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Effects on the Trunk of Erecting Pit Props at DifferentWorking HeightsP. R. DAVIS a & J. D. G. TROUP aa Royal Free Hospital School of Medicine , Hunter Street, London, W.C.IPublished online: 30 May 2007.

To cite this article: P. R. DAVIS & J. D. G. TROUP (1966) Effects on the Trunk of Erecting Pit Props at Different WorkingHeights, Ergonomics, 9:6, 475-484, DOI: 10.1080/00140136608964412

To link to this article: http://dx.doi.org/10.1080/00140136608964412

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Effects on the Trunk of Erecting Pit Props at Different Working Heights

By P. R. DAW and J. D. G. TROW Royal Free Hospital School of Medicine, Hunter Street, London W.C.1

The effects on lumbar movement and intra-abdominal pressure of erection of hydraulic props by three methods a t different working heights have been studied. Lifting in a squatting position and when on one knee was accompanied by greater trunk stress than when kneeling on both kneas. At 3 ft 6 in. (107 cm) working height the magnitudes of lumbar movements and abdominal pressure increases were much less then those a t 4 f t 6 in. (137 cm), a difference greater than could be explained by consideration of external work done. The results indicate that the optimum method of prop erection has yet to be evolved, and ahow tha t prop erection a t 4 f t 6 in. (137 cm) working height by some method6 may be unduly hazardous.

1. Introduction Hult (1954), Roantree (1963) and others have found that back injuries in

industry are alarmingly frequent, and Lawrence (1955) has shown that limitation of headroom and other causes of mechanical stress lead to an incremed frequency of such disorders. I n view of these and other dangers arising during manual handling, the National Coal Board has instituted training courses in lifting methods for mining apprentices. While there are several established schools of thought regarding lifting training, and for many purposes they have much in common, conditions of work in the mining industry impose restrictions on the worker which necessitate either the modification of established lifting procedures or, in some instances, the use of entirely different methods. The choice of lifting method is a t present empirical and the develop- ment of objective mathods for studying lifting procedures in confined spaces is of considerable importance.

A number of investigators, including Bartelink (1957), Davis (1959 a, b), Morris et al. (1961), Eie and Wehn (1962) and Davis and Troup (1964) have shown that during physical activity there is a relationship between the magnitudes of trunk stresses and increases in intra-abdominal pressure; and Davis et d. (1966), using a force platform in conjunction with pressure measure- ments, obtained correlations between these two factors of the order of r = 0.7e. It is thus clear that abdominal pressure increases can be used during physical activity to assess the relative magnitudes of trunk stresses in subjects performing differing working manoeuvres.

While mechanization of coalmining is proceeding rapidly, there remain a vast number of heavy manual operations, and even with the fullest foreseeable mechanization certain procedures will still call for manual handling in confined spaces. One of the common tasks in a pit a t present is the erection of roof supports, and i t seems likely that some support work will continue to be done by hand for many years. This work, which is repetitive, involves the erection of heavy hydraulic and other props: in doing this, the prop resting on one end is rotated by the worker through an arc of 90°, a rotation which permits fairly simple analysis of the forces involved.

Thus prop setting constitutes a common and continuing stressful situation in confined spaces in which the forces required to do the work are calculable

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476 P. R. Davis and J . D. G. Troup

with relative e a e , and in which there is no method of manual handling which is generally accepted. Accordingly, this activity was chosen for investigation in the present study with two particular aims. First, to observe the effects on the trunk of the diserent lifting methods commonly employed, to permit the choice of a method involving least back strain; and secondly to observe the effects of changes in roof height on the behaviour of the spine and trunk.

Teble 1 . Dimensions end weight8 of the props used in the study

Height of centre of gravity

Seam Length ebove height Weight overall lower end (ft in.) (kg) (cm) (cm)

2 6 3 5 4 76.2 38.6 3 6 45.7 104.1 49.5 4 6 55.0 124.5 57.8

The propa An hydraulic prop is essentially a cylindrical object 13.5 cm in diameter,

to the upper end of which are added a circuIar cap, a small handle and a n attachment for the hydraulic pump lever. In the present study props for use in seams of 2 f t 6 in., 3 f t 6 in. and 4 f t 6 in. ceiling height were employed: their dimensions are given in Table 1.

