Occupational and Environmental Medicine 1995;52:731-737

Acute effects of vibration from a chipping hammerand a grinder on the hand-arm system

Steve Kihlberg, Monica Attebrant, Gosta Gemne, Anders Kjellberg

AbstractObjectives-The purpose of this studywas to compare various effects on thehand-arm system of vibration exposurefrom a chipping hammer and a grinderwith the same frequency weighted accel-eration. Grip and push forces were mea-sured and monitored during theexposure. The various effects were: mus-cle activity (measured with surface elec-trodes), discomfort ratings for differentparts of the hand-arm system (made dur-ing and after exposure), and vibrationperception threshold (for 10 minutesbefore and 10 minutes after the expo-sure).Results-No increase in muscle activitydue to exposure to vibration was found inthe hand muscle studied. In the forearm,conversely, there was an increase in bothmuscles studied. For the upper arm themuscle activity only increased whenexposed to impact vibration. Subjectiveratings in the hand and shift in vibrationperception threshold were effected moreby the grinder than the hammer expo-sure.Conclusion-These results show that thereaction ofthe hand-arm system to vibra-tion varies with frequency quantitativelyas well as qualitatively. They do not sup-port the notion that one single frequencyweighted curve would be valid for thedifferent health effects of hand-armvibration (vascular, musculoskeletal,neurological, and psychophysiological).

(Occup Environ Med 1995;52:731-737)

Keywords: electromyography; hand-arm vibration;mechanical shocks; vibration perception

Assessment of exposure to impact vibrationhas been a subject of discussion from the timeof publication of the international standard formeasurement and assessment of hand-armvibration, ISO 5349.' The standard stated thatthe method could, to start with, be used forexposure to both impact and non-impactvibrations. The correctness of this statementcan only be confirmed in epidemiologicalinvestigations of health hazards; so far, nosuch study has been carried out. Data fromstudies on the prevalence of vibration whitefinger (VWF) also seem to challenge the state-ment.

High impulse acceleration not accountedfor by the ISO weighted curve was proposedby Starck to contribute to the high prevalenceof Raynaud's phenomenon in a group ofpedestal grinders.2 Other investigators sug-gested that the large number of frequenciesoutside the range of the ISO weighted curve(well above 1 kHz) might have contributed tothe prevalence of VWF found in workers whoused impact tools (riveting hammer).3 Otherstudies found no differences between expo-sures to impact and harmonic vibration ineither acute effects or prevalence of VWF.56Recent laboratory studies indicated that differ-ent grip and push forces have a large impacton the acute effects on the hand-arm system.78Different tools require different strengths ofgrip and push forces to operate properly. Animpact drill requires a higher push force thandoes a drill hammer. At the same vibration ofthe two tools, the impact drill would cause ahigher transmission of vibration to the hand-arm system.To obtain better knowledge about the qual-

itative and quantitative relations between thefrequency weighted curves and various healthhazards induced by vibration is a matter ofmajor importance. A project has been carriedout that studied various acute effects on manof exposure to a grinder (harmonic vibrations)and exposure to a chipping hammer (impactvibrations) with the same frequency weightedacceleration according to ISO 5349. The pur-pose was to compare the effects of vibrationwith impact characteristics and vibration withharmonic characteristics on: (a) muscularactivity in the hand and arm; (b) perceived dis-comfort; (c) vibration perception thresholdshift on the dorsum of the hand.

MethodThree test series were performed concerning:(a) muscular activities, (b) shifts in vibrationperception threshold, and (c) subjective rat-ings during exposure to two commonly usedhand held powered tools. The two tools were achipping hammer and a grinder with notablydifferent vibration characteristics: differenttypes of vibration (impact vibration from thechipping hammer and harmonic vibrationfrom the grinder), and different fundamentalfrequencies (50 Hz and 137 Hz, respectively,fig 1). Both exposures had a frequencyweighted acceleration of 8 m/s2 according toISO 5349. The two tools were simulated withan electrodynamic vibrator (Bruel and Kjaer4805 + 4812) equipped with a special handlewhere both grip and push forces could bemeasured and monitored (fig 2).

