A review of the archaeological and sports medicine literature to determine the Biomechanical markersof Equestrian Activity.

M. Sally McGrath, Inter-Disc. PhD graduate student, UNB.

2

Introduction:

Wolff’s Law (Wolff, 1892) states that living bone is shaped and

remodelled in response to the physical demands placed upon it.

Today, building upon this, is the belief that it is possible to

determine types of habitual behaviours in humans from the

evidence of specific physical stress markers on bone. In the

past, humans have engaged in equestrian activity both as part of

a nomadic lifestyle and as a form of elite transportation. It

should therefore be possible to develop a set of biomechanical

(musculoskeletal) markers associated with such activity. It is my

intention to attempt to construct such a set by surveying and

critiquing the literature for biomechanical (musculoskeletal)

stress markers that have been used in a variety of past studies

as possible evidence for equestrian activity. This survey will

highlight those various markers that appear in all or most of the

studies and therefore have a higher degree of reliability. I

have attempted to use only those studies where the identification

of equestrian activity is based on both the evidence of

biomechanical markers and the ethnographic materials that link

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the individual or population to possible equestrian activity.

This should allow me to avoid the research problems outlined by

Perreard Lopreno et al (2013). In addition to archaeological and

historical material, I shall also review the literature from the

field of sport medicine on today’s practitioners of equestrian

sports. The last step will be the evaluation of the criteria in

light of my own expertise in equestrian activity.

A library and Internet search based on a variety of search

terms, revealed a number of ethnographic and skeletal studies

with a wide temporal and geographical spread. In addition to the

review of archaeological and historical material, I searched

sport and sport medicine sources for studies of the mechanical

demands made on individuals who engaged in equestrian activities

at different levels of intensity and duration.

The use of biomechanical markers, which includes both

muscular and skeletal markers to infer habitual behaviour in past

populations, is fraught with dangers. Jurmain (2011) critiqued

in detail the different forms of musculoskeletal markers and the

multifaceted factors that effect their development. In his

critique, two features emerged that were of particular relevance:

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age and the parameters that define ‘habitual behaviour.’ Bone is

more plastic in nature in the young and muscle attachment sites

are smaller. Therefore, when stress or mechanical loading occurs

at a young age, the musculoskeletal responses should be more

evident (Villotte, 2009). This is particularly important in

relationship to determining the age when the behaviour commenced,

the length of time it continued and the frequency at which it

occurred. For the purposes of this paper I have defined habitual

behaviour as a series of actions considered as parts of a whole

that were constantly repeated over a number of years.1

Furthermore, I have made the assumption that in the past,

horseback riding was a habitual behaviour that commenced in

adolescence2. I have arrived at this assumption based on

ethnographic and historical material.

Equestrian activity infers the use of the horse for riding.

Given the fact that the animals used for riding from the

prehistoric period down into the historic period were between 13-

1 Definition formed by combining definitions of behaviour and habitual as defined in the Oxford English Dictionary, 2nd Ed.2 Adolescent age – 12-20 years as defined by White, T. & Folkens, P. 2005. The Human Bone Manual: 364.

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14hh3, weighed somewhere between 5-800 lbs, and were probably

closer to the low end due to a reliance on pasturing for food

requirements, comparison with today’s sport animal can be

problematic. Even the mounts used in Europe to carry elite

armoured soldiers in the fourteenth and fifteenth centuries AD

were only between 13-15hh (Olsen, 2006). In general, sport

related research documents riders of competition horses. These

animals range between 16-17.3hh and being grain fed, weigh in

excess of 1000lbs. They cannot be equated with the ‘backyard

horse’ that today is kept for pleasure and trail riding but they

are also larger than animals in the past. Therefore, given the

differences between ancient horses and today’s animals, I have

chosen to discount injuries to the clavicle and Colles’

fractures, which today are associated with falls from horses.

Furthermore, falls are often associated with the breaking in and

training of the horse. It cannot be assumed that individuals who

ride, or rode in the past, were also responsible for the breaking

and training of their mount. Today, and possibly in the past,

3 hh is an old form of measurement of the height of a horse from the point of the withers to ground, which is still in use world wide today. One hh = 4 inches.

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this is usually the task of an older, more experienced

individual.

Apart from the horse, the other external factor that

influences the development of biomechanical markers of equestrian

activity is the use of some form of saddle and stirrups.

