Relationship between maximum acceptable work time and physical workload

For safe job design, it is necessary to know the maximum acceptable work time (MAWT) for a given workload. The aim was to establish the relationship between MAWT and physical workload. Cycling tests at six different work rates relative to personal maximum working capacity were performed by 12 young adults in the laboratory. The oxygen uptake (VO₂) in the per cent maximum aerobic capacity (%VO_2max), relative heart rate (RHR) and relative oxygen uptake (RVO₂) were collected throughout the test. MAWT was determined by observing the heart rate data during the test. The results showed that MAWT was negatively correlated with %VO_2max, RHR and RVO₂(p<0.01). Three exponential regression models were obtained and all their R² >0.80. These models suggest that long-hour shifts (>10 h) should assign a lower work intensity than for an 8-h workday. It is also logical that the workload limit for a 4-h work shift could be set at about 10%VO_2max higher than the suggested limit for an 8-h workday.     

Complete recovery time after exhaustion in high-intensity work

This study was aimed to investigate complete recovery time (CRT) after exhaustion in high-intensity work. Twenty-four subjects were divided into two groups based on the cardiorespiratory capability index, which was measured in a maximum capacity test. Each subject then performed two cycling tests (at 60% and 70% maximum working capacity). The subject continued cycling until exhaustion in each test and then sat recovering until he/she no longer felt fatigue or until the oxygen uptake (VO2) and heart rate (HR) returned to their baselines, whichever was longer. The results indicated that HR required the longest time to recover and, consequently, HR data were adopted to set the CRT. The CRT was significantly correlated with the cardiorespiratory capability index and the relative workload indices: RVO2 and RHR. The RVO2 was the average elevation in VO2 during work from the resting level as a percentage of maximum VO2 reserve. The RHR's definition was similar to that of RVO2. Based on the obtained CRT-prediction model, the CRT for a high-cardiorespiratory-capability person was 20.8, 22.1, 23.4, and 24.7 min at 50%, 60%, 70%, and 80% RHR levels, respectively. These suggested CRT values should be increased by 10 min for a low-cardiorespiratory-capability person.     

Effect of toeclip use during cycle ergometry on ventilatory threshold and VO2 max in trained cyclists and runners

The purpose of this study was to investigate the effects of the use of toeclips on the ventilatory threshold (VT) of cyclists and runners during cycle ergometry. Ten competitive cyclists and ten well-trained runners performed two continuous maximal cycle ergometer tests, once with toeclips and once without toeclips. Respiratory data were collected every 20 s and used to determine VT and VO2 max. For cyclists, the mean (congruent to SEM) oxygen uptake at VT (VO2, VT) was greater during the trial with toeclips (48.8 +/- 1.9 ml kg-1 min-1 and 46.9 +/- 1.9 ml kg-1 min-1 during cycle ergometry with and without toeclips, respectively; p less than 0.05). No significant difference in VO2, VT was noted between trials for runners. The cyclists also demonstrated a higher VO2 max during the trial with toeclips (58.8 +/- 3.0 ml kg-1 min-1) compared to the trial without toeclips (54.4 +/- 2.0 ml kg-1 min-1; p less than 0.05). When expressed relative to VO2 max (%VO2 max) the VT during the toeclip trial for cyclists was significantly decreased (p less than 0.05). These data suggest that the cyclists in this study developed specific adaptations related to the use of toeclips, and the use of toeclips during cycle ergometry is therefore recommended. We recommend that future studies report results with VT expressed in both absolute (VO2) and relative (%VO2 max) terms.     

Effect of the number of two-wheeled containers at a gathering point on the energetic workload and work efficiency in refuse collecting

The effect of the number of two-wheeled containers at a gathering point on the energetic workload and the work efficiency in refuse collecting was studied in order to design an optimal gathering point for two-wheeled containers. Three sizes of gathering points were investigated, i.e. with 2, 16 and 32 two-wheeled containers at a gathering point. The collecting of two-wheeled containers was simulated in a test circuit. The energetic workload was quantified by the parameters oxygen uptake (l min⁻¹), heart rate (beats min⁻¹) and perceived exertion. The work efficiency was quantified as the time it took to collect 32 two-wheeled containers per time period. The maximum acceptable amount of two-wheeled containers collected during an 8-h working day was estimated using the energetic criterion of a maximum oxygen uptake of 30% VO_2max. The size of the gathering point had no effect on the oxygen uptake, heart rate or perceived exertion. However, the number of two-wheeled containers per collecting period (work efficiency) and the maximum acceptable amount during an 8-h working day were higher in the conditions with 16 and 32 two-wheeled containers at a gathering point compared to the condition with the 2 two-wheeled containers at a gathering point.     

