Metabolic and cardiopulmonary responses of older wheelchair-dependent and ambulatory patients during locomotion∗

To determine preferred velocities and magnitudes of metabolic and cardiopulmonary responses of older wheelchair-dependent (WD) patients and ambulatory (AMB) psychiatric patients during locomotion, eight WD (mean age 62 years) and ten AMB (mean age 58 years) patients travelled over a level tiled circular course. During wheelchair locomotion and walking, respectively, mean results were: velocity, 2·0, 3·1 km hour^?1; oxygen uptake, 0·532, 0·8061min^?1; net locomotive energy cost, 0·574, 0·558netkcal kg^?1 km^?1; pulmonary ventilation, 19·6, 25·71 min^?1; heart rate, 94·6, 92·7 beats min^?1. Although walking at 3·1 km hour^?1 required greater absolute energy expenditure than for wheelchair locomotion at 2·0 km hour^?1, locomotive efficiency was approximately the same. When considering differences in exercise capability between arms and legs, relative stresses experienced by the WD and AMB subjects appeared to be similar. Locomotive efficiency was reduced when the AMB subjects reduced their walking speed to 20km hour^?1. This study suggests that self-selected velocities for wheelchair locomotion and walking are related to both maximal physical capability for each activity and locomotive efficiency.     

Self-paced hard work comparing men and women

Six fit male subjects (23 years, 171 cm, 67 kg, maximal V?O₂ = 2.25mmol kg^?1 min^?1 (50.3ml kg^?1min^?1)) and six fit female subjects (22 years, 163 cm, 57 kg, maximal V?O₂= l.83mmol kg^?1 min^?1(41.1 mlkg^?1 min^?1)) performed self-paced hard work while walking over four different terrains carrying no external load, 10 kg and 20 kg. Time on each course for individual subjects was used to determine speed and energy expenditure; heart rate was recorded as each subject completed each course. Walking speed and energy expenditure of the males were found to be significantly greater (p< 005) than those of the females overall terrains (blacktop road, 1.6 km; dirt road, 1.8 km; light brush, 1.4 km; and heavy brush, 1.3 km) and for each load carriage condition. Relative energy expenditures of the males and females for all conditions were very similar(p>0.05) and remarkably constant at a value close to 45% V?O₂max, These data indicate that the voluntary hard work rate is dependent upon maximal aerobic power. The best predictor of speed for self-paced hard work of males and females for 1 to 2 hours in duration appears to be based on 45% of maximal aerobic power.     

John G. Fox (1931-2004)

The effectiveness of intermittent, microclimate cooling for men who worked in US Army chemical protective clothing (modified mission-oriented protective posture level 3; MOPP 3) was examined. The hypothesis was that intermittent cooling on a 2 min on–off schedule using a liquid cooling garment (LCG) covering 72% of the body surface area would reduce heat strain comparably to constant cooling. Four male subjects completed three experiments at 30°C, 30% relative humidity wearing the LCG under the MOPP 3 during 80 min of treadmill walking at 224 ± 5 W · m^?2. Water temperature to the LCG was held constant at 21°C. The experiments were; 1) constant cooling (CC); 2) intermittent cooling at 2-min intervals (IC); 3) no cooling (NC). Core temperature increased (1.6 ± 0.2°C) in NC, which was greater than IC (0.5 ± 0.2°C) and CC (0.5 ± 0.3°C) ( p < 0.05). Mean skin temperature was higher during NC (36.1 ± 0.4°C) than IC (33.7 ± 0.6°C) and CC (32.6 ± 0.6°C) and mean skin temperature was higher during IC than CC ( p < 0.05). Mean heart rate during NC (139 ± 9 b · min^?1) was greater than IC (110 ± 10 b · min^?1) and CC (107 ± 9 b · min^?1) ( p < 0.05). Cooling by conduction (K) during NC (94 ± 4 W · m^?2) was lower than IC (142 ± 7 W · m^?2) and CC (146 ± 4 W · m^?2) ( p < 0.05). These findings suggest that IC provided a favourable skin to LCG gradient for heat dissipation by conduction and reduced heat strain comparable to CC during exercise-heat stress in chemical protective clothing.     

