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Adam Daoud
A.B., Magna cum Laude, Human Evolutionary Biology, Harvard College 2009

Research Assistant
Harvard University
Department of Human Evolutionary Biology
11 Divinity Ave, Cambridge, MA 02138

Adam Daoud
Research Interests

Nature - Born to RunMy current research interest lies in investigating the ways in which the human body is suited particularly well for endurance running and determining why Homo sapiens possess such incredible endurance running capabilities. These remarkable endurance running abilities suggest that natural selection favored human ancestors who were able to run long distances efficiently and safely, but why? One hypothesis suggests that endurance running capabilities evolved so that humans could engage in persistence hunting. Rather than being fast sprinters (we are terribly slow sprinters), equipped with deadly “weapons” to kill our prey, we became incredible endurance runners who were able to chase animals to exhaustion in the heat of the day. In addition, endurance running capabilities would have made our ancestors more proficient scavengers. These activities would have allowed our ancestors to attain meat prior to the invention of projectile technologies such as bows and arrows and spears (Lieberman et al., 2009).

In the Skeletal Biology Lab at Harvard, at Harvard, we develop and test hypotheses about human endurance running with regards to two of the most evolutionarily important aspects of running: injury and running economy. An evolutionary prediction about endurance running is that we should be able to run long distances both efficiently and safely. The high rate of injury in runners today indicates that we may no longer be running safely; we may run differently than our barefooted ancestors. My research investigates the possibility that higher rates of injury may be due to our chronic use of modern, heavily cushioned, high-heeled running shoes beginning at an early age.

Current Research

Impact Forces & Foot Strike Type

The impact forces generated by runners who land on their forefoot are profoundly different from those who land on their heel. By landing on the forefoot runners are able to reduce the magnitude of the collision between the foot and ground at impact by reducing the effective mass involved in the collision - the mass that is brought to a stop immediately upon striking the ground. When a heel striker lands, the lower leg and foot come to a stop immediately, so the effective mass is approximately the mass of the lower leg and foot. In a forefoot strike landing, the lower leg and rearfoot continue to fall after foot strike and only the forefoot comes to a stop immediately at foot strike. The effective mass involved in a forefoot strike is just some portion of the foot. Thus, the major kinetic difference at impact between forefoot strikes and heel strikes is this difference in effective mass. It is like dropping a rod vertically compared to dropping the same rod at an angle; the former will generate a much more forceful impact. By reducing the effective mass involved at foot strike, forefoot strikers are able to generate less severe collisional forces at impact.

We are investigating the ways in which lower limb kinematics during running affect impact forces. By studying the movements of the lower limb and joint compliances we are able to determine what modifiable factors in a runner’s gait can be changed in order to reduce the severity of the impact forces.

Nature Cover

Adolescent Kenyan Who Has Never Worn ShoesRunning Footwear & Foot Strike Type

We have completed studies which show that barefoot runners in the USA and children who grew up barefoot and run a significant amount are more likely to forefoot strike. In contrast, approximately 85% of American runners heel strike. We believe that this difference may be the result of running in cushioned running shoes, which may encourage runners to heel strike.

Running Injuries & Foot Strike Type

Around 2 million years ago, there is evidence of strong selective pressure for exceptional endurance running capabilities in our ancestors. Individuals who were not only capable of running long distances, but who were capable of doing so without enduring injury may have enjoyed an evolutionary advantage. How were human ancestors able to endure the stresses of endurance running in a safe and effective way? One hypothesis is that our ancestors were able to do so by forefoot striking.

This hypothesis is yet to be tested, but several pieces of indirect evidence point towards this as a possibility. Barefoot runners are more likely forefoot strike, forefoot striking generates smaller impact forces, impact forces are implicated as a possible cause of some repetitive stress injuries, and adaptations of the foot and lower leg are utilized more in forefoot strike running that in heel strike running. This hypothesis has not been tested directly.

Running Economy: Foot Strike Type & Footwear

A future research direction is to determine the difference in running economy between heel strike and forefoot strike running and between barefoot running and running in various types of footwear. There are several factors which would affect running economy between these conditions, most notably passive elastic energy storage in the Achilles tendon and the arch of the foot and variation in muscle activity specifically in the triceps surae and tibialis anterior.

Past Research

Harvard College Honors Thesis in Human Evolutionary Biology: Kinematics and Impact Forces in Forefoot Strike Running versus Heel Strike Running

This was one of the first experiments that studied habitual barefoot runners (runners who have done a considerable amount of barefoot or minimally shod running for at least 6 months). We compared the impact forces of these habitually barefoot runners to runners who normally run in standard running shoes. We found that habitually barefoot runners were more likely to forefoot strike while habitually shod runners were more likely to heel strike. This kinematic difference in foot strike generated profoundly different impact forces with forefoot strikers generating much less severe impact forces than heel strikers. A reasonable hypothesis is that the impact forces experienced every time the foot touches down while running plays an important role in repetitive stress injuries and that by reducing the impact force, a runner will reduce their chance of getting repetitive stress injuries. This hypothesis has not been tested directly. PDF

The primary source of data for a subsequent Nature publication was from this thesis:
Lieberman DE, Venkadesan M, Werbel WA, Daoud AI, D’Andrea S, Davis IS, Mang’Eni RO, Pitsiladis Y. Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature 463(7280), 531-535, Jan 28 2010. PDF

Summer 2007: University of Michigan, School of Kinesiology, Katarina Borer. Mechanical, hormonal and temporal parameters for stimulation of osteogenesis in postmenopausal women.

We set out to determine an optimal walking exercise regime to maintain bone mineral density in postmenopausal women. We varied temporal and mechanical parameters of exercise by modifying 2 parameters of the exercise regime, one exercise session versus two sessions of half the duration and uphill versus downhill walking. Temporal parameters were varied to determine if the osteogenetic effect of walking could be produced to similar magnitudes multiple times in one day. Mechanical parameters varied the impact force experienced by the walker to determine the degree to which impact force affects the magnitude of the osteogenetic response. Osteogenetic response was assessed by measuring hormonal response and markers of bone resorption and bone deposition. University of Michigan Kinesiology: Exercise Endocrinology Lab

Borer KT, Daoud AI, Lash RW, Gross MM, Kernozek T. Parameters of exercise that increase markers of bone formation relative to resorption in postmenopausal women. American College of Sports Medicine annual meeting, Indianapolis, IN, May 28-31, 2008.

Summer 2006: University of Michigan Medical School, Department of Microbiology and Immunology, Kathy Spindler. Genetic mapping of mouse adenovirus susceptibility.

Strains of inbred mice show differing susceptibility to mouse adenovirus. Candidate genes responsible for this variation in susceptibility are identified by locating the region(s) of the mouse genome to which this variation in susceptibility maps. These candidate genes can then be further investigated to identify their role in virus susceptibility and resistance. We identified polymorphic regions between two strains of mice, one susceptible to mouse adenovirus and the other resistant. Crossbred mice were then tested for susceptibility and polymorphic regions were genotyped in order to narrow down potential candidate genes. University of Michigan Virology: Spindler Lab

Spindler KR, Welton AR, Lim ES, Duvvuru S, Althaus IW, Imperiale JE, Daoud AI, Chesler EJ. The Major Locus for Mouse Adenovirus Susceptibility Maps to Genes of the Hematopoietic Cell Surface-Expressed Ly6 Family. J Immunology, 184: 3055-62, Feb 17, 2010. Link

Last updated on August 4, 2010