RESPONSE

Abstract

Dear Editor-in-Chief: We thank Drs. Quaresima and Ferrari for their constructive comments. They pointed out some important issues regarding the comparison of the near-infrared spectroscopy (NIRS) data between the spinal cord injury (SCI) and control groups. One of their comments discusses the fact that the influence of the path length during NIRS (1), which is unknown for people with SCI, has not been considered in our manuscript (3). Since the acquired value of hemoglobin (Hb) concentration should be affected by the path length, they question the effectiveness of the comparison of the NIRS data between the two groups. We have recognized this limitation and therefore did not attempt to directly compare the NIRS data of the SCI and control groups in our manuscript (3). Instead, we focused on the time course of changes in the NIRS data for each group separately and investigated whether the oxygenation level of the paralyzed lower limb muscle covaried with the muscle EMG activity during the imposed passive leg movement. We also agree with their suggestion that the use of tissue oxy-Hb saturation for measuring the tissue oxygenation level should have been considered. However, there is a reason for not using this parameter: As shown in Figures 2 and 4 of our manuscript (3), there are no drastic concentra-tion changes in the total Hb during the passive leg motions in both of the SCI and control subjects. Under this condition, the deg of oxygenation can easily be determined from each of the oxy, deoxy, and total Hb data (2). Although our result has shown remarkable alteration of the muscle oxygenation level in the paralyzed lower limb, we cannot provide evidence for the existence of increased oxygen consumption in the paralyzed muscle. We will perform further studies to clarify this issue while considering the characteristics and limitations of the NIRS technique. Noritaka Kawashima Masami Akai Kimitaka Nakazawa Department of Rehabilitation for Movement Functions Research Institute National Rehabilitation Center for Persons with Disabilities Saitama, Japan