In general, when erecting a prop, the subject's hands lie a little below the cap. The centre of gravity of each prop is also a little below centre so that when one end of a horizontal prop is supported by the subject he is holding almost exactly half the prop weight. When the prop stands erect, with its lower end on the ground, the subject's hands support none of its weight. I n between these two extremes the weight supported by the hands is approximately

where W = the weight of the prop and e=the angle between the prop and the ground. Thus, when the prop reaches 30" the subject.stil1 supports 87 per cent of the horizontal load, and not till 60" does his burden diminish by 50 per cent.

The work done in erecting a prop can be derived from

(M1Cl2/6) + M l g , where M = prop mass, I = prop length, i2 = the maximum angular velocity of rotation, I , = height of the centre of gravity above ground in the erect position and g is the gravitational coefficient. This equation assumes that the prop behaves as a uniform thin rod, and can thus only be an approximation, but appears sufficiently accurate for our purposes. The angular velocity was obtained from the cyclographs and the cine films (see below), and the position of the centre of gravity by determining the point of balance of the prop in a horizontal position.

Lifting methods The three methods of lifting to be investigated are illustrated in Figure 1. Knees up The subject squatted on his heels, the prop lying directly in

front of him with its cap as close t o his body as possible. For

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Piprrn 1. The thrno lining methrltla. a. krl-- up, I * , k n w ~ rlnu-nan: r, rrlil~c~trn. Thh arlhjrrt I* a n t k a n ~ nnrlnt a 3 SR A In. cwl~n,q. arnrlnu nai*?y I!*-lmrt nnd knm pnrln. Now thrr nllinrl markvr pina t tmd tor nnabpis of lrrptnal innvrm-nt 'I-hc pro11 1s nnclomtl 1r1 r k i p h t a ~ l ~ l ~ t cnmr t.o which ~n nttwhTV1 R rnnrkcr mrrp 3 ~ 1 t 4 . Lhw mlppnrt h ~ t l n r > n i d l r !ha r v l l ~ n ~ 1 Ft intewnln

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P. R. Dawia and J . D. Q. Truup

the first part of the lift the main effort came from the mm; as the prop reached about 45" the hips extended and the knee fell on to the ground, the remainder of the lift being achieved by extension at hip and knee and by forward thrust of tho arm.

Kme8 down The subject adopted a posture similar to that above, with the exception that hie h e e a were on the ground at the outgot and remained thera throughout the lift. Tho effort of lifting nppearcd ta be equally divided between the knew, hips md a m ,

obi^ The subjecrt knelt on one knee at the side of the cap, with the prop obliquely in front of him. For the first part of the Iift he extended his hips and trunk and flexed his elbowa, and when the prop reached about 35' he changed his grip and continued the lift by exhnding his knees, rotating hia trunk and pushing upwards and forwards with his arms.

The threo lifta were chosen since they appeazsd Eo be those most commonly employed by ninere at the coal fm. The oblique lift is least commonly u d . Nono of them is fully satisfactmy. En the knees-up posture the impact of the knees with the ground appeam at times ta be severe, in the knw-down post;= tho body is in n most unstable po-sitbn at the ond of the lift, and with the oblique lift there is a tendency to fall sideways as the change in hand position ia made st about 36*.

2, Apparatus and Methods The intra-abdominal p m u m was recorded# on 8 pen-writing oscillogtaph

which received suitably amplified signals from radio pills swallowed by the subjects. To record the movements of the propa and lumbar spinc, high-speed synchro-

nized cin~photography and cyclophotagraphy were employed, using reflective strip markers tw described by Davis el d. (1965). For each tevrk lateral cine photographs at 48 fps and lateral cyelographs at I0 fpfpe wem obtained.

Limitation of working height was achieved by the use of a wooden frame in which the roof could be placed at the required heights {Figwe 1). The flmr of the device wns of hardboard, with a varnished and srtndd surface to give safe fmting. Hanging from the roof was it white rod for use as a reference line in posture annlysis.

In preliminary trials subjects were asked to erect props at the t h e hejghta, 2 ft 6 in., 3 ft 6 in. and 4 ft 6 in. It was found that the 2 ft 8 in. d l i n g forccd them ta lift with one hand, the trunk being supported by the other arm resting on the ground: in this type of l i f t the trunk makea little or no contribution, and no ~ipificant i n c r e ~ e s in prassure wcro recorded. Accordingly teats of l i b at 2 it 6 in. height9 were discontin~~ed and the definitive experiments were restricted to lifts at 3 it 6 in. and 4 f t 6 in. only.

For st.atistical purposes, anaiyaea of uatiame were made of the following measurements.

