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Original articleScand J Work Environ Health 1987;13(4):286-289 doi:10.5271/sjweh.2049

Ergonomics and the effects of vibration in hand-intensivework.by Armstrong TJ, Fine LJ, Radwin RG, Silverstein BS

Affiliation: University of Michigan, Center for Ergonomics, AnnArbor 48109.

This article in PubMed: www.ncbi.nlm.nih.gov/pubmed/3324309

Scand J Work En viron Health 13 (1987) 286- 289

Ergonomics and the effects of vibration in hand-intensive work

by Thomas J Armstrong, PhD, Lawrence J Fine, MD, Robert G Radwin, PhD,Barbara S Silverstein, PhD'

ARMSTRONG TJ , FINE LJ , RADWIN RG, SILVERSTEIN BS. Ergonomics and the effects of vibra­tion in hand-intensive work. Scand J Work Environ Health 13 (1987) 286-289. Along with ergonomicfactors, such as forceful and repeated exertion and certain postures, vibration has been cited as a factorof chronic nerve and tendon disorders such as carpal tunnel syndrome and tendinitis. The arguments forthe contribution of vibration come from epidemiologic studies, clinical case analyses, and studies of short­term effects. It is well established that vibration stimulates muscle contraction, which is called the tonicvibration reflex. It is also known that vibration reduces tactility and that tactility affects the amount offorce exerted to hold or manipulate a given object. For localized vibration exposure of the hand and armto occur, the hand must grip a vibrating object. Vibration may increase the risk of chronic tendon andnerve disorders by increasing the force exerted in repetitive manual tasks. This close relationship betweenforce and vibration, and difficulties in measuring force and vibration in manual work, makes it very dif­ficult to determine their relative contributions in epidemiologic and clinical studies.

Key terms: carpal tunnel syndrome, hand-arm vibration, tactility, tendinitis, tonic vibrationreflex,vibration­induced white finger.

Along with ergonomic factors, such as for ceful andrepeated exertion and certain postures, vibration hasbeen cited as an etiologic fac tor of chronic nerve andtendon disorders, including carpa l tunnel syndro meand tendinitis (I, 2, 4, 13, 14). The argume nts for theco ntribution of vibration come from epidemiologicstudies, clinical case analyses, and studies of short-termeffect s. It is well established th at vibration stimulatesmuscle contrac tion, thi s contra ction being called thetonic vibra tion reflex. It is also known that vibrationreduces tactility and that tactility affects the amountof force exerted to hold or ma nipu late a given object.For localized vibration exposure of the hand and armto occur, the hand must grip a vibrating object. Vib­ration may increase the risk of ch ro nic tendon andnerve disorders by increasing the force exerted in repeti­tive manual tasks. This close relationship between forceand vibration, and difficulties in me asuring force andvibration in manual work, makes it very difficult todetermine their relative contributions in epidemiologicand clinical studies.

Tonic vibration reflex

Mu scles exposed to vibratio n can exh ibit a tonic vi­bration reflex (TVR) in the form of a gradually increas­ing involuntary contraction (3, 7). Hagbarth & Eklund(5) observed that, if a mu scle is moderately acti ve,vibrating its tendons causes a gradual increase in its

I University of Michigan, Center for Ergonomics, Ann Arbor,Michigan, United States.

Reprint requests to: Dr TJ Armstrong, University of Michi­gan, Center for Ergonomics, 1205 Beal-IOE Building, AnnArbor, MI 48109, USA.

286

act ivity and simultaneo us decrease in the ac tivity ofits an tagonists. The results ar e either slow jointmovement or a corresponding change in active tension.Matthews (9) concluded that primary a fferent endingso f the mu scle spindle are the receptors responsible forthe refl exive response. The refl ex or igin was the well­known stretch reflex , excited by a rather unusual formof str etching.

In the det ermination of how the tonic vibra tio n re­flex affects persons using po wered hand tool s in auto­mobile assembly, vibration was measured from selectedpolishers, sa nders , wrenche s, and cutters (II ) . Mo stof the tested tool s produced a distin ctly dominant fun­dament al frequency at which the acceleration was ty­pically 10 dB higher than that at other frequencies.Dominant frequencies ranged from 20 to 160 Hz. Thetool weights were found to range between 15 to 30 N.

