![]() To our knowledge, the mechanical oscillatory stimulation parameters (30 Hz 0.3–1 g force) that increase osteogenesis in animal models ( Christiansen et al., 2008) have not yet been assessed for reflexive muscle activity in humans. For example, numerous animal studies support that these oscillatory interventions trigger anabolism of osteoblasts in isolated bone segments ( Flieger et al., 1998 Garman et al., 2007a, b Rubin et al., 2001, 2002), even in the absence of load ( Garman et al., 2007a, b). Before the mechanisms of low oscillatory gravitational loads ( g force) on bone density can be assessed in humans, we must understand if these stimuli also induce reflexive muscle forces on the skeletal system.īasic research findings support that low magnitude loads at certain oscillatory frequencies (□ 30 Hz) exert a robust osteo-regulatory influence. Large-amplitude loads, in excess of one times body weight, produced by muscle contractions, increase bone density in people with spinal cord injury (SCI) ( Dudley-Javoroski and Shields, 2008a, b Granhed et al., 1987 Shields and Dudley-Javoroski, 2006) but low load, imperceptible vibratory stimuli predominate bone's daily strain history ( Fritton et al., 2000). While the optimal parameters for osteogenesis are currently unknown, studies using animal models can form a basis for research in human subjects. The magnitude of muscle activity was low and likely does not influence the load during fixed frequency oscillation of the tibia. These findings support the g force modulated background muscle activity during fixed frequency vibration. 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. ![]() The greatest EMG occurred at the highest acceleration (5 g). Soleus and TA EMG were < 2.5% of M-max in both SCI and non-SCI subjects. Peak soleus and tibialis anterior (TA) EMG were normalized to M-max. Non-SCI subjects received the oscillation with and without a 5% MVC background contraction. ![]() Vertical mechanical oscillations were introduced at 0.3, 0.6, 1.2, 3 and 5 g force for 20 seconds at 30 Hz. Nine healthy subjects and two individuals with SCI sat with their hip and knee joints at 90° and the foot secured on an oscillation platform. 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. However, the level of reflex induced muscle contractions associated with various loads (g force) during limb segment oscillation is uncertain. 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). ![]()
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