Characterization of the metabolic demands of simulated shipboard Royal Navy fire-fighting tasks.

The purpose of this study was to quantify the metabolic demand of simulated shipboard fire-fighting procedures currently practised by men and women in the Royal Navy (RN) and to identify a minimum level of cardiovascular fitness commensurate with satisfactory performance. Thirty-four males (M) and 15 females (F) volunteered as subjects for this study (n=49). Maximal oxygen uptake (VO2max) and heart rate (fcmax) of each subject was assessed during a standardized treadmill test. During the main trials, volunteers were randomly assigned to complete several 4-min simulated shipboard fire-fighting tasks (boundary cooling (BC), drum carry (DC), extinguisher carry (EC), hose run (HR), ladder climb (LC)), at a work rate that was endorsed as a minimum acceptable standard. Heart rate (fc) and oxygen uptake (VO2) were recorded at 10-s intervals during rest, exercise and recovery. Participants completed all tasks within an allocated time with the exception of the DC task, where 11 subjects (all females) failed to maintain the endorsed work rate. The DC task elicited the highest (p<0.01) group mean peak metabolic demand (PMD) in males (43 ml min(-1) kg(-1)) and females (42 ml min(-1) kg (-1)) who were able to maintain the endorsed work rate. The BC task elicited the lowest PMD (23 ml min(-1) kg(-1)), whilst the remaining three tasks elicited a remarkably similar PMD of 38-39 ml min(-1) kg(-1). The human endurance limit while wearing a self-contained breathing apparatus (SCBA) dictates that RN personnel are only able to fire-fight for 20-30 min, while wearing a full fire-fighting ensemble (FFE) and performing a combination of the BC, HR and LC tasks, which have a group mean metabolic demand of 32.8 ml min(-1) kg(-1). Given that in healthy subjects fire-fighting can be sustained at a maximum work intensity of 80% VO2max when wearing SCBA for this duration, it is recommended that all RN personnel achieve a VO2max of 41 ml min(-1) kg(-1) as an absolute minimum standard. Subjects with a higher VO2max than the above quoted minimum are able to complete the combination of tasks listed with greater metabolic efficiency and less fatigue.     

Physiological responses of firefighters and performance predictors during a simulated rescue of hospital patients

There is incomplete information about how physically demanding rescue work may be. The aim therefore of this paper was to examine the physiological responses of firefighters during a simulated rescue of hospital patients and to relate the firefighters' performance to their endurance, strength and working technique. Fourteen part-time male firefighters with a maximal oxygen uptake (VO(2max)) of 4.4 +/- 0.3 l/min (mean +/- SD) served as subjects in this study. First, each firefighter ascended six floors (a 20.5 m vertical ascent) carrying tools, wearing protective clothing and a breathing apparatus, an extra mass of 37 kg. He thereafter 'rescued' six persons by dragging each person on a fire-sheet on a flat floor. The technique used was recorded and the O(2) uptake and the heart rate were measured continuously during the whole operation. The blood lactate concentration and the subjective rating of perceived exertion were measured during and just after the rescue. The VO(2max) and the muscle strength were measured in the laboratory. The whole operation was carried out in the course of 5-9 min. The operation was a virtual all-out effort and the peak blood lactate concentration was 13 +/- 3 mmol/l. The peak oxygen uptake was 3.7 +/- 0.5 l/min (84% of the VO(2max)) during the operation. Large and heavy firefighters carried out the task faster than smaller ones. The VO(2max) in absolute terms and the dragging technique used were both related to the rescue performance. Rescuing patients at a hospital was physically very demanding and the time needed to complete the task depended on the VO(2max) in absolute values and the working technique used. A minimum VO(2max) of 4 l/min for firefighters was recommended.     