A laboratory study was then conducted in which gripforce was measured for 14 subjects holding a cylin­dri cal handle weighing 15 and 30 N, vibrati ng at 0, 40,and 160 Hz, 9. 8 and 49 m/ s", and three orthogonalaxes (II , 12). Eac h combination of weight , frequency,amplitude, and dir ection was pre sen ted in randomorder. Each trial lasted 60 s, follo wed by 5 min of rest.Force was sampled with a computer du ring the second20 s o f the 60-s exertion . All the subjects washed anddr ied the ir hands to contro l sweating . Th e result s wereanalyzed with repeated measure s analysis o f var iance.

There were no significant main effects associa tedwith vibration di rection. The average result s for allthree directions are plotted in figur e I . There was asignificant handle weight effect across all combinationsfor vibration ; the average grip force increas ed 55 0/0from 22.5 (SO 12.7) N for the 15-N handle to 35.0 (SO12.4) N for the 30-N handle. The vibratio n effect was

only significant across the 40-Hz trials. Grip force wasincreased 21 lTJo fro m 19.1 N and no vibration to 23.1N for 40-Hz vibration and 9.8 m/ s? for a weight of15 N. Grip force increas ed 52 lTJo to 29. 1 N for 40-Hzvibration at 49 rn/ s". In oth er words, exposur e to40-Hz vibration at 49 m/ s? had about the same effec tas doubling the weight of a 15-N tool.

An electrom yographic (EMG) study indicated thatthe toni c vibration reflex was the most likely cause forincreased grip force when vibration was present (II , 12).It was hypothesized that exert ion o f excessive forceover time increases the risk of chroni c nerve and tendondisorders.

Tactility

Westling & Johansson (17) showed that the static forceexerted to hold objects between the thumb and fore­finger is proportional to object weight and friction.Local anesthesia of the index finger and thumb (5 mgMar cain/digit) resulted in a loss o f sensitivity to objectsurface characteristics, and the exertion of nearly twicethe unanesthesized force for a given object weight.

Vibra tion has been shown to produce short-term sen­sory impairments (6, 16). Recovery is reported to beexpo nential (10) and can require more than 20 min (6).Furth er studies are required to test the hypoth esis thatvibration increases the risk of chronic tendon and nerveinjuries by imp airing tactility and increasing theamount of force exerted to perform a job.

the exert ion to the neurophysiological deficits must beconsidered .

Rothfleisch & Sherman (13) studied carpal tunnelsyndrome in 25 hands of 16 workers in an automobileassembly plan t. Each of the workers was found tohave, at some time , used pneumatic tool s which vi­brated between 8.3 and 33.3 Hz. The y also found thatawkward positioning of the hand and wrist during taskperformance was a common factor. Although therewas no control population or attempt to performstatistical ana lyses, thi s study aga in shows that er­gonomic and vibratio n factors occur together and thatthe ir effects are not easily separated .

Cannon et al (2) performed a retrospective case­referent study on 30 workers with carpal tunnel syn­drome. Th e most significant factor was the use of vi­brating hand tool s (odds ratio 7.0). The tools used(buffers and grinders among others) vibrated from 10to 60 Hz. Although performance of repetitive motiontasks was less important (odds ratio 2.1) , it can be as­sumed that the exposure to vibration involved inten­sive use of the hands. Therefore sustained exertion ,high force s, and posture could account for the ap­parent vibra tion effec t.

Dimberg (4) conducted a questionnaire survey of2 814 workers at an automobile plant in Sweden forsymptoms and factors associated with chronic tendonand nerve injuries. The study found th at 420 person sworked with vibrat ing hand tools. Th e prevalence ofneck , shoulder, elbow, and hand symptoms (table I)among these persons was about twice as high as amongthose who did not work with such tool s. There wasa sma ll correlation (r = 0.06-0.08) , but highly sig-

Figure 1. Average grip force exerted by 14 subjects holdinga vibrating handle weigh ing 15 or 30 N and vibrat ing at 0, 40,or 160 Hz at acceleration magnitudes of 9.8 or 49 m/s2• Gripforce was averagedover three orthogonal vibration directions.Plus or minus one standard deviation appears above each bar.(ACCEL= acceleration, WT= weight).

