Musculoskeletal allow further investigation into physical changes of

markers like a lot of other identifiable features can be recognised through the
examination of human remains in the archaeological record. Advances within
human osteology have led to understanding the life of an individual by defining
what possible occupation they had and/ or which activities they undertook
during their life. Musculoskeletal markers (entheseal markers) have been the
key subject of recent research within both physical anthropology and
bioarchaeology (Eshed et al, 2004: 303-304; Meyers et
al, 2011: 203). The recognition of musculoskeletal markers proves to be
useful when understanding the occupation of the individual being examined. Musculoskeletal
markers allow further investigation into physical changes of the bone and additional
links to the age, sex and health status of the individual (Stirland, 1998: 354; Villotte and Knusel, 2013: 135). By
giving us this information the markers earned the name ‘markers of occupational
stress’ or ‘activity induced pathologies’ (Kennedy,
1989; Merbs, 1983).  Throughout
this essay the utility of entheses in expressing physical activity will be
discussed in addition to highlighting the limitations presented by skeletal and
clinical data and how it can be overcome. Ultimately, the inconclusive
interpretations of current knowledge regarding the nature and morphological
development of entheseal markers will be argued. There
are numerous problems regarding the establishment of clear definitions for
musculoskeletal markers. By not having a universal definition for the markers,
researchers have generalised them to be defined as the insertion sites of
stress concentration where the tendons and ligaments attach to the bone
resulting in morphological changes (Benjamin et al,
2006: 471; Villotte et al, 2010: 224). Literature has identified two
types of entheses that occur in the body; fibrocartilaginous and fibrous. Fibrocartilaginous
entheses are recognised by four transition zones; pure fibrous connective
tissue, uncalcified fibrocartilage, calcified fibrocartilage and bone (Benjamin et al, 2006: 472). In comparison, fibrous entheses are acknowledged through
the presence of fleshy attachment sites where the tendons or ligaments directly
attach to the periosteum (Niinimaki and Baiges
Sotos, 2013: 221). Research
has stated that these two forms do not have any association between one another
regarding their medical definitions. Even though the two types of entheseal
markers have clear medical definitions mentioned earlier, there are numerous
variations of the markers in shape, size and development. With no universal
description for the musculoskeletal markers, subcategories are having to be developed
to cater for specific data samples (Meyer et al,
2011: 206-208).

Throughout biological and anthropological literature,
the terms mentioned are barely touched upon and are collectively placed into either
one of these categories; ‘skeletal markers of occupational stress’ or
‘musculoskeletal stress markers’. These categories lead us to believe that the
markers are directly linked to physical activity, whether it be through an
individuals’ occupation during life or the activities they undertook. The understanding that entheseal markers
relate to occupational actions is based on the morphological changes believed
to be caused by repeated physical activity and stress on the muscle which may
result in bone remodelling (Hawkey and Merbs, 1995:
324-325). Research surrounding entheseal markers and their link to
stress have been suggested to be based on the casual relations between both
soft and hard tissues. Exposure to internal and external stress in the body
from repetitive activities or heavy loading can result in alterations to these
tissues as they have adaptive abilities (Rhodes and
Knusel, 2005: 536-537). However,
there has been no recent research to confirm this is the case, therefore it is
not conclusively proven to be exclusively the result of physical activity
leading researchers to doubt there is a link (Stirland,
1998: 354, Villotte and Knusel, 2013: 132).# There are several factors such as age, sex,
disease and levels of activity which can influence entheseal change. Sexual
dimorphism has been a focus in research when understanding how different
factors have an impact on entheseal change. It is assumed that males will have
higher entheseal change due to their stereotypical involvement in heavy labour
and their naturally bigger build. A study examining MSM scores and sex
differences found that larger individuals had higher MSM scores, and in most
populations these individuals tended to be male. Weiss et al (2010: 79) established
that it is important to state that even though females may be the smaller sex
in most populations with lower MSM scores, it is not due to less strenuous
muscle use but consequently due to their body size. Miella (2014: 3) confirms
this with a study between modern humans and gorillas, where it was found that
robusticity and sexual differences were surely linked. Associations have been
made with bone formation between the different sexes and how that may connect
to occupation. Notable differences of bone formation between males and females
had been noted by Rogers et al (1997: 90). This
suggests that the varied
formation of bone and evidence of occupational markers is rather questionable
in clinical research. Consequently, both males and females have been
found to have the same possibilities to develop entheseal form from physical
activity potentially due to the strain on the bones (Zumwalt,
2006: 445, Drapaeu, 2008: 93). Therefore, only subtle differences
between the sexes can be expressed through the development of entheseal change.


