THE INFLUENCE OF GROSS BODY WEIGHT ON OXYGEN CONSUMPTION AND ON PHYSICAL WORKING CAPACITY OF MANUAL LABOURERS

A regression line relating oxygen consumption to rate of work has been calculated on 88 men from pairs of oxygen consumption and work-rate measurements at four different levels of work. A regression line has also been calculated for maximum oxygen intake against gross body weight for 338 men. From these regression lines it is possible to estimate the proportions of their maximum oxygen intakes a light and a heavy man would use in stepping on and off a 1 ft stool at 6, 12 and 24 times per minute. The slopes of the lines are such that both men would use similar proportions of their maximum oxygen intakes at each of the three rates of stepping ; the percentages are 26 per cent, 36 per cent and 55 per cent respectively.

The distribution of the gross body weights of the 338 men has been used to calculate a body weight such that 95 per cent of the men having weights above this value would have maximum oxygen intakes of 2-0 litres/min and more and therefore be capable of a moderate rate of work. A gross body weight of 132 lb is the estimate and 43 per cent of the population lie above this weight.

The ‘ tolerance ’ limits about the o.xygen consumption/gross body weights regression line are relatively narrow indicating that gros3 body weight is the major determinant in oxygen consumption when men lift their body weights against gravity. The ‘ tolerance ’ limits to maximum oxygen intake against gross body weight are wido, which suggests that the proportion of body fat influences the maximum oxygen intake value ot a given body weight.     

Gender, women's work and ergonomics

A submaximal test for estimating the physical work capacity has been developed and compared with a more complicated bicycle test. The testing procedure is a modified Harvard step test which in its original form is a maximal test The pulse rate was counted during work.

The step height was 40 cm for young males and 27 cm for the older ones and for the females 33 cm; the stepping rate was 22·5 steps per min.

The average values for ‘ step test 40 cm ’, and ‘ bicycle test 900 kgm/min ’ for male subjects were: oxygen intake 2·11 ±0·04 and 2·15±0·02 l./min ; pulse rate during work 130±1·5 and 132± 1·9 beats/mm respectively. The average values for ‘ step test 33 cm ’ and ‘ bicycle test 600 kgm/min ’ for female subjects were : oxygen intake 1·56±0·03 and 1·48±0·02 l./min ; pulse rate during work 140±1·6 and 138 ±2·2 beats/min respectively. The mechanical efficiency did not vary with the body height or weight.

As the aerobic capacity for trained individuals without excessive fat is closely correlated to the body weight the light ones will be tested at a relatively higher intensity than the heavy ones, when the bicycle test is used with a fixed load. In the step test the load varies with the body weight but the oxygen intake per kilogram body weight is constant.     

The energy cost of women walking and running in shoes and boots∗

The purpose of this study was to determine the difference in energy cost for women walking and running in shoes versus heavier boots. Seven subjects wore athletic shoes (mean weight = 514 ± 50g) and leather military boots (mean weight = 1371 ± 104g) at three walking speeds (4·0, 5·6 and 7·3km/hour) and two running speeds (8middot;9 and 10·5 km/hour). During each walking and running trial oxygen uptake ([Vdot]O₂ ml kg^?1 min^?1) was measured. The [Vdot]O₂ for women wearing boots were significantly higher (P < 0·05) than for shoes for both walking and running, with the exception of the slowest walking speed. The average increment in energy cost was 1·0% per 100-g increase in weight per pair of footwear. These results are similar to those reported for men from other studies which found increments in energy cost of 0·7 to 0·9% per 100-g increase in weight of footwear.     

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The aim of this study was to develop a practical and reliable test to predict the maximum lifting capacity of an individual. Dynamic strength during ‘isokinetic’ motion was measured on a device that allowed movement at either 0·73 or 0·97 ms^?1. For the ten men and ten women used as subjects, peak dynamic strength was compared with the maximum dynamic lift (MDL), the maximum load that an individual was able to lift once, from the floor to a shelf 113 cm high, without risk of injury. A step-wise multiple regression analysis indicated that the ‘isokinetic’ dynamic lifting strength (DLS) measured at 0·73 ms^?1 and sex accounted for 94·1% of the variance in MDL. The following equation was derived to predict MDL: MDL = 295 + 0·66 (DLS)? 148 (SEX), where DLS was measured in newtons, and SEX= 1 for men and 2 for women. Maximum acceptable load (MAL) selected for repetitive lifting at a frequency of six per minute was 22% of the MDL for both men and women. A simple test using a portable ‘isokinetic’ dynamic strength measuring device and involving one measurement was thus found to be a good predictor of maximum dynamic lift.     