Estimated aerobic performance and energy cost of severe exercise of 24 h duration

Abstract

The maximal aerobic performance ([Vdot]O₂max) and energy cost of running at various speeds of two ultra-distance athletes were measured in the laboratory on a motor driven treadmill and the results related to observations made during a 24 h race. The athletes finished 1st and 2nd in the event and covered distances of 251·46 km and 234·56 km respectively during the 24 h period. From the measurements in the laboratory it was calculated that the average speeds sustained by the athletes during the competition were equivalent to an O₂ cost of 36·4 ml kg^?1 min^?1 and 35·3 ml kg^?1 min^?1 which represented approximately 50% of their [Vdot]O₂max. During the race the winner expended an estimated 77,829 kJ (18.595 kcal) which is three times the highest recorded value in the most severe industrial work. By the nature of the activity this figure must be regarded as at or near the upper limit of sustainable energy expenditure by man during a complete uninterrupted 24 h circadian cycle.     

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).     

Taguchi optimization approach for the polypropylene fiber reinforced concrete strengthening with polymer after high temperature

In this study, the strengthening with polymer the polypropylene fiber reinforced concrete exposed to high temperature was examined. Taguchi L₉ (3³) orthogonal array was used for the design of experiments. Three different parameters were used in the study; polypropylene fiber percentage (0 %, 1 % and 2 %), high temperature degree (300 °C, 600 °C and 900 °C) and curing period (3, 7 and 28 days). Cube samples of 100x100x100 mm sizes were produced for the compressive strength and ultrasonic pulse velocity tests. The samples were removed from the water and dried at 105?±?5 °C, and then they were exposed to temperatures of 300 °C, 600 °C and 900 °C. Then, the polymerization of monomer and the vinyl acetate monomer impregnation on the samples were carried out. The compressive strength and ultrasonic pulse velocity tests were made. Taguchi analysis showed that the largest compressive strength and ultrasonic pulse velocity were obtained at a rate of 0 % from the samples with polypropylene fiber exposed to 600 °C and kept for 28 days as cure period. It was determined as the result of Anova analysis that high temperature had made biggest effect on the compressive strength and ultrasonic pulse velocity of the concrete reinforced with polymer.     

Preliminary observations on parameters of human location

Abstract

A preliminary experimental field investigation was conducted on seventeen normal male adults to study the important observable parameters of human locomotion and the interrelationship existing among them. New generalized terms such as specific speed (statures s^?1), specific energy consumption (kJ kg^?1 min^?1), percentage increase of peak heart rate and a non-dimensionalized term, relative step length, have been introduced. Superiority of cadence and specific speed over speed and specific energy consumption over energy consumption has been observed and a single linear relationship connecting specific speed and specific energy consumption up to a speed of 6·7 m s^?1 (24 km h^?1) has been seen. Stair climbing and Baithaki exercises have been included as two other rhythmic activities for the sake of comparison with locomotion. Use of cadence as a relatively more important observable gait parameter for walking or running activity as well as for other rhythmic activities has been suggested. These findings have potential for application in the field of work study and industrial engineering.     

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.     

Thermal function of a clothing ensemble during work: dependency on inner clothing layer fit

Abstract

A tight-fitting crewneck undergarment (U) and a loose-fitting shirt (S) were studied as part of a commonly used clothing ensemble (I₁₀₁=0.22 m²KW^?1). Ten clothed male subjects performed standardized packing work ([Vdot]O₂= 0.761 min^?1) at three climatic conditions, 20°C and V _a= 0.45ms^?1(0-30min),at 5°Cand V _a= 0.39ms^?1(30-60min) and at 5°C and V _a=l.23ms^?1(76-90min). From 60-75 min the subjects rested at 20°C. The physiological and subjective responses varied with the environment from slightly warm to cool. U resulted in warmer responses than S: torso and upper arm skin temperatures were higher at both 5°C and 20°C, evaporation rate was higher at 20°C, mean skin temperature was higher during work at 20°C, sweating tended to begin earlier and skin wettedness to be higher with U than with S. No differences were observed in core temperature, heart rates, and subjective thermal evaluations. It was concluded that a tight-fitting inner layer (U) compared to a loose-fitting one (S) allows for less cooling of the skin in both a cool and a slightly warm environment     

