Relationship between pulse rate and energy expenditure during graded work at different temperatures

Abstract

Pulse rate and energy expenditure were measured on fifteen male subjects who had been given ergometer cycling of ‘O’ and 32·6 W to 97·8 W in three temperatures of 22°C, 30°C, and 37°C. The variation in pulse rate of each graded work period was compared with the variation in energy expenditure for each environmental temperature. The pulse rate was significantly increased with the rise of environmental temperature (p << 0·01) whereas the energy expenditure (kJ min^?1) was consistently or effectively decreased with higher graded work. However, a correlation was obtained between the pulse rate and energy expenditure during graded work up to a limit of 150 beats min^?1, 160 beats min^?1, and 170 beats min^?1 in temperatures of 22°C, 30°C, and 37°C respectively. The results were analysed by computing the analysis of variance and regression equation evaluated for each temperature, indicating that independent regression lines having two components, one above 95 and other below 95 beats min^?1 were required in each set of temperature. The percentage error between observed and predicted values (pooled) or energy expenditure for the two ranges of pulse rates varied from 0·3 to 11·5 and from 0·5 to 9·5 respectively in the three temperatures.     

Habitual Physical Activity of Rural Burmese Women

Abstract

Habitual physical activity of 16 Burmese women aged 19-24 yrs residing in a rural Burmese village was assessed by the questionnaire method together with the diary method and heart rate measurements. The pattern of their habitual physical activity had a seasonal variation. Their heart rate during transplanting paddy, pounding glutinous paddy and carrying water ranged from 108-132, 119-144 and 120-168 beats min_?1 respectively. Their work intensity expressed as a percentage of their maximal aerobic power varied from 1304 to 79-47. It was found that the habitual physical activity of these rural women could contribute a positive effect towards their physical performance capacity.     

Self-paced work in sleep deprived subjects

The effect of sleep deprivation and physical fatigue on self-paced work was determined in two experiments simulating sustained combat engineer operations. In experiment A, four subjects went without sleep for 69 hours. During this period they performed only four physically demanding tasks, three of them in the last 24 hours. Continuous recordings of heart rate (HR) indicated that sleep deprivation, in the absence of physical fatigue, had no effect on work intensity and the period of fatiguing work (HR above 120 beats min^?1). In experiment B, six subjects carried out a full schedule of physically demanding tasks during a period of sleep deprivation lasting 47 hours. Some of the tasks were repeated at least once so that the effects of sleep loss and physical fatigue could be assessed. For the first 14 hours of experiment B, the subjects worked at an average hr of 120 beats min^?1, equivalent to an energy expenditure of 35-40% of maximal oxygen uptake in fit young men. In the remainder of the sustained operation, work intensity declined and the subjects worked at hrs above 120 beats min^?1 for shorter periods. Rating scales confirmed that these changes coincided with the development of physical fatigue. Since sleep deprivation was without effect in experiment A, the decline in self-paced work intensity in experiment B was attributed to the combination of physical fatigue and sleep deprivation.     

The physical strain of dairy farming

The aim of this study was to estimate the physical stress and strain in dairy 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 ([Vdot]O₂ max) of female farmers (26 ± 3 ml/min/kg) was below average, and their work required over 50% of [Vdot]0₂ max during most of the tasks. The [Vdot]0₂ max of male fanners (32±10 ml/min/kg) was moderate, and most work tasks required below 50% of [Vdot]0₂ 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 men 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 [Vdot]0₂ max of women. Special attention should be paid to these factors in the occupational health services for farmers.     

Aerobic capacity of severely disabled Indians

To study the oxygen uptake capacity, the arm crank ergometer test was administered at three different loads, 25,37·5 and 50 W, on seven severely disabled subjects, and their cardiorespiratory responses were compared to that of nine normal subjects (work loads, 25, 50 and 75 W). Values of [Vdot]O₂ of the disabled subjects corresponding to heart rates of 150 and 180 beats min^?1 were significantly lower than those of the normal subjects, when expressed in l min^?1, but disappear when the results are expressed in ml kg min^?1. The observations indicate a reduced work capacity and a capacity for increasing the stroke volume of the disabled subjects.     

Manual lifting load limit equation for adult Indian women workers based on physiological criteria

A comprehensive equation for the evaluation of a maximum load limit for manual load lifting has been developed for the first time for Indian adult female workers, based on a physiological criterion due to the limitation of applicability of the NIOSH (1991) equation. Ten adult female workers, who had been engaged in building construction activities for at least 7 years participated in this study. The cut-off value was selected as the working heart rate corresponding to the 33% level of maximum aerobic power (i.e. V′O₂ max.) of this population, which was equivalent to a heart rate of 101.6 beats.min^???1. An equation was developed based on the effects of the following three lifting parameters on working heart rate: vertical height (knee, waist, shoulder and maximum reach height), lifting frequency (1, 4, 7 and 14 lifts.min^???1), and load weight (5, 10 and 15?kg). The variations of the specific lifting parameter values were selected from field observations. From this equation, the maximum load limit was calculated as 15.4?kg and the workers give this a psychophysical rating as in the moderate to heavy category.     