Effects of dynamic,static and combined work on heart rate and oxygen consumption

The effects upon heart rate and oxygen consumption of muscular exercises including simultaneous dynamic and static contractions were studied in three male subjects. Dynamic work consisted of walking at four speeds (0·56, 0·83, 1·11, 1·39 m s^?) on a horizontal treadmill; static work consisted of pushing against, pulling and holding 6, 9, 12, 18 and 24?kg; combined work associated walking with each one of the forms of static work. Physiological load is expressed in terms of cardiac cost (ΔHR) and oxygen cost (Δ[Vdot]_o2). The physiological cost of combined work increases with both the walking speed and the static load. For each parameter (HR and [Vdot]_o2) the extra-cost of combined work has been determined by computing the difference between the cost of combined work and the sum of the costs observed during static and dynamic exercises separately performed. The paired t-test shows significant differences for all of the walking-pushing tests, but only for 8 pulling tests and 2 holding tests. Linear relationships are observed between the oxygen extra-cost and load when walking at 0·56 or 0·83 ms^?1, with correlation coefficients statistically significant for pushing and pulling (p < 0·01) but not significant for holding tests. The present results show that, when the static work is combined with walking, the physiological response varies with the type of static work considered.     

Relationships of Oxygen Consumption,Ventilation and Cardiac Frequency to Body Weight during Standardized Submaximal Exercise in Normal Subjects

In normal males during submaximal exercise at a constant rate of external work on a bicycle ergometor or step test, the oxygen uptake and ventilation are linear functions of body weight. In normal females the mean oxygen uptakes do not differ materially from those for males of comparable weight. However, because of the constant terms in the regression equations, the convention of expressing results per kg body weight or m² body surface area may give rise to error; for ventilation this may be avoided by the use of the regression on oxygen uptake. Alternatively, the results may be reported at a constant oxygen uptake, for example, for men 1·5 1/min as recommended by J.L.O. and for women 10·l/min; the ventilation is then independent of body weight. By this procedure allowance is also made for differences in oxygen uptake duo to the effects of practise. For the cardiac frequency a similar adjustment to a constant oxygen uptake yields values which are negatively correlated with body weight for walking on a treadmill, but not, in this instance, for standardized stepping and cycling     

Initial training as a stimulus for optimal physical fitness in firemen

Abstract

In this investigation the physical fitness of 34 recruits to the UK Fire Service was assessed before and after their initial training (tests 1–2) and on three occasions (tests 3–5) during the first 18 months of their service (n=34+6=40). The initial training (test 2-test 1) resulted in an increase in maximum aerobic power (11% p<0·05), body mass (2 kg, p<0·001), lean body mass (2·02 kg, p<0·001), grip and lifting strengths (/><0·001), and in calf girth (p<0·05). But no change in waist girth, maximum anaerobic power or measures of lung function was noted. There was evidence therefore that the men became physically fitter. In the first eighteen months of their service, subjects' maximum oxygen consumption declined to pre-training levels, while body mass continued to increase with a decrease in lean body mass (p<0·001). Strength remained unaltered or tended to fall with a decrease in calf girth (p<0·05). These changes reflected a return towards pre-training physical fitness levels. It is suggested that the initial training, while ill-matched to the firemen's habitual activity, produced levels of physical fitness which may approximate more closely to the infrequent peak requirements experienced by the men during actual fire fighting. Consequently it is concluded that the physical training during service was insufficiently intense and that a more effective programme could be designed to maintain an appropriate level of physical fitness     

Effect of Ambient Temperatures Between 21°C and 35°C on the Responses to Progressive Submaximal Exercise in Partially Acclimated Man

The effects of variation in dry-bulb temperature between 2l°C and 35°C on the physiological responses to a 12-minute progressive submaximal exercise test have been examined in four healthy men partially acclimated to heat. On average, cardiac frequency and minute ventilation at standard oxygen uptake increased by 1·4% (r+0·85; p<0·001) and 0·4% (r+ 0·46; p<0·00l) respectively for each degree rise in dry-bulb temperature. The increase in exercise cardiac frequency with each degree rise in mean akin temperature averaged 5·1 %. A regression relationship is presented which permits adjustment of the cardiac frequency at standard oxygen uptake to either a standard dry-bulb temperature or mean skin temperature. Its use and limitations are illustrated using data collected during studies which formed part of the U.K. contribution to the International Biological Programme.     

