Energetics and mechanics of human running on surfaces of different stiffnesses.

Mammals use the elastic components in their legs (principally tendons, ligaments, and muscles) to run economically, while maintaining consistent support mechanics across various surfaces. To examine how leg stiffness and metabolic cost are affected by changes in substrate stiffness, we built experimental platforms with adjustable stiffness to fit on a force-plate-fitted treadmill. Eight male subjects [mean body mass: 74.4 +/- 7.1 (SD) kg; leg length: 0.96 +/- 0.05 m] ran at 3.7 m/s over five different surface stiffnesses (75.4, 97.5, 216.8, 454.2, and 945.7 kN/m). Metabolic, ground-reaction force, and kinematic data were collected. The 12.5-fold decrease in surface stiffness resulted in a 12% decrease in the runner's metabolic rate and a 29% increase in their leg stiffness. The runner's support mechanics remained essentially unchanged. These results indicate that surface stiffness affects running economy without affecting running support mechanics. We postulate that an increased energy rebound from the compliant surfaces studied contributes to the enhanced running economy.

[1]  A. Hill.  Dimensions of Animals and their Muscular Dynamics , 1949, Nature.

[2]  G. Cavagna,et al.  MECHANICAL WORK IN RUNNING. , 1964, Journal of applied physiology.

[3]  G. Cavagna.  Force platforms as ergometers. , 1975, Journal of applied physiology.

[4]  G. Cavagna,et al.  The sources of external work in level walking and running. , 1976, The Journal of physiology.

[5]  G. Cavagna,et al.  Mechanical work in terrestrial locomotion: two basic mechanisms for minimizing energy expenditure. , 1977, The American journal of physiology.

[6]  T. McMahon,et al.  Fast running tracks. , 1978, Scientific American.

[7]  T. McMahon,et al.  The influence of track compliance on running. , 1979, Journal of biomechanics.

[8]  R. M. Alexander,et al.  Elastic mechanisms in animal movement , 1988 .

[9]  A. Biewener.  Scaling body support in mammals: limb posture and muscle mechanics. , 1989, Science.

[10]  R. Kram,et al.  A treadmill-mounted force platform. , 1989, Journal of applied physiology.

[11]  Kenneth Blaxter,et al.  Energy Metabolism in Animals and Man , 1989 .

[12]  Rodger Kram,et al.  Energetics of running: a new perspective , 1990, Nature.

[13]  T. McMahon.  Spring-Like Properties of Muscles and Reflexes in Running , 1990 .

[14]  A. Biewener.  Biomechanics of mammalian terrestrial locomotion. , 1990, Science.

[15]  T. McMahon,et al.  The mechanics of running: how does stiffness couple with speed? , 1990, Journal of biomechanics.

[16]  T. McGeer,et al.  Passive bipedal running , 1990, Proceedings of the Royal Society of London. B. Biological Sciences.

[17]  C. T. Farley,et al.  Hopping frequency in humans: a test of how springs set stride frequency in bouncing gaits. , 1991, Journal of applied physiology.

[18]  R. Kram,et al.  Mechanics of running under simulated low gravity. , 1991, Journal of applied physiology.

[19]  R. Alexander,et al.  A model of bipedal locomotion on compliant legs. , 1992, Philosophical transactions of the Royal Society of London. Series B, Biological sciences.

[20]  C. T. Farley,et al.  Running springs: speed and animal size. , 1993, The Journal of experimental biology.

[21]  C. T. Farley,et al.  Leg stiffness and stride frequency in human running. , 1996, Journal of biomechanics.

[22]  Daniel P. Ferris,et al.  Interaction of leg stiffness and surfaces stiffness during human hopping. , 1997, Journal of applied physiology.

[23]  Daniel P. Ferris,et al.  Running in the real world: adjusting leg stiffness for different surfaces , 1998, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[24]  P. Willems,et al.  Mechanics and energetics of human locomotion on sand. , 1998, The Journal of experimental biology.

[25]  C. T. Farley,et al.  Mechanism of leg stiffness adjustment for hopping on surfaces of different stiffnesses. , 1998, Journal of applied physiology.

[26]  R. Kram,et al.  Energetics of bipedal running. I. Metabolic cost of generating force. , 1998, The Journal of experimental biology.

[27]  C. T. Farley,et al.  Leg stiffness primarily depends on ankle stiffness during human hopping. , 1999, Journal of biomechanics.

[28]  Daniel P. Ferris,et al.  Runners adjust leg stiffness for their first step on a new running surface. , 1999, Journal of biomechanics.

[29]  A. Arampatzis,et al.  The effect of speed on leg stiffness and joint kinetics in human running. , 1999, Journal of biomechanics.

[30]  R. Kram.  Muscular Force or Work: What Determines the Metabolic Energy Cost of Running? , 2000, Exercise and sport sciences reviews.