Heart rate strain indices in Greek steelworkers

Abstract

The heart rate strain of 14 Greek steelworkers was assessed during the winter and summer months of 1989 and 1990. Activity sampling was used to establish the pattern of work performed and heart rates were measured throughout work shifts. In addition, maximum aerobic capacity was estimated. The mean heart rate during work was 97 bt. min^?1(±13), while the mean relative heart rate increase was 21% (±15% ). The results indicated that the work performed could be classified as light to moderate.     

The Cost of Work on a Vehicle Assembly Line

Abstract

The physiological cost of work on men working on a truck assembly line was measured. Twenty subjects took part in the study: all had their heart rates measured during work, leisure and sleep. Thirteen subjects had their oxygen consumption measured at work using a newly described respirometer (Miser). Results confirmed that such work may be classified as light industrial with an energy expenditure of 120-200 W

Mean heart rates during work were 91 ± SD 8 bt min^-1;, mean relative work load was 24 ± SD 4% and mean relative heart rates were 21 ± SD 7%. The mean of the ratios of work, sleep and leisure: sleep heart rates were 1 -45 ± SD 015 and 1-28 ± SD 012 respectively.     

Investigation into the performance of strenuous work at high environmental temperatures—The relationship between heart rate and a fixed work/rest ratio

Employees in industry may be required to work in hot conditions which can result in heat strain. If work is to continue in potentially dangerous conditions, recommendations are needed to ensure that adequate precautions are taken. A requirement for the implementation of these recommendations is a simple means of assessing the suitability of work/ rest periods. This paper describes the first part of a study to develop simple predictive methods, related to the World Health Organization limit of a heart rate during an average work/rest cycle, of 110 beats min⁻¹.Subjects were six acclimatised, fit males. Skin temperature, rectal temperature and heart rate were monitored. They performed block-stepping at a metabolic rate of 450 W at 27, 28, 29, 30 and 31°C wet-bulb globe temperature. Humidity was low. Exposures were for five hours on each day, on a 45/15 minute work/rest schedule. Heart rates were measured and heart-rate indices calculated. Correlation between the indices and the resting heart rate were determined. The highest correlation ($\text{r = 0.747, p < 0.001}$) was found between resting rate and the “5th hour cycle rate” (the average work/rest cycle heart rate during the fifth hour). Results indicate that the resting heart rate (measured on a seated individual after 10 min exposure to the conditions under investigation), has predictive value for calculating “cycle rate”.     

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.     

Metabolic and cardiovascular responses to exercise with caffeine

The effect of caffeine on circulation and metabolism was studied during a discontinuous maximal oxygen uptake (VO₂ max) test on a bicycle ergometer. Eight male subjects were chosen for their minimal use of caffeine of which six normally did not ingest caffeinated beverages. Two caffeinated and two decaffeinated (control) trials were administered to each subject following double-blind and counterbalanced testing procedures. One hour before exercise, subjects ingested decaffeinated coffee with or without 350 mg of caffeine anhydrous added. Cardiac output (Q) was measured by a C0₂ rebreathing technique. Compared to control trials, caffeine increased the VO₂ max by an average of 140ml min?¹ (p <0-0·5)l. In addition, during caffeine trials, the average maximal heart rate (HR max) was elevated by 5 beats min^?1 (p<0·01). There were no other statistically significant changes in metabolic (VO₂ and R) and cardiovascular (Q, HR, SV and (a-v) 0₂ diff) variables during either submaximal or maximal exercise. Performance, as measured by total exercise time on the VO₂ max test, was not significantly different (p>0·05). It was concluded that caffeine has a small physiological but a statistically significant effect on VQ₂ max and HR max. During submaximal exercise, caffeine did not significantly effect the cardiovascular system.     