Archaeologically, there is evidence of saddles dating back to

1000 BC from the mortuary remains of semi-nomadic Steppe people

(Barber, 1999). The actual evidence for the use of metal

stirrups amongst Steppe populations does not appear until the

first millennium AD (Vainshtein, 1989) but there is iconographic

evidence of stirrup use from India dating to the end of the 1st

millennium BC (Littauer, 1981). Wooden stirrups and iconographic

evidence of stirrup straps push this date back further (Ibid),

but this use of organic materials means that evidence could be

missing from the archaeological record.

Temporal and Geographical areas covered.

Horses do not appear worldwide; from the ethnographic and

skeletal remains, they were present in wide areas across the

Eurasian Steppes, in Western Europe and North Africa from the end

of the Pleistocene (10,000 BC). While their ancestors appear in

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the North American fossil record, Equus caballus, the modern horse

was introduced with the arrival of European settlers in the

second millennium AD. The use of the horse in Western Europe and

on the Steppes for purposes other than meat is only firmly

documented from the fourth millennium BC (Olsen, 2006). Horse

bridles and woollen trousers, the latter that may or may not

indicate use of a saddle, have been found as far back as the

thirteenth century BC (Beck et al, 2014).

Biomechanical markers of Equestrian Activity:

From my review of the literature I have found repeated evidence

for the use of the following markers. In particular, I have

concentrated on the vertebral column, aspects of the pelvic

collar, the femur, and the distal end of the femur with the

patella.

1. Vertebral column:

Lipping and degenerative processes of the vertebral body are not

indicators that can be assigned only to equestrian activity. In

general, different form of mechanical loading of the upper body,

will, with age, cause degenerative changes to vertebral bodies.

The examination of a group of elite competitive riders and a non-

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riding control group using MRI technology did not determine a

greater prevalence of degenerative discs in any group despite

symptoms of lower back pain (Kraft et al, 2009). The only group to

display some evidence of degenerative discs were the dressage

riders, and the authors attributed this to their practice of

sitting to the trot.4 The authors found 80% of the dressage

riders showed some degenerative disc evidence in particular

between the lumbar vertebrae L3-4, L4-5, L5-S1. This same group

of dressage riders had more evidence of disk bulging than the

other riders or the control group. All the riders in this study

ranged in age from 19-41 years and were mixed gender. However,

the 19 year olds, in order to be elite competitive riders must

have started their riding careers before age 19.

2. Schmorl’s nodes:

There is some evidence that Schmorl’s nodes: the depressions left

in the surface of the vertebral body by compression of the

intervertebral disc, are associated with habitual behaviour

particularly when the activity commences early and continues over

4 Two beat gait where the horse moves diagonal pairs of legs. Optimum pace for traveling over distance but only if the rider posts. Posting involves the rider rising up and out of the saddle in rhythm with the movement of the horse’s back.

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a number of years. In an examination of vertebral remains from

two different populations; one rural and the other urban, Novak

and Slaus (2011) concluded that only Schmorl’s nodes might be

considered indicators of activity related stresses. Ustundag

(2009) came to a similar conclusion as Novak and Slaus (2011),

but suggested that small Schmorl’s nodes were the result of

small, repeated stresses while large Schmorl’s nodes could be

related to a traumatic event (Ustundag, 2009; Jurmain, 2011).

An examination of the Medici family skeletons found

evidence of Schmorl’s nodes on both thoracic and lumbar vertebra

of both an adolescent male (aged 19 years) and older males

(Fornaciari et al, 2007; Fornaciari et al, 2014). Wentz and De

Grummond (2009) in their examination of a Scythian burial found

Schmorl’s node on the lumbar vertebra of the adolescent male

(late teens) and similar nodes on the lumbar and thoracic

vertebrae of the older male (40-50 years). Researchers using

Native American skeletal materials from both the pre and post

contact period have found significant differences in the

incidences of Schmorl’s nodes (Wentz & De Grummond, 2009;

Sandness and Reinhard, 1992; Reinhard et al, 1994), in particular

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amongst males. They have equated this difference to the

introduction of the horse and riding. Today, stress associated

with athletic activity in adolescents has also been found to

result in the presence of Schmorl’s nodes (Micheli, 1979). From

the research cited above, I would suggest that the presence of

Schmorl’s nodes as a marker of habitual riding occurs in those

vertebra that correspond to where the vertebral column curves

away from a vertical imaginary sagittal line dissecting the rider

from skull to pelvis. Those vertebrae that fall either anterior

or posterior of this line would experience an uneven rate of

impact from the movement of the horse.

