Changes in Cortical Oxyhaemoglobin Signal During Low-Intensity Cycle Ergometer Activity: A Near-Infrared Spectroscopy Study.

Near-infrared spectroscopy (NIRS) is a widely used non-invasive method for measuring human brain activation based on the cerebral hemodynamic response during gross motor tasks. However, systemic changes can influence measured NIRS signals. We aimed to determine and compare time-dependent changes in NIRS signal, skin blood flow (SBF), and mean arterial pressure (MAP) during low-intensity, constant, dynamic exercise. Nine healthy volunteers (22.1±1.7 years, 3 women) participated in this study. After a 4-min pre-exercise rest and a 4-min warm-up, they exercised on a bicycle ergometer at workloads corresponding to 30% VO2 peak for 20 min. An 8-min rest period followed the exercise. Cortical oxyhaemoglobin signals (O2Hb) were recorded while subjects performed the exercise, using an NIRS system. Changes in SBF and MAP were also measured during exercise. O2Hb increased to 0.019 mM cm over 6 min of exercise, decreased slightly from 13 min towards the end of the exercise. SBF continued to increase over 16 min of the exercise period and thereafter decreased till the end of measurement. MAP fluctuated from -1.0 to 7.1 mmHg during the exercise. Pearson's correlation coefficients between SBF and O2Hb, and MAP and O2Hb differed in each time phase, from -0.365 to 0.713. During low-intensity, constant, dynamic exercise, the profile of changes in measurements of O2Hb, SBF, and MAP differed. These results suggested that it is necessary to confirm the relationship between O2Hb and systemic factors during motor tasks in order to detect cortical activation during gross motor tasks.