Changes in Kinematics, Metabolic Cost, and External Work During Walking with a Forward Assistive Force

We examined how the application of a forward horizontal force applied at the waist alters the metabolic cost, kinematics, and external work of gait. Horizontal assist forces of 4%, 8% and 12% of a subject’s body weight were applied via our testing apparatus while subjects walked at comfortable walking speed on a level treadmill. Kinematic and metabolic parameters were measured using motion capture and ergospirometry respectively on a group of 10 healthy male subjects. Changes in kinematic and metabolic parameters were quantified and found similar to walking downhill at varying grades. A horizontal assist force of 8% resulted in the greatest reduction of metabolic cost. Changes in recovery factor, external work, and center of mass (COM) movement did not correlate with changes in metabolic rate and therefore were not driving the observed reductions in cost. The assist force may have performed external work by providing propulsion as well as raising the COM as it pivots over the stance leg. Assist forces may decrease metabolic cost by reducing the concentric work required for propulsion while increasing the eccentric work of braking. These findings on the effects of assist forces suggest novel mobility aids for individuals with gait disorders and training strategies for athletes.

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Human Skeletal Muscle Phosphorylase Activities with Exercise and Training

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y72-150 ◽

1972 ◽

Vol 50 (11) ◽

pp. 1038-1042 ◽

Cited By ~ 7

Author(s):

A. W. Taylor ◽

M. A. Booth ◽

S. Rao

Keyword(s):

Skeletal Muscle ◽

Work Load ◽

Bicycle Ergometer ◽

Healthy Male ◽

Maximal Aerobic Capacity ◽

Work Time ◽

Muscle Phosphorylase ◽

Male Subjects ◽

Exercise And Training ◽

And Training

Fifteen healthy male subjects classified as sedentary (7) or active (8), exercised to exhaustion on a bicycle ergometer at a work load requiring 70% of their maximal aerobic capacity. Biopsy samples of the vastus lateral is muscle were taken at rest, at the time of fatigue, and after a 10 min recovery. Training increased [Formula: see text], [Formula: see text], work time to fatigue, skeletal muscle glycogen levels, and phosphorylase a activity (P < 0.01). An exhaustive submaximal exercise reduced the glycogen levels of the trained group to values similar to the fatigue levels of the nontrained subjects: the higher the initial glycogen levels, the longer the subjects were able to exercise before the onset of fatigue. Skeletal muscle phosphorylase a activities decreased with exercise to fatigue in all groups whereas phosphorylase b activities were maintained. Training had no effect on resting phosphorylase b activity.

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Do mechanical gait parameters explain the higher metabolic cost of walking in obese adolescents?

Journal of Applied Physiology ◽

10.1152/japplphysiol.91240.2008 ◽

2009 ◽

Vol 106 (6) ◽

pp. 1763-1770 ◽

Cited By ~ 55

Author(s):

Nicolas Peyrot ◽

David Thivel ◽

Laurie Isacco ◽

Jean-Benoît Morin ◽

Pascale Duche ◽

...

Keyword(s):

Body Fat ◽

Mechanical Energy ◽

Center Of Mass ◽

Three Dimensional ◽

Metabolic Cost ◽

Normal Weight ◽

Mechanical Work ◽

Percent Body Fat ◽

External Work ◽

Obese Subjects

Net metabolic cost of walking normalized by body mass ( CW·BM−1; in J·kg−1·m−1) is greater in obese than in normal-weight individuals, and biomechanical differences could be responsible for this greater net metabolic cost. We hypothesized that, in obese individuals, greater mediolateral body center of mass (COM) displacement and lower recovery of mechanical energy could induce an increase in the external mechanical work required to lift and accelerate the COM and thus in net CW·BM−1. Body composition and standing metabolic rate were measured in 23 obese and 10 normal-weight adolescents. Metabolic and mechanical energy costs were assessed while walking along an outdoor track at four speeds (0.75–1.50 m/s). Three-dimensional COM accelerations were measured by means of a tri-axial accelerometer and gyroscope and integrated twice to obtain COM velocities, displacements, and fluctuations in potential and kinetic energies. Last, external mechanical work (J·kg−1·m−1), mediolateral COM displacement, and the mechanical energy recovery of the inverted pendulum were calculated. Net CW·BM−1 was 25% higher in obese than in normal-weight subjects on average across speeds, and net CW·BM−67 (J·kg−0.67·m−1) was significantly related to percent body fat ( r2 = 0.46). However, recovery of mechanical energy and the external work performed (J·kg−1·m−1) were similar in the two groups. The mediolateral displacement was greater in obese subjects and significantly related to percent body fat ( r2 = 0.64). The mediolateral COM displacement, likely due to greater step width, was significantly related to net CW·BM−67 ( r2 = 0.49). In conclusion, we speculate that the greater net CW·BM−67 in obese subjects may be partially explained by the greater step-to-step transition costs associated with wide gait during walking.

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