Local oxygen consumption in a muscle (V̇O2) 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 V̇O2 and external force, or between V̇O2 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 V̇O2 and external moments and (2) to determine whether differences exist between the EMG-moment relationship and the V̇O2-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 V̇O2. For the BB V̇O2 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 V̇O2 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, V̇O2 can be used for the validation of musculoskeletal models. © 2003 Elsevier Science Ltd. All rights reserved.