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International Journal of OsteoarchaeologyInt. J. Osteoarchaeol. 8: 305310 (1998)

Markers of Occupational Stress:Conspectus and Prognosis of Research

KENNETH A.R. KENNEDY*

Ecology and Systematics,Division of Biological Sciences,Cornell University,Ithaca,

NY 14853, USA

ABSTRACT In his role as discussant of the papers presented at the symposium on Activity Patterns andMusculoskeletal Stress Markers: An Integrative Approach to Bioarchaeological Questionsat the66th Annual Meetings of the American Association of Physical Anthropologists held in St. Louis,Missouri, on 4 April 1997, the author summarizes topics presented by the participants andothers, discusses innovative methodological procedures and statistical approaches advanced bythese contributors, and offers concluding remarks about the present status of studies of markersof occupational stress (MOS), which include investigations of specific markers of musculoskeletalstress (MSM) and degrees of skeletal robusticity (RM). The recent resurgence of interest inidentification and diagnosis of habitual patterns of activity, as registered on bone and dentaltissues, is exemplified in this collection of reports by scholars active in the fields of forensicanthropology, palaeodemography, palaeopathology and human skeletal biology. Earlier hy-potheses are reassessed by new methodologies, but formulation of reliable standards forrecognizing MOS and interpreting their underlying causes remains a challenge for the advance-ment of future research programmes. 1998 John Wiley & Sons, Ltd.

Key words:occupational stress; musculoskeletal stress; skeletal robusticity; markers

Introduction

The scientific study of osseous and dental mod-ifications produced by habitual patterns of activ-ity which are observable in living skeletalhuman subjects has found its place as an ac-cepted component in the protocol of palaeode-mographic research and forensicanthropological investigations. Commonly re-ferred to as markers of occupational stress

(MOS), these indicators of activity-inducedchanges include musculoskeletal stress markers(MSM) and robusticity markers (RM) in caseswhere muscles or tendons insert into the corti-cal tissue of bone via the periosteum, or wherethere is hypertrophy of muscular attachmentson the bones. Physiological and cytological pro-cesses involved in osteon remodelling and thebiomechanical effects of stress on bone are welldocumented in the anatomical literature [13].Diagnosis of activity-induced stress began in the

Middle Ages [4] with a medical literatureemerging with the onset of the Industrial Revo-lution [5]. Anthropologists and anatomists be-came interested in MOS at the time of the firstdiscovery of hominid fossils in Europe in themid-19th century, and a survey conducted in1989 documented over 145 cases of MOS re-ported in the annals of industrial medicine,sports medicine, performing arts and anthropol-ogy [6].

The papers presented in the symposiumActiv-ity Patterns and Musculoskeletal Stress Markers: An

Integrative Approach to Bioarchaeological Questionstestify to the advances achieved in the study ofMOS since the 1960s when the late J. LawrenceAngel [7] revived this area of scientific endeav-our and recommended procedures for achievingmore accurate observations and diagnosis.Present-day anthropologists are more critical oftheir data than were their predecessors, andsimplistic explanations for the causes of specific

MOS have given way to more careful scrutinyand reassessment of both etiologies and mani-

* Correspondence to: Ecology and Systematics, Division of Bio-logical Sciences, Cornell University, Ithaca, NY 14853, USA.

CCC 1047482X/98/05030506$17.50 1998 John Wiley & Sons, Ltd.

Received 29June 1998Accepted 3 July 1998

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K.A.R. Kennedy306

festations of bone remodelling changes [8]. Themost exciting aspect of modern trends is theapplication of the MOS data to test hypothesesin the archaeological record of historic andprehistoric populations and, in some cases, con-

firm earlier interpretations of MOS from writtenaccounts [9].