3. Acetabula:

The spinal column and lower legs are anchored by the pelvic

collar that is the actual contact region of the rider with the

back of the horse. It is the acetabula, and the femoral head and

neck that respond to the width of the chest of the horse and

where movement of the lower leg is controlled. The femoral head

articulates with the acetabula and it is here, in the shape of

the acetabula that there appears to be evidence of habitual

riding. Using adult male skeletons from two populations of

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Arikara indigenous Americans: one from pre-contact and early

contact (1679-1733) and a second, post-contact population (1803-

1832), Erickson, Lee and Bertram (2000) measured the acetabula

using Fourier coefficients. Their results demonstrated that the

acetabula of the later, post-contact population were distorted in

shape with an anterior-superior expansion of the rim of the

acetabula resulting in an asymmetrical shape in comparison to

those of the earlier populations. Similar anterior-superior

expansion of the acetabula rim was observed on the remains of the

Medici males (Fornaciari et al, 2007; Fornaciari et al, 2014).

Both Reinhard et al (1994) in their examination of the skeletal

material from an Omaha post-contact site and Baillif-Ducros et al

(2012) in their examination of the remains of a young adult male

buried with a horse at Saint-Dizier, found the same thing. In all

these cases, bony deposits were observed on the superior outer

rim of the acetabula.

4 The femoral head and fovea capitis:

Lipping around the lower margins of the femoral head was also

observed along with the elongation of the acetabula while bony

deposits (osteophytes) were found around the region of the fovea

12

capitis. Robin (2008) observed asymmetry in the appearance of

these markers as too, did Ballif-Ducros et al (2012). All the

Medici adult males displayed varying developments of osteophytes

from the fovea capitis (Fornaciari et al, 2007).

5. Femoral neck features:

Radi et al (2013) set out to examine a known twentieth century

skeletal collection to test assumptions concerning the presence

of features that could be tied to specific habitual behaviours

including riding. They concluded that only Poirier’s facet might

be useful for determining habitual behaviour. When examining

femoroacetabular impingement, Villotte

and Knusel (2009) concluded that Poirier’s facet and herniation

pits on the femoral neck were the result of repeated movements

requiring extreme hip flexion and internal rotation of the

femoral head. This description accords well with the physical

movements associated with mounting and dismounting from a horse.

I have therefore included this in my list of physical markers of

equestrian activity.

6. Lesions on the distal anterior surface of the femur:

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Few researchers have dealt with skeletal markers of stirrup use

from archaeological remains. Only Baillif-Ducros and McGlynn

(2013) and McGlynn, Immler and Zapf, (2012) have examined this

feature recently. Stirrups provide a basis of support for the

lower leg and depending on their length, cause a bend at the

knee. Osteoarthritic lesions were identified on the upper outline

of the patella surface of the femur. The opening and closing of

this joint associated with the rider standing in the stirrups

when needing to rise above the motion of the horse could be a

cause of such markers.

Enlarged muscle site attachments:

Moravia skeletal material from an early medieval castle was

retrieved along with remains from a nearby rural cemetery

(Havelkova et al, 2011). In this study, examination for markers of

habitual behaviour was restricted to skeletal material from

health adults. Strong muscle insertion sites were observed on

both the proximal and distal end of the femur and on the pelvis

for males aged between 20-50 years from the castle. The authors

assumed that the attachments found on the greater and lesser

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trochanter of the femur were associated with balancing the weight

of the upper body over a standing leg. Furthermore they

concluded that these and the strong attachments on the distal

posterior end of the femur were the result of every day

activities of walking and rising from a sitting position

(Havelkova et al, 2011:501). However, the presence of horse bones

and horse tack in the vicinity of the castle suggests that elite

males practiced equestrian activity. Historically, saddles and

stirrups would have been in use in this period, which would allow

for the practice of ‘posting’ at the trot. This is a movement of

the rider’s body upward and slightly forward in rhythm with the

movement of the horse and is a similar action to that used when

rising from a sitting position with a change in the angle of both

the hip and knee joints. I would therefore suggest that these

specific muscle attachments might be attributed to habitual

equestrian activity. Unfortunately, the authors of this paper did

not offer any information concerning skeletal markers other than

muscular attachments. Wagner et al (2011) found similar lesions on

the posterior distal end of femurs of 1st millennium BC nomadic

herds whose mortuary remains showed use of saddles.

