NIR spectroscopic measurement of local muscle metabolism during rhythmic, sustained and intermittent handgrip exercise Mireille C.P. van Beekvelt a,b , Karin Orbon b , Baziel G.M. van Engelen a , Ron A. Wevers a , and Willy N.J.M. Colier c,d Department of Neurology a , Department of Physiology b , and Department of Geriatric Medicine c , University Medical Centre St. Radboud, Nijmegen, the Netherlands. Artinis Medical Systems, Arnhem, the Netherlands d . ABSTRACT The aim of this study was to investigate local muscle oxygen consumption ( 2 O V m ) during various protocols of isometric handgrip exercise. 2 O V m was measured by near-infrared spectroscopy (NIRS) during sustained, rhythmic, and intermittent isometric handgrip exercise. Whereas rhythmic handgrip exercise has the advantage that local muscle metabolism can be measured over the full range from low- to high-intensity work, the advantage of sustained handgrip exercise is that it is less prone to movement artifacts. Intermittent isometric handgrip exercise enables calculation of 2 O V m at short time intervals providing information about the time response of local oxygen consumption in relation to the onset of exercise. Ten healthy subjects participated in this study. The different protocols were performed on separate days and in random order. 2 O V m during rhythmic exercise was significantly higher than that during sustained exercise at all work intensities tested (P 0.05). However, the highest oxygen consumption value for the three exercise protocols was measured during the steady state of intermittent exercise (P 0.05). These results show that the measurement of task-specific muscle metabolism during exercise can be measured noninvasively and with relative ease by near-infrared spectroscopy. Keywords: Near-infrared spectroscopy, oxygen consumption, isometric exercise protocols, noninvasive measurement, muscle oxygenation 1. INTRODUCTION The foremost indispensable substance for human survival is oxygen, as it is of essential importance for the energy production of the body. It is extracted from the atmospere and transported to the cell. If a problem originates somewhere along this path from lungs to tissue, it will irrevocably affect the energy production. Apart from disorders in lung function (O 2 extraction) or circulation (O 2 delivery), a defect might also be present at the peripheral level of the cell (O 2 consumption). Within the cell, oxygen is used in the mitochondria for the production of adenosine triphosphate (ATP), the chemical compound for storage of energy. Roughly 90% of the energy that is needed for the functionality of the body is provided by the mitochondria, which are, for this reason, considered to be the “power plants” of the cell. They are present in practically every living cell, but are most abundant in tissues that require a high energy-turnover such as heart, brain, liver, or muscle tissue. Especially muscle tissue demands a high flexibility as oxidative energy production can increase more than two orders of magnitude reflecting a metabolic rate that is unique among tissues 1,2 . Measurement of muscle O 2 consumption is of great importance in the investigation of in vivo muscle metabolism in health and disease. Whereas the more conventional techniques like strain-gauge plethysmography combined with blood gas analysis and pulse oximetry are invasive and provide regional values of the total limb, it is now possible to measure local tissue oxygenation noninvasively and directly in the muscle using near-infrared spectroscopy (NIRS). One of the advantages of NIRS is the fact that oxygenation and haemodynamics can be monitored during exercise. With the more conventional techniques this has practically been impossible. This potential benefit of NIRS enables the measurement of muscle oxygenation in exercise-related pathology like e.g. vascular disease 3-6 or mitochondrial impairment 7-12 . Moreover, NIRS measurements during exercise enables complementary use with 31 P-MRS 4-6,8-16 , Photon Migration and Diffuse-Light Imaging, David A. Boas, Editor, Proceedings of SPIE-OSA Biomedical Optics, SPIE Vol. 5138 (2003) © 2003 SPIE-OSA · 1605-7422/03/$15.00 35