Assessment of physical strain in younger and older subjects using heart rate and scalings of perceived exertion

Physical strain is usually evaluated physiologically by using the heart rate (HR) or psychologically using scaled perceived exertion (PE). In order to explore the relationship between these approaches, we compared the series of both measurements taken simultaneously during work on a bicycle ergometer. A total of 29 participants aged between 27 and 41, 42 and 56, and 57 and 71 years took part in 28 minutes of cycling with systematically increased and decreased load as well as in 7 hours of continuous cycling with low to medium exertion, interrupted by brief peak loads at high to very high exertion levels. Results revealed that, while both measurements are suitable to capture physical strain, HR is not as specific as PE. The older participants further perceived comparable physical loads as more demanding as the younger participants. With an aging workforce, results have potential implications for the organisation of work places.     

Low mean level sustained and intermittent grip exertions: Influence of age on fatigue and recovery

The goal of this study was to quantify localised muscle fatigue resulting from low mean levels of exertion in younger (< 40 years) and older (>50 years) adults. Fatigue, elicited in the finger flexor muscles by intermittent (10% mean maximum voluntary contraction (MVC)) and sustained (8% MVC) handgrip exercises, was quantified by a muscle twitch force response before, immediately after and during 3 h following exercise. Despite greater mean loads, recovery time was shorter following intermittent than sustained contractions, which suggests that recovery from fatigue is more sensitive to rest within the work cycle than mean work. The more pronounced effects for younger than older individuals following the sustained exertion indicate that changes in muscle fibre type composition might predispose older individuals to be more resistant to fatigue resulting from sustained contractions of low level. Performing hand exertion tasks requiring low mean force levels contributes to similar long-lasting fatigue effects regardless of gender and age. Intermittent periods of complete rest reduce muscle fatigue. Since fatigue was not perceived during recovery from the tested sustained and intermittent contractions, subjective evaluations may not be a reliable indicator of localised muscle fatigue.     

The effects of VDT work on the regulation of hemodynamics compared with aging

Urinary excretions of aldosterone, blood pressure, and heart rate were examined for three age groups of volunteers searching for target words on VDT for two hours. Aldosterone excretion did not change in the young and middle-aged groups, but increased in the elderly group. Blood pressure decreased midway through the work in the young group, and increased during the work in the middle-aged and elderly groups. Aldosterone excretion did not increase during hard-copy work or during VDT work with large letters, but increased during VDT work with small letters. During VDT work with both large and small letters, blood pressure increased. During hard-copy work, neither blood pressure nor heart rate changed, although blood pressure increased after the work. These data suggest that the sympathetic nervous activation represented by the increases in aldosterone excretion and blood pressure occurred definitively during VDT work with small letters under the conditions of this study. It is also suggested that this effect is enhanced by aging.     

The effects of VDT work on the regulation of hemodynamics compared with aging

Abstract

Urinary excretions of aldosterone, blood pressure, and heart rate were examined for three age groups of volunteers searching for target words on VDT for two hours. Aldosterone excretion did not change in the young and middle-aged groups, but increased in the elderly group. Blood pressure decreased midway through the work in the young group, and increased during the work in the middle-aged and elderly groups.

Aldosterone excretion did not increase during hard-copy work or during VDT work with large letters, but increased during VDT work with small letters. During VDT work with both large and small letters, blood pressure increased. During hard-copy work, neither blood pressure nor heart rate changed, although blood pressure increased after the work.

These data suggest that the sympathetic nervous activation represented by the increases in aldosterone excretion and blood pressure occurred definitively during VDT work with small letters under the conditions of this study. It is also suggested that this effect is enhanced by aging.     

Further studies of shoulder and neck pain and exposures in customer service work with low biomechanical demands