The effect of aerodynamic handlebars on oxygen consumption while cycling at a constant speed

Abstract

In this study, the oxygen consumption ([Vdot]O₂) of bicycling was measured at a fixed speed (40 km·h^?1on level terrain, with normal and aerodynamic handlebars using a Douglas bag collection system. Eleven elite (USCF category I or 2) men cyclists age 24 to 40 years (X¯=28·5, SD±4·6) performed four consecutive (two with each bar in alternating order) steady state rides at 40 km· h^?1over a 4 km flat course (same direction each trial). Expired gases were collected in a 1501 Douglas bag attached to a following vehicle during the last 45 s (approx. 0·5 km) of each trial. A repeated measures analysis of variance revealed a significant (p<0·02) handlebar effect. Specifically, [Vdot]O₂was 2% lower under the aerodynamic handlebar treatment (X¯=4·26, SD±0·36 1 min^?1when compared with that of the normal handlebar treatment (X¯=4·34, SD±0·35 1 min^?1The results of this study demonstrate that the reported aerodynamic advantage of the aerodynamic handlebars produces a small but significant reduction in the [Vdot]O₂of bicycling at 40 km·h^?1     

Study of Electrical Conductance of Pressed Chemically Pure MnO2 Powder†

Variation of electrical conductance and capacity of chemically pure MnO₂ in pressed powder form under a stress 6·0 × 10¹¹ dynes/sq. cm has been studied within the temperature range 26^°c to 110^°c at 1 MC/s, Electrical conductance of samples in tablet, form (3 mm thick and 15 mm in diameter) was measured between 26^° C and 110^° before and after heat treatment at 300^°c for 36 hours. Capacitance values were also measured simultaneously within the above temperature range. Electrical conductance was found to attain a maximum at about 78^°c. There is a marked hysteresis in ‘; ln conductance’ ? 1 / T graph when measurements are made while temperature is rising and while falling.

Differential thermal analysis of the samo MnO₂ powder was also carried out. Measurements were made while heating and also while cooling. Two marked changes are clearly seen, one at mean temperature of 56^°c and the other at mean temperature of 80^°c, suggesting some second-order solid to solid phase changes at these temperatures. Corresponding breaks occur in the ‘ln conductance ’ ? 1/T and capacity-temperature graphs at the above-mentioned temperatures.     

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.     

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     

Aerobic Capacity of Steel Workers in India

Abstract

Seventy-six workers, aged 21–43 y. drawn from three major steel plants—two located in the eastern and one in the central region of India (referred to as Group A, Group B and Group C respectively)—were studied on the bicycle ergometer to determine their aerobic capacity ([Vdot]_O2max), Both the direct and indirect methods were employed, the direct one being used only in the case of the workers in Group C. The mean [Vdot]_O2max of these workers was found to be 42·6 cm³ kg^?1 with a standard error of ± 0·71 cm³ kg^?1 min^?1. The highest values were observed among the workers in Group B (mean 47·0± 1·35 (S.E.)cm³kg^?1 min^?1) who are ethnically distinct and have a high level of customary activity, and the lowest among workers in Group C (mean: 39·0±0·74(S.E.) cm³kg^?1 min^?1).

As expected, the [Vdot]_O2max was found to be correlated positively with body weight, and negatively with age in a multiple regression analysis. Furthermore, the active Group B has values for [Vdot]_O2max that are significantly higher than those for the other Groups, a difference that is not attributable to weight or age.     

The Measurement of Fatigue in Hot Working Conditions

Abstract

The N.S.W. Division of Occupational Health was requested to provide information to assist a Mines Rescue Station to choose a type of self-contained breathing apparatus which would be likely to permit the greatest duration of exposure of Mines Rescue personnel to hot and humid environment whilst performing heavy work, without collapse.