Symposium papers

The effects of age, sex and handedness regis-tered in quantitative measurements of muscularinsertions are addressed by Cynthia Wilczakwho examined skeletal series of prehistoricagrarian populations from New Mexico(Hawikah) and Kentucky (Hardin Village), ahunting-foraging population from Kentucky (In-dian Knoll), whaling communities in Alaska(Mummy Cave and the Kuskokwim River site)and modern populations of Afro-American andEuro-American ancestry from the Terry andTodd collections. Except for osteoarthritis, stud-ies of age effects on bone have been relativelyneglected, as have observations of skeletalasymmetry, differences in body size and hor-

monal factors in ontogenetic development.These variables are addressed by Wilczak in herdevelopment of a methodology to assess muscu-lar robusticity in males and females of differentages. She has isolated certain features of skeletaldevelopment which can be separated from otherfactors exerting habitual stress on the body. Atwo-way MANOVA procedure was performedseparately for specimens of both sexes to dis-cern the effects of age and ethnicity on the sizesof eight insertion sites. This procedure was

followed by ANOVA analysis to test the effectsof age on specific insertion sites without inter-ference from ethnic variables. Wilczak con-cludes that the asymmetry encountered in thisstudy of differential use of muscle groups neednot result in hypertrophic expressions on thesame side of the upper extremity for all inser-tions, and that the sizes of insertion sites maynot be expressed in a manner that consistentlyreflects handedness. In short, random variationmust not be excluded from consideration in theexamination of side-specific stress hypertrophy.Pathological and nutritional variables may result

in insertion asymmetry. Further analysis of thesevariables will prove rewarding to the biologicalanthropologist as new methodologies are devel-oped within the compass of MOS analysis.

Also set in the southwestern sector of North

America is Diane Hawkeys study of muscu-loskeletal markers in prehistoric skeletal materialfrom Gran Quivira, New Mexico, but with afocus upon an osteobiographical interpretation.This involves an individual who suffered from asevere skeletal disability. The pathological con-dition is diagnosed as a systemic form of juve-nile chronic arthritis, as supported byhistological and morphometric data. Assumingthe onset of this condition in late adolescenceand survival of its victim until early middleadulthood, it is obvious that his survival de-pended upon care by at least one member of hiscommunity over an extended period of time.Hawkey dismisses the arguments put forth byDettwyler [10] and others that survival of aphysically impaired individual does not implyreceipt of compassionate care. Neglect of thesick is not a characteristic behavior pattern ofour species, and evidence for care of the dis-abled is suggested elsewhere in the palaeonto-

logical and archaeological record, as among theNeanderthals of Shanidar in Iraq [11]. ThisGran Quivira individual suffered entire loss oflower back mobility due to ankylosis, ossifica-tion of the flavian ligaments, ventral collapse ofthe vertebral bodes, degenerative joint diseaseand severe osteoporosity of the vertebrae.Hawkeys study should lead to other investiga-tions into the place of disabled individuals inancient and contemporary societies with respectto age at time of death and recognition of the

development of pathology, trauma and habitualstress.

What is the utility of analyzing variations inskeletal marking and robusticity as a measure oflabour intensity? This question is posed bySteven Churchill and Alan Morris who examinemuscle scar rugosity in three samples of Khoisanskeletons derived from distinctive ecologicalsettings in the southern Cape Province of SouthAfrica within a time frame of 91002000 yearsago. Robusticity was measured for eight upperextremity muscles and six lower extremity mus-cles in a sample of 75 skeletons; between-group

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Markers of Occupational Stress 307

differences were examined by sex. The authorsconclude that biotic differences had a greatereffect upon males, especially with respect togreater robusticity of the upper extremities. Aheavy reliance upon marine resources may have

ameliorated differences on terrestrial resourcedistribution among one of the Khoisan groups.Furthermore, a near-significant correlation offemoral collo-diaphyseal angles is present be-tween males who were savannah foragers andmales whose foraging activities took placewithin forest environments. They suggest thatpeak efforts of activity may do more to increaserobusticity than habitual contractions. Lifting ananimal carcass may significantly promote en-thesic rugosity to a greater degree than lower-stress habitual contractions of the lowerextremities, as in walking. Between the sexes oftheir sample, Churchill and Morris suggest thatbiotic differences between regions had a greatereffect upon male than female subsistence labour,assuming a sexual division of labour in thesegroups comparable to that observed in ethno-graphic studies of the San people. This studyfinds support in Wilczaks examination of theeffects of age, sex and handedness on quantita-

tive measurements of muscle insertion.Another prehistoric population is investigatedby Jane Peterson, the terminal Pleistocene Natu-fians of Palestine and Jordan whose hunting-for-aging practices may have been combined withincipient agriculture some 1250010000 yearsago. She also looks for signs of musculoskeletalstress scars on bones of the upper extremities,but with specific attention to weapon technol-ogy and use. Muscle and ligament attachmentsare examined at 24 loci for both sexes of speci-

