HOME > RESEARCH > QUESTIONS	Email to: Brian Umberger
	The following are some of the primary questions that have driven my research efforts over the last several years. The entries nearest the top represent studies that are just getting started, or that are currently under way. The common thread that ties all of these studies together is the desire to better understand the mechanics, energetics, and control of the musculoskeletal system in basic forms of human movement. How do mechanical power and energy transfer relate to metabolic cost in walking? Mechanical work is thought to be a major determinant of the cost of locomotion, while passive transfer of mechanical energy within the body should provide energy-savings. In this study, the interrelationships between mechanical power, energy transfer, and metabolic cost are being determined, using more accurate measures of mechanical energy and transfer than have been employed in earlier research. How does muscle fiber type influence the mechanics of maximal effort movements? On average, successful athletes in explosive sports have a higher percentage of fast twitch muscle fibers than their endurance counterparts. The influence of fiber type, per se, however, is difficult to assess experimentally. In this study, the role of fiber type distribution is examined in isolation from other confounding factor, using a forward dynamics simulation model of human vertical jumping. How is mechanical energy generated, absorbed, and transfered throughout the body during walking in children? A forward dynamics computer simulation model of the whole body is being used in conjunction with 3D experimental kinematic and kinetic data to determine how the net moments at each joint control the flow of energy through the body in walking. We are also examining the changes that occur during growth. How do specific musculoskeletal impairments interfere with the flow of mechanical energy during walking in children? The same forward dynamics model just described is being used to determine how mechanical energy management during walking is disrupted in children who have heel cord contractures (due to cerebral palsy). Due to the complex nature of locomotor disability, we have limited this first study to a population with one relatively well-defined impairment. What determines the metabolic cost of human walking? A forward dynamic musculoskeletal model was used in conjunction with a model of muscle energy expenditure to address two specific issues related to the cost of human walking. Simulations of walking were used to determine the relative costs of: a) leg swing versus stance, and b) the cost of generating muscular force versus the cost of doing work. Why do people use the stride rates that they do in walking? Most adults tend to walk using stride rates around 55 stride/min, even though they are capable of walking with much higher or lower stride rates. In this study, we investigated how mechanical power output and mechanical efficiency varied with walking stride rate. The results suggested that power output and efficiency may constrain stride rate to a fairly narrow range (centered around 55 stride/min) at which both are close to optimal. How does muscle fiber type influence the energetics of submaximal movements? It has been suggested that humans with a greater percentage of fast twitch muscle fibers will have a greater metabolic cost of movement, due to the energetic properties of their muscles. It is difficult to isolate the effects of fiber type per se experimentally, but this can be done easily in a musculoskeletal model. Using a forward dynamics simulation model of bicycle pedaling, we found that varying fiber type distribution in the lower limb muscles produced changes in metabolic cost that were in good agreement with experimental data. What might the energetics of walking been like in an extinct human ancestor? In conjunction with a colleague (A. Nagano), we analyzed the energetics of a computer reconstruction of walking in the most famous of all extinct human ancestors: Lucy (aka., Australopithecus afarensis, A.L. 288-1). Our analyses suggested that Lucy likely walked upright, much like modern humans, with an energy cost similar to a modern human of the same size (an 8-9 year old child).