Effects of Lower Limb Vibrations in the Supine Position on Autonomic Activity inHealthy Adults
2017
Background: Short duration massage of the lower limbs reduces fatigue sensation in working adults. However, the
effects of lower limb vibrations on autonomic activity,
which potentially could improve sleep onset, have not been
fully investigated. This study aimed to examine the effects
of lower limb vibrations on heart rate variability (HRV) as a
marker of autonomic activity.
Methods: The study involved two aspects. In the first
experiment, the optimal frequency of vibration was
determined in five healthy adults (one male and four
females; mean age, 20.4 ± 0.5 years). The second
experiment involved assessing the effects of vibration at the
optimal frequency on nine healthy adults (four males and
five females; mean age, 26.3 ± 16.8 years).
Electrocardiograms (recorded with bipolar lead CM5) were
obtained in the supine position, and HRV was used as an
index for autonomic activity. The power spectra at 0.04-0.15
Hz (low frequency (LF) power) and 0.15-0.40 Hz (high
frequency (HF) power) were quantified, and HF power and
LF/HF ratio were calculated. In the first experiment,
vibrations at four different frequencies (i.e., 25, 30, 35, and
40 Hz) were randomly applied for 10 minutes. In the second
experiment, HF power and LF/HF ratio were measured at a
vibration frequency of 35 Hz for 10 minutes and for 10
minutes of interruption. As a control, HF power and LF/HF
ratio were recorded for 20 minutes without vibration.
Findings: The percent change in HF power tended to be
higher at a vibration frequency of 35 Hz compared to vibrations at frequencies of 25, 30, and 40 Hz. Vibrations at
this frequency significantly increased HF power and reduced
the LF/HF ratio compared to when vibrations were not
applied.
Conclusion: Our findings suggest that the lower limbs
vibration in the supine position at the frequency of 35 Hz
may increase parasympathetic activity and presumably
promote the rapid onset of sleep.
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