The aim of the study was to establish insight into work exposures that cause shoulder and neck pain among occupational groups that have low biomechanical exposure and experience work stress from client/customer contact, among other exposures. Four occupational groups were studied, in health care (n = 20), retail (n = 22), banking (n = 26), and university secretaries (n = 26), a total of 94 volunteers. Thirty-nine were classified as pain-afflicted in the shoulder and neck, while 55 were pain-free. The subjects' perceptions of biomechanical and psychosocial exposures were established by use of quantitative questionnaires and by explorative interviews with open-ended questions, covering the same themes. Heart rate and trapezius EMG were recorded over a full workday and the following leisure period. Trapezius median and static activity during work were 3.3% and 0.3% EMG(max), only marginally higher than trapezius activity in the leisure period (2.7% and 0.2% EMG(max)). The quantitative questionnaire did not identify any variable that correlated with shoulder and neck pain except perceived general tension. The interviews established that the interaction with clients or customers was an important source of work stress. Such stress appeared to be a complex entity not easily characterized by established psychosocial questionnaires. The physiological variables were at most weakly elevated in periods with high stress as compared to periods with low stress. The authors caution against relying on standardized quantitative questionnaires and/or physiological recordings to characterize work stress in occupations with emotional stress through client/customer service work.     

Visual search for traffic signs: the effects of clutter, luminance, and aging

Latency and eye movement measures were used to examine the effects of aging, clutter, and luminance on visual search for traffic signs embedded in digitized images of driving scenes. Initially 14 older and 14 younger observers classified daytime and nighttime traffic scenes as containing low or high amounts of clutter. Next, an independent sample of 14 younger and 14 older participants searched for traffic signs contained within these scenes. Errors were more common among the elderly. Search efficiency declined with increased clutter and with aging. However, relative to the young, older adults did not suffer disproportionately as a result of increased clutter. The methods developed might be profitably employed to assess sign conspicuity and sign acquisition during driving.     

Effectiveness of rest pauses and cooling in alleviation of heat stress during simulated fire-fighting activity

This study examined whether cooling a fire-fighter with a high velocity fan, during 10 min rest pauses between, and following, 10 min work periods, decreases heat stress during repetitive fire-fighting activity. Twelve professional fire-fighters (mean age 31.8 +/- 6.7 years) completed two, 40 min work/recovery trials in an environmental chamber at 40 degrees C and 70% relative humidity (RH). One trial was termed an enhanced recovery (ER) trial and the other was termed a normal recovery (NR) trial. In both conditions subjects wore full protective clothing and breathing apparatus during the work. In the ER trial a subject removed his protective coat and sat in front of a fan during each recovery period. In the NR trial a subject merely unbuckled his coat and was not cooled by a fan during either recovery period. The group mean metabolic cost (VO2), and the exercise and recovery heart rates were significantly lower (p < or = 0.05) during the ER trial than in the NR condition. Group mean rectal temperature increased by 1.5 degrees C in the NR trial but by only 0.8 degree C during the ER trial. The latter group's more effective cooling indicates the potential of fan cooling to reduce physiological strain and decrease the risk of heat exhaustion during repetitive fire-fighting activity. The results suggest that a fire-fighter's short 10 min exposure to heavy work in a hot environment of 40 degrees C and 70% RH produces minimal heat stress in a healthy fire-fighter. However, a period of fire-fighting exposure greater than 10 min without adequate rest and cooling may lead to a significant accumulation of heat stress and fatigue during further fire-fighting activity, irrespective of physical prowess.     

Mayday,Mayday, Mayday: Using salivary cortisol to detect distress (and eustress!) in critical incident training

The understanding of stress and its impact on human performance is crucial to mitigate human error in the face of a threat. This is especially the case for critical incidents on a ship bridge, where human error can easily lead to severe danger for crew, cargo, and other vessels. To overcome the current limitations of robust objective stress measures that reliably detect (di-)stress under highly noisy conditions, we set out to explore whether salivary cortisol – the stress biomarker in medicine and psychology – is a valuable complementary assessment tool in a high-stress/emergency context. In a controlled within-subjects experiment (N = 12) using a ship bridge simulator, we measured stress levels under three conditions (80 min each): baseline, low stress (open water navigation task in autopilot), and high stress (open water emergency scenario). We sampled salivary cortisol at 10 min intervals in conjunction with heart rate (variability) monitoring, and subjective stress assessments from both participants and expert evaluators. Results validate salivary cortisol as a successful tool for detecting distress. Unlike the other stress measures, salivary cortisol strongly correlated with expert stress assessments (r = 0.856) and overt stress behavior like instances of freezing and missing response cues. Surprisingly, data further revealed decreased salivary cortisol across periods of self-assessed improved performance (i.e., eustress). In fact, data suggests an inverted u-relationship between performance and salivary cortisol. The findings have direct implications for the vast field of emergency training, and serve as a first important validation and benchmark to proceed with real life applications.     

