Article

The ability to accelerate and decelerate is important for daily activities and
likely more demanding than maintaining a steady-state walking speed. Walking
speed is modulated by anterior-posterior (AP) ground reaction force (GRF)
impulses. The purpose of this study was to investigate AP impulses across a wide
range of speeds during accelerated and decelerated walking. Kinematic and GRF
data were collected from 10 healthy subjects walking on an instrumented
treadmill. Subjects completed trials at steady-state speeds and at four rates of
acceleration and deceleration across a speed range of 0-1.8 m/s. Mixed regression
models were generated to predict AP impulses, step length and frequency from
speed, and joint moment impulses from AP impulses during non-steady-state
walking. Braking and propulsive impulses were positively related to speed. The
braking impulse had a greater relationship with speed than the propulsive
impulse, suggesting that subjects modulate the braking impulse more than the
propulsive impulse to change speed. Hip and knee extensor, and ankle
plantarflexor moment impulses were positively related to the braking impulse, and
knee flexor and ankle plantarflexor moment impulses were positively related to
the propulsive impulse. Step length and frequency increased with speed and were
near the subjects' preferred combination at steady-state speeds, at which
metabolic cost is minimized in nondisabled walking. Thus, these variables may be
modulated to minimize metabolic cost while accelerating and decelerating. The
outcomes of this work provide the foundation to investigate motor coordination in
pathological subjects in response to the increased task demands of
non-steady-state walking.
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