Division ofWork andEnvironmentalPhysiologyS KihlbergDivision ofAppliedWork PhysiologyM AttebrantDivision ofOccupationalMedicineG GemneDivision ofPsychophysiology,National Institute ofOccupational Health,S-171 84, Solna,SwedenA KjellbergCorrespondence to:Dr S Kihlberg, Division ofWork and EnvironmentalPhysiology, NationalInstitute of OccupationalHealth, S-171 84 Solna,Sweden.Accepted 19 June 1995

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Figure 1 113 Octaveband spectra of thechipping hammer andgrinder exposures used.

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Figure 2 Hand-armposture during theexperiments.

Chipping hammerGrinder

were asked to keep the pointers within a speci-fied area during the test. The subject trainedfor the task before the actual test, especially tobe able to keep an eye on the two pointers atthe same time.

/. X w - MUSCLE ACTIVITY- ^ . | / | . The muscular activity was measured by

If1 , | / ,r1electromyography with surface electrodes- -I Ad ---- (Medicotest). Four muscles in the right hand

and arm were studied: hand (interosseus dor-

- . lJ - ' salis I), forearm flexor (flexor carpi ulnaris),forearm extensor (extensor carpi radialis), and

..... upper arm (triceps brachii).The muscular activity was compared with a

t tr--; the X - t-A-- -,t---t- - reference voluntary electrical activationrecorded for 10 seconds each. The reference

.. /- l -activities were chosen to give an adequateelectromyography signal. The reference volun-

/ tary electrical activity for the interosseus musclewas recorded at a steady palmar flexion of theindex finger with a force of 1ON against a

,, Ii, i, sling around the distal phalanx. The hand andl0 100 1000 arm were resting on a table with the fingers

Frequency (Hz) outside the edge of the table. The referencevoluntary electrical activity for the forearm

CTS AND TEST SET UP muscles was recorded during a steady contrac-n healthy men, who had not been occu- tion at a grip force of 85 N exerted on the test

tally or otherwise regularly exposed to handle with the arm in the same position as inion, participated in the studies. There the test. For the triceps muscle the subject wasno signs of neurological or other disor- standing erect with his right arm resting on a

Long the subjects. The mean age of the support at the elbow with an elbow angle of 90:ts was 34 (range 22-58) years, the mean degrees. From that position the reference vol-t was 75 (63-85) kg, and the mean untary electrical activity was recorded duringe was 178 (171-192) cm. an extension of the forearm with a force ofe subject held his upper arm almost verti- 50 N against a sling around the wrist.with an elbow angle of about 1100 dur- The muscle activity was recorded duringe tests (fig 2). The direction of excitation the two types of vibration exposure and a staticlong the forearm. Both the push and grip exposure without vibration, but with the samewere about 30 N during all three test grip and push forces as during vibration. Eachto avoid fatigue. The forces were moni- exposure was repeated six times and recordedby two analog devices mounted on the for 20 seconds. The three exposures were

n front of the subjects and the subjects rotated between the subjects with rest periodsof four minutes in between to avoid fatigue.The amplitude of the recorded electromyo-

graphic signal was full wave rectified and lowpass (800 Hz) and high pass (20 Hz) filteredand integrated with an integrating time of

\9QZ14 4;; 50 ms. The signal was sampled at 2 kHz andstored in a frequency analyser (Bruel andKjaer 2032). The amplitude probability distri-bution function (APDF, Jonsson 1982) wascalculated with the help of the frequency

) > analyser to express the activity distributionduring the different exposures.9 The medianmuscle activities for the three exposures (sta-tic, grinder, and chipping hammer) were thencompared. The frequency analyser was alsoused to control the electromyographic signalfor noise and artefacts. In such a control oneof the subjects had to be excluded due to poorquality of the electromyographic signals.