Faces and Pictures: Understanding age differences in two types of graphical authentications

Recall of knowledge-based authentication codes such as passwords and PINs can be problematic, particularly for older adults given the known memory decline associated with ageing. We explored the extent to which recognition-based Graphical Authentication Systems were effective alternatives to PINs and passwords in a study in which users were asked to commit several different codes to memory and recall them at different time periods. Populations of younger and older adults were given face-based and picture-based authentication codes to remember over the course of three weeks. Results show a pronounced age effect, with younger participants outperforming older participants. Older participants fared better with the face-based system over the picture-based system while younger participants exhibited the opposite effect. A significant performance drop was observed for older participants over time, as additional codes were introduced.     

Workload and psychophysiological stress reactions in air traffic controllers

Interactions between workload and psychophysiological stress symptoms were investigated in a population of 205 predominantly male air traffic controllers (ATCs) from the area control centre (ACC) and the airport control tower (TWR) in Zurich and Geneva. Each subject completed two questioning sessions and two working sessions, the first time during a period of low traffic and the second time during a period of high traffic. For the questioning sessions standardized questionnaires were used. For all investigated working sessions, different aspects of the subjective and objective workload were recorded. Before and after each session, a saliva sample for assessing the concentration of secreted cortisol was taken. The questionnaire parameters represented psychological stress symptoms, such as complaints of physical discomfort, depression, negative self-communication, work-increased anxiety, coping behaviour and subjective rating, and interpretation of various aspects of the working situation. The mean values measured were within the normal range, and only a few significant differences between the two questioning sessions were found. However, about 10 to 15% of the ATCs showed elevated values in psychological stress symptoms to an extent indicating that they might have serious stress problems at work and/or in their private life. The investigated working sessions showed that the ATCs' subjective ratings correspond clearly to their cortisol response and the objective workload. Thus, ATCs' complaints regarding excess work stress should be taken seriously.     

Inversion of the Sleep Wakefulness Pattern: Effects on Circadian Variations in Psychophysiological Activation

Abstract

Thirty-six habitually dayworking railway repairmen were exposed to a 3 week period of nightwork. The subjects were studied with respect to circadian rhythms in catecholamine excretion, body temperature, subjective alertness and mood. For half the group the measurements covered one 24 h period before nightwork, the first week of night work, the third week of night work, and the first week after return to day work. For the other half measurements were made during the first and third day week after the night work. During day work weeks all variables exhibited pronounced circadian variation, peaking in the early afternoon, with the exception of body temperature which reached its maximum in the evening. During the first week of night work the day-oriented pattern of adrenaline excretion persisted but the mean 24 h level was increased and day sleep levels were very high. By the third week of night work thecircadian pattern had flattened out at a very low mean level. For noradrenaline excretion considerable adjustment (comparable to an inversion) to night work was seen with high night values. For body temperature, selfrated alertness and mood circadian functions flattened out during night work. It was concluded that all variables were strongly affected by the exposure to night work and that adrenaline excretion indicated a stress response of the organism. With reference to other studies it was also concluded that adrenaline excretion is not easily phase-shifted through a three week spell on night work, while noradrenaline in contrast appears to adjust very rapidly.     

Further studies of shoulder and neck pain and exposures in customer service work with low biomechanical demands

The aim of the study was to establish insight into work exposures that cause shoulder and neck pain among occupational groups that have low biomechanical exposure and experience work stress from client/customer contact, among other exposures. Four occupational groups were studied, in health care (n = 20), retail (n = 22), banking (n = 26), and university secretaries (n = 26), a total of 94 volunteers. Thirty-nine were classified as pain-afflicted in the shoulder and neck, while 55 were pain-free. The subjects' perceptions of biomechanical and psychosocial exposures were established by use of quantitative questionnaires and by explorative interviews with open-ended questions, covering the same themes. Heart rate and trapezius EMG were recorded over a full workday and the following leisure period. Trapezius median and static activity during work were 3.3% and 0.3% EMG_max, only marginally higher than trapezius activity in the leisure period (2.7% and 0.2% EMG_max). The quantitative questionnaire did not identify any variable that correlated with shoulder and neck pain except perceived general tension. The interviews established that the interaction with clients or customers was an important source of work stress. Such stress appeared to be a complex entity not easily characterized by established psychosocial questionnaires. The physiological variables were at most weakly elevated in periods with high stress as compared to periods with low stress. The authors caution against relying on standardized quantitative questionnaires and/or physiological recordings to characterize work stress in occupations with emotional stress through client/customer service work.     