I . The time4required for the prop ta reach 30'. 2. The time required for t h e lift to be completed.

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Effects of Erecting Pit Props at Different Working Heights 479

3. The peak abdominal pressure occurring at the outset of each lift (the snatch pressure, Davis 1959 b).

4. The mean abdominal pressure sustained during the lift multiplied by the duration of the pressure (the pressure-time product).

The timing and extent of lumbar movement and the work done in erecting the props were also calculated.

The peak pressure is an index of the maximum trunk stress, the pressure- time product indicates the overall stress, the time to 30' was used as an indication of the magnitude of the initial acceleration, and the completed time as an indication of the overall speed of'the lift.

In addition, graphs were prepared comparing the angular movement of the prop, the abdominal pressure and the movements of the spine.

Twelve subjects participated in parts of this work, all being males between 18 and 24 years. Eight took part in the early development work: four were used for the definitive investigation, and it is the results from these that are reported here.

3. Results The mean results of the measurements of times of lift and pressure changes

are given' in Table 2.

Table 2. Mean peak abdominal pressures, pressure-time products, times for the complete lift, end times for the first 30' of lift in subjects lifting pit props of two different lengths by three different methods. In each Case the reedings constitute the means of three lifts by each of the four subjects. Standard errors are given in parentheses

Knees up Lifting method slow fast

3 St 6 in. prop Peek pressure (mm Hg) 46.3 . 71.3

(4.0) (7.2) Pressure-time product 52.5 53.8

(7.2) (5.5) Time for whole l i f t (sec) 1.7 1.1

(0.12) (0.06) Time to 30' (sec) 0.77 0.54

(0.03) (0.03)

4 f t 6 in. prop Peak pressure (mm Hg) 65.0 88.3

(5.7) (4.3) Pressure-time product 84.2 67.1

(8.1) (2-0) Time for whole lift (sec) 1.9 1.3

(0.17) (0.1 2) Time to 30' (sec) 0.91 0.58

(0.03) (0.03)

Knees down slow fast

Oblique slow fast

Peak intra-abdominal pressures of 70-100 mm Hg were consistently recorded when erecting 4 ft 6 in. props a t speed with the knees-up and oblique lifts, and even when carrying out these manoeuvres slowly, pressures of u p to 90 mm Hg were observed. With the knees-down method the peak pressures were less in all cases, this being significant and most noticeable when the prop was erected slowly. The times taken for the first 30" of the lift by any method did not differ significantly, so that differences in speed of lift do not appear materially to have influenced these findings. ~ o r " t h e 3 ft 6 in. props, peak

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480 P. R. Davh and J . D. G. Troup

pressures were generally lower than those for the 4 ft 6 in. props, but again the knees-up and oblique methods produced higher pressures than did the knees- down lift. The statistical significances of the mean differences arising in the different postures are given in Table 3. Thus, overall, it is quite clear that the knees-down method used in this study was less likely to produce high-peak pressures than were the other methods. When the results of peak pressure measurement a t the two roof heights were compared between subjects, i t was found that the two taller subjects (5 ft 10 in. and 6 ft) showed greater differences ( p < 0.05) than the two shorter individuals (5 ft 8 in. and 5 ft 9 in.). On average the pressures observed a t 3 ft. 6 in. were of the order of two-thirds those observed a t 4 ft 6 in., but in the tallest subject the mean difference wm of the order of one-quarter.

Tablo 3. Probabilities (p) in between-lifts comparisons of the peak intre-abdominal pressures, times to 30°, and pressure-time products between the various lifting methods

Oblique Oblique Knees up- knees up knees down knees down

Prop Speed P P P length of lift ft in. 3 6 Slow N.S. < 0.001 < 0.001 3 6 Fast N.S. < 0-01 < 0.05

Preasure peaks 4 6 Slow N.S. < 0.01 < 0.001 4 6 Fast N.S. < 0.01 N.S.

3 6 Slow N.S. N.S. X . S . 3 6 Faat N.S. N.S. N.S.

Lift time to 30' 4 6 Slow N.S. N.S. N.6 . 4 6 Fest N.S. N.S. N.S.

3 6 Slow N.S. < 0.02 < 0.05 3 6 Fast N.S. < 0.01 < 0.02

Pressure-time product 4 6 Slow N.S. < 0.05 < 0.01 4 6 Fast N.S. < 0.05 N.S.

N.S. -not significant

3.1. External Work Done The calculated work applied to the props in the various lifts is summarized

in Table 4.