SUBJECTIVE RATINGSRatings of discomfort and other subjectivequalities were collected after 30 seconds andafter an additional 110 seconds of a threeminute long exposure to the two types ofvibration and the static exposure, as well as

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Acute effects of vibration from a chipping hammer and a grinder on the hand-arm system

every minute during a five minute period afterthe exposure. Separate ratings were made ofthe discomfort felt in the hand, forearm, andupper arm. The three experimental sessions(static, grinder, and chipping hammer) werecarried out on separate days with the condi-tion order rotated.

Discomfort was rated on a 20 point scalewith verbal labels at seven of the points. To geta qualitative description of the subjectiveeffects of the two types of vibration six addi-tional scales were used. These scales werebased upon a pilot study in which factor analy-ses were made of ratings of different types ofvibrations on rating scales, which all consistedof an adjective and a five point rating scale(from not at all to very much). These analysesyielded a three factor solution for ratings madeboth during and after exposure. Each factorwas represented by two or three scales, andfactor scores were computed as means of rat-ings on these scales. The three factor scorescomputed from the ratings made during expo-sure were labelled pricking (mean of ratingson two scales: pricking, tickling), piercing(piercing, insensitising) and jerky (jerky, hard,shaky). The scales used for describing the feel-ings after the exposure were called pricking(prickly, itchy, throbbing), warm (warm,cold), and stiff (stiff, numb). Furthermore,pain was rated both during and after exposurewith the same type of five point scale. TheSwedish adjectives used in the original scaleswere all common everyday words.

In another test series, overall discomfort rat-ings were made of the two types of vibration atfive levels with 5 dB intervals (1 -6-16 m/s2).

VIBRATION PERCEPTION THRESHOLDThe assessment of the vibration perceptionthreshold was made with commercially avail-able equipment, Vibrameter (Somedic,Stockholm).'0 The probe consisted of a mas-sive plastic cylinder with a cross sectional areaof 1 cm2. The vibration of the probe was sinu-soidal and had a frequency of 100 Hz. Theapparatus was mounted in a stand with a piv-oting arrangement and was allowed to restwith part of its own weight (about 0 4 kg)against the skin. It was placed perpendicularlyagainst the skin above the second metacarpalbone of the dorsum of the right hand at themidpoint between the proximal interpha-langeal joint and the carpometacarpal joint.The forearm and the hand rested in an impres-sion of plaster to prevent variation in the posi-tion of the probe from one experimentalsession to another. The temperature of theskin and tissues of the hand was kept stablewith an infrared lamp placed about 15 cmabove the hand. The subjects were wearing earmuffs during the experiment to avoid distur-bance from irrelevant background noise.The vibration perception threshold of each

subject during recovery after exposure tovibration from the tools was assessed accord-ing to the following procedure: (1) The non-vibrating probe was placed against the skin,the intensity of vibration being initially zero.The intensity (expressed as the amplitude of

probe displacement) was then slowly increasedwith constant speed until the subject statedthat he perceived vibration. The increase wasallowed to continue for about another two sec-onds, after which intensity began to decrease.The decrease continued until the subjectstated that the vibration perception hadstopped, and the intensity was then allowed todrop to zero.

(2) For each such measurement cycle(duration 40-60 s), the vibration amplitude atthe start of vibration perception was noted asthe appearance threshold together with thetime when this occurred (in seconds afterexposure). When perception stopped the cor-responding disappearance threshold wasnoted. The vibration perception threshold wasthen determined as the mean of the appear-ance and disappearance values.

(3) The procedure was then repeated byrestarting the measurement cycle as soon aspossible after the end of the previous cycle.The repetition continued, with as little delayas possible between cycles; the whole durationof vibration exposure to recovery was 10-15minutes.The time it took for one cycle to be com-

pleted varied widely because of-for instance,variation in the time when vibration percep-tion appearance and disappearance occurred.This is why the individual observations ofthresholds could not be made at precise, pre-determined times. Instead, the thresholdvalues at 120, 360, and 600 seconds weremeasured from a curve fitted to the values atthe various measuring times with the methodof least squares.The threshold assessments were made in

two different sessions, one for each tool, with aminimum interval of six hours. Each test seriesstarted with a pre-exposure perception thresh-old test for 10 minutes, after which the threeminute exposure took place. As soon as possi-ble after the exposure, the threshold was testedfor a 10 minute period. The shift in perceptionthreshold was calculated as the percentage dif-ference between the threshold before and afterexposure.