Additionally, age has shown to be a primary
source of skeletal change especially change of entheseal markers (Villotte et al, 2010;
Miella et al, 2012). Degenerative
processes of tendons have been found to induce mechanical stress which results
in entheseal change (Villotte and Knusel, 2013:
139-149). A study to
explore the alterations entheseal markers had on lower limbs was investigated
using an early 20th century sample. The sample was analysed using Hawkey and Merbs (1995) scoring method for fibrous and fibrocartilaginous
entheses. Factors including age, body size and occupations were all
considered when analysing the markers. It was found that age was the leading
contributor for entheseal change even though age did not affect all entheses of
the lower limb (Niinimaki and Baiges Sotos, 2013:
226-227). Overall, it is
understood that activity related entheseal changes are more likely to appear in
an older individual due to the reduced vascularity of the tendons (Villotte and Knusel, 2013: 140). Compared to this, a
younger individual is more likely to display signs of the impact of mechanical
stress and sometimes pathological changes. Similarly, to factors such as age and sex
having an impact on entheseal change, accumulative stress from everyday life
have also been associated with the markers. Research has found that both
exercise and heavy labour have an impact on muscle insertion sites due to a
collective of muscles working together rather than individually at certain
sites (Stirland,
1998: 356). Numerous studies have been carried out on
animals which have provided fascinating insights to entheseal change. Montgomery et al’s (2005)
study on mice analysed different muscle attachments and musculature.
Results found that there was resorption of entheses due to inactivity or
skeletal unloading (Montgomery et al, 2005: 815). Correspondingly,
Benjamin et al (2002) found that resorption of
entheses occurred when astronauts were exposed to low gravity and when other
individuals endured paralysis (Benjamin et al, 2002:
942). Inactivity was also researched by Laros et
al (1971) where caged, inactive and immobilised dogs were studied. The
dogs showed a decrease in entheseal activity especially at the insertion point
of the tibial collateral ligament which is where a lot of movement would have
had an impact on (1971: 282).

The use of skeletal data alone for research
into entheseal change may not be persuasive enough, therefore, more evidence
needs to be considered. Evidence can be found within other fields of research
such as historical sources which can be applied to the skeletal data to provide
a useful insight to physical activity. Some studies have applied a
multidisciplinary approach where evidence is gathered from numerous fields and
combined to overcome potential limitations of relying solely on skeletal data. Henderson et al (2013) analysed
entheseal change on 18 skeletons from St. Lawrence and St. Michael, Fewston,
North Yorkshire. This study aimed to identify occupational mobility in 19th
century England and it was found that those individuals who changed their job
tended to be affected by entheseal change and degenerative joint disease (2013: 205). The rates of degenerative joint
disease and entheseal change was suggested to be a result of adjustment periods
during the occupation changes. However, certain occupations were found to have
higher entheseal change rates and joint disease due to the requirements of the
job such as farmers who had high rates specifically on the lower limbs. Henderson et al (2013) also found that skilled workers
such as tailors had high entheseal change biased to their right side of their
body due to it being the dominant working side (2013:
207). This study can inform us of the occupations which may have endured
high entheseal change and degenerative joint disease in addition to
understanding the individuals’ preference for the use of their skills from the
application of historical data. Similarly, to Henderson et al’s work, another
study considered the biased functions in the body. Mays,
Steele and Ford (1999) investigated the function of the clavicle in
juveniles from Anglo-Saxon Wharram Percy and found right sided laterality. The
right sided laterality in the juveniles confirmed their initial hypothesis that
bone growth would be restricted on the individual’s dominant side due to the
stress of movements (Mays, Steele and Ford, 1999:26-27). The study of entheseal markers is complex and
research focused on them face numerous limitations. Studies have highlighted
the lack of understanding around the relationships between different entheseal
markers and movements in addition to the comprehension of differences in
ligaments, tendons and tissue structure (Benjamin et al, 2002: 934, Benjamin et al, 2006: 475). The investigation into markers have
been conducted before a strong understanding of them had been established as
well as minimal clinical research being applied (Santos,
2011: 142). This suggests that the research is not only limited but
based off minimal, inconclusive data. Not only is research on entheseal markers
limited but a lot of the data relies on animal studies. As mentioned
previously, there are several studies on animals that give us primary knowledge
for entheseal change such as Montgomery et al’s (2005) mice
study and Laros et al’s (1971) study on
immobilised dogs. Using animal samples within research proposes many
difficulties in establishing applicable conclusive results as they are not
representative of human behaviour. Therefore, it can be said that
interpretations made throughout research into entheseal morphologies cannot
always be suitable or applicable to the population (Stirland,
1998: 360).

from the limitations to knowledge and inconclusive interpretations,
anthropologists also face a dilemma when utilising MSM scores (Weiss et al, 2010: 70-80). It is highlighted by Weiss
et al (2010) that there are three main models which can help us understand MSM
scores. The three models state that body size and sex can cause inconsistency in MSM scores, as well as
variability in body mass across the sexes also resulting in variability in MSM
scores through activities. Finally, the models state that sex causes varied MSM
scores through activity in addition to body size (Weiss et al, 2010: 70-80). This study suggests that researchers
must take into consideration several factors that may influence MSM scores
before concluding their explanation of the data. To
conclude, the discussion of the utility of musculoskeletal markers in
expressing physical activity has been reviewed. The study of entheseal markers
have found that there is a wide range of factors which influence the
development of entheseal change in the body. By reviewing archaeological,
medical and biometric case studies this paper has been able to focus on the
impact of age and sex on entheseal sites. It must be noted that research
regarding the nature of entheseal markers is based on limited data and even
when observed alongside historical sources, is not able to provide conclusive
answers as to what occupation an individual held in their life. Therefore,
studies that explore the nature and development of the entheseal structures are
insufficient and inconclusive. Nevertheless, information already gained from
previous studies have provided usefulness to our understanding of
musculoskeletal markers and allow further development on the topic.