Table 4. The work applied to the props ( J o h ) in the various tasks

Lift 3 f t 6 in. prop Knees up Slow

Fast Knees down Slow

Fest Oblique Slow

Fast 4 ft 6 in. prop Knees up Slow

Fast Knees down Slow

Fast Oblique Slow

Fast

Work done (Joulea) Mean S.E. 232.8 1.9 242.6 1.9 237,6 2.7 244.7 3.3 232.3 0.6 251.8, 6.7 357.0 1.1 378.4 3.7 356.7 2.3 377-2 2.0 356.1 2.2 377.9 2.9

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EfSech of Erecling Pit Props at Different Working H e i q b 481

I t - can be seen that there is little difference in the amount of external work done when a given prop is erected by any method and by any person. Increasing the speed of erection within the limits of the present series resulted in increases in external work of the order of 10 per cent a t most. Erecting a 4 f t 6 in. prop required about 50 per cent more external work done than that needed to erect a 3 ft 6 in. prop.

3.2. Lumbar Movement The amounts of lumbar extension occurring during the various tasks are

summarized in Table 5.

Table 6. Amplitudes of lumbar movement observed in the four eubjects during the various tasks

Lift

a ft 6 in. props Knees up Slow Faat

Kneea down Slow Past

Oblique Slow Fast

4 ft 6 in. props Knees up Slow Fast

Knees down Slow Fast

Oblique Slow Fast

Total observed lumbar extension (degrees) Mean S.E. 18.5 1.5 22.0 3.7 17.7 1.6 24.0 1.6

8.7 2.7 12.6 2-5 46.0 1.8 51.0 2.9 48.0 5.6 53.7 1.8 29.9 3.5 37.7 3.8

Extension a t 30° (degrees)

Mean S.E. 0 6.3 1.0

8.7 0.9 16.4 1.6 14.6 1.1 7.0 1.6 4.7 0.8

22.7 1.3 24.0 1-7 . 31.0 1.5 31.7 2.8 14.6 1.6 14.8 3.5

For all lifts, the amount of lumbar extension a t 3 f t 6 in. was a t most half t h d required at 4 ft 6 in. A fast lift resulted in more movement than did a slow lift at any height. The amount of extension was similar in the knees-up and knees-down lifts, and was considerably less during the oblique lifts. By measuring the lumbar extension that had occurred as the prop reached the 30" position, and comparing this with the total extension an indication of the timing of the extension can be obtained. At 3 ft 6 in. less than half the h a 1 extension occurred by 30" in the knees-up and fast oblique lifts, much more than half being obtained ip the other tasks. At 4 ft 6 in. less than half the extension had occurred at 30' in all lifts except for the knees-down lift. However, when the timing of lumbar extension was compared with that of the peak abdominal pressure, it was found consistently that lumbar extension was occurring as the peak pressure developed in lifts at 4 ft 6 in., whereas a t 3 f t 6 in. in most cases lumbar extension was delayed until after the peak pressure had subsided.

4. Discussion While considerations of stability and accuracy suggest that none of the three

lifts investigated is fully satisfactory as a procedure, it is clear that of the three the knees-down lift induced significantly lower intra-abdominal pressures than did the others. It is equally clear that a slow lift produced less pressure increase than did a fast lift. By inference i t seems that the lift least likely to produce high spinal stress is one done slowly in the knees-down position. However, towmds the end of a knees-down lift the trunk is well forward of the knees in an unstable posture, whereas in the oblique lift the end position

I G ERG.

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482 P. R. Davis and J. D. Cf. Trowp

was stable. It would therefore seem likely that some combination of the two methods of lift may provide a compromise between the needs of safety in the early stressful part of the lift and the later requirements of bodily stability as the prop approaches its final erect position.

The mean pressure rise multiplied by the duration of pressure, which we have called the pressure-tim product, gives an indication of the overall stress on the trunk. This varied considerably from individual to individual, but waa consistent for a given subject repeating a given task. There was little difference in pressuretime product between slow and fast lifts by a given method, and this would seem logical, since there was only a small difference in the external work done when slow and fast lifts were compared, and one would expect the overall reaction on the trunk from the prop to reflect this. Since the peak pressures were significantly greater for the faster lifts, and these are thought to reflect moments of peak stress on the trunk, it appears likely that this type of task is best performed at a moderate speed, thus spreading the load on the c pine with less risk of momentary overstress.

l l l l r l l r l 0.8 1.0 1-2 1.L 1.6 1.8 2.0 2.2 2 . 4

L I F T TIME (SEC.)