DESIGNThe design of the test series for the muscleactivity was a 3 (exposure) x 4 (muscle) facto-rial design with repeated measurements. Thedesign of the rating test series was a 3 (expo-sure) x 3 (hand, forearm, upper arm) x 2(time during exposure) or 5 (time after expo-sure) factorial design with repeated measure-ments for the discomfort rating scale. For theother rating scales the design of the rating testseries was a 3 (exposure) x 3 (hand, forearm,upper arm) x 5 (time) factorial design withrepeated measurements. Models suitable forthese designs were used for the analyses ofvariance. Follow up tests were made withFisher's least significant difference test. Theshifts in vibration perception threshold for thegrinder and the chipping hammer were calcu-lated with the functions fitted to the observedvalues at 120, 300, and 600 seconds and com-pared by paired Student's t test.

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Figure 4 Rateddiscomfort in different partsof the hand-arm systemduring and after the static,grinder, and chippinghammer exposures. Mean(SEM) of 15 subjects is

shown.

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cr-

Hand Forearm Forearm Upperflexor extensor arm

ResultsMUSCLE ACTIVITYThere was an interaction between muscles andexposure, for static, grinder, and chippinghammer (F(6/84) = 2-895, P < 0-02). Followup tests showed that there was a tendency toincreased muscle activity due to vibration in

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the interosseus muscle (F(2/26) = 3-062,P > 0 06). In both the forearm muscles therewas an increase in muscle activity whenexposed to vibration compared with the staticexposure, flexor muscle (F(2/26) = 4 123,P < 0 03), and extensor muscle (F(2/26) =

11-737, P = 0 0002). In the extensor musclethe activity during the chipping hammer expo-

sure was insignificantly higher than during thegrinder exposure. In the flexor muscle therewere significant differences in muscle activitybetween all three exposures. The muscle activ-ity in the upper arm increased only during thechipping hammer exposure

(F(2/26) = 12-924, P = 0 0001). Figure 3shows these interactions between exposures

and muscles.

SUBJECTIVE RATINGS

Discomfort during exposure increased fromthe first to the second rating (F(1/14) = 26 7,P = 0.0001). Figure 4 shows that discomfortwas rated higher in all parts of the arm duringexposure to vibration than during the staticexposure (F(2/28) = 18-16, P = 0 0001).There were also consistent differencesbetween the two vibration exposure condi-tions. Thus, grinder vibration yielded higherdiscomfort ratings than the chipping hammervibration in the hand, whereas the oppositeapplied to the upper arm. This was supportedby the analysis of variance, which showed a

significant interaction between exposure andpart of the arm (F(2/28) = 7-55, P = 0 003).The discomfort ratings made after exposure

showed a general decline to very low ratingsafter five minutes (F(4/56) = 40 85), P =

0 000 1). The ratings of discomfort in the handin the vibration exposure were significantlyhigher than the static exposure ratings duringthe first five minutes (F(2/28) = 14<1, P =

0-0001), and there was a tendency (F(1/14) =

3*75, P = 0 07) for the grinder vibration togive stronger effects after the exposure thanthe chipping hammer vibration did (fig 5). Inthe forearm, the exposure conditions yieldedvirtually identical ratings, although both were

higher than in the control condition. The rat-ings of discomfort in the upper arm showed no

differences between types of vibration.The grinder vibration was rated as having

more pricking (F(1/14) = 6-69, P = 0 03),

!i |= StaticWn 2.5 _ GrinderCl) - Chipping

E 2.0llhammerE n 15

CaD 1.5-

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:3 Pricking Jerking Piercing PainC,)

Figure 5 Subjective rating ofpricking, jerking, piercing,and pain during static, grinder, and chipping hammerexposures. Mean (SEM) of 15 subjects is shown.

