The purpose of this study was to measure the influences of muscle contraction and exercise intensity on brachial artery blood flow during incremental forearm wrist flexion exercise to fatigue. Twelve subjects performed incremental forearm exercise (increments of 0.1 W every 5 min) with their nondominant arms. Doppler waveforms and two-dimensional images of the brachial artery were recorded during the last 2 min of each stage. Exercise intensities were expressed as a percent of the maximal workload achieved (% WLmax). Blood flow was calculated during each of the concentric (CP), eccentric (EP), and recovery phases (RP) of the contraction cycle. Blood flow during the CP of the contraction did not increase above resting values (25.0+/-10.5 mL. min-1) at any intensity (100% WLmax= 21.6+/-6.5 mL. min-1). Conversely, blood flow during the EP and RP increased from 25.6+/-3.0 to 169.1+/-12.8 (P< 0.05), and from 24.7+/-3.1 to 137.9+/-19.5 mL. min-1 (P< 0.05), respectively from rest to maximal exercise. Time averaged blood flow increased linearly from rest to maximal exercise (75.3+/-26.3 to 334.6+/-141.6 mL. min-1, P< 0.05). Thus, a significant impairment in blood flow occurs with concentric contractions during forearm dynamic exercise. The implications of a temporal disparity in blood flow to oxygen delivery and skeletal metabolism during exercise are discussed.