Force and frequency in manual handling tasks are known risk factors for work related upper arm disorders. Three force levels and three frequencies are used to define the external load in a pinching task. The effects of these external loads on subjective and objective responses are studied. Subjective ratings poorly reflect the levels of external load. EMG variables P50 en P10 of the prime mover muscle seem useful variables in evaluating the effects of task frequency above a certain threshold in task frequency. P90 of the prime mover muscle is useful in evaluating the effects of external forces. It can be concluded that the P50 does not reflect the differences in force levels in tasks with low intensities.