Distribution and determinants of maximal physical work capacity of Korean male metal workers

The distribution of maximal physical work capacity (MPWC) can be used to establish an upper limit for energy expenditure during work (EEwork). If physically demanding work has wearing effects, there will be a negative relationship between MPWC and workload. This study was conducted to investigate the distribution of MPWC among Korean metal workers and to examine the relationship between workload and MPWC. MPWC was estimated with a bicycle ergometer using a submaximal test. Energy expenditure was estimated by measuring heart rates during work. The study subjects were 507 male employees from several metal industries in Korea. They had a lower absolute VO2max than the Caucasian populations described in previous studies. The older workers had a lower physical capacity and a greater overload at work. A negative relationship was found between MPWC and workload across all age groups. Upper limits for EEwork for all age groups and for older age groups are recommended based on the 5th percentile value of MPWC.     

The physical strain of dairy farming

The aim of this study was to estimate the physical stress and strain in diary farming, using ambulatory heart rate and oxygen consumption measurements. The rate of perceived exertion was estimated with Borg scale. The maximal oxygen consumption was measured in the laboratory. The study group consisted of eight male and 15 female farmers. The handling of feed and manure was the heaviest work task in dairy farming. The aerobic capacity (VO2 max) of female farmers (26 +/- 3 ml/min/kg) was below average, and their work required over 50% of VO2 max during most of the tasks. The VO2 max of male farmers (32 +/- 10 ml/min/kg) was moderate, and most work tasks required below 50% of VO2 max. The mean heart rate in dairy farming tasks was 99 beats min-1 in men and 116 beats min-1 in women. However, according to the rate of perceived exertion, the mean experienced the same work tasks as subjectively more heavy than did the women. The physical strain of female farmers in dairy farming seems to be too high because of heavy work tasks and relatively low VO2 max of women. Special attention should be paid to these factors in the occupational health services for farmers.     

Hyperoxia improves maximal exercise with the self-contained breathing apparatus (SCBA)

The effects of hyperoxia on maximal exercise while breathing from a self-contained breathing apparatus (SCBA) were studied in 25 males. Each participant completed three graded exercise tests (GXT) for the assessment of maximal oxygen uptake (VO(2max)): two with 20.95 +/- 0.28% O(2) and the third (GXT(40)) while breathing hyperoxia (40.64 +/- 1.29% O(2)). No significant differences were found between the two normoxic tests, except for a 16W increase in maximal power output (PO(max)) in the second trial (GXT(21)). Compared to GXT(21), hyperoxia significantly increased VO(2max) and PO(max) by 10.0 +/- 3.8% and 10.2 +/- 7.1%, respectively. This was likely due to an increase in O(2) delivery as suggested by the significantly higher oxyhemoglobin saturation. The increase in VO (2max) with hyperoxia was similar to the increase in carbon dioxide production (9.3 +/- 6.5%). No other significant di.fferences were found at maximal exercise. However, at the intensity that elicited VO(2max) in GXT(21), pulmonary ventilation and SCBA mask pressure were significantly lower during GXT(40), suggesting a decrease in the work of breathing. These findings could have significant implications for occupations that involve heavy work with SCBA.     

Physiological strain during kitchen work in relation to maximal and task-specific peak values

Six female and three male subjects from a hospital kitchen volunteered for the study. The subjects were working on a conveyor belt collecting and sorting dirty plates, glasses and cutlery for cleaning. In the study, a medical examination, a maximal clinical exercise test with a 12-lead electrocardiogram (ECG) and a maximal arm cranking test were performed in the laboratory. Further, each subject was studied for 30 min during a normal work shift in the kitchen. Oxygen uptake (VO2) and heart rate (HR) were continuously registered. During the work period, a rating of perceived exertion (RPE) was asked at the 5th, 15th and 30th minute. Physiological responses were measured by a portable system (K4) both in the laboratory and in the field. VO2 and HR measured in the field were proportioned to corresponding maximal values during cycling and to peak values during arm-cranking. The mean VO2 for the male and the female subjects during kitchen work was 0.65 +/- 0.16 l min-1. This corresponded to 24% of VO2max and to 41% of VO2peak during arm-cranking. The difference was significant (p < 0.001). Owing to a magnetic field at the conveyor belt, reliable HR values were obtained only from the female subjects. The mean HR during work among the female subjects was 101 beats min-1. It corresponded to 55% of HRmax and 67% of HRpeak during arm-cranking (p < 0.05). The present study shows that the relative work intensity is markedly higher when it is expressed relative to the corresponding muscle group's VO2peak instead of the VO2max. Similar difference was also seen in the HR response. More task-specific testing of physical capacity may provide improved evaluation of physical strain in a job.     