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Both the older and younger Medici males exhibited strong

muscle attachments and from the historical evidence can be

assumed to have started riding in adolescence (Fornaciari, 2007).

All the Medici were large men and the results of an examination

of other femurs from both pre-historic and historic bone

collections suggest that while age is the most prevalent

influencer of size of musculoskeletal markers, size differences

are also significant (Robb, 1994; Robb, 1998; Weiss, 2004).

Therefore I would suggest caution in using muscle attachment size

as an indicator of habitual equestrian behaviour unless there is

present other physical markers along with ethno-cultural evidence

for the presence of horses.

Biomechanical markers NOT included:

The seven elements discussed above were the only ones that I

found consistently used and which, from my own experience, could

reflect habitual equestrian activity. Apart from the Colles’

fractures and clavicle fractures, which I discounted initially

based on the size of horse, I also found other criteria that I

discarded.

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Initially, I had reasoned that the angle formed by the

femoral neck and shaft would change due to equestrian activity

and was involved in testing this hypothesis on femurs from a

known Bronze Age Noua cemetery in Romania. The measurements

varied between 118 – 142 degrees, but in most instances fell

between 126-127 degrees (Gloux, McGrath, Green and Gonciar,

2012). According to Gillian, Chandraphak and Mahakkanukrauh

(2013) this angle is thermo regulated and the real difference to

be measured is the difference if any between the two femurs of an

individual, which is something that we did not do. I have now

discounted this as a possible indicator of habitual riding.

Another marker that I rejected was that of asymmetrical

cross-sectional long bone geometry, in particular as it relates

to the femur and tibia. Initially I thought this could be used

given that Pearson & Lieberman (2004) in their review of Wolf’s

Law concluded that bone geometry and cortical bone morphology

were most likely to reflect biomechanical influences during

adolescence with the mean age of commencement of the activity

between 9.5 and 13.7 years of age (Pearson & Lieberman, 2004:

89). This appeared to fit if individuals learnt to ride as

17

adolescents. I have however, chosen to discount cross-section

long bone asymmetry of the femur and tibia in part because of the

research of Sparacello et al. (2015). In their paper considerable

asymmetry was discovered in the cross-section of humerus of elite

males from the Orientalizing-Archaic period (circa 800-550 BC),

which was associated with the habitual behaviour of unimanual

action involved in the use of javelins (Sparacello et al., 2015,

311-312). Riding does not equate to the violent, swift, twisting

and torsion associated with the throwing of a javelin. Rather,

the pressure on the lower long bones of the leg when riding is

slow and persistent, thus even when the activity commences at an

early age, it is unlikely that long bone symmetry would have been

affected. Ruff (1994) in his analysis Northern and Southern

Plains Native American femora reached the same conclusion.

Stress fractures on bones of the feet, and changes to the

morphology of a calcaneus were observed by Wagner et al. (2011) on

remains of nomadic herders. However, in their study of elite

riders, Kraft et al. (2009) found no evidence of impact injuries

among equestrian vaulters who mount and dismount at speed. I

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have chosen as of now to discount stress markers associated with

the feet.

Discussion:

Obviously with equestrian activity it is necessary to have a

clear idea of the purpose of the activity in a specific culture,

as well as information that would lead to an estimation of who,

when, where, and for how long individuals would be engaged in

this activity. Therefore, the bio-cultural information is

imperative. There is a difference between those individuals who,

in pre-industrial societies, used the horse in a limited way for

transport, or those who lived a semi or nomadic lifestyle, and

finally, those elites who waged war from the back of a horse.

These differences should be reflected in the degree of

biomechanical markers found and in the gender of the individual.

Horseback riding is an activity that demands a high degree

of symmetrical co-ordination of both the upper and lower limbs

with the vertebrae column and pelvic area positioned above the

horse’s vertebrae. The greatest reaction to the movement of the

animal will then be transmitted to the corresponding human pelvis

and vertebrae, which must absorb the shock of such movement.

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Therefore there should, if this activity is repetitive and life

long, be signs of shock absorbsion on the vertebrael bodies and

the pelvic region. The natural curviture of the spine moderates

the transfer of weight down the spinal column, but with riding,

the jaring impact of the horse is sent up the spine. Schmorl’s

nodes would appear to occur between those vertebra where the

curvature of the spine moves away from the verticle line of

gravity. Novak and Slaus (2011) found a decrease in the

occurrence of Schmorls from L1 through L5 while that part of the

spinal column where maximum flexion and rotation is possible,

T11-T12, and T12-L1 had more Schmorl’s nodes which lessened in

frequency through to T4. Schmorl’s nodes do not appear to be

found higher up the spinal column. Analysis of rider position at

the walk, trot and canter has revealed subtle changes in the

angle of the vertebral column with the hip in all three gaits

which must have an effect on the ability of the vertebral column

to absorb shock (Lovett et al., 2005).

