Diego MA, Field T. Moderate pressure massage elicits a parasympathetic nervous system response. (2009). International Journal of Neuroscience, 119(5), 630-38.
This study examined the impacts of 15 minutes of chair massage with light or normal treatment pressures on cardiac vagal tone as measured using heart rate variability including high frequency to monitor parasympathetic tone and high to low frequency ratio to monitor cardiac vagal balance.
Twenty subjects of a medical school were recruited that represented a diverse ethnic population, however, socioeconomic status was quite similar throughout. The results indicate that the moderate pressure results in increased heart rate variability, indicated more parasympathetic activity, yet light pressure massage elicits a decrease in heart rate variability. Also of note was the time during which parasympathetic activity peaked, which was during the first 10 minutes of treatment.
As socioeconomic status has been associated with different stress responses, this may only apply to those of middle to high SES. This paper is of value in that it may help determine specific treatment length to influence heart rate variability and suggestive of requisite treatment pressures that may modulate cardiac vagal tone with manual therapy.
I found it interesting that the light treatment group experienced a decrease in heart rate variability, which indicates that pressures may matter and that the treatment effect is not simply one of being able to “take a load off.” The peak in heart rate variability was at only 10 minutes into the session, which can lead to questioning the purpose of hour-long or more sessions if increases in HRV are necessary.