Reliability of the assessment of the oxygen/heart rate relationship during a workday

The purpose of the present study was to evaluate the reliability of the oxygen consumption/heart rate (VO(2)/HR) relationship used to estimate energy expenditure during a workday. Before and after a 6-10 h work shift, the VO(2)/HR relationship was measured in 57 workers (28 female, 29 male) in our laboratory. VO(2) was similar before and after the shift at HR of 100 and 125 beats per minute (bpm). However, the VO(2)/HR relation and perceived exertion (RPE) became less accurate after a work shift as VO(2) and RPE were, respectively, increased at HR above 150 and 125 bpm. Increase of RPE for a same exercise intensity was higher in female subjects. Our results suggest good reliability of the VO(2)/HR relationship at HR usually found in workplaces.     

Oxygen consumption during fire suppression: error of heart rate estimation.

Ten male firefighters were tested on a treadmill to determine their heart rate (HR) x oxygen consumption (VO2) relationship. These men then performed a simulated fire suppression protocol during which HR and VO2 were measured simultaneously by a portable physiological monitoring system. Average VO2 in the simulated setting was 31.0 +/- 7.0 ml.kg-1.min-1 at a HR of 176 +/- 9 bpm. This VO2 was significantly (p less than or equal to 0.05) less than the VO2 that would have been predicted by treadmill testing (38.9 +/- 5.0 ml.kg-1.min-1) at a corresponding HR. Fifty-nine per cent of this variability could be accounted for by regression analysis. Firefighters worked on average at 73 +/- 10% VO2 max with a range of 54% to 88%. There was a significant (-0.82; p less than or equal to 0.05) inverse relationship between performance time of the fire suppression protocol and the relative intensity of VO2 max at which the firefighters worked. These findings indicate that the prediction of energy expenditure from HR is not straightforward in fire suppression settings. Furthermore, the relative intensity of work firefighters self-select is variable and should be considered as an additional physiological determinant of work behaviour.     

Comparison of work rates, energy expenditure, and perceived exertion during a 1-h vacuuming task with a backpack vacuum cleaner and an upright vacuum cleaner

The purpose of this study was to evaluate two types of industrial vacuum cleaners, in terms of cleaning rates, energy expenditure, and perceived exertion. Twelve industrial cleaners (six males and six females, age 28-39 yr) performed two 1-h vacuuming tasks with an upright vacuum cleaner (UVC) and a backpack vacuum cleaner (BPVC). Measures for oxygen uptake (VO2) and ratings of perceived exertion (RPE) were collected continuously during the 1-h vacuuming tasks. Cleaning rates for the UVC and BPVC were 7.23 and 14.98 m2min(-1), respectively. On a separate day subjects performed a maximal treadmill exercise test to determine their maximal aerobic capacity (peak VO2). Average absolute energy costs (in Metabolic equivalents), relative energy costs of the vacuum task compared to the subjects' maximal aerobic capacity (% peak VO2), and RPE responses for the 1-h vacuuming tasks were similar between vacuum cleaners, but % peak VO2 and RPE values differed between genders. These results indicate that the BPVC was more efficient than the UVC. With the BPVC, experienced workers vacuumed at a cleaning rate 2.07 times greater than the UVC and had similar levels of energy expenditure and perceived effort, compared to the slower cleaning rate with the UVC.     