Figure 2. Pressure-time products (quotients) graphed against completed time for the lift for all knees-down lifts at 3 ft 6 in. working height. The figure suggests that the lowest pressure- time product (and by inference the least overall trunk stress) occurs where erection of a prop by this method takes about 1.5 8ec.

By plotting the pressure-time product against the time for completion of the lift, one can obtain curves (Figure 2) which suggest that there is a speed of lift which, by keeping the peak pressure fairly low and yet erecting the prop reasonably fast so that it is not held against gravity for long, results in least overall trunk stresses. While the present observations are too few in number for this method to be exact and the scatter was considerable, in general they suggest that the optimum speed of lift is one taking about one-third as long again as the fastest performed in this series. Further work will be needed on this aspect before one can be certain that such a deduction is generally applicable.

One of the outstanding observations made in this series was the considerable decrease in spinal movement observed in those setting props a t 3 fh 6 in. aa

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EfSecta of Erecting Pit Props at Uifferent Working Heights 483

opposed to 4 f t 6 in. In general, the amount of movement a t 3 f t 6 in. was less than half that observed a t 4 ft 6 in.; in the latter the movement was of the same order as that observed by Davis et d. (op. cit.) in lifts of similar weights in an unrestricted environment. This suggests that there is a critical height some- where near 4 ft 6 in. below which lumbar movement is considerably reduced. This reduction in range of movement was present even with the oblique lifts, in which movement was less than in the other lifts a t either seam height.

At 4 f t 6 in. up to half the lumbar extension occurred during the &st 30" of prop movement, during which time the prop was being accelerated against the greatest resistance, and the intra-truncal pressures were a t their peak. Davis et al. (op. cit.) found that, with lifts of comparable severity in unconfined surrounds, subjects delayed lumbar extension until the major part of the work had been completed. They considered that this delay in spinal movement has certain theoretical advantages for triink mechanisms, and thus it may be that the early extension encountered at 4 ft 6 in. is a product of the limited roof height which is here working against the advantages of spinal fixity a t this time of greatest spinal stress. At 3 f t 6 in. spinal movement was small during the early part of the knees-up and oblique lifts, at which times the pressure records indicate that trunk stresses were comparatively high. In the knees-down lifts a t this height greater lumbar extension occurred during the early phases, although it was commonly delayed until after the pressure peak. However, the observed pressures indicate that with this lift trunk stresses were relatively small, and may not have been large enough seriously to influence spinal movement.

It could be argued that the differences observed between the 3 f t 6 in. and 4 ft 6 in, lifts arose purely from the merent prop weights. Since the lengths and heights of the centres of gravity of the 3 ft 6 in. and 4 f t 6 in. props had ratios similar to that of their masses, namely 415, one would expect the ratios of work done to be proportional to the squares of mass, i.e. (4/5)2==2/3, a ratio which agrees closely with the ratios of work done derived from the cyclographs. Indeed, the differences in spinal stress aa assessed by the pressure measure- ments are roughly of the order of 213, suggesting that spinel stress is closely related to the work done. However, the differences in degree of spinal move- ment were considerably more marked, so that while the differences in weight clearly had some effect, the observed variations were larger than could have arisen from this cause alone.

In this study the differences in working height were large, and i t seems probable that the initial factor will depend on the relation between ceiling height and the bodily dimensions of the siibjects. This is further emphmized by the greater differences encountered between 4 f t 6 in. and 3 ft 6 in. in the taller subjects, although the differences in the shorter subjects were still considerable. The exact requirement causing the changes in reaction remains undiscovered, but may well emerge if the tests are repeated, using working heights proportional to the subjects' stature rather than of absolute dimensions.

5. Conclusions 1. Of the three lifts studied during the erection of hydraulic props, that

employing the knees-down position appears most satisfactory for the heaviest

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Effects of Erecting Pit Props at Different Working Heights

part of the work, but the instability of this lift a t the end of the manoeuvre is undesirable.

2. Somewhere between workingiheights of 3 f t 6 in. and 4 f t 6 in. there is a critical point below which trunk stresses and lumbar movement are greatly reduced. The critical height probably depends upon the stature of the individual relative to mam height.

3. The presuure-time product when plotted againat the speed of lift appears to offer a simple method of assessing that optimum rate of lift causing the least overall spinal stress; however, further work will be needed before this can be known for certain.