An Appreciation

Five male subjects were trained to work in non-erect task postures and then shovelled in five task postures: normal erect, under ceilings set at 80 and 60% of normal stature; kneeling without ceiling restraint; and, kneeling under a ceiling set at 80% of kneeling height. The steady-state data for all five task postures were averaged with a resulting heart rate of 131 beats min^?1 and an oxygen uptake of 1·41^?1 These averaged values compared very well with studies of actual coal miners shovelling in normal working environments     

Ergonomics diary

Physiological, perceptual and physical responses to a typical circuit weight-training (CWT) regimen were recorded in two studies. The aims were to assess the intensity of exercise during CWT; and to determine whether physical responses as evaluated by spinal shrinkage were related to physiological and perceptual responses to CWT. In the first study (n = 10) heart rate (HR), oxygen consumption (VO), ventilation (VE), blood lactate (La) and perceived exertion (RPE) were measured in response to CWT. Mean ( ± SD) time to complete three circuits of CWT was 17.8 (± 1-4) min. The HR max, VO₂max and peak La, measured first during an incremental treadmill test, were 195 (±13) beats.min ^?159-7 (±4-8) ml.kg^?1.min^?1 and 14-3 (±3-5) mM respectively. Mean HR and vO₂ during CWT were 69% and 50% of the respective maximal values. The HR-VO₂ ratio observed on the treadmill was elevated during CWT, with VO₂ being lowered relative to HR. Mean VE and La values were 52-7 (± 14-5) l.min^?1 and 6-9 ( ± 3-6) mM. The effect of the same CWT regimen on spinal loading as indicated by change in stature (shrinkage) was investigated in a second study (n = 8). The mean ( ± SD) time taken to complete the circuit was 17-4 ( ± 1-3) min. Mean shrinkage due to CWT (2-5 ± 1 -5?mm) was unrelated to the time taken to complete the circuits, to HR, RPE or to low back pain ratings (p > 0-05). Observations suggest that CWT as represented in these studies engages anaerobic as well as aerobic mechanisms but the exercise intensity may not provide sufficient stimulation for aerobic training. The physical load on the spine indicated by spinal shrinkage was not related to the physiological or perceptual strain.     

Cardio-respiratory performance of porters carrying loads on a treadmill

Four workers, accustomed to load carrying, carried loads (no load, 60, 80 and 100?kg) at 0·89 and 1·03?m s^?1 on a treadmill during the pre- and post-lunch period respectively, to obtain information regarding the degree of exhaustion from similar load carrying in their usual working situation. The rate of work is expressed in Watts. During pre- and post-lunch work there was a rise of 6 to 71 of pulmonary ventilation with each increment of 163 W. beyond the initial work level. The oxygen consumptions in the pre-lunch period were 15 to 27% higher, suggesting a greater anaerobic metabolism in the post-lunch period. The average work-pulse-rate varied from 116 to 162 beats min^?. Cardiac demand for a particular load is more or less constant, irrespective of time of day. During the pre-lunch period the work-pulse-sum was 78, 71, 65 and 54 beats per 163 W for respective four loads;-where-as in the post-lunch period, except the initial load, it varied only between 56 to 60 beats per 163 W. indicating a proportionate rise of pulse beats during post-lunch work. The 1st, 2nd and 3rd min recovery pulses of the 3rd and 4th loads were much beyond a level sustainable throughout the day. The recovery-pulse-sum varied from 39 to 104 beats and 36 to 117 beats min^? during the pre- and post-lunch period respectively, which were mostly beyond the permissible endurance limit. The oxygen-pulse for similar loads were 18 to 44% higher in the pre-lunch period, indicating better ability to work. To arrive at a reasonable load and rate of work, simple and multiple regression equations have been evolved. Indian workers may be allowed to work up to 1140 W (i.e. 50 to 55% of maximum oxygen uptake).     

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 ([Vdot]O₂) (63.4 vs. 34.0 ml kg^-1min^-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 &Vdot;O₂ values that were 56% of [Vdot]O₂ max, while snowshoeing with the fixed toe-cord design at 3.86 km h^-1 evoked mean [Vdot]O₂ values that were 60% of [Vdot]O₂ 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.     

The relation between performance in a throwing task and work-induced activation

The effect of work-rate on psychomotor performance was investigated in 24 male subjects. Five work levels were employed on a bicycle ergometer and a throwing task used as criterion. After a controlled level of unresisted pedalling, loads were set lo elicit heart rates of 100, 125, 150 and 175 beats min^?1 based on individual heart rate/power output regression lines determined in a preliminary investigation. Perceived exertion (RPE) and hearl rate were recorded after 4-5 to 5-25 min. Over the last 90 s of work subjects threw 20 squash balls at an archery target 4-25 m away. Performance was found to deteriorate at the severest work level (p?0.05), no other differences being significant. The shape of the performance curve suggested a shallow and distorted inverted U pattern.     

The Cost of Work in Medical Nursing

Abstract

The physiological cost of work was measured on the nursing staff of a general medical ward. Fourteen subjects took part in the study. Heart rates were measured during work and sleep on 13 nurses, and oxygen consumption measurements were made on 12, using the Miser Respirometer. In addition, maximum aerobic capacity was estimated on eight of the subjects

Mean heart rates during work were 93 ± SD 10 bt min^-1 significantly higher on the late than the early shift. The mean rate of energy expenditure was 147 ± SD 31 W. and was significantly higher in the morning than the afternoon or the evening

The mean relative work toad was 22% ± SD5%. The mean individual relative heart rate was 26% ± SD 9% and the mean ratio of work : sleep heart rates was 145 ± SDO-19 The findings placed medical nursing in the same category as light industrial work.     