When mounting and dismounting as well as any activity

performed by the rider when on the horse, there will be flexion,

abduction and rotation of the hip, in particular the rotation of

20

the femurial head in the acetabula. The leg falls vertically

along the belly of the horse and depending on the presence or

absence of a saddle, will attempt to follow the rounded contours

of the horse’s belly. The presence of stirrups changes the

position of the leg, pushing the distal end of the femur forward

while the lower leg contracts somewhat depending on the shortness

of the stirrup strap. The stirrups provide two points of

stability upon which the rider can depend for support and balance

allowing the rider to rise above the back of the horse and

therefore negate the upward thrust of the animal’s motion.

Therefore, use of stirrups should be evident in the area of the

knee joint.

Biomechanical indicators of equestrian activity should by

the very nature of riding, be observable on both the sides of the

lower appendicular skeleton. However, given the fact that

individuals are in strength and flexibility more one sided

(Bagesterio & Sainburg, 2002; Kellis and Katis, 2007; Symes and

Ellis, 2009; Bussey. 2010), and that their mount, the horse, is

afflicted with the same discrepancy, the degree of the indicator

may differ from one side to the other. Acetabula and fovea

21

capitis measurements taken by Baillif-Ducros et al., (2012) revealed

such asymmetry. Furthermore, a higher incidence of lower back

pain than that found in the general population was reported for

riders (Kraft et al, 2009), the management of which could also

leave asymmetrical biomechanical markers. Hobbs et al (2014) in

their study suggest that pelvic asymmetry as a response to pain,

is related to length of time in years, spent riding. There is no

reason to think that riders in the past did not also suffer pain

and that pelvic asymmetry did not develop.

Modern research into strength requirements for equestrian

activity (Douglas et al., 2012) revealed no significant difference

between riders and non-riders in strength requirements with the

exception of thigh strength. The authors attributed this to

muscle activity associated with ‘posting’5 at the trot. Terada et

al., (2004) examined the use of pelvic and upper and lower body

muscles at the trot and reached the conclusion that the use of

muscles in riding was primarily for co-ordination and posture

stabilisation (balance) and not for the production of strength.

5 Posting is the action of rising out of the saddle in rhythm to the horse’s forward motion at the trot.

22

The results of modern sport related research, needs to be

used with caution when applied to archaeological or historical

remains. The advantages of using modern imaging techniques on

living populations has to be weighed against the problems of

using results from the examination of elite competition riders

whose other environmental stresses are likely to be totally

different in degree and type from those experienced by past

populations. Finally, when considering research on elite riders,

it must be kept in mind, that there is a disproportionate number

of females over males engaged in this sport and much of the sport

literature is over-weighted with information gathered from female

riders.

Conclusion:

All the historical individuals examined in the literature for

markers of habitual riding were male. Historically, ethnographic

material would seem to indicate that males were more likely to be

engaged in riding than females and from the evidence above, I

would suggest started this behaviour as adolescents. However,

there are now a number of kurgan burials on the Eurasian Steppes,

which have on the examination of the skeletal material proven to

23

be female although the grave goods include weapons (Berseneva,

2010). Pazyryk sites have also revealed females with weapons

(Polosmark, 2001:58). The examination of these remains for

markers of equestrian activity has either not been published or

translated yet. Once this information is available, it shall be

possible to evaluate both the sexual dimorphism in markers of

habitual behaviour and to answer better the question – did women

engage in habitual equestrian activity?

As most, but not all, of the archaeological and historical

markers discussed here have come from studies of individuals

known to have been associated with horses, the next step would be

to test the validity of this compiled list of specific

musculoskeletal markers by the examination of skeletal remains of

a population that might include individuals that practice

habitual equestrian activity. Such an examination should:

1. Include where possible both adult and adolescent skeletal

material of both genders.

2. Include a historical/archaeological study to determine how

equestrian activity was reflected in the socio-cultural

character of the population.

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3. Investigate the role of riding as it relates to the

identification of sub-groups within the population.

4. While not all indicators of habitual riding activity may be

present, numbers 2, 3, and 4 should be observable on the

skeletal remains.

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