mens excavated from five Natufian sites. Asym-metry in musculoskeletal stress scars anddegenerative joint diseases suggest that maleswere engaged in habitual activities that weremore lateralized than in females, especially fortriceps brachii and anconeus. Peterson associatesasymmetry with hunting activities by males,particularly with respect to spear throwing andatlatl use. Several weapon systems may havebeen used simultaneously including, perhaps,the bow and arrow. Evidence for this latter typeof armature has been based upon the archaeo-logical record of microlithic points of which

some might be arrowheads. But Peterson iscautious in proposing that humeral asymmetrymay be the consequence of unilateral flexion ofthe right elbow and extension of a compressiveforce of the left arm when a more convincing

case can be made for throwing activities as theagent behind male upper extremity lateraliza-tion, an interpretation supported by other inves-tigators familiar with terminal Pleistoceneskeletal series [12,13].

In their evaluation of musculoskeletal stressmarkers and habitual activities in skeletons fromtwo Alaskan Eskimo populations of the NortonSound region, Susan Steen and Robert Laneconclude that males and females engaged indifferent practices in harvesting seasonally avail-able plant and animal food resources. Differ-ences occur within the populations fromGolovin Bay and Nunivak Island skeletal seriesas well as between these two groups. Samplesizes are 47 males and 57 females from the firstarea, and 64 males and 70 females from thesecond area. The Golovin Bay skeletons datefrom 300 to 80 years ago; the Nunivak Islandskeletons are from nine prehistoric sites.Golovin Bay females exhibit greater usage of

pterygoid medialis and massetermuscles in chewingactivities than do Nunivak Island females. Otherdifferences in musculoskeletal markers are ob-served in the lower extremities, and the authorsdiscuss possible causes for these bone modifica-tions. This study highlights the importance ofstandardization of recording and scoring proce-dures in analyses of activity-related markers aswell as demonstrating that there may be mor-phological differences between populations in-habiting similar ecological settings.

Furthermore, within these arctic hunting-forag-ing communities there may be striking differ-ences in stress markers between males andfemales.

Ann Stirlands study emphasizes the impor-tance of determining how muscles function ingroups (rather than singly), as represented inher observations of humeral muscular insertionsin skeletons of professional archers from HenryVIIIs flagship, the Mary Rose, which sank offPortsmouth in 1545, and from the medievalcemetery of St. Margaret in Norwich. In com-paring her samples of 100 pairs of humeri of

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young and mature adults males from these ar-chaeological contexts with radiographs of 49young divers in the Royal Navy, Stirlandranked scores for entheses at the insertion ar-eas of pectoralis major, latissimus dorsi, teres major

and deltoid. Significant differences were ob-served in cortical areas and percentages of cor-tex presence between different ages ofindividuals and between right and left humeri.Attempts to evaluate areas of insertion by met-rical and morphological observations were con-sidered to be of limited scientific value. Thisproblem is attributed to the fact that onlygroups of muscles should be considered inevaluating activity patterns from skeletal speci-mens. Stirland notes that the modern Britishdivers enjoy a higher standard of health andnutrition than individuals represented in herarchaeological series. However, the archers ofthe Mary Rose were professionals on boardwho had carried out their skills over relativelylong periods of time. Stirland questions theassumptions of some of her colleagues thatterms such as Skeletal Markers of Occupa-tional Stress, Markers of Occupational Stressand Musculoskeletal Stress Markers properly

define structures on bones which are formedby entheses or syndesmoses as a result of ha-bitual activity patterns.

These reservations about associating musclemarkings with a certain activity are shared byJohn Robb. Not only are muscle insertion sitesmorphologically complex and difficult to iden-tify, but the skeleton registers a mosaic of ac-tivities over the course of each individualslifetime. Furthermore, interpretations of activitypatterns of ancient peoples may be influenced

by current gender and social biases unsup-ported by historical or ethnographic documen-tation, and by the limitations of observationsbased upon analyses of single individuals. Byfocusing upon general patterns of behaviouralvariability within a population or sample,rather than identifying specific activitiesthrough muscular insertion loci, Robb analyzeddata from 18 muscle sites in 56 adult malesfrom the Iron Age necropolis of Pontecagnaro,Italy. His reference collection was a series of61 adult skeletons from a 19th century ceme-tery in Syracuse, Sicily. Skeletal developments

are related to an individuals sex, age and activ-ities performed, and are revealed by results ofstatistical measures which may reflect lifewaysand organization of work within the socialstructure of a community. Employment of

bivariate and multivariate methods demonstratehow surface markings on bone are susceptibleto this approach. Comparisons made betweenage-balanced populations are recommended be-cause muscle markings are expressions of ongo-ing skeletal changes from young adulthood toadvanced age.