A new kayak ergometer based on wind resistance

Abstract

An ergometer for kayak paddlers has been developed and used for winter training, measurements of work capacity and maximal oxygen uptake ([Vdot]O₂ max). Force is transmitted from the paddle by means of a wire connected to a flywheel mounted with six 9 × 9cm blades. Resistance, therefore, is based on wind turbulence generated by the flywheel. The mechanical efficiency of the ergometer at 63% (range 48-77) of [Vdot]O₂ max was 17% (range 16-18) (n= 13). The [Vdot]O₂ max was similar during bicycling (median 4·9; range 4·4-5·4l/min), arm cranking (median 4·8; range 4·3-5·11/min), on-water rowing in a kayak (median 4·7; range 4·0-4·91/min) and during rowing the kayak ergometer (median 4·8; range 4·3-5·21/min), (n = 6, p> 0·05). Work capacity during a 5 min ‘all-out’ test was 272 W (range 253–304 W) on the kayak ergometer (n = 17). The use of the ergometer for training helped to increase the aerobic power during arm exercise of Danish paddlers. Before introduction of the ergometer (February 1986), their VO₂ max was 4·6 (range 3·8-5·2) 1/min while 12 months later, it was 50 (range 4·2–5·7) 1/min (n = 14, p < 0·01). The ergometer has thus been found.useful for training and evaluation of work capacity in kayak paddlers.     

Psychophysical modelling for combined manual materials-handling activities

Most psychophysical studies in manual materials handling (MMH)are involved only with single MMH activities, i.e. lifting, lowering, carrying, holding, pushing or pulling. Very little research has been reported on the determination of operator capacities for combinations of MMH activities (e.g. lifting a box, then carrying the box, or carrying a box, then lowering the box). These kinds of combined activities are prevalent in industry and in our daily lives. The objective of this study was to utilize the psychophysical approach to examine the effects of combinations of lifting, carrying and lowering activities. Twelve male students served as subjects for the study. The capacities that were determined as the maximum acceptable workloads for a 1-h work period for four individual MMH activities—lifting from floor to knuckle height (LFK), lifting from knuckle to shoulder height (LKS), lowering from knuckle to floor height (LOW) and carrying for 3·4 m (C) —and three combined MMH activities—LFK + C, LFK + C + LKS and LFK + C + LOW—were determined psychophysically under three frequency conditions: one time maximum, one handling per minute and six handlings per minute. Combined MMH capacities models were developed using the following three methods: a limiting individual MMH capacity, isoinertial 1·83-m maximum strength and fuzzy-set theory. The advantages and disadvantages of different models were discussed.     

Physiological Cost and Air Flow Resistance of Respiratory Protective Devices

Using one of three respiratory protective devices or a ‘no mask’ control, five male subjects were tested at grades of 0, 5 and 10 per cent and a constant speed of 3·5 miles per hour for a total of twelve tests per man. Exercise heart rates and recovery oxygen consumption values were recorded. Air flow resistance values were determined in laboratory bench tests. The resistance of the devices did not significantly alter the exercise pulse rates but did significantly increase the recovery oxygen consumption, particularly at the higher work levels. Recovery oxygen consumption values and the air flow resistance figures were positively related at the higher levels of work. It is suggested that the relationship offers further support for the use of laboratory bench tests as an estimator of the added physiological burden imposed on the wearer.     

Energy cost of backpacking in heavy boots

Previous studies have investigated the oxygen cost ([Vdot]0₂) of increasing boot weight during unloaded walking or running, and have shown that for each 100 g increase in weight of footwear there is a 0·7-1·0% increase in [Vdot]O₂ In reality (except in athletic events) the use of heavy footwear is associated with load carriage, usually backpacking. We therefore investigated the effects of increasing boot weight by 5% of body weight on the [Vdot]0₂ of backpacking a load amounting to 35% of the body-weight in five healthy young males who walked at 4·5 km/hour (0% grade) on a motor-driven treadmill. The results indicated a mean increase of 0·96% in [Vdot]0₂ whilst backpacking for each 100thinsp;-g increase in boot weight. In contrast the oxygen cost of increasing the backpack load was only 0·15% indicating that it was 6·4 times more expensive to carry weight on the feet as compared to the back. It is concluded that the relation between boot weight and oxygen cost, previously developed for unloaded walking and running, can reasonably be extended to include heavier boots and backpacking.     

