Muscle oxygen consumption, determined by NIRS, in relation to external force and EMG

Local oxygen consumption in a muscle ( V ̇ O 2 ) can be determined by near infrared spectroscopy (NIRS). In principle it should be possible to use this measure to validate musculoskeletal models. However, the relationship between V ̇ O 2 and external force, or between V ̇ O 2 and surface EMG, as a measure for muscle activity, is hardly known. The aim of this study was: (1) to evaluate the characteristics of the relationship between V ̇ O 2 and external moments and (2) to determine whether differences exist between the EMG-moment relationship and the V ̇ O 2 -moment relationship. Subjects ( n=5) were asked to perform isometric contractions exerting combinations of elbow flexion and pro/supination moments at force levels up to 70% of their maximum. Simultaneous surface-EMG and NIRS measurements were performed on the m. biceps breve (BB) and the m. brachioradialis (BR). A linear relationship was found between EMG and V ̇ O 2 . For the BB V ̇ O 2 and EMG were linearly related to both the flexion moment and the pro/supination moment. However, for the BR only a linear relationship with flexion moment was found. As expected, based on the findings above, the relationship between V ̇ O 2 and elbow flexion moment can be described by a linear equation, under the conditions of this study (isometric, and force levels up to 70%). These findings suggest that load sharing is independent of force level and that next to EMG, V ̇ O 2 can be used for the validation of musculoskeletal models.