Figure 3 The muscleactivity in percentage ofrelative voluntary electricalactivation (RIVE (%/o)) forthe static, grinder, andchipping hammer exposure.Mean (SEM) of 15subjects is shown for themuscles, interosseusdorsalis I (hand), flexorcarpi ularis (forearmflexor), extensor carpiradials (forearmextensor), and tricepsbrachii (upper arm).

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Acute effects of vibration from a chipping hammer and a gender on the hand-arm system

Figure 6 Subjectiverating ofpricking andstiffness as a function oftime after static, grinderand chipping hammerexposures. Mean (SEM)of 15 subjects are shown foreach point.

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0U)0).00)

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Pricking

1.0 2-0 3-0 4-0 5.0 0.0Time (min)

equal piercing, and less jerking (F(1/14) =42-66, P = 0-0001) than the impact vibrationduring exposure (fig 5). In all these factorscores, both vibration exposures were givensignificantly higher ratings than the staticexposure. This was not the case for the painratings, which were about 05 in all three con-ditions.

After exposure the effects rated with thefactor scores pricking, warmth, stiffness, andpain, showed no differences between thevibration exposure conditions. Only the stiff-ness and pricking scores were higher in thevibration exposures than the static exposure(F(2128) = 10-66 P = 0 0004, F(2128) = 3-94P = 0-031, respectively, fig 6).

VIBRATION PERCEPTION THRESHOLDThe effect of vibration exposure from bothtools was a threshold increase followed by asteady recovery of perception lasting for 10minutes or more, as seen in the example fromone subject (fig 7).The rise in vibration perception threshold

caused by exposure to grinder vibration wasgenerally twice that of the chipping hammerexposure. Figure 8 shows that the difference inrises in vibration perception thresholdbetween the two exposures was significant at120 seconds after stimulation (341% and149% respectively; t = 2-23, P < 0-05), non-significant at 300 seconds, and again signifi-cant at 600 seconds (78% and 35%,respectively; t = 2-63, P < 0-05).

StiffnessE Static* GrinderA Chipping hammer

4.0 5.01.0 2.0 3-0Time (min)

DiscussionThe extent to which movements of the jointsoccur that are induced by vibration dependson the characteristics of the transmission ofvibration in the hand-arm system.8

Frequencies <50 Hz are transmitted un-attenuated to the elbow, whereas frequencies>100 Hz are attenuated already at the wrist.The acute effects of vibration found in the pre-sent study therefore reflect the differences infundamental frequencies (50 Hz and 137 Hz)of the tools under investigation. Because ofthese differences, the results cannot be usedfor general conclusions about impact v non-impact vibration. They do contribute, how-ever, to the knowledge about vibrationaleffects of two commonly used tools that repre-sent two basic types of vibration (impact andharmonic). Impact tools usually havefundamental frequencies of 20-60 Hz, thefrequencies of grinders are 100-400 Hz.

MUSCLE ACTIVITYThe increase in electromyographic activitywhen exposed to vibration reflects the wellknown tonic vibration reflex of a muscle, andpossibly other mechanisms dependent onneuromuscular vibration.'1 12 The differencesin electromyographic activity between the twovibration exposures found in the forearmflexor and triceps muscles could be explainedby the differences in transmission of the vibra-tion through the hand and along the arm. Inanother experiment performed under the same

Figure 7 Example fromone subject of vibrationperception before anddirectly after exposure as afunction of time.

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60

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* After grinder* After chipping hammero Before grindero Before chipping hammer

100 200 300 400 500 600 700Time (s)

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-100

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hammer

P < 0-05

120 360 600Time after exposure (s)

Figure 8 Increase in vibration perception threshold afterthree minutes ofexposure wo grinder and chipping hammerat 120, 360, and 600 seconds after the exposure. Mean(SD) of 14 subjects is shown.