The physical and physiological workload of refuse collectors

In order to secure a safer and healthy work situation, the heavy physical loads imposed on 23 refuse collectors (aged 26-54) working in the city of Haarlem, in The Netherlands, were studied in a series of three experiments between 1984 and 1987. The aims were respectively (1) to study the load for workers collecting dustbins or polythene bags; (2) to introduce changes to reduce the load to avoid exceeding the overload criteria by individual refuse collectors; and (3) to investigate the effects of interventions to improve the efficiency of refuse collecting. The maximal isometric lifting force (Fmax) and the maximal aerobic power (VO2max) of 23 refuse collectors were measured in the laboratory. Fmax was measured with an isometric dynamometer pulling with one arm from the floor; the mean value was 912 (+/- 127)N. VO2max was measured running on a treadmill; the mean value was 43.3 (+/- 0.8)ml O2 per kg body mass per min. The physical load on the oxygen transport system was measured through work analysis and by a continuous registration of the heart rate over three working days. Criteria for overload were set at a mean external load of 20% Fmax and a mean energy expenditure of 30% VO2max and an energy expenditure of 50% VO2max or more for a maximum of 60 min per day. Replacement of dustbins by polythene bags resulted in a 70% increase in the total amount of refuse collected, an increase in throwing frequency, but a lower mean load per throw, and no significant differences in the mean heart rate over the working day. When polythene bags were used the mean values did not exceed the overload criteria, but 39% of the individual collectors did have a workload that was too high with respect to one of the criteria. In the last experiment the collectors were advised to reduce their work load by (a) lifting no more than two bags at a time; (b) reducing their walking pace; and (c) taking more breaks. Although compliance with the recommendations was good, and the weight lifted and the walking speed decreased, the physiological load remained the same. This may have been caused by a 15% increase in the total amount of refuse that had to be collected at that time.     

Performance evaluation of lower extremity disabled people with reference to hand-cranked tricycle propulsion

A study was designed to evaluate physiological cost and work performance of lower extremity disabled people with reference to hand-cranked tricycle propulsion. Eleven volunteers took part in this study. For an average body weight of 39.7 kg, VO2 max (arm cranking) was only 0.777 l/min at STPD. The pulmonary demand and oxygen uptake of the disabled subjects during tricycle propulsion at 8.45 +/- 0.6 km/h corresponded to about 70% of their maximal response; hence, work stress was categorised as heavy. Mechanical efficiency of cranking was best when a hand-rim propulsion system was arranged for two-arm cranking at the heart level of the disabled person and at a cranking pace of 60 rev/min.     

Energy cost and physiological responses of males snowshoeing with rotating and fixed toe-cord designs in powdered snow conditions

The purpose of this study was to measure the energy cost and physiological responses of males while snowshoeing with two separate toe-cord designs (rotating toe-cord system vs. fixed toe-cord design) in powdered snow conditions. Eight males snowshoed at self-selected intensity for two, 1600 m trials in two snowshoes, with a rotating toe-cord system and a fixed-toe cord design. It was found that heart rate (HR) (140 vs. 134 beats min(-1)), oxygen consumption (VO(2)) (63.4 vs. 34.0 ml kg(-1)min(-1)), energy cost (56.0 vs. 52.4 kJ min(-1)), and ratings of perceived exertion (RPE) (13 vs. 12) were significantly (p < 0.05) higher while snowshoeing with the fixed toe-cord design than with the rotating toe-cord system. Snowshoeing with the rotating toe-cord system at an average speed of 3.96 km h(-1) produced mean VO(2) values that were 56% of VO(2) max, while snowshoeing with the fixed toe-cord design at 3.86 km h(-1) evoked mean VO(2) values that were 60% of VO(2) max. Mean HR while snowshoeing with the rotating toe-cord system was 70% of HR max, while the mean HR when snowshoeing with the fixed toe-cord design was 74% of HR max. These findings suggest that snowshoeing with a rotating toe-cord system results in lower cardiorespiratory strain in powdered snow conditions compared to snowshoeing with a fixed toe-cord design.     