Oiir gratitude is due to the National Coal Roard for generoue financial assistance and for the provision of pit props and other apparatus, and to the Peter Samuel Royal Free Fund for their grant for the chrono-cyclograph.

We are particularly indebted to the subjects who took part in the experirnenta, and ta our colleagues, especi~lly Professor R. E. M. Bowrlen, for their advice. Our thanks are also due to Mr. A. W. Amott for ns~listance with.the experiments, and to Mies F. M. Ellis for much help with the photography.

Mpercuasions sur lo tronc d'un mouvement de dbplecement vertical d'btaia de galerie de mine B diffbrentes hauteurs de travail.

On a 6tudiB les effet.8, s w les mouvements de la region lombaire et la pression intraabdorninale, du deplacement vertical d'itais hydrauliques par trois methodes e t A di£fbrentes hauteurs de travail. Lorsque le sujet soulevoit la charge en position accroupie ou eur un genou, la contrainte imposbe au tronc Btei t plus importante que lorsqu'il prenait appui sur les deux genous.

Pour une hauteur de 3 piods 6 pouces (107 cm) l'augmentation d'amplitude des mouvements de lo region lombaire e t de la preasion intreabdominalo 6tait trks infbrieure A l'augmentation observbe pour une hauteur de 4 pieds 6 pol~cas (137 cm), cette difference btant superiewe A celle qui pourreit Btre expliqube par la e u l e priscb en considbration du travail Bvalub d 'apds la formule qui le definit. Les r&ultata indiquent que la technique optime pow soulever dea btais doit encore

'&re BlaborBe, e t que leur dbplacement vertical jmqu'A une hauteur de 4 pieds 6 pouces (137 cm) solon certaines methodes peut s'avbrer excessivement haeardew.

Hydrauliacho Grubemtempel wurden euf 3 verschiedene Arten aufgerichtet. Die Wirkungen ouf die Lendenwirbelsiiule und auf den intraabdominalen D ~ c k wurden untersucht. Heben in einer kauernden und einer mit einem Knie knienden Stellung strengte die WirbeMule stiirker a n n.ls Knien auf beiden Knien. Boi 107 cm Arbeitshohe waren die Bewegungen der Wirbelaliule und der Anstieg des intraebdominalen D r u c b mhr vie1 kleiner el8 bei 137 cm, eine Differenz, die sich aue dem Untarschied der geleisteten iiul3eren Arbeit nicht erklaren 1a13t. Die Resultate zoigen, dafl die optima10 Methode des Stempel-Aufrichtens noch gesucht werden muD; Aufrichten bei 137 cm ist bei manchen Methoden unzumutbar gefihdend.

References BARTELLNK, D. L., 1957, The role of abdominal pressure in relieving the pressure on the l u m b k

intervertebral di~cs. J . bone jt. Surg., 39B, 718-725. . .

DAVIS, P. R., 1959 a. The posture of .the trunk during the lifting of weights. Brit. med. J . , 1, 87-89.

DAVIS, P. R., 1959 b, The cemation of herniae by weight-lifting. Lam&, 2, 15C167. DAVIS, P. R., and TROUP. J. D. (2.. 1964, Pressures in the trunk cavities when pulling, pushing and

lifting. Erqonomim, 7, 465-474. DAVIS, P. R. ,!horn, J. D. G., and BUBNARD, J. H., 1966. Movements of the thoracic and lumbar

spine when lifting: a chrono-cyclophotographic study. J . A d . , Lmd., 09, 13-26. DAVIS, P. R., TROUP, J. D. a., and W H ~ E Y , R. 3.. 1966 (In preparation). Ers, N., and WEAN, P., 1962, M e m m e n t a of the intra-abdominal pressure in relation to weight

beering of the lumbosecrel spine. 3. 0810 Cay Hospilob, 12, 205-217. HULT, L., 1954, Cervical, dorsal and lumbar spinal syndromes. A& Orthop. Scand., Supple-

ment 17. ];AWREN~E, J. 6.. 1955, Rheumatism in coahiners. Part 111, Occupational factom. Brit. J .

indust. Med., 12, 249-261. MORRIS, J. M., Lnoas, D. B., and BRESLEB. B., 1061, Role of the trunk in stability of the spine.

, . J . bone jl. Surg., 43A, 327-351.

,ROANTREE, W. B., 1963, The mobilization and. use of heavy mining equipment as a C 8 W of beolc strain. M e d d Ofifcers' Brodheet ( N & d Coal Board), IV, 3.

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