Maximum acceptable repetitive lifting workloads for an 8-hour work-day using psychophysical and subjective rating methods

The psychophysical method used by Snook (1978) to determine maximum acceptable workloads for repetitive lifting during an 8-hour work-day in industrial populations was evaluated for application in military ergonomics. Under the conditions ofthe present experiment, the mean load selected by 10 soldiers (17·5 kg) was lower than reported by Snook (1978) for industrial workers and by Garg and Saxena (1979) for college students. When the soldiers lifted and lowered their selected load for an 8-hour work-day, 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. A subjective rating method tended to identify slightly lower loads than the psychophysical method. The results indicate that with good subject cooperation and firm experimental control in a laboratory, the psychophysical method can identify loads that soldiers can lift repetitively for an 8-hour work-day without metabolic, cardiovascular or subjective evidence of fatigue     

Metabolic,cardiovascular and spinal strain of a representative fuel replenishment task

The metabolic, cardiovascular and spinal strain of a representative fuel replenishment task for a tank crew were assessed using nine military subjects wearing coveralls in a comfortable ambient climate. The task involved lifting 5 gal jerry cans (weighing 23·4?kg) from the ground to a height representing a tank deck (1·676 m) at a rate of two lifts per minute for 15 min. Oxygen uptake ([Vdot]O₂), minute ventilation ([Vdot]E), heart rate (HR) and intra-abdominal pressure (IAP) were monitored continuously. After 15 min of lifting the mean [Vdot]O₂ was 0·821 min^?1 (S.D. 0·18). This was 27% of the predicted [Vdot]O₂ max. The mean [Vdot]E was 21·81 min^?1 (S.D.4·1) and the HR was 111·3 beats min^?1 (S.D. 17·8). The mean peak IAP was 105·6?mmHg, with 56% of the peak IAPs exceeding 90?Hg. The mean intrasubject coefficient of variation was 10·7% (range 7·2–24·2). In a separate series of 20 consecutive bimanual straight arm vertical lifts of 10?kg at 15 s intervals, the mean intrasubject COV% was 7·2% (range 3·2–11·2%). The replenishment task was considered acceptable in terms of the metabolic and cardiovascular strain. In terms of spinal strain, there may be an unacceptable risk of back injury if the task was normally undertaken as part of a soldier's full-time occupation over many years     

Human capabilities in repetitive lifting

In emergencies, it may be necessary for men to manually handle very large quantities of materials. Although data are available for loads carried on the back and there are specific civilian and military recommendations concerning safe maximum loads and acceptable workloads for repetitive lifting, data quantifying maximum capabilities for repetitive lifting tasks are not available. We have therefore undertaken a preliminary study to determine the relationship between lifting rate and time to exhaustion using three standard loads.

Eight healthy, fit, well-trained young soldiers bimanually lifted three loads (25, 50 and 75% of their maximal lifting capacity (MLC) for a single lift to waist height) from the floor to a platform at waist height (40% stature) situated directly in front of them at lifting rates of 2, 3 and 4 lifts min ^?1 (75% MLC), 4, 6 and 8 lifts min^?1 (50% MLC) and at 8, 10 and 12 lifts min^?1 (25% MLC) for 1 hour or until they become exhausted or were unwilling or unable to continue or maintain the prescribed lifting rate. The observed lifting duration (LD obs) was noted, or if the subject was not exhausted after 1 hour of lifting, he estimated his lifting duration (LD est). Oxygen consumption (VO₂) and heart rate (HR) were measured for 1 min each 10 min.

The mean (S.D.) LD obs and LD est at 25% MLC were 156(57), 99(61) and 65 (34) min for 8, 10 and 12 lifts min^?1, respectively. At 50% MLC they were 111(65), 72(45) and 35(18) min for 4, 6 and 8 lifts min^?11 respectively. At 75% MLC they were 93(69), 61(35) and 30(23)min for 2, 3 and 4 lifts min^?1, respectively. The mean relationships between load and lifting rate at 50, 35 and 23% V˙O₂ max (determined for uphill treadmill running), and for an HR of 110 beat min ^?1 were constructed.

These results provide a preliminary quantification of maximum human capabilities in repetitive lifting and an indication of the upper limits of tolerance for industrial workers undertaking repetitive lifting over an 8 hour workday. Further work is necessary to evaluate interpersonal and ergonomic factors in repetitive lifting tasks.