Findings show swinging the limbs is expensive; suggest 'force hypothesis' needs modification
01-02-04 - Researchers at Northeastern University today announced that they have demonstrated that, contrary to previous research, swinging the limbs during the act of running requires a significant fraction of energy. In contrast to the established hypothesis, which asserted that force produced when the foot is on the ground (stance-phase) is the only determinant of the energy cost of running, Northeastern researchers observed that a significant fraction energy was used to fuel muscles that move the limb while it is off the ground (swing-phase).
In the study, the researchers estimated energy use by measuring blood flow to the hind leg muscles of guinea fowl in an effort to better explain the energetics of walking and running. In contrast to C. Richard Taylor's "force hypothesis," which suggests that swing-phase costs were low enough to be ignored, the researchers were able to demonstrate that the swing-phase muscles, in fact, consume 26 percent of the energy used by the limbs when running while the stance-phase muscles consume the remaining 74 percent of the energy. These findings represent the first time anyone has been able to look directly at the muscles during running and suggest that the force hypothesis needs modification. The swinging motion backwards is,indeed, the researchers assert, expensive energy-wise. Results of the study were published in the January 2nd issue of Science.
"The pioneering effect of this research is that by looking directly at blood flow to all of the individual muscles during running we were able to establish more directly the consumption of energy during the swing-phase," said Marsh. "Taylor's force hypothesis tried to unify the mechanics and energetics of running and explain the effects of body size and locomotor speed on the energy cost of running. Not everyone was necessarily convinced of all of the details of this hypothesis, but no one had been able to prove otherwise because most research on running has been based externally observable phenomena. By being able to estimate the energy use by the individual muscles, we were able to account to for energy consumption during swing-phase. Our work maintains Taylor's emphasis on using energetics to understand terrestrial locomotion, but our findings suggest the force hypothesis will need to be modified to account for a more detailed partitioning of the energetics among muscles used during running."
Senior author of the article titled, "Partitioning the Energetic of Walking and Running: Swinging the Limbs is Expensive," is Richard Marsh from the department of biology at Northeastern University. Contributors to the article include NU researchers Jennifer Carr, Havalee Henry and Cindy Buchanan and David Ellerby from the University of Leeds in England.
This ability to demonstrate energy consumption in the swing-phase of running is significant because it provides a technique to answer other questions about the energetics of running, which could lead to a more in-depth understanding of which specific muscles are used to support weight and how changes in energy use are caused by differences in body size and speed. The report's findings may potentially improve our current knowledge of rehabilitative medicine.
"The potential application of these findings are many," said Marsh. "Future research will allow us to connect the mechanical functions of individual muscles with their energy use. This detailed information will be useful in models that integrate the energetics and mechanics of running. Because running birds are the best bipedal runners other than humans, our research should provide many valuable clues to understanding human locomotion."
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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