Metabolic and cardiovascular cost,and perceived effort over an 8 hour day when lifting loads selected by the psychophysical method

The psychophysical method used by Snook [576] to determine maximum acceptable workloads for repetitive lifting during an 8 hour workday in industrial populations was evaluated for application in military ergonomics. Under the conditions of the present experiment, the mean load selected by 10 soldiers (17-5 kg) was lower than reported by Snook [576] for industrial workers, and by Garg and Saxena [243] for college students. When the soldiers lifted and lowered their selected load for an 8 hour workday, the average heart rate was 92 beats min^?1 and the mean oxygen cost was 21% of their maximum oxygen uptake (determined for uphill treadmill running). There was no evidence of cardiovascular, metabolic or subjective fatigue. The results indicate that with good subject co-operation and firm experimental control in a laboratory, the psychophysical method can identify loads that soldiers can lift repetitively for an 8 hour workday without metabolic, cardiovascular or subjective evidence of fatigue, but it is not clear to what extent this is a maximum workload consistent with a physiological steady state.     

Maximum acceptable repetitive lifting workload by Chinese subjects

This study used psychophysical methods to determine the acceptable mean maximum lifting workload for eight Chinese young male subjects, and examined the effects of lifting technique (including freestyle, stoop and squat), lifting frequency (including 2, 3, 4, 5 and 6 lifts/min) and physical characteristics on the maximum acceptable workload. The results are described as follows: (1) The maximum acceptable weights selected by subjects varied from 11.34 to 18.33 kg with changes in lifting technique and frequency. These data were lower than those previously obtained; (2) The upper limit of physiological tolerance over an 8 h workday was also generally lower than previously suggested. However, this upper limit varied with changes in lifting technique and frequency, and in some circumstances it was the same as or even higher than previous limit; (3) Lifting efficiency was affected significantly by technique and frequency. The rank order of efficiency for three lifting techniques were freestyle, stoop and squat. Efficiency was greatest when lifting frequency was between 5 and 6 lifts/min; and (4) The correlations between the maximum acceptable workloads selected by subjects and anthropometric sizes were significant, but those between maximum acceptable workload and isometric strength were not.     

Measurement of oxygen consumption with the Cosmed K2: a comparative study

An instrument that accurately measures oxygen consumption (VO2) during field performance is valuable for investigations of physiological workload. Cosmed (Rome, Italy) has introduced such an instrument, the Cosmed K2. In this study the Cosmed K2 was compared with the Oxyconbeta (Jaeger, Breda, The Netherlands) to investigate the reliability of the ventilatory data obtained with the Cosmed K2. The measured values of the Cosmed K2 ranged from 780 to 3700 ml min(-1). When measuring light to heavy work situations (VO2 < 1400 ml min(-1)), the Cosmed K2 did not reproduce very well. This random error prohibits accurate measurements on individuals for those workloads. In very heavy to extremely heavy work situations (VO2 > 1500 ml min(-1)) the Cosmed K2 measured oxygen consumption values that were too low. This systematic error can be corrected. A correction relation was calculated by comparing the results of the Cosmed K2 with those of the Oxyconbeta in a laboratory setting. In the field of ergonomics, where mean values of workloads have to be determined, the Cosmed K2 can be used. In the field of sports, where individual improvement is important, the Cosmed K2 can be useful to measure oxygen consumption at moderate and high strain levels (VO2 > 1500 ml min(-1)).     

Maximum acceptable repetitive lifting workload by Chinese subjects

This study used psychophysical methods to determine the acceptable mean maximum lifting workload for eight Chinese young male subjects, and examined the effects of lifting technique (including freestyle, stoop and squat), lifting frequency (including 2, 3, 4, 5 and 6 lifts/min) and physical characteristics on the maximum acceptable workload. The results are described as follows: (1) The maximum acceptable weights selected by subjects varied from 11-34 to 1833?kg with changes in lifting technique and frequency. These data were lower than those previously obtained; (2) The upper limit of physiological tolerance over an 8?h workday was also generally lower than previously suggested. However, this upper limit varied with changes in lifting technique and frequency, and in some circumstances it was the same as or even higher than previous limit; (3) Lifting efficiency was affected significantly by technique and frequency. The rank order of efficiency for three lifting techniques were freestyle, stoop and squat. Efficiency was greatest when lifting frequency was between 5 and 6 lifts/min; and (4) The correlations between the maximum acceptable workloads selected by subjects and anthropometric sizes were significant, but those between maximum acceptable workload and isometric strength were not.