scholarly journals Center of mass motion and the effects of ankle bracing on metabolic cost during submaximal walking trials

2006 ◽  
Vol 24 (12) ◽  
pp. 2170-2175 ◽  
Author(s):  
Stephanie K. Herndon ◽  
Bradford C. Bennett ◽  
Adam Wolovick ◽  
Andrew Filachek ◽  
Glenn A. Gaesser ◽  
...  
Keyword(s):  
Center Of Mass ◽  
Metabolic Cost ◽  
Mass Motion ◽  
Ankle Bracing

Mechanical work for step-to-step transitions is a major determinant of the metabolic cost of human walking

2002 ◽  
Vol 205 (23) ◽  
pp. 3717-3727 ◽  
Author(s):  
J. Maxwell Donelan ◽  
Rodger Kram ◽  
Arthur D. Kuo
Keyword(s):  
Metabolic Rate ◽  
Center Of Mass ◽  
Metabolic Cost ◽  
Step Length ◽  
Mechanical Work ◽  
Major Determinant ◽  
Fourth Power ◽  
Mass Motion ◽  
Step Frequency ◽  
Positive Work

SUMMARY In the single stance phase of walking, center of mass motion resembles that of an inverted pendulum. Theoretically, mechanical work is not necessary for producing the pendular motion, but work is needed to redirect the center of mass velocity from one pendular arc to the next during the transition between steps. A collision model predicts a rate of negative work proportional to the fourth power of step length. Positive work is required to restore the energy lost, potentially exacting a proportional metabolic cost. We tested these predictions with humans (N=9) walking over a range of step lengths(0.4-1.1 m) while keeping step frequency fixed at 1.8 Hz. We measured individual limb external mechanical work using force plates, and metabolic rate using indirect calorimetry. As predicted, average negative and positive external mechanical work rates increased with the fourth power of step length(from 1 W to 38 W; r2=0.96). Metabolic rate also increased with the fourth power of step length (from 7 W to 379 W; r2=0.95), and linearly with mechanical work rate. Mechanical work for step-to-step transitions, rather than pendular motion itself, appears to be a major determinant of the metabolic cost of walking.

NUCLEON IN NUCLEAR MEDIUM

2009 ◽  
Vol 18 (05n06) ◽  
pp. 1166-1175
Author(s):  
SHASHIKANT C. PHATAK
Keyword(s):  
Standard Procedure ◽  
Center Of Mass ◽  
Critical Density ◽  
Magnetic Interaction ◽  
Nuclear Medium ◽  
Mass Motion ◽  
Field Equations ◽  
Dielectric Model ◽  
Chiral Color Dielectric Model

The behavior of a nucleon in nuclear medium is discussed in Chiral Color Dielectric Model. It is assumed that the nucleons in nuclear medium produces a background dielectric field and the quark and dielectric field equations are solved self consistantly in presence of the dielectric field. A nucleon in nuclear medium is then constructed by means of standard procedure followed in chiral bag models. The corrections due to center of mass motion, color magnetic interaction and meson interaction are included. The calculations show that the nucleon becomes bigger in the medium but its mass does not change much. It is found that beyond a certian density, bound solutions in which quarks are bound in self-generated dielectric field are not possible. Thus, the calculations indicate that there is a critical density beyond which the matter consists of deconfined quarks.

scholarly journals Walking in simulated reduced gravity: mechanical energy fluctuations and exchange

1999 ◽  
Vol 86 (1) ◽  
pp. 383-390 ◽  
Author(s):  
Timothy M. Griffin ◽  
Neil A. Tolani ◽  
Rodger Kram
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Gravitational Potential ◽  
Inverted Pendulum ◽  
Mechanical Energy ◽  
Center Of Mass ◽  
Metabolic Cost ◽  
Metabolic Energy ◽  
Gravitational Potential Energy ◽  
Reduced Gravity

Walking humans conserve mechanical and, presumably, metabolic energy with an inverted pendulum-like exchange of gravitational potential energy and horizontal kinetic energy. Walking in simulated reduced gravity involves a relatively high metabolic cost, suggesting that the inverted-pendulum mechanism is disrupted because of a mismatch of potential and kinetic energy. We tested this hypothesis by measuring the fluctuations and exchange of mechanical energy of the center of mass at different combinations of velocity and simulated reduced gravity. Subjects walked with smaller fluctuations in horizontal velocity in lower gravity, such that the ratio of horizontal kinetic to gravitational potential energy fluctuations remained constant over a fourfold change in gravity. The amount of exchange, or percent recovery, at 1.00 m/s was not significantly different at 1.00, 0.75, and 0.50 G (average 64.4%), although it decreased to 48% at 0.25 G. As a result, the amount of work performed on the center of mass does not explain the relatively high metabolic cost of walking in simulated reduced gravity.

Spontaneous emission in a standing-wave cavity: Classical center-of-mass motion

1992 ◽  
Vol 46 (11) ◽  
pp. 7162-7178 ◽  
Author(s):  
W. Ren ◽  
J. D. Cresser ◽  
H. J. Carmichael
Keyword(s):  
Standing Wave ◽  
Spontaneous Emission ◽  
Center Of Mass ◽  
Mass Motion

scholarly journals Effects of obstacle height on the control of the body center of mass motion during obstructed gait

2007 ◽  
Vol 30 (3) ◽  
pp. 471-479 ◽  
Author(s):  
Ting‐Ming Wang ◽  
Hao‐Ling Chen ◽  
Tung‐Wu Lu
Keyword(s):  
Center Of Mass ◽  
The Body ◽  
Mass Motion ◽  
Body Center ◽  
Obstacle Height

Mechanics of a rapid running insect: two-, four- and six-legged locomotion

1991 ◽  
Vol 156 (1) ◽  
pp. 215-231 ◽  
Author(s):  
R. J. Full ◽  
M. S. Tu
Keyword(s):  
Periplaneta Americana ◽  
Mechanical Energy ◽  
Center Of Mass ◽  
Reaction Force ◽  
Metabolic Cost ◽  
Legged Locomotion ◽  
American Cockroach ◽  
Stride Frequency ◽  
Gravitational Potential Energy ◽  
Vertical Ground Reaction Force

To examine the effects of variation in body form on the mechanics of terrestrial locomotion, we used a miniature force platform to measure the ground reaction forces of the smallest and, relative to its mass, one of the fastest invertebrates ever studied, the American cockroach Periplaneta americana (mass = 0.83 g). From 0.44-1.0 ms-1, P. americana used an alternating tripod stepping pattern. Fluctuations in gravitational potential energy and horizontal kinetic energy of the center of mass were nearly in phase, characteristic of a running or bouncing gait. Aerial phases were observed as vertical ground reaction force approached zero at speeds above 1 ms-1. At the highest speeds (1.0-1.5 ms-1 or 50 body lengths per second), P. americana switched to quadrupedal and bipedal running. Stride frequency approached the wing beat frequencies used during flight (27 Hz). High speeds were attained by increasing stride length, whereas stride frequency showed little increase with speed. The mechanical power used to accelerate the center of mass increased curvilinearly with speed. The mass-specific mechanical energy used to move the center of mass a given distance was similar to that measured for animals five orders of magnitude larger in mass, but was only one-hundredth of the metabolic cost.

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