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conditions an impact exposure with a funda-mental frequency of 50 Hz was found to betransmitted almost without attenuation to theelbow.8 A grinder exposure with a funda-mental frequency of 137 Hz was in the samestudy attenuated by about 20 dB at the wristand therefore should have less influence thanthe grinder on the muscle activity in the arm.During the impact exposure, the triceps mus-cle would thus be more affected than duringthe grinder exposure.

There were no significant differences inactivity of the extensor muscle between the twovibration exposures. The discrepancy in resultsbetween the flexor muscle and the extensormuscles may depend on the large variation inmuscle activity between subjects, dependingon how they stabilise the wrist for the impulseforces caused by the chipping hammer. If thesubjects hold their wrist in the neutral position,there will be an extension force acting on thewrist at every impact, and because of a stretchreflex the activity in the flexor muscle will behigher than in the extensor muscle.

SUBJECTIVE RATINGSDiscomfort in the hand was rated higher duringexposure to grinder vibration, than duringexposure to chipping hammer vibration. In theforearm, there was no difference between thetwo exposures, whereas discomfort in theupper arm was rated higher for the chippinghammer. These differences in discomfort rat-ings between different parts of the hand-armsystem could depend on different fundamentalfrequencies of the two exposures and theshape of the transfer function of the hand-armsystem. Although there was no relationbetween discomfort ratings and muscle activ-ity in the hand and forearm, in the upper armimpact exposure produced both higher dis-comfort ratings and higher muscle activity.The fact that the muscle activity in the tricepsmuscle was low indicates, however, that thediscomfort ratings probably did not originatefrom muscle activity.

VIBRATION PERCEPTION THRESHOLDThe strong effect on the vibration thresholdand perception of the grinder vibration may bean indication that nerve functions in the hand-arm system (particularly the hand) would bemore at risk after grinder vibration than afterchipping hammer vibration.The vibration perception threshold depends

on test frequency, as has been shown forinstance by Lamore and Keemink, Haradaand Griffin, and Lundstrom et al."3-'5 This fre-quency dependency has also been found todepend on probe size and probe surround-ings.'6 The shape of the threshold curve alsovaries depending on whether the vibration isexpressed as displacement, velocity, or accel-eration.'3 14 The differences in perceptionthreshold over the frequency range could alsoplay an important part in the effects measuredafter exposure to vibrations with different fun-damental frequencies.Maeda and Griffin found differences in

temporary threshold shift in vibrotactile per-

ception after exposure for five minutes torepetitive shocks with the same frequencyweighted root mean squares (2.5, 5, or 10M/s2) but with different rates of shock repeti-tion.'7 They used one period of 100 Hz as theshock and repeated it 5, 25, 50, and 100 timesa second. The temporary threshold shift mea-sured at the fingertip with a stimulus fre-quency of 125 Hz, increased with frequency ofshock repetition. The highest temporary shiftin threshold was found for the continuous 100Hz frequency. Frequency spectra (octave or1/3 octave) for the four exposures broadenedwith decreasing shock frequency. This mightindicate that man is more sensitive to a puretone of vibration than to random vibration orvibration containing several frequencies, as isthe case for noise.'819 An alternative explana-tion is that the difference in excitation fre-quency (5, 25, 50, and 100 Hz) and testfrequency are reflected in the results. Theresults found by Maeda and Griffin coincidewith the results found in the present study-that is, a higher shift in threshold after thegrinder exposure (at 137 Hz) than after thechipping hammer exposure (at 50 Hz) with atest frequency of 100 Hz.The shifts in vibration perception threshold

found in the present study also harmonise withthe results of the discomfort ratings tests, withhigher discomfort rating scores in the handand larger shifts for the grinder than for theimpact vibration exposure.