Durations of Safe Exposure for Men at Work in High Temperature Environments

Times taken to reach a state of imminent heat collapse were examined in a sample of 87 fit, unacclimatized young men dressed in overalls. Subjects wore required to perform a routine of continuous work at approximately 310 J/s in environmental conditions within the range 37·0/30·0°c to 83·4/4l·2°c dry-bulb/wet-bulb temperature in which air movement was either 0·76m/s or 1·02 m/s and air and wall temperatures were equivalent.

From the analysis of 440 observations, a general equation expressing a rectangular hyperbolic relationship between imminent heat collapse times and environmental Severity, described in terms of 0·22661 dry-bulb-+-0·77339 wet-bulb temperature in °c, was derived. On the basis of this equation lower confidence limits for individual observations were calculated as recommendations of safe exposure times from 120 mins to 10 mins. The durations of safe exposure presented are intended to protect from imminent heat collapse 75%, 90%, 95% or 99% of exposes from populations represented by the samples of subjects studied.     

Estimating physical working capacity and training changes in the elderly at the fatigue threshold (PWCft)

The test for estimating physical working capacity at the fatigue threshold (PWC_ft), previously validated for young men, was evaluated for use with elderly men and women. A sample of 27 volunteer subjects (67·6 ± 5·6 years, 11 male, 16 female) was divided into three matched groups: (1) controls (n = 10), (2) low intensity (70% PWC_ft) training group (n = 10) and (3) high intensity (85% PWC_ft) training group (n = 7). The subjects were tested for PWC_ft before and after 10 weeks of exercise training on cycle ergometers (30min/day, 3 days/week). Controls did not exercise but met once a week for a health lecture. No significant pre-test to post-test change was noted in the mean PWC_ft of the control group (78·8-78·5 W); low intensity training resulted in 29·8% improvement in PWC_ft (81·0 to 105·0 W); and the high intensity group realized an improvement of 38·4% (83·6-115·7 W). One-way ANOVA -indicated that the gains made by each of the groups were significantly different (p < 0·01). Post hoc analysis revealed that the gains made by each exercise training group were significantly greater than controls (p <0·05) with no significant difference between high and low intensity groups. Reproducibility of the PWC_ft was excellent (R = 0·976). Since RPE averaged 14·2 at PWC_ft and 64% of subjects provided useful data, this test appears to be useful for evaluating the fitness of the elderly.     

Biomechanically and electromyographieally assessed load on the spine in self-paced and force-paced lifting work

The purpose of this study was to measure dose of spinal load when different pacing methods were applied to lifting work and to develop methodology for such measurements. The compressive load on the spine computed by a dynamic biomechanical model and the electromyographic activity of back muscles were used for describing the spinal load. Five men and five women worked in a laboratory on two days lifting a box up and down for 30 min on both days, on one day force-paced (4 lifts/min), and on the other self-paced in random order. The weight of the box was rated by the subjects to be acceptable for the work done. The lift rate of our female subjects was higher and that of the male subjects lower in self-paced than in force-paced work. There were no significant differences in peak lumbosacral compressions nor in the amplitude distributions of electromyography between the two pacing methods. The biomechanically-calculated compressive forces on the spine were lower (about 2·7 kN for the men and 2·3 kN for women) than the biomechanical recommendations for safe lifting, but the EMG activity showed quite high peaks so that for 1% of work time the activity was on women above 60% and on men above 40% of the activity during maximum isometric voluntary test contraction.     

A psychophysical study of high-frequency arm lifting

Ergonomics research on worker lifting in industry, and the many tools and methods that have resulted from it, have most often concentrated on the maximum amount of weight that a worker is capable and willing to lift in a given situation. In most psychophysical research on lifting, the frequency is one of a number of controlled variables along with container size, lift range, etc. Most of the relatively few studies that have investigated frequency as the response variable have used relatively heavy loads. In the study reported here, the focus was on the lifting of light weights and the subject acceptance of maximum frequency of lift for a two-handed lifting task. The lift range was set at approximately knuckle to shoulder height and was intended to simulate industrial jobs where the worker is tasked with either loading or unloading relatively light weight items to or from a processing line operation. Twelve college-age male subjects were used. Two conditions of weight, 0.7 kg (1.5 lb.) and 4.45 kg (10 lb.) were used and the subject adjusted his frequency of lift by communicating with the researcher, who adjusted a metronome to pace the task. The subjects were instructed to work at as fast a rate as they could for an hour period without becoming overheated, overly tired, out of breath or in pain. Measurements of oxygen consumption and heart rate were taken to supplement the psychophysical measure of lift frequency. Two replications of each weight condition were performed. At the conclusion of the metronome-paced sessions, an additional session for each weight condition was performed where the subject was instructed to lift as fast and consistently as they could with no external cuing device. The mean frequencies of lift identified in the experiment were 31.21 lifts per minute and 23.50 lifts per minute for the 0.7 kg and 4.5 kg lift weights respectively. The two weight conditions were significantly different from each other in their effects on subject metabolic energy expenditure with the subjects tending to work significantly harder physiologically at the heavier weight.     

