift; tasks with a predominantly physical demand should be allocated to the morning when heart rate responses to exercise are at a minimum.")



Lia Buarque de Macedo Guimarães, Jose Luis Duarte Ribeiro, Tarcísio Abreu Saurin and Paulo Ivo Homem de Bittencourt, Jr, (2012), Circadian Rhythms as a Basis for Work Organization: A Study With Live Line Electricians, Human Factors, published online 9 July 2012, DOI: 10.1177/0018720812451855. The full research article is available online to Human Factors subscribers at

Lia Buarque de Macedo Guimarães, PhD, CPE (BCPE), is an Associate Professor at the Graduate Program in Industrial Engineering, Federal University of Rio Grande do Sul (UFRGS)  Av. Osvaldo Aranha, 99, 5o andar, Porto Alegre, RS, 90035-190, Brazil. E-mail: Tel: +55 51 33083948; Fax: +55 51 33084007, and earned a PhD in Industrial Ergonomics (Human Factors) from the University of Toronto, Canada, in 1992.

Jose Luis Duarte Ribeiro is an Associate Professor at the Department of Industrial Engineering and Transportation, Federal University of Rio Grande do Sul (UFRGS), Av. Osvaldo Aranha, 99, 5o andar, Porto Alegre, RS, 90035-190, Brazil, E-mail: Tel: +55 51 33084005; Fax: +55 51 33084007, and did a Pos-Doc at Rutgers University – The State University of New Jersey, in 1993, and earned a Dr. Eng. (Civil Engineering) from the Federal University of Rio Grande do Sul, Brazil, in 1989.

Tarcísio Abreu Saurin is an Associate Professor at the Department of Industrial Engineering and Transportation, Federal University of Rio Grande do Sul (UFRGS), Av. Osvaldo Aranha, 99, 5o andar, Porto Alegre, RS, 90035-190, Brazil, E-mail: Tel: +55 51 33083048; Fax: +55 51 33084007, and earned a Dr. Eng. (Industrial Engineering) from the Federal University of Rio Grande do Sul, Brazil, 2002

Paulo Ivo Homem de Bittencourt Jr. is an Associate Professor at the Department of Physiology, Institute for Basic Health Sciences, Federal University of Rio Grande do Sul (UFRGS), Rua Sarmento Leite, 500, 2o andar, Cellular Physiology Laboratory (Lab. 2) Centro, Porto Alegre, RS, 90050-170, Brazil, E-mail: Tel: +55 51 33083151 Fax: +55 51 33084555, and earned a Dr. Sciences (Physiology) from the University of Sao Paulo (USP), Biomedical Sciences Institute, 1995


This article originally appeared in The Ergonomics Report™ on 2012-08-02.