A number of subjects were tested in a heat chamber, performing a work cycle of 2 minutes duration, followed by a 3-minute rest period, at temperatures of 30°c, 35°c, 38°C and 4l°c Dry Bulb with a Wet Bulb temperature about 1° lower in each case, until the subject was either unable to continue or until the rectal temperature reached 38·8°c to 38·9°c.

Pulse rates, skin temperature, and sweat losses were also recorded.

The experiments confirmed that a rectal temperature of 38·8°c to 38·9° will, in most cases, coincide closely with the onset of exhaustion.

Sweat loss and pulse rate were found to be unreliable methods of measuring fatigue and that skin temperature was completely unreliable as an index of fatigue except when the temperature and humidity were high.     

Maximum weights of lift acceptable to male and female industrial workers for extended work shifts

Abstract

This paper reports the development of maximum acceptable weight of lift databases for male and female industrial workers for 12-hour work periods. Using a psychophysical methodology, 37 males and 37 females, experienced in manual lifting, performed various lifting tasks involving four frequencies, three box sizes, and three height levels. The maximum acceptable weight of lift was significantly influenced by the frequency of lift, height of lift, and box size. Box size effects were, however, less profound than frequency, and height effects. The maximum weight, acceptable for 12 hours of lifting, elicited an average heart rate of 90 and 101 beats min ^?1 for males and females, respectively. Males selected weights that, on average, resulted in metabolic energy expenditure rates of 23% of their aerobic capacity for 12 hours of lifting. Females required metabolic energy expenditure rates equivalent to 24% of their aerobic capacity for lifting acceptable levels of weight for 12 hours.     

Hygrometer-based calibration method for syringe pumps providing ultra-low liquid flows

Traceable and accurate measurements are critical in many areas where syringe pumps are used to provide microscale liquid flow. Especially, drug delivery demands for low flow rate calibrations have been increasing, but currently available calibration methods are very limited in range and accuracy at flow rates below 100 μl min^?1. This paper presents a new hygrometer-based method for the calibration of syringe pumps providing traceability down to the 0.1 μl min^?1 level. In this method, liquid water from the syringe pump under calibration is injected into a porous cloth from which it evaporates and mixes with a dry gas flow. By measuring the humidity, temperature, pressure and flow rate of the gas, the injected water flow rate can be calculated. To test the method, a calibration set-up was constructed and a syringe pump was calibrated at flow rates from 0.1 to 10 μl min^?1. A thorough uncertainty analysis carried out as a part of the work shows that a relative uncertainty of 0.4 % (at 95 % confidence level) is achieved at the largest calibration flow rate. The uncertainty increases to 3.3 % towards low end of the flow rate range. The achieved uncertainty level is significantly better than achieved with gravimetric methods so far.     

Cardiac frequency throughout a working shift in coal miners

Despite the ever-increasing mechanization of industrial activities, coal mining still remains a physically demanding occupation as it is not always possible to extensively mechanize the extraction process. To estimate the physical effort necessary to sustain coal mining activities in a poorly-mechanized mine, cardiac frequency (?/_c) was measured throughout the working shift with a Sport-Tester PE3000 (Polar Electro OY. Finland) in a representative sample of 73 Asturian miners engaged in a full spectrum of underground work. The mean ± SD of the overall?/_c values measured in miners working at the coal face (Group 1, 33 subjects, mean age 32·7 years, age range 21–48 years R was 106·5 ± 18·2 beats min^?1. In other miners (Group 2, 40 subjects, mean age 34·6 years, age range 23–48 years) corresponding figures were 1031 ±177 beats-min_?1 (p<0·05). Subjects' average working shift?_c Lbeats. Min^?1) was not related to age, measured (treadmill) VO₂ max nor VO₂ max.kg body weight^?1, while average working-shift? _c (%? _c max) was weakly related to age (r = 0·396, p<0·05), VO₂ max (r equals; 0·295, p < 0·05) and VO₂max.kg body weight^?1 (r= 0·352, p<0·05). Working-shift peak? _c (beats · min^?1) was negatively related to age (r = 0·334, p < 0·05). Our study has provided the distribution of the overall ? _c values likely to be found in subjects working in these poorly-mechanized mines. However, average working-shift ? _c differs considerably from subject to subject and is largely unpredictable.     

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