The effects of different types of cognitive tasks in conjunction with circadian regulation on heart rate variability and performance parameters.

Every day, humans are exposed to a variety of tasks in the workplace, at home or even in activities of daily living. These tasks all require, to some extent, cognitive processing and activity. In order to perform a task, information from the environment must be perceived, interpreted and an appropriate response elicited (Wickens et al., 1998). The information processing places a certain amount of strain or demand on the resources available to process it (Wickens, 1985; Wickens et al., 1998). Therefore, the extent of this strain needs to be measurable to ensure that cognitive overload and performance impairment does not occur.

This authors aimed with this study to determine to which extent heart rate variability (HRV) is sensitive to changes in different forms of cognitive workload. The second objective was to determine the effects of cognitive tasks on HRV during different times of the day, in conjunction with the variability of performance parameters.

Five tasks were utilized, each at two levels of difficulty in order to ascertain specific cognitive resources. These tasks included a reading task, a decision-making task, a memory task and two forms of modified Fitts tasks. Only one of the modified Fitts tasks, which isolated motor organisation and the spelling error parameter for the difficult reading task showed a time of day effect with respect to performance. With respect to HRV, time domain analysis (rMSSD) and the low frequency (LF) band of a frequency domain analysis showed an overall significant effect of difficulty over all five tasks. The LF band, the high frequency (HF) band, rMSSD and heart rate frequency were sensitive to changes in cognitive workload for the memory task. The LF band was also sensitive to changes in cognitive workload for the modified Fitts task, which isolated motor organisation. The LF-HF ratio was the only HRV parameter that was influenced by the time of day during cognitive task performance.

In conclusion, in some instances, HRV was sensitive to changes in cognitive workload for specific HRV parameters and tasks, with selected HRV variables also being affected by time of day. However, no straightforward assignment of workload to HRV parameters and vice versa can be made yet.

Huysamen, K. C., Göbel, M., & Davy, J. (2013). The effects of different types of cognitive tasks in conjunction with circadian regulation on heart rate variability and performance parameters. Ergonomics SA, 25(1), 52-67. 

Comparisons of Muscular Activity in Males and Females While Walking in Restricted Postures

Increasing numbers of females are entering industrial workplaces. In the mining industry in South Africa, for example, this is partly the result of employment equity laws, which have ruled that by 2009 at least 10% of the workforce must be female (Department of Minerals and Energy, 2004). Differences in factors such as anthropometry and strength are evident between males and females. Males are generally taller and heavier than females, and possess a higher percentage of muscle mass and a lower percentage of body fat compared to females (McArdle et al, 2001). Furthermore, males are seen to possess significantly greater absolute strength than females, while females maintain approximately 50% of the upper body strength of males and 70% of the lower body strength of males (McArdle et al, 2001). Gender is also a factor that influences movement patterns during walking and running, and intrinsic characteristics, including skeletal alignment, muscle strength and anthropometric differences, are likely to contribute to this (Chiu and Wang, 2007). As a result, it is expected that responses to manual tasks are likely to differ between males and females.

The purpose of the authors to do this study was to examine differences in muscular activation between males and females while walking in restricted postures. Restricted postures are evident in various industries, including mining, construction and agriculture. These postures are associated with musculoskeletal disorders and lower back pain. Studies generally focus on a male workforce; however, more females are entering industrial workplaces.

Twelve male and 12 female subjects between the ages of 18 and 25 years participated in the study. Subjects walked on a treadmill at a speed of 3.5 km/h for four minutes under conditions of upright walking, and stooped walking under restrictions at 85% and 70% of stature. Electromyographic activity was measured on seven muscles (trapezius, latissimus dorsi, erector Spinae, rectus femoris, biceps femoris, medial gastrocnemius and tibialus anterior). Ratings of Perceived Exertion (RPE) and Body Discomfort were also obtained. The extent of vertical restriction significantly altered levels of muscle activation. Female subjects had significantly lower levels of activation of the medial gastrocnemius than males. Local RPE was greatest under the lowest restriction, and body discomfort of the neck, lower back and hamstrings was evident during restricted walking. Work place design and interventions should consider these consequences.

Hodgskiss, J., & Zschernack, S. (2013). Comparisons of muscular activity in males and females while walking in restricted postures. Ergonomics SA, 25(1), 39-51. 

A study of ergonomic factors leading to computer vision syndrome among computer users

The invention of computers has transformed and modernized both the work place and the home environment (Blehm et al., 2005). It has been estimated that the number of computer users globally was 670 million in 2007, and rising to 1 billion in 2010 (Izquierdo et al., 2007). With the rate at which the google computing system has grown, the total number of computer users is currently likely to be much higher than 1 billion. According to the National Institute of Occupational Health and Safety (NIOHS), USA, any individual who works with a computer for more than three hours per day is likely to experience symptoms of CVS (Jaschinki-Kruza, 1991; Atenio, 1996). CVS is defined as a complex of eye and vision problems which are experienced during computer use or a task related to the use of a computer (Wimalasundera, 2006; Yan et al, 2008). The symptoms of CVS can be divided broadly into two categories; eye and vision-related symptoms (e.g. dry eyes, watery eyes, irritated and burning eyes, eye strain, eye fatigue, headache, blurred vision and double vision) and posture-related symptoms (e.g. neck, shoulder and back pain) (Verma, 2001, Blehm et al., 2005; Sheedy, 2000; Yan et al., 2008). Other reported symptoms include light and glare discomfort, after-image distortion and colour distortion (Verma, 2001; Sen and Richardson, 2007).

The authors aim of this study was to investigate the ergonomic factors that might lead to computer vision syndrome (CVS) among non-presbyopic computer users in a University staff population. A complete eye examination was performed on each participant before he or she was interviewed using a structured questionnaire probing into demographic status and factors that could lead to CVS.
Eighty seven participants were included in the study. An observation and measurement of the participant's computer workstation was then made in order to identify the risk factors leading to CVS. Data were analysed with descriptive statistics. 72% of participants reported taking breaks after 2 hours while 28% reported taking breaks after every hour of computer use. Eye strain and visual fatigue (89%), headaches (81%), neck and back pains (77%) were the most severe and frequently reported symptoms among the participants. In general, the computer workstations were not economically designed and users were not aware that they were not adhering to ergonomie requirements for computer use.

This suggests the need for awareness campaigns on ergonomic factors that can prevent computer vision syndrome among computer users and early intervention programs for computer users that experience computer vision syndrome.

Mashige, K. P., Rampersad, N., & Oduntan, O. A. (2013). A study of ergonomic factors leading to computer vision syndrome among computer users. Ergonomics SA, 25(1), 3-12.