Application of near Infrared Spectroscopy in Evaluating Cerebral and Muscle Haemodynamics during Exercise and Sport

Near infrared (NIR) spectroscopy is a non-invasive optical technique that has been used to evaluate cerebral and muscle haemodynamic responses during exercise in situ. Its ease of use, portability, relatively low cost, along with the capability of evaluating cardiorespiratory responses simultaneously, has made it a useful technique to study exercise performance in a more holistic manner. The evidence indicates that there are systematic changes in the muscle and cerebral haemodynamic responses which are coincident with the respiratory gas exchange alterations occurring at the lactate and respiratory compensation thresholds during incremental exercise. During the Wingate (anaerobic) test, the peak oxygen uptake and degree of muscle deoxygenation is comparable to that attained during maximal incremental exercise, implying that there is a large aerobic component during a short duration of intense anaerobic exercise. Studies that have measured cerebral and muscle NIR spectroscopy simultaneously during dynamic whole body exercise support the hypotheses that at exercise intensities above the respiratory compensation threshold: (i) the accessory respiratory muscles compromise oxygen availability to the muscles directly involved in exercise, thereby contributing to fatigue and (ii) there is a systematic decline in cerebral oxygenation until exercise is terminated, thereby supporting the possibility of a supraspinal component to fatigue. Research pertaining to the application of NIR spectroscopy on cerebral and muscle haemodynamics under hypoxic conditions has indicated that the reductions in maximal exercise and aerobic capacity cannot be explained solely on the basis of these acute changes. Additionally, the improvements in maximal and submaximal exercise performance subsequent to endurance, interval and simulated hypoxic training programmes can occur independently of any alterations in cerebral and muscle haemodynamics. Wireless NIR spectroscopy is a useful technique to evaluate sport performance in the field setting and will evolve as an important method for designing and implementing training methods for this purpose.