Abstract. The purpose of this study was to investigate the effects of enhancement of systemic circulation due to repetitive hot water bathing on work-related chronic shoulder-neck muscle pain. Eight female office workers reporting chronic shoulder-neck muscle pain used a bath additive, KYN, while they took baths at home for 2 weeks and then took baths without KYN for another 2 weeks. KYN contained CO 2 generators and 3-octylphthalide that produced final concentrations of 100 ppm and 3 ppm in 150 L bath water, respectively. The effects of KYN were evaluated during and after the use of KYN using a visual analog scale (VAS), fatigue scores, muscle hardness, near-infrared spectroscopy (NIRS), and the pressure pain threshold (PPT). During the use of KYN, VAS significantly decreased (p<0.05), as did fatigue score III expressing "sense of physical discomfort" (p<0.01) and muscle hardness (p<0.01). These indices expressed increases during the next 2 weeks of hot water baths without KYN. In conclusion, the effects of repetitive use of KYN were clarified by subjective and physiological parameters on work-related chronic shoulder-neck pain, and they could be ascribed to cumulative immediate enhancement of systemic circulation. Further studies are necessary to clarify the correlations among parameters and underlying mechanisms.

Abstract. The purpose of this study was to investigate the effects of thermotherapy using a bath additive containing a vasodilation agent on chronic shoulder-neck pain in comparison with conventional remedies. Male subjects reporting chronic shoulder-neck muscle pain and receiving frequent established remedies (group A: acupuncture; group B: massage; and group C: over-the-counter medicine) participated in this study. These treatments were replaced by treatment with carbon dioxide baths containing 3-octylphthalide (KYN) for 2 weeks. Changes in the subjects' symptoms were evaluated during the 2 weeks of KYN use and the following 2 weeks with a return to the initial treatments. Differences in the effects of treatment with KYN were found among these groups. In group B, significant decreases in VAS of overall symptoms in the shoulder-neck region, feelings of muscle tension, pain and difficulty in movement of the shoulder joint, and muscle hardness were found during the 2 weeks using KYN. Although decreases in the feelings of muscle tension, pain and difficulty in movement of the shoulder joint in group A, and decreases in the feelings of muscle tension, pain, and muscle hardness in group C were found, VAS of overall symptoms and other individual parameters did not significantly change. In conclusion, repeated treatments with KYN are thought to be more effective than conventional remedies. The differences in the effects of the treatment with KYN are ascribed to the etiology and symptoms that led to the subjects' initial remedies. Further studies are necessary to enhance these beneficial effects on shoulder-neck pain.