IMPACT V HARMONIC VIBRATIONThe differences in acute effect between expo-sures to the grinder and chipping hammerfound in the present study may be chieflyexplained by the difference in the excitationfrequency. There is, however, another differ-ence of possible significance between theimpact and harmonic exposures, namely theshock wave, pressure wave or elastic wavepropagation in the bones in the forearm.8These types of waves have been used by sev-eral investigators to study bone characteristicsin vivo.2022

In a study of stone quarry workersSakakibara et al found that duration of vibra-tory tool operation may correlate with disor-ders in the right elbow joint but not in the leftelbow joint.23 The tools they used were chip-ping hammers and scalers, both impact tools.The difference in exposure between the leftand right arms was: no shock waves weretransmitted along the left forearm, but neverthe less, the overall vibration level in the lefthand was high because the workers were guid-ing the tool bit with the left hand.

In a study on 67 foundry workers and acontrol group of 46 heavy manual workers,Bovenzi et al found that the prevalence ofosteoarthritis in the wrist and olecranon spursin the elbow increased with increasing dailyexposure to impact vibration.24 They found nocorrelation between the occurrence of vibra-tion white finger and radiological changes inthe arms.

Similar results were found by Burdorf andMonster, with more complaints of pain or

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stiffness of joints among the riveters thanamong the controls.25Louda et al found seven cases of carpal tun-

nel syndrome among 23 women exposed tohand-arm shocks from nail or staples airguns.26 The frequency weighted accelerationsof the air guns were about 1-5 m/s2 at the high-est. These authors proposed that it was themechanical shocks that overload the hand-armsystem. Carlsoo and Mayr measured the accel-eration in tool handle, wrist, elbow, and shoul-der and calculated the shock loads duringwork with a pneumatic hammer and a boltgun.2 They found high shock loads in boththe wrist and elbow joints and they also foundrelatively high stretch reflexes in the bicepsbrachii and the ventral part of the deltoidmuscle.

In the future models of how to assessimpact vibration should be developed. Oneway may be to study the shock or pressurewaves and try to measure them, or find amethod to measure or calculate the impulsethey cause.

ConclusionExposures with a predominantly low fre-quency (around 50 Hz) had a greater effect onthe arm muscles than exposure with a funda-mental frequency of about 137 Hz.

Subjective ratings and vibration perceptionthresholds shift measurements suggested thatthe effects on the hands were stronger for theexposure with the fundamental frequencyaround 137 Hz than around 50 Hz.The differences in acute effects from the

grinder and the chipping hammer exposure(harmonic and impact vibration) found in thisstudy could mostly be explained by differencesin the fundamental frequency of the excitationexposure.The results of this study do not support the

notion that one single frequency weightedcurve would be valid for the different healtheffects of hand-arm vibration (vascular,musculoskeletal, neurological, and psycho-physiological).

This study was supported by the Swedish Work EnvironmentFund.

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2 Starck J. High impulse acceleration levels in hand-heldvibratory tools. Scand J Work Environ Health 1984;10:171-8.

3 Dandanell R, Engstrom K. Vibration from riveting tools inthe frequency range 6 Hz-10 MHz and Raynaud's

phenomenon. Scand Jf Work Environ Health 1986;12:338-42.

4 Engstrom K, Dandanell R. Exposure conditions andRaynaud's phenomenon among riveters in the aircraftindustry. ScandJ Work Environ Health 1986;12:293-5.

5 Mirbod S, Inaba R. A study on the vibration-dose limit forJapanese workers exposed to hand-arm vibration. IndHealth 1992;30:1-22.

6 Schafer N, Dupuis H, Hartung E. Acute effects of shock-type vibration to the hand-arm system. Int Arch OccupEnviron Health 1984;55:49-59.

7 Hartung E, Dupuis H, Scheffer M. Effects of grip and pushforces on the acute response of the hand-arm systemunder vibrating conditions. Int Arch Occup Environ Health1993;64:463-7.

8 Kihlberg S. Biodynamic response of the hand-arm systemto vibration from an impact hammer and a grinder.International Journal of Industrial Ergonomics 1995;16: 1-8.

9 Jonsson B. Measurement and evaluation of local muscularstrain in the shoulder during constrained work. _J HumErgol (Tokyo) 1982;11:73-88.

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