Article

Mechanical oscillation (vibration) is an osteogenic stimulus for bone in animal
models and may hold promise as an anti-osteoporosis measure in humans with spinal
cord injury (SCI). However, the level of reflex induced muscle contractions
associated with various loads (g force) during limb segment oscillation is
uncertain. The purpose of this study was to determine whether certain
gravitational loads (g forces) at a fixed oscillation frequency (30 Hz) increases
muscle reflex activity in individuals with and without SCI. Nine healthy subjects
and two individuals with SCI sat with their hip and knee joints at 90 degrees and
the foot secured on an oscillation platform. Vertical mechanical oscillations
were introduced at 0.3, 0.6, 1.2, 3 and 5 g force for 20 s at 30 Hz. Non-SCI
subjects received the oscillation with and without a 5% MVC background
contraction. Peak soleus and tibialis anterior (TA) EMG were normalized to M-max.
Soleus and TA EMG were <2.5% of M-max in both SCI and non-SCI subjects. The
greatest EMG occurred at the highest acceleration (5 g). Low magnitude mechanical
oscillation, shown to enhance bone anabolism in animal models, did not elicit
high levels of reflex muscle activity in individuals with and without SCI. These
findings support the g force modulated background muscle activity during fixed
frequency vibration. The magnitude of muscle activity was low and likely does not
influence the load during fixed frequency oscillation of the tibia.
CI - Copyright (c) 2011 Elsevier Ltd. All rights reserved.

Langue : ANGLAIS