When assessing cardiac vagal activity using the HF component of HRV, it is recommended that a respiratory rate of at least 9 breaths/min be maintained to account for the effect of respiratory rate [12]. In this study, respiratory rates exceeded 9 breaths/min in all cases, which was considered a valid assessment method.
In the control group, the HRV results showed that the relaxation effect due to sitting at rest appeared after approximately 10 min. Six negative mood items decreased significantly after rest, but two positive mood items also decreased significantly.
In this study’s POMS2 assessments, post-intervention scores on negative items fell significantly, as in previous studies [13, 14]. The results of autonomic nervous activity during 15 min of conversation suggested that the response pattern of sympathetic hyperactivity was nearly that of the treatment under conversation. During conversation, parasympathetic nerve activity decreased, and sympathetic nerves were activated; however, after conversation, a negative mood-reducing and positive mood-increasing tendency were observed. From the POMS2 perspective, appending conversation to the sitting-at-rest state may potentially amplify positive mood states, while reducing negative mood states.
Influence on massage recipient
Similarly, in this study, a significant intra-intervention reduction in MHR was demonstrated. Compared with prior research [6], this study’s intervention assessments were performed on a more precise time series basis. In massage recipients, the HR significantly declined at around the 4–5-minute mark, signaling a relaxation effect. Moreover, relative to the preliminary resting state, the post-massage resting state showed a significant decrease in HR. This effect started approximately 5 min into the intervention and persisted until the post-intervention resting phase, demonstrating that rest after receiving a massage led to a predominance of parasympathetic nervous activity.
Vagus nerve C-tactile fibers reportedly react sensitively to slow strokes in the skin [15]. The massage points in this study were distributed along hairy skin areas (i.e., the forearm’s outer side and the dorsal surface of the hand). Studies have shown that a massage pace of 3–10 cm/s, coinciding with the range of maximal C-tactile fiber sensitivity [16, 17], is the most pleasant to healthy recipients. Because the massage pace in this study’s video was approximately 10–11 cm/sec, roughly corresponding to the most pleasant pace, it can be inferred that massage stimulation induced C-tactile fiber reactions in the recipients, stimulating the parasympathetic nervous system.
During the intervention accompanied by conversation, the recipient’s log HF significantly decreased, while log LF/HF significantly increased. While these changes may be ascribed to the influence of conversation, the MHR was significantly lower. This finding raises the possibility that hand-mediated interventions suppress the activation of sympathetic nerves during conversation. Accordingly, when assessing the relaxation effect on the recipient of massage accompanied by conversation, instead of using HF as the index of parasympathetic nervous activity, HR might be a more feasible alternative. Although conversing and being massaged hardly constitute an exercise load, prior research advocating time-domain based analytical methods, impervious to the influence of respiratory pattern changes and requiring no stationarity, for the assessment of cardiac autonomic nervous activity during exercise may be applicable here [18].
The significant increase in log HF for massage recipients in the absence of conversation denotes the predominance of parasympathetic nervous activity, an unequivocal indicator of the relaxation effect. Hence, the increase in sympathetic nervous activity observed among massage recipients in Intervention I was evidently due to the influence of conversation.
As in Intervention I, Intervention II’s MHR measurements showed a significant reduction. The timing of the onset of the relaxation effect (approximately 7–8 min into the intervention) coincided with the foregoing frequency domain measurement outcomes. For recipients of massage unaccompanied by conversation, significant changes in parasympathetic nervous activity were noted in both frequency and time domain measurements, indicating that a relaxation effect could be obtained.
In Intervention II’s pre- and post-intervention POMS2 comparisons, relative to Intervention I, no significant changes were noted in CB and DD, implying that the declines in “confusion-bewilderment” and “depression-dejection” were primarily due to conversation.
Influence on massage practitioner
Although prior studies on hand-mediated therapies have reported subjective assessments in which positive reactions were also elicited by the practitioner, research assessing autonomic nervous activity in practitioners [19, 20] is scarce.
In Intervention II, log HF significantly fell approximately 4–5 minutes into the intervention, and log LF/HF significantly increased relative to the post-intervention resting phase. A significant increase in the MHR was observed in both Interventions I and II. As the autonomic nervous system is affected by physical activity, such as sports and psychological stress [21], it can be inferred that the effect of the practitioner’s massage-related upper limb movements on the entirety of autonomic nervous functions was expressed by the increased HR. Based on the Metabolic Equivalent of Task (MET) table for physical activity and movement intensity [22], activities such as “conversing while seated,” “knitting while seated,” and “ironing,” equal approximately 1.5 METs. Considering the exercise load involved, the state of sympathetic nervous activity while conversing and administering massage is approximately at the same level.
Meanwhile, the practitioner’s POMS2 assessment showed a significant decline in six negative mood states. Since no POMS2 assessments of massage practitioners were found in the literature, this study’s assessment constitutes a novel achievement. The practitioner’s reduction in tension and anxiety presumably emanates from feelings of relief and achievement arising upon confirming the recipient’s satisfaction once the massage is completed.
In the absence of conversation (Intervention II), no increase in frequency-measured or time-domain-measured parasympathetic nervous activity was observed among practitioners. The relaxation effect on practitioners reported in previous studies [19, 20] could not be corroborated in this study.
Limitations
A limitation of this study was its small sample size. In addition, although we devised a method of pre-study and treatment using a demo DVD to reduce the variation in massage methods, this may not have been sufficiently effective. In the future, it will be necessary to increase the number of research participants and control the variability of massage to further verify the results of this study.