50 "1 ACCEL &. WTCJ Om/s

t. IS N

_ Om/ . ' .30 N

t:ZJ 9.8 m/.l

• 15N :t2 0 . 3

40llJ. 9.8 m/,I. 30 NIZil (9 mi. , 15 Nil;jI (9 m/.',30 N

:13.7

b %8 .2

30 17.,::;LUU0::0 %11.0I..L.

a.. 20 :t7 . 70:o

10

Population studies

Lukas (8) examined 108 workers with upp er extremityneurological symptoms. Most of the subjects workedin ore quarr ies and were expo sed to segmental vibra­tion in the 20- to 80-Hz ran ge. Fifty-three percent ofthe subjects showed pathological electromyographicchanges. The author stated that it was not possible toconclude that vibration was the prim ar y cause for theneurological signs and symptoms. The clinical neu­rolo gical findings could be explained as secondarysequel s to basic damage of the spina l section of theneck, the elbow joint, and its vicinity or to the carpaland ulnar tunnels.

Seppalainen (14) reported on the neurophysiologicalexaminations o f nine lumberja cks who regularl y usedchain saws and eight men who regul arly worked withpneum at ic rock drills. Eight of the chain-saw userscomplained of numbness and presented neurophysio­logical deficit s. Seven of the drill users complained ofpar esthesia and presented neurophysiological deficits.Although there was no formal description of the lum­berjack and rock driller jobs, it ca n be assumed that,in addition to being expo sed to vibration, these wor k­ers also performed repeated and sustai ned exert ion ,and possibly exerted high forces. The contribution of

oo 40

FREQUENCY (Hz)

zl G.'

160

287

Table 1. Symptom prevalence, tool usage patterns, correla­tions, and significances for a survey of 2814 Swedish autoworkers [from Dimberg (4)].

nificant relation , between the use of vibrating handtool s and symptoms. It is not possible to determine,from the information presented, if there were differ­ences in repetitiveness, for cefulness, or posturebetween jobs requiring vibrating tools and non vibrat­ing tool s that could account for these differences. Theauthor concluded that vibration was an important fac­tor and recommended vibration damping sleeves forthe tools .

A cross- sectional study was performed on 652 ac­tive workers in 39 jobs located in seven different in­du strial plants in the United States to investigate oc­cupational risk factors of carpal tunnel syndrome (I,IS). The study design included two levels each of force­fulne ss and repetitiveness. Nine sets of jobs, each in­cluding four combinations of extreme forcefulness andrepetitiveness, were selected from seven companies in­cludin g telecommunications, investment casting, gar­ment, home appliances, foundry, and bearing manu­facturing plants. Repetitiveness and force fulness weredetermined initially on the basis of work content, cycletimes, and the weight of the handle of the object. Laterthese initial classifications were verified th rough theanalysis of video tapes and surface electromyography.Each combination of repetitiveness and for cefulnessincluded approximately 20 workers. The overall stud ypopulation was approximately equall y divided betweenmen and women although specific jobs were not equal­ly divided. An interview and physical examination wereperformed on each subject to identify those with a his­tory of recurring problems that indicated carpal tun­nel syndrome or hand and wrist tendinitis.

The prevalence of carpal tunnel syndrome rangedfrom 0.6 010 for workers in the low-force/low-repeti­tive reference jobs to 5. 1 % for those in the high­force /high-repetitive stud y jobs. The crude odd s ratio sshowed that workers performing the high-force/high­repetitive jobs were 8.4 times more likely to have carpaltunnel syndrome than those performing the referen cejobs. Four of the nine high-force jobs involved nearl ycontinuous exposure to vibration (buffing, grinding,cutting), while none of the reference jobs involvedvibration exposure. The crude odds ra tio for theworkers in the high-force/high-repetitive jobs withvibration versus those in reference jobs was 11 .3(P < 0.02). The odds ratio for the workers in the high­force /high-repetitive jobs with no vibration versustho se in the same reference jobs was only 5.9

Users of Nonusers~um~er vibrat ing of vi- Correlation

o wor ers tools (%) bratingtools ('I.)

Locationof

sympt oms

NeckShould erElbowHand

293370169199

17191011

91357

0.080.070.070.06

Signifi·cance

P<0.001P<0.001P<0.01P <0.01

(P < 0.10). When workers in high-force /high-repetitivejobs with vibration were compared with those in jobswithout vibration , the odd s ratio was 1.9 (P <0.30) .Th e lack of significa nce could be due to the smallsample sizes.

In summary, these data suggest that the risk of car­pal tunnel syndrome is increased by a factor of 6 forworkers performing high-repetitive/high-force workover low-repetitive/low-force work and that risk iselevated by a factor of 2 by nearl y continuous vibra­tion exposure. While hand and wrist tendinitis washighly associated with high-force/high-repetiti ve work(odd s ratio 18.9, P <O.OI), no association with vibra­tion was found (15).