Driving in an urban environment,the stress response and effects of exercise

Driving may be detrimental to health, with one hypothesis suggesting that driving may elicit an acute stress response and, with repeated exposures, may become a chronic stressor. The present study examined the stress response to driving and the effectiveness of a prior exercise bout in dampening this response. Twenty healthy adults performed three tasks: control, driving and exercise plus driving. Heart rate (HR), heart rate variability (HRV), blood pressure (BP) and cortisol were measured to quantify the acute stress response to each condition. Data indicated a stress response to driving: HR was elevated and HRV was reduced during the driving task compared with control. HR was elevated and HRV was reduced comparing the exercise plus driving with the driving condition. BP and cortisol were not different among conditions. The potential of interventions, such as exercise, to counter daily stressors should be evaluated to safeguard long-term health.

Practitioner Summary: this study confirms that driving induces a stress response, with the exercise intervention providing mixed results (an increase in cardiovascular measures and a decrease in cortisol measure trending significance). Given the known consequences of stress and evidence that exercise can mitigate acute stress, further evaluation of exercise interventions is recommended.     

Heart rates of surgeons in theatre

Abstract

The heart rates often surgeons were measured during work, leisure and sleep over 4 × 24 hour periods. Oxygen consumption was measured while the surgeons were Operating; the environmental conditions in the operating theatres were monitored. In addition, each surgeon performed two multi-staged exercise tests to ascertain the oxygen-consumption/hcart-rate relationship. The findings were that oxygen consumption was rather low (0 26-0.411min^?1) during operations, heart rates during operating were commensurate with the oxygen consumption, and the additional factors of arm work and isometric contractions, suggesting that little of the heart rate during operating resulted from mental stress.     

Effects of Chinese character size,number of characters per line,and number of menu items on visual search task on tablet computer displays for different age groups

The goal of this study was to investigate the effects of Chinese character size, number of characters per line, and number of menu items on visual search task performance on a tablet computer for different age group users. Forty-two participants participated the visual search experiment. Gender, age group (younger, middle-aged, and older), Chinese character size (15, 17, 19, 21, 23, and 25 point), number of characters per line (2–5 characters, 9–14 characters, and 15–18 characters), and number of menu items (5, 7, 9, 11, and 13 items) were the independent variables. The dependent variables included search time and error rate. Gender had a large effect size on search time. Female participants had a faster search time than male participants. Significant differences and large effect sizes were found in search performance for different character sizes, number of characters per line, and number of menu items. Nine to fourteen characters per line achieved the fastest search time and lowest error rate. The fastest search time was for a 19-point character size in the younger group; 21-point character size in the middle-aged group; and 23-point character size in the older group. Besides, the fastest search time was found when showing 9 items in the younger group; 7 items in the middle-aged group; and 5 items in the older group. The optimum visual search performance was achieved with 19-point character size showing 9 items and 9–14 characters per line for the younger group; 21-point character size showing 7 items and 9–14 characters per line for the middle-aged group; and 23-point character size showing 5 items and 9–14 characters per line for the older group. The results provide useful information for tablet computer interface-presentations for different age group users.     

Cardiovascular state changes during performance of a simulated ambulance dispatchers' task: Potential use for adaptive support

Adaptive support has the potential to keep the operator optimally motivated, involved, and able to perform a task. In order to use such support, the operator's state has to be determined from physiological parameters and task performance measures. In an environment where the task of an ambulance dispatcher was simulated, two studies have been carried out to evaluate the feasibility of using cardiovascular measures for adaptive support. During performance of this 2–3 h lasting planning task, a pattern of results is found that can be characterized by an initial increase of blood pressure and heart rate and a decrease of heart rate variability (defense reaction pattern) followed by an ongoing increase of blood pressure counteracted by a decrease in heart rate. This pattern can be explained by an augmented short-term blood pressure control (baroreflex), which is reflected in an increase of baroreflex sensitivity. Additionally, in this latter phase heart rate variability (HRV) increases as a function of time, while blood pressure variability decreases. In the two studies performed, the baroreflex pattern was consistent for all the relevant variables.In both studies there were periods with high and low workload. Effects of task load are mainly reflected in the variability measures, while in the second study, additionally, blood pressure level was higher during periods with high task demands.The conclusion of the studies is that consistent cardiovascular response patterns can be recognized during this semi-realistic planning task, where variability measures are most sensitive to task demand changes, while blood pressure and baroreflex sensitivity are most informative with respect to cardiovascular state changes. These findings can be seen as a great potential benefit for future use in adaptive support applications.     

