Postural instability caused by extended bed rest is alleviated by brief daily exposure to low magnitude mechanical signals

Abstract

Loss of postural stability, as exacerbated by chronic bed rest, aging, neuromuscular injury or disease, results in a marked increase in the risk of falls, potentiating severe injury and even death. To investigate the capacity of low magnitude mechanical signals (LMMS) to retain postural stability under conditions conducive to its decline, 29 healthy adult subjects underwent 90 days of 6-degree head down tilt bed-rest. Treated subjects underwent a daily 10 min regimen of 30 Hz LMMS at either a 0.3 g-force ( n = 12) or a 0.5 g-force ( n = 5), introduced by Low Intensity Vibration (LIV). Control subjects ( n = 13) received no LMMS treatment. Postural stability, quantified by dispersions of the plantar-based center of pressure, deteriorated significantly from baseline in control subjects, with displacement and velocity at 60 days increasing 98.7% and 193%, respectively, while the LMMS group increased only 26.7% and 6.4%, reflecting a 73% and 97% relative retention in stability as compared to control. Increasing LMMS magnitude from 0.3 to 0.5 g had no significant influence on outcomes. LMMS failed to spare loss of muscle extension strength, but helped to retain flexion strength (e.g., 46.2% improved retention of baseline concentric flexion strength vs. untreated controls; p = 0.01). These data suggest the potential of extremely small mechanical signals as a non-invasive means of preserving postural control under the challenge of chronic bed rest, and may ultimately represent non-pharmacologic means of reducing the risk of debilitating falls in elderly and infirm.