Research

Estimating humeral torsion   
Humeral torsion (or retroversion) is the highly variable angle between 
the humeral head in the shoulder and the distal condyle of the
humerus in the elbow. We know that individuals who throw often,
such as baseball pitchers, tend to have lower torsion (higher
retroversion) in their throwing arm than non-throwers. We also know
that humeral torsion affects the range of motion available in the
shoulder. This study investigates the relationship between humeral
torsion and shoulder range of motion. We also use CT scan images 
to test a new method for estimating humeral torsion from range of
motion data.

Elastic energy storage
Elastic energy is often used to increase the power or efficiency of 
human and animal movement. Ligaments and tendons can stretch 
like elastic bands, storing up elastic energy which is returned
when they are released. We have proposed that this is occurring
in the shoulder during the throwing motion, allowing us to throw
objects faster than we would be able to using our muscles alone.
We test this hypotheses by collecting high speed 3D video data
on the throwing motion. We then process these data using
inverse dynamics analysis, which uses Newtonian physics to break
down these complex motions into the individual motions at each
joint in the body. We also mathematically model muscle force in
the arm and shoulder.

Evolution of throwing
Humans are unique in our ability to throw with both great velocity
and accuracy. Our closest relatives, the chimpanzee, do
occasionally throw albeit poorly. Human's remarkable throwing
ability therefore must have arisen during the evolution of our
lineage. Such high performance throwing could have helped our
hominin ancestors hunt and protect themselves. When exactly our
ancestors began to throw well is poorly understood. To address
this question, we look at how a number of important changes in
the shoulder, arm, wrist, and torso known to occur during human
evolution affect throwing ability. We test the effects of each
change experimentally by altering anatomical parameters in
human throwers. 

Projectile Penetrance
We know from the archaeological record that our hominin ancestors
began hunting almost 2 million years ago. Yet, projectile weapons
don't appear in the record until around 300 thousand years ago. 
Does this mean that projectile weapons, like spears, weren't used
during this early hunting or just that they were not preserved? To
address this question, we look at whether sharpened wooden
spears (with no stone tip) could be effective hunting weapons. We
measure the differences in kinetic energy required to effectively
penetrate an animal's hide between un-tipped and stone tipped
spears.

Fieldwork
I have also participated in a number of field projects in the Kenyan
Rift Valley. These projects have included archaeological and 
geological survey of Middle Stone Age deposits in the Kapthurin
formation (Baringo) and the Kapedo formations (southern
Turkana). I have also studied the geology of East and West Turkana
and conducted a survey of Middle Stone Age deposits at
Olorgesailie in the southern Kenya.