Conclusions

It is generally accepted that ergonomic factors, suchas repeated or sustained exertion, in combination withcertain postures cause, precipitate or aggravate chronicupper extremity tendon and nerve disorders. It hasbeen suggested that vibration may also cont ribute tothese disorders. There is evidence that vibrationproduces short-term neurological effects includingmuscle contractions and paresthesia . As a result ex­cessive for ce may be exerted to hold vibrating tool sand parts and thus increase the risk of a tendon ornerve disorder. Vibration has been observed as a com­mon factor in persons undergoing clinical evaluationfor chronic nerve disorders. In addi tion there are someepidemiologic data that support the contribution ofvibration. Unfortunately, these stud ies are often con­founded by the co-mingling of ergonomic and vibra­tion exposure variables. If there is a direct contribu­tion of vibration to chronic nerve and tendon dis­orders, it probably is not large. In either case, futureresearch will be required to settle the issue.

Acknowledgments

This work was made possible by The National Institutefor Occupational Safety and Health , The Ford MotorCompany, and The Motor Vehicle Manufactur ers As­socia tion.

References

I . Armstrong TJ, Fine LJ, Silverstein BA. Occupationalrisk factors of cumulative trauma disorders of the handand wrist: A final report. National Institute for Oc­cupational Safety and Health, Cincinnati, OH 1985.(Contract no 200-82-2507).

2. Cannon LJ, Bernacki EJ, Walter SO. Personaland oc­cupational factors associated with carpal tunnel syn­drome. J Occup Med 23 (1981) 255-158.

3. DeGail P, Lance JW, Neilson PD. Differential effectson tonicand phasic reflex mechanisms produced by vi­bration of muscles in man. J NeurolNeurosurg Psychi-

288

atry 29 (1966) I-II.4. Dimberg L. Symptoms from the neck and upper ex­

tremities - An epidemiological, clinical and ergonomicstudy. Swedish Work Environment Fund, Solna (Sweden)1985.

5. Hagbarth KE, Eklund G. Motor effects of vibratorymuscle stimuli in man. In: Granit R, ed. Muscular af­ferents and motor control. John Wiley & Sons, NewYork, NY 1965, pp 177-186.

6. Kume Y, Maeda S, Hashimoto F. Effect of localizedvibration in work environment on organic functions atfinger tip for surface roughness. In: Human FactorsSociety of Canada. Proceedings of the 1984internationalconference on occupational ergonomics. Redale, Ontario1984, pp 457-461.

7. Lance J, De Gail J, Neilson P. Tonic and phasic spinalcord mechanisms in man. J Neurol Neurosurg Psychi­atry 29 (1966) 535-544.

8. Lukas E. Lesion of the peripheral nervous system dueto vibration. Work Environ Health 7 (1970) 67-79.

9. Matthews P. The reflex excitation of the soleus muscleof the decerebate cat caused by vibration applied to itstendon. J Physiol 184 (1966) 450-472.

10. Nishiyama K, Watanabe W. Temporary threshold shift

of vibratory sensation after clasping a vibrating handle.Int Arch Occup Environ Health 49 (1981) 21-33.

II. Radwin RG. Neuromuscular effects of vibrating handtools on grip exertions, tactility, discomfort, and fatigue.The University of Michigan, Department of Industrialand Operations Engineering, Ann Arbor, MI 1986. (Doc­toral dissertation).

12. Radwin RG, Armstrong TJ, Chaffin DB. Power handtool vibration effects on grip exertions. Ergonomics 30(1987) 833-855.

13. Rothfleisch S, Sherman D. Carpal tunnel syndrome,biomechanical aspects of occupational occurrence andimplications regarding surgical management. Orthop Rev7 (1978) 107-109.

14. Seppalainen AM. Nerve conduction in the vibrationsyndrome. Work Environ Health 7 (1970) 82-84.

15. Silverstein BA, Fine LJ, Armstrong TJ. Occupationalfactors and carpal tunnel syndrome. Am J Ind Med II(1987) 343-358.

16. Streeter H. Effects of localized vibration on the humantactile sense. Am Ind Hyg Assoc J 31 (1970) 87-91.

17. Westling G, Johansson RS. Factors influencing the forcecontrol during precision grip. Exp Brain Res 53 (1984)277-284.

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