By Shirley Vanderbilt
Originally published in Massage & Bodywork magazine, April/May 2005.
Much of what we have learned over the past decade about the physiological and psychological effects of massage therapy has been generated by researchers at the Touch Research Institute (TRI) in Miami, Fla. Their investigations cover a wide range of medical conditions, subjects, and ages, in a variety of applications. We know from these studies, for instance, that massage appears to reduce anxiety and depression, positively alter biochemical markers, and stimulate growth in preterm infants. Positive changes in cognitive function and electroencephalogram (EEG) readings have also been documented, as well as a decrease of symptoms in conditions such as asthma, migraines, and attention deficit disorder, to name a few.1
Adding to the fund of knowledge are two recently published reports differentiating the effects of moderate and light pressure during massage, an aspect awarded minimal investigation in the past. Despite vast differences between the two studies regarding sample population, application, and measurement tools, a common denominator is the significantly positive findings for moderate pressure. TRI’s director, Tiffany Field, Ph.D., says, “The reason it seems moderate pressure is more effective than light is that light pressure is experienced like a tickle stimulus; it’s arousing.” In contrast, moderate pressure affects a flowing of positive physiological changes. “Clearly the central nervous system is interpreting these kinds of touch very differently. For long-term benefits of massage, moderate pressure is more suitable.”
One of the earliest studies on pressure comparisons dates to 1983 (McKechnie et al.). In contrast to several physiological changes (e.g., decreased heart rate) induced by moderate stroking, no such effect was found for light pressure.2 Although the pilot sample was small (n=5), researchers concluded the response was significant and supportive of moderate massage effectiveness for anxiety states in some patients.3 Later controlled studies also documented differences in physiological response: Sullivan et al. (1991) reported moderate pressure affected alpha motor neuron excitability while light pressure did not; and Shoemaker et al. (1997) found no evidence for effect of light pressure on limb blood flow. In an earlier blood flow study comparing deep pressure stroking to percussion movements (Hovind and Nielsen, 1974), only percussion was shown to increase blood flow.4 With these initial results as a springboard, TRI teams delved further, addressing the issue with two diverse populations and study designs.
Adult EEG and Heart Rate
TRI’s team of Diego et al. (2004), investigating differences between moderate and light massage pressure and that of mechanical vibratory massage (Thumper Mini Pro), utilized EEG and electrocardiogram (EKG) readings along with self-report measures to assess effects on stress and anxiety in a sample of healthy adults.5
In three previous studies documenting massage therapy’s effect on EEG readings, researchers have noted positive findings: Klimesch et al. (2000) reported decreased alpha and beta power associated with facial massage; decrease in alpha and beta along with increased delta power was noted by Field (1996) for 15-minute massage; and Jones and Field (1999) found decreased right frontal EEG asymmetry in depressed adolescents following 15-minute massage. To translate into less technical terms, decreased alpha and beta (faster wave) and increased delta (slower wave) power indicate an increase in relaxation and alertness, while a shift from right toward greater left frontal EEG asymmetry is associated with positive affect and mood.6
The results of TRI’s study supported these findings and also differentiated effects for the three pressures of touch. A sample of 36 participants (mean age 28; 58 percent female, 42 percent male) were randomly assigned to groups of equal numbers. Prior to administration of the touch protocol, participants completed self-reports related to baseline stress and anxiety levels and touch aversion. With EEG cap and EKG electrodes remaining in place, recordings were established prior to, during, and after a 10-minute administration of treatment. Self-report measures were also repeated post-session.7
Overall, participants reported reduced stress and anxiety with treatment, but results were more significant for the moderate pressure group. Researchers say the increase in frontal delta power and decreased heart rate for the moderate pressure subjects suggests a relaxation response with lower arousal. In contrast, the light pressure group experienced an increase in heart rate and decreased delta power, indicating physiological arousal and decreased relaxation. Vibratory stimulation resulted in no EEG change, with minimal increase in heart rate. Additionally, moderate pressure subjects exhibited a greater shift toward left frontal asymmetry — again, this is associated with the emotional response of positive mood and affect. As all groups displayed this shift to varying degrees, the team suggests all three treatment procedures were perceived by participants as pleasant, with results more pronounced for moderate pressure.8
Infant Growth and Development
Field and her associates are perhaps best known for research on infant massage. Among the positive results documented are improved development, sleep, and weight gain for preterm newborns. Similar benefits of touch have also been found in studies with cocaine- and HIV-exposed newborns and infants of depressed mothers. In some cases, including studies of children with chronic illness, parents have been the ones trained to administer massage over the course of the study.9