Microbreak length, performance, and stress in a data entry task

The effects of brief rest pauses on performance and well-being were evaluated for a highly repetitive, data entry task. Experienced data entry operators (N = 20) performed the task in a two-day experiment in a simulated office environment. Each day was divided into six, 40-min work periods. Subjects took a brief rest pause at the workstation (microbreak) in the middle of each work period. Subjects were instructed to terminate this microbreak when ready to resume work. Keystroke rate, error rate, correction rate, heart rate and heart rate variability were scored for each half of the work period. In addition, mood states before and during the work period were assessed. Microbreaks were found to average 27.4 s in duration. High ratings of fatigue and boredom during the work period were associated with longer microbreaks, suggesting that the break period was self-adjusted relative to mood state. In addition, correction rate and heart rate were lower following long microbreaks, implying that the degree of recovery was linked to the length of the microbreak. Comparison of keystroke output and correction rate before and after the microbreak, however, revealed that performance worsened after the microbreak, suggesting that subjects terminated microbreaks before complete recovery could occur.     

Age-related biomechanical differences during asymmetric lifting

This study investigated age-related biomechanical differences during asymmetric lifting. Eleven younger and twelve older participants were instructed to lift loads of different weights to an asymmetric destination. The trunk kinematics and low back moments were examined. The results showed that older adults adopted safer lifting strategies compared with younger adults. Specifically, the peak trunk sagittal flexion angle was 32% lower and the peak trunk transverse twisting angle was 22% lower in older adults compared with those in younger adults. It was also found that the average low back moment in the deposit phase was 32% higher in older adults than that in younger adults, most probably due to the age-related increased body weight. Based on these findings and the fact of age-related decreased muscle strengths, physical exercise programs were suggested to be more effective than instructions of safe lifting strategies in LBP risk reduction during asymmetric lifting for older adults. For younger adults, safe lifting strategy instructions might be effective to reduce risks of LBP.     

The effect of age on the hand movement time during machine paced assembly tasks for female workers

The share of older adults in the workforce is increasing in many countries. In the manufacturing industry a high proportion of assembly tasks are machine paced. Previous studies have shown that older adults tend to have longer movement times than younger adults when working at a self-selected pace. However, it is unclear whether older adults can obtain the same hand movement time as a younger group when performing machine paced work at the assembly line. In the current study, 10 older and 10 younger female participants performed simulated light-duty assembly tasks during which the hand movement times were recorded. The results showed that the older participants were capable of working at the set pace and there was no significant difference between age groups in hand movement times (989.9 msec vs. 986.6 msec, p = 0.5647). A likely explanation to the results is that the older participant had to work closer to their physical limits or capacity in order to compensate for the age effect on movement time.     

Comparative study of the effects of auditory, visual and multimodality displays on drivers' performance in advanced traveller information systems

A simulator study was conducted to compare 16 younger (mean age 22 years) and 16 older (mean age 68 years) drivers' ratings of workload (time, visual, psychological stress) and performance of navigation and button-pushing (identification of vehicle or road hazards) tasks under both high- and low-load driving conditions when simple or complex advanced traveller information (ATI) was presented visually only, aurally only or by multimodality (visual and auditory) display. For all participants, both the auditory and multimodality displays produced better performance in terms of response times, total number of correct turns and subjective workload ratings than those of using the visual-only display. Participants using the multimodality display also made the fewest errors related to push-button and navigation tasks, and controlled their vehicles properly. The visual display led to less safe driving, apparently because it imposed higher demands on the drivers' attention. An age effect was found in the present study, with younger drivers performing better and reporting less stress than older drivers. Notably, however, use of the multimodality display significantly improved the older drivers' performance in the button-pushing task.