The Aerobic and Anaerobic Components of Work during Submaximal Exercise on a Bicycle Ergometer

Abstract

Inter-subject variability of oxygen intake ([Vdot]O₂)n relation to the anaerobic component of work has been investigated intensely on two healthy subjects and extensively on two groups of young and older men during work on an upright, stationary bicycle ergometer.

Significant differences (p<0·001) in [Vdot]O₂ were shown to exist between the two groups of subjects and the healthy men at the higher work-loads which could not be eliminated entirely by correction for body weight. The residual variation of [Vdot]O₂ on work-load was shown to be a consequence of the variation of anaerobic component of exercise. During work on a bicycle ergometer at exercise above about 50% [Vdot] O₂ max this should be taken into account if a valid assessment of energy expenditure is to be made.     

The Relationship between Energy Expenditure and Performance Index in the Task of Shovelling Sand

An examination is made of the relationship between the energy expenditure in litres of oxygen consumed per minute, as measured by the physiologist, and the performance index, as assessed by the work-study engineer. The data used in the analysis were obtained from 16 Bantu labourers engaged in shovelling sand at four different rates of work into a mine car of 1 ton capacity.

A close relationship between mean oxygen consumption and mean performance index over the range of work levels was found. A linear model appeared to describe the relationship between these two variables adequately. The particular linear relationship between the variables was, however, dependent on the observer, i.e. the lines for the two work-study engineers were different from each other. A performance index value of about 75 was found to be equivalent to an oxygen consumption of about 1-5 litres per minute. This is 50 per cent of the average Bantu mine labourer's maximum oxygen intake and, on physiological grounds, this is the rate of work which the Bantu labourer can maintain easily for a shift of 6-8 hours. However, it appears from the results of these preliminary studies that men working at a performance index value of 100 (i.e. well motivated in the work-study sense) are liable to work at a rate which is about 70 per cent of the maximum oxygen intake. This would be excessive for the average labourer. The existence of this close relationship is most encouraging and means that the work-study engineer would be able to relate his assessments to rates of energy expenditure and hence estimate the physical effort of men engaged on heavy manual labour.     

Work tolerance and subjective responses to wearing protective clothing and respirators during physical work

This study examined work tolerance and subjective responses while performing two levels of work and wearing four types of protective ensembles. Nine males (mean age = 24·8 years, weight = 75·3 kg, [Vdot]O₂ max = 44·6 ml/kg min) each performed a series of eight experimental tests in random order, each lasting up to 180 min in duration. Work was performed on a motor-driven treadmill at a set walking speed and elevation which produced work intensities of either 30% or 60% of each subject's maximum aerobic capacity. Work/rest intervals were established based on anticipated SCBA refill requirements. Environmental temperature averaged 22·6°C and average relative humidity was 55%. The four protective ensembles were: a control ensemble consisting of light work clothing (CONTROL); light work clothing with an open circuit self-contained breathing apparatus (SCBA); firefighter's turnout gear with SCBA (FF); and chemical protective clothing with SCBA (CHEM). Test duration (tolerance time) was determined by physiological responses reaching a predetermined indicator of high stress or by a 180-min limit. Physiological and subjective measurements obtained every 2·5 min included: heart rate, skin temperature, rectal temperature, and subjective ratings of perceived exertion, thermal sensation, and perspiration.

The mean tolerance times were 155, 130, 26, and 73 min, respectively, for the CONTROL, SCBA, FF, and CHEM conditions during low intensity work; and 91, 23, 4, and 13 min, respectively, during high intensity work. Differences between ensemble and work intensity were significant FF and CHEM heart rate responses did not reach a steady state, and rose rapidly compared to CONTROL and SCBA values. SCBA heart rates remained approximately 15 beats higher than the CONTROL ensemble during the tests. At the low work intensity, mean skin.     

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).