The reduction in heart rate and skin conductance levels during both guided relaxation and supine rest, are similar to another report of physiological relaxation during supine rest and guided relaxation (Bera, Gore, & Oak, 1998). The changes in the HF power values suggest that during guided relaxation, cardiac vagal activity is increased (Hayano, Taylor, Yamada, Mukai, Hori, Asakawa, Yokoyama, Watanabe, Takata, & Fujinami, 1993). A decrease in finger plethysmogram amplitude is suggestive of increased peripheral vasoconstriction related to increased sympathetic vasomotor tone (Delius & Kellerova, 1971), which occurred after supine rest, as the After recording was made while seated erect, compared to the supine position, during the Test period. The fact that the same change did not follow the Test period for guided relaxation may be attributed to decreased sympathetic tone after guided relaxation. This decrease in sympathetic tone may be speculated to reduce the magnitude of reflex augmentation in sympathetic activity occurring as a reflex postural readjustment. The change in posture from sitting to supine may also explain the decrease in the low frequency power during supine rest as compared to before. Hence the decrease in the power of the low frequency component during guided relaxation, may also, in part be due to the change in posture. Hence the change in posture in three states, i.e., Before (sitting), During (supine), and After (sitting), also makes it difficult to interpret the results, conclusively. The decrease in oxygen consumption and increase in breath amplitude following guided relaxation suggest that this practice reduces physiological arousal as has been found during Transcendental Meditation (Wallace, 1970; Wallace, Benson, & Wilson, 1971).
When the subjects were subdivided based on their baseline LF /HF ratio (LF/HF > 0.5 or LF/HF < 0.5) which suggested higher or lower sympathetic activity, respectively, (Malliani et al., 1991), a significant difference was found in the changes after guided relaxation and supine rest. Following guided relaxation subjects with baseline LF /HF > 0.5 showed a significant decrease in the LF /HF ratio, whereas the same subjects showed no change after supine rest. Also, subjects with LF /HF < 0.5 at baseline showed no change in this ratio after guided relaxation. This suggests that the practice of guided relaxation may be most effective in reducing sympathetic tone in subjects with higher levels at base line.
In summary, both guided relaxation and supine rest reduce physiological arousal, with changes in a larger number of autonomic measures following guided relaxation. The findings are limited by factors such as the fact the two types of measurements (oxygen consumption and autonomic) were not recorded in all subjects; also the guided relaxation technique has a number of components (muscle relaxation, imagery etc.), which makes it difficult to understand which component influences the result). However, in spite of these limitations the results suggest that instructions to relax (as in guided relaxation) do facilitate relaxation even in subjects who are trained through yoga practice to be able to relax without external instructions. Hence the relaxation effects of yoga practice would be expected to be augmented by guiding instructions.