In this second comparison of light and moderate pressure, Field et al. (2004) focused on a sample of 96 full-term newborns during the first month of life. After randomization to either light or moderate pressure groups, the infants’ mothers were instructed in the massage protocol, with specific attention addressed to physical skin signs of the appropriate amount of pressure. For both groups, the treatment sessions, administered at bedtime, consisted of 5-minute stroking (according to instructed pressure and sequence) with the infant in prone position, followed by five minutes extension and flexion of arms and legs, and ending with another five minutes of stroking as in the first portion. Although the mothers’ daily recordings of their sessions were monitored through periodic checks, researchers say the expertise with which a mother demonstrated her massage technique for the team made it easier to determine her level of compliance.10
Measurements taken on the first and last days of the study included physical measures of weight, length, and head circumference; the Brazelton Neonatal Behavior Assessment Scale; and observation of sleep/wake behavior during a 45-minute coding session. Brazelton’s scale addresses seven main factors: habituation, orientation, motor behavior, range of state, state regulation, autonomic stability, and abnormal reflexes. Additionally, Brazelton evaluators recorded scores for robustness, excitability, and depressive behavior. Observers recording sleep/wake behaviors used a criteria of seven states ranging from quiet sleep to crying. They also recorded limb and body movements and gestures such as grimacing, smiles, and clenched fists.11
As with the Diego study, researchers found that light pressure results suggested greater arousal, with infants in this group displaying increased scores for excitability, agitation, fussiness, and gross body movement during sleep. In contrast, the moderate pressure group showed significantly higher performance in several Brazelton scores, including orientation — a behavior associated with increased alertness.12 Field says this indicates a slowed physiological state in which the infant is more attentive and responsive to the examiner and testing stimulus. In a state of increased arousal and agitation, the infant would not have this level of concentration. As noted previously, Diego’s team found moderate massage to be associated with increased slower wave EEG, suggesting lowered arousal and increased attentiveness. Infants in the moderate pressure group also had significantly lower depression and excitability scores on the Brazelton scale. Changes in sleep/wake behavior for this group included decreases in agitation and multiple-limb movement, while as noted, these increased with light pressure.13
Field’s team says, “The growth gains made by the moderate versus the light pressure massage therapy group are perhaps more surprising.” Infants in the moderate pressure group showed significantly greater weight gain and increase in body length. Although weight gain benefits have been documented in several massage studies with preterm infants, the same results for full-term infants with a higher baseline weight might not be expected, researchers say.14 They do note these results are consistent with two previous studies15: Field et al. (1996) reported increased weight gain in full-term infants of depressed mothers after twice-weekly massage over six weeks16; and Moyer-Mileur et al. (1995) documented increased bone mass in preterm infants with a program of physical activity.17
Field and her associates are getting closer to putting together a model for the effects of massage on growth and development. “We’ve actually measured the activity of the vagus nerve,” Field says, explaining the influence of this nerve as it extends to other parts of the body. For instance, when someone is depressed, there is little intonation and facial expression because of low vagal activity in the face. Similarly, vagal activity is connected to functioning of the gastrointestinal tract and the stimulation of food absorption, as well as glucose levels. TRI researchers are also measuring gastric motility, which Field says increases with massage. “We do know these phenomenon are occurring,” and that several are related to weight gain in babies.
In the present study, the team speculates that weight gain in the moderate pressure group is related to stimulation of pressure receptors, leading to increased vagal activity and, in turn, stimulation of “gastric motility and the release of food-absorption hormones in the gastrointestinal tract,” as reported in a previous study by Field and Schanberg (1990). There may also be growth hormone secretion effects, and TRI researchers are currently involved in a study on IgF (growth hormone) increases associated with massage.18
Answers — and More Questions
Thus we have two diverse studies leading to similar conclusions, but also more questions. From the first, we have laboratory evidence of the EEG and EKG changes brought about by varied pressures for a single application of massage. Diego et al. point out a discrepancy between their findings and those of Field’s 1996 study in that the moderate pressure group evidenced lowering of alpha and beta power only during the massage procedure.19 Field’s previous study sample was also larger, with longer duration of application and study period.20 Diego’s team suggests their smaller sample and/or shorter treatment duration might have influenced these new results. They recommend further research to assess EEG effects of massage therapy sessions of varying lengths.21 However, research involving equipment such as EEG is costly, Field says, and the practical element of funding limits does, of necessity, factor into decisions on study design.
The second trial on infants gives us evidence of cumulative effects of the two pressures, light and moderate, following month-long treatment. Indications for future exploration into underlying mechanisms aside, the immediate applications for moderate pressure massage are certainly encouraging. As researchers state in conclusion, “This therapy would appear to be an easy, effective way for parents to enhance their infants’ weight gain, body length, and performance on developmental assessments.”22