Intramuscular pressure (IMP) and EMG mirror muscle force in the non-fatigued muscle during static contractions. The present study explores if the constant IMP/EMG relationship with increased force may be extended to dynamic contractions and to fatigued muscle. IMP and EMG were recorded from shoulder muscles in three sessions: 1) brief static arm abductions at angles from 0 - 90° with and without 1 kg in the hands, 2) dynamic arm abductions at velocities from 9 - 90°/s with and without 1 kg in the hands, and 3) prolonged static arm abduction at 30° for 30 min followed by recovery. IMP and EMG increased in parallel with increasing shoulder torque during brief static tasks. During dynamic contractions peak IMP and EMG increased to values higher than those during static contractions; and EMG, but not IMP, increased significantly with speed of abduction. In the non-fatigued m. supraspinatus a linear relationship was found between IMP and EMG; in contrast, during fatigue and recovery significant time-wise changes of the IMP/EMG ratio occurred. The results indicate that IMP should be included along with EMG when evaluating mechanical load sharing between muscles during dynamic and fatiguing contractions.