Summary and Conclusions

These symposium papers are impressive be-cause of the variety of topics and diversity ofapproaches undertaken by their authors in thestudy of markers of occupational stress. Theymark the resurgence of interest in this topicduring the past few years, but more impor-tantly they offer reorientations of methodologyin defining MOS and their anatomical expres-sions as musculoskeletal stress markers and ro-busticity markers. What have we learned from

these present studies which is less apparent inthe pioneering works of earlier investigators?No longer can we attribute a specific modifi-

cation of bone or dental tissue to a singlepattern of activity however useful this practicemight be in establishing individuation in thecontext of a medical-legal investigation. Rather,it is the overall pattern of stress which bestdescribes the habitual activities in which anindividual may have engaged in life. In somecases our diagnosis must be restricted to stating

that an individual had engaged in some formof strenuous labour; at best we may be able toisolate markers of habitual stress to certainanatomical regions, such as the bones of theupper extremities, lower extremities, thorax,manual and pedal appendages, etc. From theseobservations it is possible to suggest a range ofcultural practices which may have wroughtthese skeletal modifications with reference toarchaeological or historical records. In short,MOS must be interpreted in relation to theentire individual, viz. the skeleton, and not asisolated phenomena.

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Markers of Occupational Stress 309

We perceive in these symposium papers thatthere is a thin line between the diagnoses ofdiseases and the activities in which their suffer-ers habitually engaged. This is demonstrated bydescriptions of osteoarthritic changes and heavy

labour, such as load-bearing. However, it isquestionable that excessive joint activity leadsto joint deterioration in every case. If degenera-tive joint disease is an inevitable consequence ofaging, then its degree of expression must beweighed against behavioural activities thatwould exacerbate this relentless process. It iswith problems of this sort that the presentstudies of lateralization are helpful, particularlywhen examined in the contexts of age and sex

of individuals in the study sample.While the present studies point the way tothe future, a significant obstacle stands in ourpath and needs to be addressed. This is theabsence of standards for making accurate identi-fications of MOS and determining their etiolo-gies. Too much of the earlier literature on thesubject is anecdotal and earlier untested inter-pretations persist in the scientific literature.With the compilation of a catalogue of MOS bythis author in 1989 [6] it was deemed useful tolist those modifications of bones and teethwhich previous investigators had assigned tospecific activity patterns. It was not within thescope of that study to assess the reliability ofthe diagnosis of each marker of occupationalstress. Now we are at the threshold of achievinga rigorous assessment of anatomical variablesattributed to habitual activity patterns by appli-cation of new observational and statistical analy-ses, such as those discussed in this set of

symposium papers, and thereby establishingstandards which will evolve from sound physio-logical and anatomical data. Rather than contin-uing the venerable practice of first deciding thata bone modification is a marker of occupationalstress, it is recommended that we initiate inves-tigations with a sharper perception of how boneremodelling takes place and which kinds ofmodifications bone may assume within the con-figurations of habitual activity revealed in ar-chaeological and historical sources. To do sowill deliver us from the blunder of Currus bovemtrahit praepostere.1

Acknowledgements

The author thanks Drs Jane Peterson and DianeHawkey, organizers of the symposium Activity

Patterns and Musculoskeletal Stress Markers: An

Integrative Approach to Bioarchaeological Questions,for inviting me to serve as their Discussantfollowing the presentation of papers at theAnnual Meeting of the American Associationof Physical Anthropologists held in St. Louis,Missouri, in April 1997. My colleague DrCynthia Wilczak is thanked for her valuablecomments on the materials summarized in thisfinal paper of the symposium series. RosieBrainard provided invaluable assistance in vari-ous clerical tasks in the preparation of thismanuscript.

Notes

1. To put the cart before the ox.

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